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  • 1.
    Bjurenstedt, Anton
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Seifeddine, Salem
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Dahle, Arne
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    The effect of Fe-rich intermetallics on crack initiation in cast aluminium: an in-situ tensile study2019Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 756, s. 502-507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To evaluate the role of Fe-rich intermetallics on crack initiation, two fully modified Al-Si alloys, one containing plate-like β-Fe and the second containing primary α-Fe intermetallics, were investigated by in-situ tensile testing in the scanning electron microscope. In the first alloy, large plate-like β-Fe intermetallics oriented parallel to the test direction were the first to crack at an elongation of about 1.8%. More transversely oriented intermetallics caused crack initiation in the matrix which linked up with the final fracture. In the second alloy, the cracking of α-Fe intermetallics initiated at an elongation of about 0.9%. It is concluded that large α-Fe intermetallics crack first and that clusters of α-Fe are the most potent crack initiation sites.

  • 2.
    Bogdanoff, Toni
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Riestra, Martin
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Seifeddine, Salem
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Prototyping of a high pressure die cast al-si alloy using plaster mold casting to replicate corresponding mechanical properties2019Inngår i: Minerals, Metals and Materials Series, Springer, 2019, s. 435-442Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Prototyping prior high pressure die casting (HPDC) is used for product/mold design optimization. Plaster mold casting is a cost-efficient prototyping technique providing good surface quality and dimension accuracy, similar to HPDC components. However, the corresponding mechanical properties of a component produced with these two methods are diverging significantly, mainly due to differences in the cooling rate. This work presents a procedure to optimize the plaster mold casting for prototyping to replicate mechanical properties of a commonly used Al-Si alloy (A380). Two commercial alloys with compositions close to the A380 alloy (A356.0 and A360.2) were used. Yield strength was considered as the main design criteria, thus the target mechanical property. Tensile testing results showed that with an optimized T6 heat treatment, not only the yield strength, but also ultimate tensile strength and elongation correspond well to the properties in the HPDC component.

  • 3.
    Dini, Hoda
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Andersson, Nils-Eric
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Microstructural Scale Effects on Thermal Expansion Behaviour of Cast AZ91D2015Inngår i: Magnesium Technology 2015 - TMS 2015 144th Annual Meeting and Exhibition, Orlando, March 15-19, 2015, Hoboken: John Wiley & Sons, 2015, s. 361-365Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The effect of microstructure on thermal expansion of AZ91D cast alloy was studied. Samples with equiaxed grains and a controlled secondary dendrite arm spacing (SDAS) were fabricated using gradient solidification. SDAS was chosen to represent the range ofmicrostructural scale found in sand castings down to that of high pressure die casting. Optical microscopy and electron backscatter diffraction (EBSD) were used for microstructural characterization. The relation between thermal expansion and microstructuralscale of existing phases precipitated, in particular grain size, SDAS and fraction of Mg17Al12 was analyzed.

  • 4.
    Dini, Hoda
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Svoboda, A.
    Andersson, Nils-Eric
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Maskinteknik.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Lindgren, L.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Maskinteknik.
    Modeling the Deformation Behavior of As-Cast AZ1D Including the Effect of The Cast Microstructure2017Inngår i: Proceedings of PLASTICITY ’17: The Twenty Third International Conference on Plasticity, Damage, and Fracture, 2017, s. 37-39Konferansepaper (Fagfellevurdert)
  • 5.
    Dini, Hoda
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Svoboda, Ales
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Andersson, Nils-Eric
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Lindgren, L.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Dislocation Density Model for Flow Stress of AZ91D Magnesium Alloy-Effect of Temperature and MicrostructureInngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154Artikkel i tidsskrift (Fagfellevurdert)
  • 6.
    Dini, Hoda
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Svoboda, Ales
    Department of Materials and Manufacturing, School of Engineering, Jönköping University, Jönköping, Sweden.
    Andersson, Nils-Eric
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Lindgren, Lars-Erik
    Division of Mechanics of Solid Materials, Luleå University of Technology, Luleå, Sweden.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Optimization and validation of a dislocation density based constitutive model for as-cast Mg-9%Al-1%Zn2018Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 710, s. 17-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dislocation density-based constitutive model, including effects of microstructure scale and temperature, was calibrated to predict flow stress of an as-cast AZ91D (Mg-9%Al-1%Zn) alloy. Tensile stress-strain data, for strain rates from 10-4 up to 10-1 s-1 and temperatures from room temperature up to 190 °C were used for model calibration. The used model accounts for the interaction of various microstructure features with dislocations and thereby on the plastic properties. It was shown that the Secondary Dendrite Arm Spacing (SDAS) size was appropriate as an initial characteristic microstructural scale input to the model. However, as strain increased the influence of subcells size and total dislocation density dominated the flow stress. The calibrated temperature-dependent parameters were validated through a correlation between microstructure and the physics of the deforming alloy. The model was validated by comparison with dislocation density obtained by using Electron Backscattered Diffraction (EBSD) technique.

  • 7.
    Ghasemi, Rohollah
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Elmquist, Lennart
    SinterCast AB, Sweden.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E. W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Effect of interaction between lamellar graphite and cat-fines on tribological behaviour of cast iron under abrasion2015Inngår i: Proceeding of ITC, 2015Konferansepaper (Fagfellevurdert)
  • 8.
    Ghasemi, Rohollah
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Elmquist, Lennart
    Swerea SWECAST, Jönköping, Sweden.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Salomonsson, Kent
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Abrasion resistance of lamellar graphite iron: Interaction between microstructure and abrasive particles2018Inngår i: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 120, s. 465-475Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study focuses on abrasion resistance of Lamellar Graphite Iron (LGI) using microscratch test under constant and progressive load conditions. The interactions between a semi-spherical abrasive particle, cast iron matrix and graphite lamellas were physically simulated using a sphero-conical indenter. The produced scratches were analysed using LOM and SEM to scrutinise the effect of normal load on resulting scratch depth, width, frictional force, friction coefficient and deformation mechanism of matrix during scratching. Results showed a significant matrix deformation, and change both in frictional force and friction coefficient by increase of scratch load. Furthermore, it was shown how abrasive particles might produce deep scratches with severe matrix deformation which could result in graphite lamella's coverage and thereby deteriorate LGI's abrasion resistance.

    Fulltekst tilgjengelig fra 2020-01-04 00:00
  • 9.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Hernando, Juan Carlos
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Stefanescu, Doru M.
    The Ohio State University, Columbus, OH, United States.
    Diószegi, Attila
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Dluhoš, Jiří
    TESCAN Brno, Brno, Czech Republic.
    Petrenec, Martin
    TESCAN Brno, Brno, Czech Republic.
    Revisiting the graphite nodule in ductile iron2019Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 161, s. 66-69Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The growth mechanism of graphite nodules in ductile iron was experimentally investigated using high-resolution 3D tomography of an individual graphite nodule in a near-eutectic ductile iron. The dual beam scanning electron microscopy (FIB-SEM) technique was used for this purpose. Iron particles elongated in the radial direction were observed inside a graphite nodule. Some micro-voids were detected inside the nodule, mostly located at the end of the iron particles. These observations were compared with established theories about the growth of graphite nodules and iron entrapment/engulfment in between the graphite sectors during solidification of ductile iron. 

  • 10.
    Ghassemali, Ehsan
    et al.
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Jarfors, A. E. W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Maskinteknik. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Tan, Ming-Jen
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Lim, Samuel Chao Voo
    Singapore Institute of Manufacturing Technology (SIMTech).
    On the microstructure of micro-pins manufactured by a novel progressive microforming process2013Inngår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 6, nr 1, s. 65-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microforming is defined as the process of production of metallic micro-parts with at least two dimensions in sub-millimeter range. Many of these microforming processes have been investigated in laboratory-scale, which is not suitable for industrial applications. In this work, the feasibility of producing copper micro-pins using a novel progressive microforming process is demonstrated. This process has a good potential for mass production of micro-parts. The material flow behavior and the microstructure of the formed micro-pins were investigated by means of optical microscopy and simulation. From this study of material flow behavior with respect to different process conditions (die diameter, die design and punch diameters used), it will be shown how the respective material flow behavior in the progressive forming process influenced the microstructure evolution in the formed micro-pin. It was found in the experimental results that there is a soft zone on the micro-pins surface under specific process conditions. The microhardness results were consistent with the microstructural observations. Simulation was employed to understand the material flow direction under the punch during the microforming process and evaluate the position of the neutral zone in the disk-shape head of the micro-pin produced. This understanding of the neutral zone position with relation to the metal dead-zone as well as the material flow behavior was necessary to explain the dead-zone leakage in the microstructure and the occurrence of the soft zone. By decreasing the punch to die diameter ratio, and also choosing a die without entrance fillet radius, it was shown that the soft zones at the pin surface could be either minimized or entirely removed.

  • 11.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Diószegi, Attila
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    On the Formation of Micro-Shrinkage Porosities in Ductile Iron Cast Components2018Inngår i: Metals, E-ISSN 2075-4701, Vol. 8, nr 7, artikkel-id 551Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combination of direct austempering after solidification (DAAS) treatment and electron backscatter diffraction (EBSD) method was used to study the formation of micro-shrinkage porosities in ductile iron. Analyzing the aus-ferritic microstructure revealed that most of micro-shrinkage porosities are formed at the retained austenite grain boundaries. There was no obvious correlation between the ferrite grains or graphite nodules and micro-shrinkage porosities. Due to the absolute pressure change at the (purely) shrinkage porosities, the dendrite fragmentation rate during the DAAS process would be altered locally, which caused a relatively finer parent-austenite grain structure near such porosities.

  • 12.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Tan, Ming-Jen
    School of Mechanical & Aerospace Engineering, Nanyang Technological University.
    Chua, Beng Wah
    Singapore Institute of Manufacturing Technology (SIMTech).
    Microstructure versus substructure size effect2016Inngår i: AIP Conference Proceedings / [ed] Francisco Chinesta, Elias Cueto and Emmanuelle Abisset-Chavanne, American Institute of Physics (AIP), 2016, Vol. 1769, s. 1-6, artikkel-id 090001Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In metal deformation, size effect is generally attributed to the interactive effect of grain size and specimen dimension. This work shows, however, that relative substructure dimensions should also be considered. Micro-compression tests on the micro-pins having different grain sizes revealed no significant size effect with respect to the mechanical behavior, even if the number of grains over the diameter of the micro-pins falls below its critical value. To justify the reason laying under this fact, a recovery annealing cycle was applied on the micro-pins to change the substructure properties without altering the mean grain size. A surprising drop in the flow stress of the recovery-annealed micro-pins implied the importance of considering subgrain size rather than grain size over the diameter of component for the size effect investigation.

  • 13.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders
    Sch. of Mech. & Aerospace Eng., Nanyang Technological University, Singapore.
    Tan, M.J.
    Sch. of Mech. & Aerospace Eng., Nanyang Technological University, Singapore.
    Lim, S.C.V.
    Singapore Institute of Manufacturing Technology (SIMTech)..
    Dead-zone formation and micro-pin properties in progressive microforming process2011Inngår i: ICTP 2011, 10th International Conference on Technology of Plasticity, Steel Research International: Special Edition, Aachen, DE, Sep 25-29, 2011, Weinheim: Wiley-VCH Verlagsgesellschaft, 2011, nr 9, s. 1014-1019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A novel progressive microforming process that consisted of a two step operations, punching and blanking was studied. Micropins with diameter of 300 µm were manufactured from metal strip to cater for a set-up with good potential for mass production. Investigations showed that the microstructure contains some deformed zones surrounded by less-deformed zones or "dead-zones" which is unique to the progressive microforming process. The aim of this work was to understand the origin and evolution of the "dead-zones" in the microstructure of the final products during the progressive microforming process, and find a way to avoid this phenomenon. To do this, the microstructure of the 300 µm pins with punch diameters of 3.2 and 2.2 mm at different punch displacement was investigated experimentally and by simulation. Experimental observations showed that dead-zones appear just after starting the microforming process, which is due to the friction at the workpiece-die interface. This dead zone leaks into the die cavity as a result of work-piece compression. It was shown that the inhomogeneous mechanical properties could be significantly improved by selection of an appropriate punch.

  • 14.
    Ghassemali, Ehsan
    et al.
    Department of Materials Engineering, Isfahan University of Technology.
    Kermanpur, A.
    Department of Materials Engineering, Isfahan University of Technology.
    Najafizadeh, A.
    Department of Materials Engineering, Isfahan University of Technology.
    Microstructural Evolution in a Low Carbon Steel During Cold Rolling and Subsequent Annealing2010Inngår i: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, E-ISSN 1533-4899, Vol. 10, nr 9, s. 6177-6181Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cold rolling with subsequent annealing of lath martensite structure could lead to the formation of nanostructures in low carbon steels. In the present work, the microstructural evolution of a 0.13% C steel during this process was studied. The specimens were austenitized at 950 °C followed by quenching in ice-brine to get martensitic structure. The quenched samples were aged at 200 °C for 30 min. These specimens were cold rolled up to 90% reduction in thickness without any intermediate annealing and then annealed at the temperatures from 400 to 600 °C. Scanning and transmission electron microscopy and color metallography was used to investigate the microstructure. Microscopic investigations showed that a multiphase nanostructure composed of equiaxed ferrite grains with the mean grain size of about 188 nm and small blocks of tempered martensite can be achieved under annealing at 400 °C for 90 min. Formation of the nanostructure was discussed from the viewpoint of characteristics of the martensite starting structure. Fragmentation of martensite lathes in cold rolling stage play an important role on recrystallization at annealing stage to get the ultrafine structure.

  • 15.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Riestra, Martin
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Bogdanoff, Toni
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Kumar, Bharath S.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Seifeddine, Salem
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Hall-Petch Equation in a Hypoeutectic Al-Si Cast Alloy: Grain Size vs. Secondary Dendrite Arm Spacing2017Inngår i: Procedia Engineering, Elsevier, 2017, Vol. 207, s. 19-24Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Al-Si cast alloy family is widely used in the production of complex castings for various applications and known for its very good castability and high strength-to-weight ratio. However, early cracking under tensile loading is sometimes a limiting factor. Among other parameters, it is yet controversial whether grain boundaries are dominant strengthening factor in cast alloys, instead of dendrite/eutectic boundaries. This study presents the effect of secondary dendrite arm spacing (SDAS) and grain size on crack initiation and propagation of Al-Si cast alloys under tensile loading. The Al-10Si (wt.%) alloy with modified Si morphology was cast using inoculants (Al-5Ti-B master alloy) under different cooling rates to obtain a range of grain sizes (from below 138 μm to above 300 μm) and SDAS (6, 15 and 35 μm). Conventional tensile test as well as in-situ tensile test in a scanning electron microscope, equipped with an electron backscatter diffraction (EBSD) was carried out to understand the deformation mechanisms of the alloy. Observation of slip bands within the dendrites showed that in modified Si structure, the interdendritic (eutectic) area takes more portion of the strain during plastic deformation. Besides, only a few cracks were initiated at the grain boundaries; they were mostly initiated from dendrite/eutectic interface. All cracks propagated trans-granularly. Hall-Petch calculations also showed a strong relationship between SDAS and flow stress of the cast alloy. Although statistically correct, there was no physically meaningful relationship between the grain size and the flow stress. Nevertheless, formation of identical slip bands in each grain could be an evidence for the marginal effect of the grain size on the overall strength development of the alloy. Consequently, among other effects, the combinational dominant effect of SDAS and modest effect of grain size shall be considered for modification of the Hall-Petch equation for precise prediction of mechanical properties of cast alloys.

  • 16.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Singapore Institute of Manufacturing Technology, Singapore; Nanyang Technological University, Singapore.
    Song, Xu
    Singapore Institute of Manufacturing Technology, Singapore.
    Zarinejad, Mehrdad
    Singapore Institute of Manufacturing Technology, Singapore.
    Atsushi, Danno
    Singapore Institute of Manufacturing Technology, Singapore.
    Tan, Ming Jen
    Nanyang Technological University, Singapore.
    Bulk Metal Forming Processes in Manufacturing2014Inngår i: Handbook of Manufacturing Engineering and Technology / [ed] Andrew Y C Nee, Berlin: Springer Berlin/Heidelberg, 2014Kapittel i bok, del av antologi (Fagfellevurdert)
  • 17.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Sonkusare, Reshma
    Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, India.
    Biswas, Krishanu
    Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, India.
    Gurao, Nilesh P.
    Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur, India.
    Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy: an in situ study2018Inngår i: Philosophical Magazine Letters, ISSN 0950-0839, E-ISSN 1362-3036, Vol. 98, nr 9, s. 400-409Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of a possible phase transformation or precipitation of the face-centred cubic (FCC) phase on intermediate-temperature deformation of a dual-phase AlCoCrFeNi high-entropy alloy has been studied using in situ tensile testing at 550°C. Electron backscatter diffraction (EBSD) results showed localised precipitation of the FCC phase during the intermediate-temperature deformation. The overall fracture behaviour and crack propagation of the material was not altered much compared to the room-temperature behaviour, namely brittle trans-granular fracture. Deformation at higher temperatures (above 750°C) is suggested as a way to enhance the dynamic FCC phase precipitation, in order to improve the ductility or deformability of the alloy. 

  • 18.
    Ghassemali, Ehsan
    et al.
    School of Mechanical & Aerospace Engineering, Nanyang Technological University and Singapore Institute of Manufacturing Technology (SIMTech).
    Tan, Ming-Jen
    School of Mechanical & Aerospace Engineering, Nanyang Technological University.
    Chua, Beng Wah
    Singapore Institute of Manufacturing Technology (SIMTech).
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Lim, S.C.V.
    Materials Engineering, Monash University.
    Grain size and workpiece dimension effects on material flow in an open-die micro-forging/extrusion process2013Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 582, nr 10, s. 379-388Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The interactive effect of grain size and specimen dimensions on the material flow and microstructural evolution was studied in a progressive open-die microforming process. Particular interest was paid on the effect of the number of grains over the initial specimen thickness, on the evolution of the dead metal zone (DMZ) in the final micro-component's microstructure. Such a DMZ is deemed unfavorable for mechanical properties of the pin. Interestingly, experimental results revealed that the DMZ can be removed at the pin surface by increasing the initial grain size. This behavior was attributed to the role of the strain gradient on the deformation. In the aspects of the forming load and dimensional measurements of the final parts, there were no significant size-effects observed in this process. This is because the neutral plane, which demarcates the two directions of material flow in the open-die forging/extrusion process, determines the amount of material flow towards the die orifice, regardless of the initial grain size.

  • 19.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. School of Mechanical & Aerospace Engineering, Nanyang Technological University and Singapore Institute of Manufacturing Technology (SIMTech).
    Tan, Ming-Jen
    School of Mechanical & Aerospace Engineering, Nanyang Technological University.
    Chua, Beng Wah
    Singapore Institute of Manufacturing Technology (SIMTech).
    Lim, Samuel C.V.
    Materials Engineering, Monash University.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Friction effects during open-die micro-forging/extrusion processes: An upper bound approach2014Inngår i: Procedia Engineering / [ed] Ishikawa, T, Mori, KI, Elsevier, 2014, Vol. 81, s. 1915-1920Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In microforming processes it is preferred to not to use lubricants, due to their complex behavior in micro-scale. Nevertheless, using lubricants could increase the life time and decrease the required forming load. Thus, it is necessary to study and develop an analytical solution for different lubrication conditions in microforming processes. A previously studied upper bound model was modified in this study for various lubrication conditions in an open-die micro-forging/extrusion process. Two approaches were chosen for identifying the friction factor in the model: (i) global friction factor, (ii) localized friction factor. Comparison of the modeling results with the experimental showed the reliability of the second approach, providing a better fit.

  • 20.
    Ghassemali, Ehsan
    et al.
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Tan, Ming-Jen
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Lim, S.C.V.
    Materials Engineering, Monash University, Wellington Road, Clayton, Victoria, Australia.
    Optimization of axisymmetric open-die micro-forging/extrusion processes: An upper bound approach2013Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 71, s. 58-67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is a trend towards component miniaturization and strong drive towards cost effective and sustainable metal forming techniques of miniaturized components. This paper presents an upper bound solution for the optimization of open-die forging/extrusion processes in the forming of micro-pins from a sheet metal. Using such an analytical modeling approach, the critical blank thickness, the resulting final part geometry, together with the required forming load were predicted based on the location of the neutral plane under the punch during the process. Based on the phenomenological findings of the process, the geometry size factor, x, was introduced explaining its relative importance to the model. Experimental results obtained from C11000 copper samples using a progressive microforming process was found to agree well with the results predicted by the model. The results were also validated with other results reported before from a similar process.

  • 21.
    Ghassemali, Ehsan
    et al.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University and Singapore Institute of Manufacturing Technology (SIMTech).
    Tan, Ming-Jen
    School of Mechanical and Aerospace Engineering, Nanyang Technological University.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Lim, S.C.V.
    Singapore Institute of Manufacturing Technology (SIMTech).
    Progressive microforming process: Towards the mass production of micro-parts using sheet metal2013Inngår i: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 66, nr 5-8, s. 611-621Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although there is considerable published literature on micro-metal forming processes, there is still a lack of research towards implementing these processes commercially. Some of the challenges are handling of micro-parts and process intermittency. This work demonstrates the feasibility of producing symmetric micro-parts using a progressive forming set-up. Such a progressive forming process alleviates the challenges in handling and removal of micro-parts. Micro-pins with diameters of 0.3, 0.5, and 0.8 mm were successfully manufactured without defects. Experimental observations together with process simulation results showed that this process has three main stages: (1) indentation at the very beginning, (2) upsetting, and (3) extrusion predominantly occurring at the very end stage of the stroke. The bulk of the pin forming occurs at the end stroke of the process (extrusion stage). The effects of punch/pin diameter ratio on the pin aspect ratio and the maximum forming load were also investigated. In addition, the finite element results also revealed that a hybrid friction model was required to be implemented for better fit with experimental results as compared to the shear and Coulomb friction models.

  • 22.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Nanyang Technological University, Singapore; Singapore Institute of Manufacturing Technology, Singapore.
    Tan, Ming-Jen
    Nanyang Technological University, Singapore.
    Lim, Samuel Chao Voon
    Monash University, Clayton, Australia.
    Wah, Chua Beng
    Singapore Institute of Manufacturing Technology, Singapore.
    Jarfors, Anders
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Experimental and Simulation of Friction Effects in an Open-Die Microforging/Extrusion Process2014Inngår i: Journal of Micro and Nano-Manufacturing, ISSN 2166-0468, Vol. 2, nr 1, s. 011005-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Friction effects during a progressive microforming process for production of micropins of various diameters were experimentally investigated and were analytically modeled, using a hybrid friction model. The response surface method and ANOVA analysis were used to generalize the findings for various pin diameters. Besides, it was shown that to get an accurate result in simulation, the friction model must be considered locally instead of a global friction model for the whole process. The effect of friction factor on the final micropart dimensions (the effect on the instantaneous location of the neutral plane) and the forming pressure were investigated. The results showed a reduction in the friction factor as die diameter increased. Following that, the optimum frictional condition to obtain the highest micropart aspect ratio was defined as the maximum friction on the interface between the die upper surface and the punch surface, together with a minimum friction inside the die orifice.

  • 23.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Tan, Ming-Jen Tan
    School of Mechanical & Aerospace Engineering, Nanyang Technological University, Singapore.
    Wahb, Chua Beng
    Singapore Institute of Manufacturing Technology (SIMTech), Singapore.
    Lim, S.C.V.
    Materials Engineering, Monash University, Australia.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Effect of cold-work on the Hall–Petch breakdown in copper based micro-components2015Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 80, part A, s. 124-135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Effects of substructural dimensions on the mechanical properties of micro-pins produced by an open-die micro-extrusion/forging process were studied. Micro-pins of diameter 0.3 mm were manufactured from copper strips, having different initial grain sizes. Micro-compression tests on the micro-pins revealed no significant size effect, even if the number of grains over the diameter of the micro-pins falls below its critical value. However, relaxation of the as-formed substructure using recovery annealing led to a surprising drop in the flow stress of the micro-pins. This was explained and attributed to the number of subgrains over the diameter of the micro-pins, showing the important role of subgrains rather than grains in determining the mechanical properties.

  • 24.
    Ghassemali, Ehsan
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Sonkusare, Reshma
    Indian Institute of Technology, India.
    Biswas, Krishanu
    Indian Institute of Technology, India.
    Gurao, Nilesh P.
    Indian Institute of Technology, India.
    In-situ study of crack initiation and propagation in a dual phase AlCoCrFeNi high entropy alloy2017Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 710, s. 539-546Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study reports the effect of phase distribution on crack propagation in a dual phase AlCoCrFeNi high entropy alloy (HEA) under tensile loading. The alloy is characterized by the presence of a brittle disordered BCC phase that can be toughened by precipitation of a ductile FCC phase during homogenization heat treatment. The stress and strain partitioning between the two phases is of paramount importance to determine the mechanical response of this alloy. The as-cast alloy was subjected to homogenization at 1273 K for 6 h to prevent the formation of detrimental sigma phases and to precipitate the ductile FCC phase. In-situ tensile test in a scanning electron microscope with an electron backscatter diffraction facility was carried out to understand the micro-mechanisms of deformation of the alloy. Precipitation of the FCC phase at the BCC grain boundaries reflected the effect of the FCC phase on crack deflection and branching during propagation. The strain partitioning between the two phases and the evolution of misorientation distribution was investigated. It is observed that the presence of ductile FCC high entropy phase can impart good room temperature ductility to the brittle BCC phase. As there are very few investigations performed on the dual phase HEAs, a proper microstructural design can be be achieved and can be utilized to toughen the brittle HEAs.

  • 25.
    Ghatei Kalashami, A.
    et al.
    Isfahan University of Technology, Iran.
    Kermanpur, A.
    Isfahan University of Technology, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Najafizadeh, A.
    Isfahan University of Technology, Iran.
    Mazaheri, Y.
    Isfahan University of Technology and Bu-Ali Sina University, Iran.
    Correlation of microstructure and strain hardening behavior in the ultrafine-grained Nb-bearing dual phase steels2016Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 678, s. 215-226Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultrafine-grained dual phase (DP) steels with different Nb contents (0.00, 0.06 and 0.12 wt%) were produced by cold-rolling followed by intercritical annealing of ferrite/martensite starting microstructure at 770 °C for different holding times. Scanning electron microscopy, equipped with electron backscattered diffraction (EBSD) detector, nanoindentation and tensile testing were used to characterize microstructural evolutions and their correlations to the strain hardening and fracture behavior. EBSD results confirmed the retardation effect of Nb on recrystallization. It was found that the strains stored in the grains and density of geometrically necessary dislocations (GNDs) were increased with the addition of Nb. Strain hardening analysis showed that plastic deformation of the DP steels occurred in three distinct stages, which based on the EBSD results, nanoindentation and fracture analysis, were controlled by microstructural features such martensite volume fraction and size, density of GNDs and individual ferrite and martensite tensile properties.

  • 26.
    Ghatei Kalashami, A.
    et al.
    Isfahan University of Technology, Iran.
    Kermanpur, A.
    Isfahan University of Technology, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Najafizadeh, A.
    Isfahan University of Technology, Iran.
    Mazaheri, Y.
    Isfahan University of Technology and Bu-Ali Sina University, Iran.
    The effect of Nb on texture evolutions of the ultrafine-grained dual-phase steels fabricated by cold rolling and intercritical annealing2017Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 694, s. 1026-1035Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dual phase (DP) steels with different amounts of Nb were produced by utilizing cold rolling and intercritical annealing of a ferrite-martensite duplex starting structure. The effects of Nb contents (0.00, 0.06, 0.12 and 0.18 wt%) on microstructure and texture evolutions were studied. Addition of Nb promoted formation of ultra-fine grained structures with the ferrite grain size of about ~1 mm and uniformlydispersed martensite particles. The results showed increasing the fraction of the high angle grain boundaries and formation of {111} fiber components in the microstructures with increasing Nb content. In addition, the texture power was decreased with the addition of Nb, resulting in random texture components

  • 27.
    Hajiannia, I.
    et al.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Shamanian, M.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Atapour, M.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Saeidi, N.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Development of Ultrahigh Strength TRIP Steel Containing High Volume Fraction of Martensite and Study of the Microstructure and Tensile Behavior2018Inngår i: Transactions of the Indian Institute of Metals, ISSN 0972-2815, E-ISSN 0975-1645, Vol. 71, nr 6, s. 1360-1367Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new transformation induced plasticity (TRIP) steel containing high volume fraction of martensite was produced by austempering heat treatment cycle. Microstructure and tensile properties of this TRIP steel were investigated and compared to those of a dual phase (DP) steel with high martensite volume fraction. Microstructural analysis showed a mixture of ferrite, bainite, retained austenite and about 25–30 vol% of martensite in the TRIP steel. As a result of the strain induced transformation of retained austenite to martensite, the TRIP steel showed a strength elongation balance of 86% higher than that for the DP steel. In comparison to the commercial TRIP780 steel, the current TRIP steel showed a 15% higher ultimate tensile strength value while maintaining the same level of ductility. TRIP steel also had a larger work hardening exponent than DP steel at all strains. 

  • 28.
    Hajiannia, Iman
    et al.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Shamanian, Morteza
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Atapour, Masoud
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Ashiri, Rouholah
    Department of Materials Science and Engineering, Dezful Branch, Islamic Azad University, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    The assessment of second pulse effects on the microstructure and fracture behavior of the resistance spot welding in advanced ultrahigh-strength steel TRIP11002019Inngår i: Iranian Journal of Materials Science and Engineering, ISSN 1735-0808, Vol. 16, nr 2, s. 79-88Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the effects of the second pulse resistance spot welding on the microstructure and mechanical properties of transformation induced plasticity 1100 steel were evaluated. The thermal process after welding was designed to improve metallurgical properties with pulse currents of 6 kA, 9 kA, and 12 kA after initial welding with 10 kA current. The effect of the second pulse on mechanical and microstructural properties was investigated. The fracture of the welds was for pulsed samples of 6 kA and 9 kA pull out with mechanical test. Due to the existence of the microstructure including the equiaxial dendritic and finer in fusin zone in the pulsed current of 9 kA, the maximum fracture energy, and maximum force were observed. A significant decrease in the FZ hardness in 6 kA current was observed in the nano-hardness results, which was attributed to the existence of martensitic and ferrite temper. The highest ratio of CTS/TSS was obtained for 6 kA and 9 kA, respectively, and force-displacement evaluation was maximum in 9 kA. The fracture surfaces included dendrites and dimples. The results of partial fracture revealed separation in the coherent boundaries of the coarse grain of the annealed region.

  • 29.
    Hajiannia, Iman
    et al.
    Isfahan Univ Technol, Dept Mat Engn, Esfahan, Iran.
    Shamanian, Morteza
    Isfahan Univ Technol, Dept Mat Engn, Esfahan, Iran.
    Atapour, Masoud
    Isfahan Univ Technol, Dept Mat Engn, Esfahan, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ashiri, Rouholah
    Islamic Azad Univ, Dezful Branch, Dept Mat Sci & Engn, Dezful, Iran.
    A microstructure evaluation of different areas of resistance spot welding on ultra-high strength TRIP1100 steel2018Inngår i: Cogent Engineering, Vol. 5, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study, the microstructure of resistance spot welds of advanced ultra-high strength TRIP1100 steel was investigated. For this purpose, welding was performed after determining the best welding parameters. Four sections of the heat-affected zone (HAZ) regions were selected in the regions where the heat exchange was used to control the microstructure. Then, they were used with EBSD by scanning electron microscopy (SEM). The results showed that the TRIP1100 steel microstructure consisted of polygonal ferrites, bainites, residual austenite (RA) and martensite/austenitic islands (M/A). They also showed that the melting zone (FZ) has a lath martensite structure, and the grains are larger in packets. The structure of the martensite and different orientation grains are located in the Upper-critical area (UCHAZ). In the inter-critical region (ICHAZ), the high carbon martensitic content is higher due to the presence and the structure of ferrite and martensite. In the sub-critical region (SCHAZ), due to the tempering of martensite at a temperature below A(C1), the structure is similar to the base metal (BM), with the difference that the RA degradation reduces its structure by 50%. It was found that the RA in the BM had completely transformed. The results showed that with the movement of the BM to the weld metal, the boundaries with a low angle were increased.

  • 30.
    Hernando, Juan Carlos
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Elfsberg, Jessica
    Scania CV AB, Södertälje, Sweden.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Dahle, Arne
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Diószegi, Attila
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    The effect of coarsening of primary austenite on the ultimate tensile strength of hypoeutectic compacted graphite Fe-C-Si alloys2019Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 168, s. 33-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of primary austenite morphology on the ultimate tensile strength (UTS) of hypoeutectic compacted graphite Fe-C-Si alloys (CGI) is studied by isothermal coarsening experiments. Secondary dendrite arm spacing (SDAS) and the morphological characteristics related to the surface area of primary austenite, M γ and D ID Hyd , increase with the cube root of coarsening time. UTS decreases linearly with increasing coarseness of primary austenite. The eutectic and eutectoid microstructures are unaffected by the primary austenite morphology. These observations demonstrate the strong influence of primary austenite morphology on the mechanical properties of hypoeutectic CGI alloys.

    Fulltekst tilgjengelig fra 2021-04-22 00:00
  • 31.
    Hernando, Juan Carlos
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Diószegi, Attila
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    The morphological evolution of primary austenite during isothermal coarsening2017Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 131, s. 492-499Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The morphological evolution of primary austenite in an industrial hypoeutectic lamellar cast iron was studied under isothermal conditions for coarsening times varying from 0 min to 96 h. The dendritic austenite structure formed during the primary solidification suffered major morphological changes during the isothermal coarsening process. After a sufficient coarsening time, dendrite fragmentation, globularization, and coalescence of austenite were studied using electron backscatter diffraction (EBSD) technique. This study confirmed that the secondary dendrite arm spacing (SDAS) is an inappropriate length scale to describe the primary austenite coarsening process for longer times. The application of shape independent quantitative parameters confirmed the reduction of the total interfacial area during microstructural coarsening. The modulus of the primary austenite, Mγ, which represents the volume-surface ratio for the austenite phase, and the spatial distribution of the austenite particles, measured as the nearest distance between the center of gravity of neighboring particles, Dγ, followed a linear relation with the cube root of coarsening time during the whole coarsening process. The mean curvature of the austenite interface, characterized through stereological relations, showed a linear relation to Mγ and Dγ, allowing the quantitative characterization and modeling of the complete coarsening process of primary austenite.

  • 32.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ciavatta, Matteo
    University of Bologna, Bologna, Italy.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Svensson, Ingvar L.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Effect of Boron and Cross-Section Thickness on Microstructure and Mechanical Properties of Ductile Iron2018Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 925, s. 249-256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Eeffect of Boron addition on the microstructure and mechanical properties of ductile iron, GJS-500-7 grade was studied. Three cast batches with the Boron content of 10, 49 and 131ppm were cast in a casting geometry containing plates with thicknesses of 7, 15, 30, 50 and 75mm. Microstructure analysis, tensile test, and hardness test were performed on the samples which were machined from the casting plates. Addition of 49 ppm Boron decreased pearlite fraction by an average of 34±6% in all the cast plates. However, minor changes were observed in the pearlite fraction by increasing Boron from 49 to 131 ppm. Variation in the plate thickness did not affect the pearlite fraction. The 0.2% offset yield and ultimate tensile strength was decreased by an average of 11±1% and 18±2%, respectively. Addition of 49 ppm Boron decreased Brinell hardness by 16±1%, while 11±2% reduction was obtained by addition of 131ppm Boron.

  • 33.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Elmquist, Lennart
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Development of a pattern making method for strain measurement on microstructural level in ferritic cast iron2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The current paper focuses on development of a method for studying micro-scale strains on the microstructure of ferritic cast iron. For this purpose, in-situ tensile tests were done under the optical microscope combined with digital image correlation (DIC). Critical in this development was to be able to achieve a reliable high spatial resolution of strain around microstructural features, such as graphite particles. Measurement of local strain fi elds in cast iron materials have so far been relying on displacement of naturally occurring microstructure patterns such as graphite particles, which limits the spatial resolution of strain measurement. In order to increase the spatial resolution of the measured strain, a pit etching procedure was applied to generate a random speckle pattern on the ferritic matrix. Th e critical challenges of in-situ investigation of microstructural deformation were identifi ed as speckle pattern quality and accurate selection of subset size and strain window size. Th e traceability of this method was studied by benchmarking the measured elastic modulus with that obtained from full-scale tensile test. Th e elastic modulus calculated from average strains, measured by DIC, showed a good agreement with material’s elastic modulus. Th is validates the measured localized strain values and can be used as a validation for modeling of local deformation.

  • 34.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Micro-Crack Initiation in High-Silicon Cast Iron during Tension Loading2015Inngår i: TMS2015 Supplemental Proceedings, The Minerals, Metals, and Materials Society, 2015, John Wiley & Sons, 2015, s. 947-953Konferansepaper (Fagfellevurdert)
  • 35.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Salomonsson, Kent
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Produktutveckling. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    Jarfors, Anders E. W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Microstructural strain distribution in ductile iron; Comparison between finite element simulation and digital image correlation measurements2015Rapport (Annet vitenskapelig)
    Abstract [en]

    This paper presents a study on micro-scale deformation and the effect of microstructure on localised deformation of ductile iron, utilizing in-situ tension testing, digital image correlation (DIC) and finite element analysis (FEA). A tensile stage integrated with an optical microscope was used to acquire a series of micrographs during the tensile test. Applying DIC and an etched speckle pattern, a high resolution local strain field was measured in the microstructure. In addition, a finite element (FE) model was used to predict the strain maps. The materials parameters were optimized based on Ramberg-Osgood model. The DIC and simulation strain maps conformed to a large extent resulting in the verification of the model in micro-scale level. It was found that the Ramberg-Osgood theory can be used to capture the main trends of strain localization. The discrepancies between the simulated and DIC results were explained based on microstructure dimensionality, differences in spatial resolution and uncertainty in the FE-model.

  • 36.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Salomonsson, Kent
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    Jarfors, Anders E. W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Microstructural strain localization and crack evolution in ductile iron2015Rapport (Annet vitenskapelig)
    Abstract [en]

    This paper focuses on the deformation and crack evolution in ductile iron under tension, investigated by coupled in-situ tensile test and finite element simulation. Micro-crack initiation and development were tracked at the microstructure level. The local strain around micro-cracks were measured by using Digital Image Correlation (DIC). The results obtained from the experiments were compared to a finite element  model including cohesive elements to enable crack propagation. The resulting local strains were analyzed in connection to the observed micro-crack incidents in both DIC and simulation. The predictions of the finite element model showed good agreement with those obtained from the experiment, in the case of early decohesion, the amplitude of the strain localization and macroscopic stress-strain behavior. The results revealed that decohesion was commonly initiated early around graphite surrounded by ferrite which was identified as high strain regions. By increasing the global deformation, micro-cracks initiated in these areas and propagated but were arrested within the ferrite zone due to strain hardening and stress shielding of pearlite. Both the DIC and the simulation revealed that irregular shaped graphite were more susceptible to strain localization and micro-crack initiation. It could be observed that the cohesive model was able to capture the main trends of localized plastic deformation and crack initiation

  • 37.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Salomonsson, Kent
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Produktutveckling.
    Sujakhu, S.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Castagne, S.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Strain localization and crack formation effects on stress-strain response of ductile iron2017Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 702, s. 265-271Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The strain localization and crack formation in ferritic-pearlitic ductile iron under tension was investigated by in-situ tensile tests. In-situ tensile tests under optical microscope were performed and the onset of the early ferrite-graphite decohesions and micro-cracks inside the matrix were studied. The results revealed that early ferrite-graphite decohesion and micro-cracks inside the ferrite were formed at the stress range of 280–330 MPa, where a kink occurred in the stress-strain response, suggesting the dissipation of energy in both plastic deformation and crack initiation. Some micro-cracks initiated and propagated inside the ferrite but were arrested within the ferrite zone before propagating in the pearlite. Digital Image Correlation (DIC) was used to measure local strains in the deformed micrographs obtained from the in-situ tensile test. Higher strain localization in the microstructure was measured for the areas in which the early ferrite-graphite decohesions occurred or the micro-cracks initiated.

  • 38.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Salomonsson, Kent
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Sujakhu, Surendra
    Nanyang Technological University, School of Mechanical and Aerospace Engineering, Singapore.
    Castagne, Sylvie
    KU Leuven, Department of Mechanical Engineering, Leuven, Belgium.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Microstructural strain mapping during in-situ cyclic testing of ductile iron2018Inngår i: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 140, s. 333-339Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper focuses on local strain distribution in the microstructure of high silicon ductile iron during cyclic loading. In-situ cyclic test was performed on compact-tension (CT) samples inside the scanning electron microscope (SEM) to record the whole deformation and obtain micrographs for microstructural strain measurement by means of digital image correlation (DIC) technique. Focused ion beam (FIB) milling was used to generate speckle patterns necessary for DIC measurement. The equivalent Von Mises strain distribution was measured in the microstructure at the maximum applied load. The results revealed a heterogeneous strain distribution at the microstructural level with higher strain gradients close to the notch of the CT sample and accumulated strain bands between graphite particles. Local strain ahead of the early initiated micro-cracks was quantitatively measured, showing high strain localization, which decreased by moving away from the micro-crack tip. It could be observed that the peak of strain in the field of view was not necessarily located ahead of the micro-cracks tip which could be because of the (i) strain relaxation due to the presence of other micro-cracks and/or (ii) presence of subsurface microstructural features such as graphite particles that influenced the strain concentration on the surface.

    Fulltekst tilgjengelig fra 2020-04-12 00:00
  • 39.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Svensson, Ingvar L.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Olofsson, Jakob
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning. Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Characterization and modeling of the mechanical behavior of high silicon ductile iron2017Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 708, s. 159-170Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper investigates the effect of the solidification conditions and silicon content on the mechanical properties of ductile iron and presents empirical models for predicting the tensile behavior based on the microstructural characterizations. Two ductile iron grades of GJS-500-7 and GJS-500-14 were cast with silicon content of 2.36% and 3.71%, respectively. The cast geometry consisted of six plates with different thicknesses that provided different cooling rates during the solidification. Microstructure analysis, tensile and hardness tests were performed on the as-cast material. Tensile behavior was characterized by the Ludwigson equation. The tensile fracture surfaces were analyzed to quantify the fraction of porosity. The results showed that graphite content, graphite nodule count, ferrite fraction and yield strength were increased by increasing the silicon content. A higher silicon content resulted in lower work hardening exponent and strength coefficient on the Ludwigson equation. The results for 0.2% offset yield and the Ludwigson equation parameters were modeled based on microstructural characteristics, with influence of silicon content as the main contributing factor. The models were implemented into a casting process simulation to enable prediction of microstructure-based tensile behavior. A good agreement was obtained between measured and simulated tensile behavior, validating the predictions of simulation in cast components with similar microstructural characteristics.

  • 40.
    Kasvayee, Keivan Amiri
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Salomonsson, Kent
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Produktutveckling. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning. Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Microstructural strain distribution in ductile iron: Comparison between finite element simulation and digital image correlation measurements2016Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 655, s. 27-35Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a study on microstructural deformation of a ferritic–pearlitic ductile iron, utilizing in-situ tensile testing, digital image correlation (DIC) and finite element analysis (FEA). For this purpose, the in-situ tensile test and DIC were used to measure local strain fields in the deformed microstructure. Furthermore, a continuum finite element (FE) model was used to predict the strain maps in the microstructure. Ferrite and pearlite parameters for the FE-model were optimized based on the Ramberg–Osgood relation. The DIC and simulation strain maps were compared qualitatively and quantitatively. Similar strain patterns containing shear bands in identical locations were observed in both strain maps. The average and localized strain values of the DIC and simulation conformed to a large extent. It was found that the Ramberg–Osgood model can be used to capture the main trends of strain localization. The discrepancies between the simulated and DIC results were explained based on the; (i) subsurface effect of the microstructure; (ii) differences in the strain spatial resolutions of the DIC and simulation and (iii) abrupt changes in strain prediction of the continuum FE-model in the interface of the phases due to the sudden changes in the elastic modulus.

  • 41.
    Keller, Christina
    et al.
    Högskolan i Jönköping, Internationella Handelshögskolan, IHH, Informatik.
    Wass, Sofie
    Högskolan i Jönköping, Internationella Handelshögskolan, IHH, Informatik.
    Zetterlind, Madelene
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Industriell organisation och produktion.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Seifeddine, Salem
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Teacher roles in a blended learning materials engineering master program: "It's not a new role, it's a new way!"2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Engineering education are characterized by laboratories, mathematical foundations and design tools. These pillars of engineering education do not seem to be ideal for online education as the field lags behind other fields in adopting online education. Laboratories are for instance hard to implement online due to the need of direct operation of instruments. Likewise, course materials requiring use of mathematics have traditionally not been as easy to implement as topics that require only text-based instructions (Bourne et al., 2005). Real laboratory sessions have also shown to be more motivated for engineering students than virtual simulations (Stefanovic, 2013). In spite of this, there are increasing evidence of use of blended and online learning in engineering education. For example, online self-study environment to supplement the classroom instruction in engineering courses in graphical communication (Sun et al., 2014), virtual laboratories and simulation environments (Balamuraithara & Woods, 2007; Bourne et al., 2005) and online platforms for developing learning networks for global engineering (Meikleham et al. 2015). The School of Engineering at Jönköping University, the Swedish foundry association, the research institute Swerea/SWECAST and twelve foundry industries cooperate to develop a blended learning one-year master program in product development in materials and manufacturing. As previously performed courses have been given on campus, teachers needed to take on new roles as blended learning teachers. In this paper, we present the initial results from a study that aims to investigate the perceived roles of university teachers in a blended learning materials engineering master program.

  • 42.
    Kermanpur, A.
    et al.
    Department of Materials Engineering, Isfahan University of Technology.
    Ghassemali, Ehsan
    tment of Materials Engineering, Isfahan University of Technology.
    Salemizadeh, S.
    tment of Materials Engineering, Isfahan University of Technology.
    Synthesis and characterisation of microporous titania membranes by dip-coating of anodised alumina substrates using sol–gel method2008Inngår i: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 461, nr 1-2, s. 331-335Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this work was to synthesis microporous titania membranes by dip-coating of symmetric mesoporous anodised alumina substrates using sol–gel method. A stable titania sol containing nanoparticles was first prepared by establishing the proper values of the acid/alkoxide and the water/alkoxide molar ratios and pH. The titania sol was then utilised to dip-coat the anodised alumina substrates. The effects of dipping time, withdrawal rate, and sintering temperature were studied for both single- and double-layer coated samples. The thickness, structure and phase analysis of the coated membranes were characterised using thermogravimetric analysis, scanning electron microscopy and X-ray diffraction. The process conditions to achieve uniform, microporous titania coatings on the mesoporous alumina substrates were proposed.

  • 43.
    Matsushita, Taishi
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Saro, Albano Gómez
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Elmquist, Lennart
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    On Thermal Expansion and Density of CGI and SGI Cast Irons2015Inngår i: Metals, ISSN 2075-4701, Vol. 5, nr 2, s. 1000-1019, artikkel-id met5021000Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The thermal expansion and density of Compacted Graphite Iron (CGI) and Spheroidal Graphite Iron (SGI) were measured in the temperature range of 25–500 °C using push-rod type dilatometer. The coefficient of the thermal expansion (CTE) of cast iron can be expressed by the following equation: CTE = 1.38 × 10−5 + 5.38 × 10−8 N − 5.85 × 10−7 G + 1.85 × 10−8 T − 2.41 × 10−6 RP/F − 1.28 × 10−8 NG − 2.97 × 10−7 GRP/F + 4.65 × 10−9 TRP/F + 1.08 × 10−7 G2 − 4.80 × 10−11 T2 (N: Nodularity, G: Area fraction of graphite (%), T: Temperature (°C), RP/F: Pearlite/Ferrite ratio in the matrix).

  • 44.
    Rasouli, D.
    et al.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Kermanpur, A.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Najafizadeh, A.
    Department of Materials Engineering, Isfahan University of Technology, Isfahan, Iran.
    On the reversion and recrystallization of austenite in the interstitially alloyed Ni-free nano/ultrafine grained austenitic stainless steels2019Inngår i: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 25, nr 4, s. 846-859Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The martensite reversion treatment was conducted on two grades of Ni-free austenitic stainless steels interstitially alloyed with C and N. The hot rolled sheets of steels were cold rolled up to 80% thickness reduction to acquire strain-induced α′-martensite and subsequently reversion annealed at temperatures from 700 to 850 °C for 1 to 1000 s to revert the α′-martensite to austenite. Microstructural evolution was investigated using optical microscopy, X-ray diffraction, electron backscatter diffraction, and magnetic measurement techniques. Mechanical properties were measured using tensile tests at room temperature. The resultant microstructures contained both reverted and recrystallized austenite when reverted at 700 and 750 °C with the annealing time less than 100 s. A nonuniform grain structure was characterized under these conditions consisting of nano/ultrafine grains formed via α′-martensite reversion and coarser grains by recrystallization of the retained austenite. However, a more uniform austenite grain size with average size of 1 μm was obtained at 850 °C for 1000 s. The specimens having nonuniform grain structure exhibited excellent combinations of strength and ductility. A variety of mechanical properties was achieved depending on the annealing condition. The work hardening behavior affected UTS and ductility of the studied steels. The shift of the work hardening peaks to the higher strains was found suitable for ductility. Addition of C to N-containing Ni-free steels deteriorated mechanical properties. Best combination of strength and elongation was obtained in the test material with lower C/N ratio. 

  • 45.
    Rastegari, H.
    et al.
    Department of Engineering, Birjand University of Technology.
    Kermanpur, A.
    Department of Materials Engineering, Isfahan University of Technology.
    Najafizadeh, A.
    Fould Institute of Technology.
    Somani, M.C.
    Centre for Advanced Steels Research, University of Oulu.
    Porter, D.A.
    Centre for Advanced Steels Research, University of Oulu.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH. Forskningsmiljö Material och tillverkning – Gjutning.
    Determination of processing maps for the warm working of vanadium microalloyed eutectoid steels2016Inngår i: Materials Science and Engineering: A, ISSN 0921-5093, Vol. 658, s. 167-175Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Microalloying of an eutectoid steel with V may facilitate formation of dispersed nano-scaled VC particles in the microstructure during thermomechanical processing or subsequent heat treatment. In this research, the constitutive flow behavior of vanadium microalloyed eutectoid steel has been investigated in the temperature range 620–770 °C at strain rates in the range 0.01–10 s−1. Microstructural characterization of the deformed specimens was conducted using SEM and EBSD techniques. In this context, various deformation mechanisms occurring during warm deformation have been characterized and delineated through construction of a processing map by establishing a power dissipation map and an instability map for the steel and superimposing them. The results show that the pearlitic microstructure exhibits several deformation mechanisms within these warm working conditions. Dynamic spheroidization of cementite lamella takes place in the range 660–720 °C and 0.01–0.1 s−1 with a power dissipation efficiency of 27–33%, characterizing a safe window of processing this steel. The presence of vanadium carbides at grain boundaries strengthened the pearlitic microstructure and retarded the occurrence of some deformation defects during low temperature, high speed deformation in the range 620–720 °C and 1–10 s−1.

  • 46.
    Riestra, Martin
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Bjurenstedt, Anton
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Bogdanoff, Toni
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Complexities in the assessment of melt quality2018Inngår i: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193, Vol. 12, nr 3, s. 441-448Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    If high-performance aluminium castings are to be produced, the melt quality needs to be properly assured. Multiple tests for melt quality assessment exist and have previously been analysed. In most studies, the techniques were used separately. In this work, reduced pressure, fluidity, Prefil and tensile tests were evaluated. A commercial EN 46000 alloy was used as the base material with additions of 25 and 50 wt% machining chips to degrade the melt quality. In reduced pressure and fluidity tests, oxides floated to the top of samples, decreasing the reliability. Bifilm index increased with addition level, but not correspondingly. Density index, Prefil and fluidity tests did not present significant variations, and tensile properties only deteriorated with the 50 wt% addition level. The investigated techniques provided information, but measuring the melt quality reliably remains a challenge.

  • 47.
    Riestra, Martin
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Bogdanoff, Toni
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Seifeddine, Salem
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Interactive effects of grain refinement, eutectic modification and solidification rate on tensile properties of Al-10Si alloy2017Inngår i: Journal of materials processing & manufacturing science (Print), ISSN 1062-0656, E-ISSN 1530-8065, Vol. 703, s. 270-279Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study aims to clarify the effect of grain size and Si modification on the microstructure and tensile properties of the Al-10Si cast alloy, solidified under various cooling rates. To replicate the effect of cooling rate, directionally solidified samples were produced by remelting of the as-cast cylindrical bars. Tensile properties, grain sizes, Si modification level and chemical composition profiles were evaluated. Results showed that fast cooling rates alone, without the addition of grain refiners (Al-5Ti-1B master alloy), did not lead to equiaxed grain morphologies. On the other hand, for the slowest cooling rate tested, combined additions of the Al-5Ti-1B and the Al-10Sr master alloys resulted in equiaxed grain structures while addition of only grain refiner resulted in columnar grains. The combined additions effectively produced an equiaxed grain structure at all cooling rates tested, and further improved the tensile properties.

  • 48.
    Sujakhu, S.
    et al.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Castagne, S.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Sakaguchi, M.
    Department of Mechanical Engineering, Tokyo Institute of Technology, Tokyo, Japan.
    Kasvayee, Keivan Amiri
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Jarfors, Anders E.W.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Wang, W.
    Advance Remanufacturing and Technology Centre, Singapore.
    On the fatigue damage micromechanisms in Si-solution-strengthened spheroidal graphite cast iron2018Inngår i: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 41, nr 3, s. 625-641Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Graphite nodules in spheroidal graphite cast iron (SGI) play a vital role in fatigue crack initiation and propagation. Graphite nodules growth morphology can go through transitions to form degenerated graphite elements other than spheroidal graphite nodules in SGI microstructure. These graphite particles significantly influence damage micromechanisms in SGI and could act differently than spheroidal graphite nodules. Most of the damage mechanism studies on SGI focused on the role of spheroidal graphite nodules on the stable crack propagation region. The role of degenerated graphite elements on SGI damage mechanisms has not been frequently studied. In this work, fatigue crack initiation and propagation tests were conducted on EN-GJS-500-14 and observed under scanning electron microscope to understand the damage mechanisms for different graphite shapes. Crack initiation tests showed a dominant influence of degenerated graphite elements where early cracks initiated in the microstructure. Most of the spheroidal graphite nodules were unaffected at the early crack initiation stage, but few of them showed decohesion from the ferrite matrix and internal cracking. In the crack propagation region, graphite/ferrite matrix decohesion was the frequent damage mechanism observed with noticeable crack branching around graphite nodules and the crack passing through degenerated graphite elements. Finally, graphite nodules after decohesion acted like voids which grew and coalesced to form microcracks eventually causing rapid fracture of the remaining section.

  • 49.
    Svidró, József Tamás
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Seifeddine, Salem
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Innovation in knowledge transfer from academia to the foundry industry - An advanced case2018Inngår i: 73rd World Foundry Congress "Creative Foundry", WFC 2018 - Proceedings, Stowarzyszenie Techniczne Odlewnikow Polskich/Polish Foundrymen's Association , 2018, s. 633-633Konferansepaper (Fagfellevurdert)
  • 50.
    Vahiddastjerdi, H.
    et al.
    Department of Materials Engineering, Isfahan University of Technology (IUT), Isfahan, Iran.
    Rezaeian, A.
    Department of Materials Engineering, Isfahan University of Technology (IUT), Isfahan, Iran.
    Toroghinejad, M. R.
    Department of Materials Engineering, Isfahan University of Technology (IUT), Isfahan, Iran.
    Dini, G.
    Department of Nanotechnology Engineering, Faculty of Advanced Sciences and Technologies University of Isfahan, Isfahan, Iran.
    Ghassemali, Ehsan
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Material och tillverkning.
    Optimizing pulsed Nd: YAG laser welding of high-Mn TWIP steel using response surface methodology technique2019Inngår i: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 120, artikkel-id 105721Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, the microstructural and mechanical properties of laser beam-welded thin sheet twinning-induced plasticity (TWIP) steel were investigated. The pulsed neodymium: yttrium-aluminum-garnet (Nd: YAG) laser beam welding process parameters were modeled and optimized based on experimental data and statistical analysis using response surface methodology (RSM) technique. Process parameters range, i.e. the power input (2000–3000 W), welding speed (0.2–1 mm/min), and spot size (0.3–0.7 mm) were selected properly in order to obtain the desired mechanical properties. Main effects of each factor along with interaction effect with other factors were determined quantitatively. The predicted and actual values of the mechanical properties compared using analysis of variance (ANOVA) in order to verify the adequacy of the developed model. Optimal laser beam welding parameters were identified as the power input, welding speed and spot size of 2586 W, 0.53 mm/min, and 0.48 mm, respectively. Using parameters in the optimal conditions, a welding joint with tensile load of 2001 N (% 94 strength of the base metal) was obtained. In addition, the welding zone with an average grain size coarser than the one for the base metal and a random texture was identified.

12 1 - 50 of 52
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