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Sreekanth, S., Ghassemali, E., Hurtig, K., Joshi, S. & Andersson, J. (2020). Effect of direct energy deposition process parameters on single-track deposits of alloy 718. Metals, 10(1), Article ID 96.
Open this publication in new window or tab >>Effect of direct energy deposition process parameters on single-track deposits of alloy 718
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2020 (English)In: Metals, ISSN 2075-4701, Vol. 10, no 1, article id 96Article in journal (Refereed) Published
Abstract [en]

The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm2 and 1.0 J/mm2) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4–9.6% area fraction, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The <100> crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.

Place, publisher, year, edition, pages
MDPI, 2020
Keywords
Columnar dendritic morphology, Columnar to equiaxed transition (CET), Constitutional supercooling, High deposition rate, Laser metal deposition (LMD)
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hj:diva-47590 (URN)10.3390/met10010096 (DOI)000516827800096 ()2-s2.0-85077843217 (Scopus ID)GOA JTH 2020 (Local ID)GOA JTH 2020 (Archive number)GOA JTH 2020 (OAI)
Funder
VinnovaKnowledge Foundation
Available from: 2020-01-29 Created: 2020-01-29 Last updated: 2020-03-31Bibliographically approved
Hernando, J. C., Elfsberg, J., Ghassemali, E., Dahle, A. & Diószegi, A. (2020). The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys. International Journal of metalcasting
Open this publication in new window or tab >>The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys
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2020 (English)In: International Journal of metalcasting, ISSN 1939-5981, E-ISSN 2163-3193Article in journal (Refereed) Epub ahead of print
Abstract [en]

This work investigates the role of primary austenite morphology on the eutectic and eutectoid microstructures and the ultimate tensile strength (UTS) in a hypoeutectic compacted graphite iron (CGI) alloy. The morphology of primary austenite is modified by isothermal coarsening experiments in which holding times up to 60 min are applied to the solid–liquid region after coherency. The cooling conditions for the subsequent eutectic and eutectoid reactions are similar. Miniaturized tensile tests are performed to evaluate the UTS. The morphological characteristics related to the surface area of primary austenite, the modulus of primary austenite, Mγ, and the hydraulic diameter of the interdendritic region, DHydID, increase with the cube root of coarsening time. The eutectic and eutectoid microstructures are not significantly affected by the morphology of primary austenite, thus indicating that the morphology of the interdendritic regions does not control the nucleation frequency and growth of eutectic cells or graphite. UTS decreases linearly with the increasing coarseness of primary austenite for similar eutectic and eutectoid microstructures, demonstrating the strong influence of primary austenite morphology on the UTS in hypoeutectic CGI alloys.

Place, publisher, year, edition, pages
Springer, 2020
Keywords
cast iron, compacted graphite iron, CGI, solidification, dendrites, primary austenite, UTS
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-47569 (URN)10.1007/s40962-020-00410-9 (DOI)000515610600001 ()2-s2.0-85078435803 (Scopus ID)
Funder
Vinnova, 2013-03303Knowledge Foundation, 2018-0033
Note

This paper is an invited submission to IJMC selected from presentations at the 2nd Carl Loper 2019 Cast Iron Symposium held September 30 to October 1, 2019, in Bilbao, Spain.

Available from: 2020-01-28 Created: 2020-01-28 Last updated: 2020-03-18
Rasouli, D., Kermanpur, A., Ghassemali, E. & Najafizadeh, A. (2019). On the reversion and recrystallization of austenite in the interstitially alloyed Ni-free nano/ultrafine grained austenitic stainless steels. Metals and Materials International, 25(4), 846-859
Open this publication in new window or tab >>On the reversion and recrystallization of austenite in the interstitially alloyed Ni-free nano/ultrafine grained austenitic stainless steels
2019 (English)In: Metals and Materials International, ISSN 1598-9623, E-ISSN 2005-4149, Vol. 25, no 4, p. 846-859Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Interstitially alloyed austenitic stainless steel, Mechanical properties, Nano/ultrafine grain size, Ni-free stainless steel, Recrystallization, Reversion annealing
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-45489 (URN)10.1007/s12540-019-00255-w (DOI)000473163200003 ()2-s2.0-85061302943 (Scopus ID)
Available from: 2019-08-08 Created: 2019-08-08 Last updated: 2019-08-08Bibliographically approved
Vahiddastjerdi, H., Rezaeian, A., Toroghinejad, M. R., Dini, G. & Ghassemali, E. (2019). Optimizing pulsed Nd: YAG laser welding of high-Mn TWIP steel using response surface methodology technique. Optics and Laser Technology, 120, Article ID 105721.
Open this publication in new window or tab >>Optimizing pulsed Nd: YAG laser welding of high-Mn TWIP steel using response surface methodology technique
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2019 (English)In: Optics and Laser Technology, ISSN 0030-3992, E-ISSN 1879-2545, Vol. 120, article id 105721Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Pulsed Nd: YAG laser welding, Twinning-induced plasticity (TWIP) steel, Response surface methodology (RSM), Optimization
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-45493 (URN)10.1016/j.optlastec.2019.105721 (DOI)000487569900046 ()2-s2.0-85070098714 (Scopus ID);JTHMaterialIS (Local ID);JTHMaterialIS (Archive number);JTHMaterialIS (OAI)
Note

PP-check JTH 2019 embargo 24 / EE

Available from: 2019-08-08 Created: 2019-08-08 Last updated: 2019-10-29Bibliographically approved
Bogdanoff, T., Ghassemali, E., Riestra, M. & Seifeddine, S. (2019). Prototyping of a high pressure die cast al-si alloy using plaster mold casting to replicate corresponding mechanical properties. In: Minerals, Metals and Materials Series: . Paper presented at Light Metals Symposium held at the TMS Annual Meeting and Exhibition, 2019, San Antonio, United States, 10 - 14 March 2019 (pp. 435-442). Springer
Open this publication in new window or tab >>Prototyping of a high pressure die cast al-si alloy using plaster mold casting to replicate corresponding mechanical properties
2019 (English)In: Minerals, Metals and Materials Series, Springer, 2019, p. 435-442Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Aluminium alloys, Heat treatment, Prototyping, Aluminum alloys, Die casting, Light metals, Mechanical properties, Molds, Plaster, Product design, Software prototyping, Tensile strength, Tensile testing, Yield stress, Commercial alloys, Design criteria, Design optimization, Dimension accuracy, High pressure die casting, High pressure die casts, T6 heat treatment, Ultimate tensile strength, Silicon alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-43728 (URN)10.1007/978-3-030-05864-7_56 (DOI)2-s2.0-85064856753 (Scopus ID)9783030058630 (ISBN)9783030058647 (ISBN)
Conference
Light Metals Symposium held at the TMS Annual Meeting and Exhibition, 2019, San Antonio, United States, 10 - 14 March 2019
Available from: 2019-05-22 Created: 2019-05-22 Last updated: 2019-05-22Bibliographically approved
Ghassemali, E., Hernando, J. C., Stefanescu, D. M., Diószegi, A., Jarfors, A. E. .., Dluhoš, J. & Petrenec, M. (2019). Revisiting the graphite nodule in ductile iron. Scripta Materialia, 161, 66-69
Open this publication in new window or tab >>Revisiting the graphite nodule in ductile iron
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2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 161, p. 66-69Article in journal (Refereed) Published
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. 

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
3D reconstruction, FIB, Growth mechanism, Solidification, Ductility, Graphite, Iron, Scanning electron microscopy, 3-d tomographies, Graphite nodules, Growth mechanisms, High resolution, Iron Particles, Micro voids, Radial direction, Cast iron
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-41986 (URN)10.1016/j.scriptamat.2018.10.018 (DOI)000450375500015 ()2-s2.0-85055115924 (Scopus ID);JTHMaterialIS (Local ID);JTHMaterialIS (Archive number);JTHMaterialIS (OAI)
Available from: 2018-11-07 Created: 2018-11-07 Last updated: 2020-01-20Bibliographically approved
Hajiannia, I., Shamanian, M., Atapour, M., Ashiri, R. & Ghassemali, E. (2019). The assessment of second pulse effects on the microstructure and fracture behavior of the resistance spot welding in advanced ultrahigh-strength steel TRIP1100. Iranian Journal of Materials Science and Engineering, 16(2), 79-88
Open this publication in new window or tab >>The assessment of second pulse effects on the microstructure and fracture behavior of the resistance spot welding in advanced ultrahigh-strength steel TRIP1100
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2019 (English)In: Iranian Journal of Materials Science and Engineering, ISSN 1735-0808, Vol. 16, no 2, p. 79-88Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Iran University of Science and Technology, 2019
Keywords
Dendritic microstructure, Fracture surface, Resistance spot welding, Second pulse current, Shear tensile
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-45390 (URN)10.22068/ijmse.16.2.79 (DOI)000472646400008 ()2-s2.0-85068678947 (Scopus ID)POA JTH 2019;JTHMaterialIS (Local ID)POA JTH 2019;JTHMaterialIS (Archive number)POA JTH 2019;JTHMaterialIS (OAI)
Available from: 2019-07-23 Created: 2019-07-23 Last updated: 2019-07-23Bibliographically approved
Hernando, J. C., Elfsberg, J., Ghassemali, E., Dahle, A. & Diószegi, A. (2019). The effect of coarsening of primary austenite on the ultimate tensile strength of hypoeutectic compacted graphite Fe-C-Si alloys. Scripta Materialia, 168, 33-37
Open this publication in new window or tab >>The effect of coarsening of primary austenite on the ultimate tensile strength of hypoeutectic compacted graphite Fe-C-Si alloys
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2019 (English)In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 168, p. 33-37Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Coarsening, Compacted graphite iron, Dendrites, Mechanical properties, UTS, Austenite, Dendrites (metallography), Graphite, Morphology, Ostwald ripening, Silicon alloys, Tensile strength, Morphological characteristic, Primary austenite, Secondary dendrite arm spacing, Si alloys, Surface area, Ultimate tensile strength, Iron alloys
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-43550 (URN)10.1016/j.scriptamat.2019.04.010 (DOI)000470798400008 ()2-s2.0-85064563538 (Scopus ID)PP JTH 2019 embargo 24 (Local ID)PP JTH 2019 embargo 24 (Archive number)PP JTH 2019 embargo 24 (OAI)
Funder
Vinnova, 2013-03303; 2013-04720Knowledge Foundation, 2018-0033
Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2019-08-06Bibliographically approved
Bjurenstedt, A., Ghassemali, E., Seifeddine, S. & Dahle, A. (2019). The effect of Fe-rich intermetallics on crack initiation in cast aluminium: an in-situ tensile study. Materials Science & Engineering: A, 756, 502-507
Open this publication in new window or tab >>The effect of Fe-rich intermetallics on crack initiation in cast aluminium: an in-situ tensile study
2019 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 756, p. 502-507Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Al-Si alloy, Cast aluminium, Fracture mechanics, Tensile testing in SEM, α-Fe, β-Fe, Aluminum alloys, Crack initiation, Cracks, Fracture testing, Intermetallics, Materials testing apparatus, Metal testing, Scanning electron microscopy, Silicon alloys, Tensile testing
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:hj:diva-36962 (URN)10.1016/j.msea.2018.07.044 (DOI)000469893400058 ()2-s2.0-85064717473 (Scopus ID)
Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2019-06-20Bibliographically approved
Ashrafi, H., Shamanian, M., Emadi, R. & Ghassemali, E. (2019). Void formation and plastic deformation mechanism of a cold-rolled dual-phase steel during tension. Acta Metallurgica Sinica (English Letters)
Open this publication in new window or tab >>Void formation and plastic deformation mechanism of a cold-rolled dual-phase steel during tension
2019 (English)In: Acta Metallurgica Sinica (English Letters), ISSN 1006-7191, E-ISSN 2194-1289Article in journal (Refereed) Epub ahead of print
Abstract [en]

The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.

Place, publisher, year, edition, pages
Springer, 2019
Keywords
Dual-phase steel, Void nucleation, Fracture mechanism
National Category
Materials Engineering
Identifiers
urn:nbn:se:hj:diva-47166 (URN)10.1007/s40195-019-00967-3 (DOI)000500608900001 ()2-s2.0-85076148088 (Scopus ID);JTHMaterialIS (Local ID);JTHMaterialIS (Archive number);JTHMaterialIS (OAI)
Available from: 2019-12-18 Created: 2019-12-18 Last updated: 2020-01-02
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-7527-719X

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