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  • 1. Bergman, A
    et al.
    Jarfors, Anders
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Liu, Zhen
    Fredriksson, Hasse
    Insitu fomation of carbide composites by liquid-solid reactions1992In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 79/80, p. 213-234Article in journal (Refereed)
  • 2.
    Diószegi, Attila
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Björklind, Tobias
    Scania CV AB.
    Diószegi, Zoltán
    Volvo Powertrain AB.
    Surface Turbulence at Flow of Gray Cast Iron2011In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 457, p. 422-427Article in journal (Refereed)
    Abstract [en]

    Gray cast iron has been investigated with respect to surface turbulence during mould filling. Different levels of flow velocities have been provoked in a vertically parted sand mould. The thermal resistant transparent front side of the mould permitted the observation of the flow pattern due to high speed camera registration. The registered frames including the liquid surface were investigated using image analyses. The results show good correlation between the average flow velocity and the liquid iron surface extension. Consequently it has been demonstrated that an increased absorption of hydrogen and nitrogen during mould filling is dependent on the level of liquid surface turbulence.

  • 3.
    Elmquist, Lennart
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Diószegi, Attila
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting. Jönköping University, School of Engineering, JTH, Materials and Manufacturing.
    Björklind, Tobias
    On the Formation of Shrinkage Porosity in Gray Iron Castings2011In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 457, p. 416-421Article in journal (Refereed)
    Abstract [en]

    The formation of shrinkage porosity is a concern in the production of high-quality gray iron castings. In this work, a geometry known to generate this type of defect was used to investigate some of the parameters that influence its formation. The geometry is based on the presence of a migrating hot spot that at the end of the solidification is located close to the interface between the casting and the mold. The occurrence of shrinkage porosity at this position was investigated and the cavities examined using a scanning electron microscope equipped with EDS. It is believed that this type of defect is in contact with the atmosphere during solidification. The risk for shrinkage porosity decreases with increasing carbon content. The effect of high levels of molybdenum and phosphorus was investigated and shown to influence the defect formation. Inoculation is used to control the nucleation and the effect of high levels of inoculants was also examined. The microstructure was investigated by the use of a color etching technique, and the quantification considered eutectic cell size and secondary dendrite arm spacing. The quantification was done on the microstructure in the vicinity of defects as well as in areas without porosity.

  • 4.
    Elmquist, Lennart
    et al.
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Diószegi, Attila
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Svidró, Peter
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Influence of Primary Austenite on the Nucleation of Eutectic Cells2011In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 457, p. 61-66Article in journal (Refereed)
    Abstract [en]

    The solidification of gray cast iron starts with the precipitation of primary austenite. This phase nucleates either as columnar or equiaxed dendrites depending on whether nucleation occurs on the mould wall or on particles and impurities in the melt. In this work, the nucleation of primary austenite and its influence on the eutectic solidification has been investigated using different amounts of iron powder as inoculants. Besides, the influence of different cooling rates was also examined. Within each austenite grain there is a microstructure, and this microstructure was investigated using a color etching technique to reveal the eutectic cells and the dendritic network. It is shown how the cooling rate affects the dendritic network and the secondary dendrite arm spacing, and how the microstructure can be related to the macrostructure through dendrite arm spacing. The secondary dendrite arm spacing is a quantification of the primary austenite belonging to the primary solidification, and it will be shown how the eutectic cell size is related to the secondary dendrite arm spacing. The total amount of oxygen influences the microstructural dimensions. This effect, on the other hand, is influenced by the cooling rate. The number of eutectic cells versus eutectic cell size show two distinct behaviors depending on whether being inoculated with iron powder or a mixture of iron powder and commercial inoculant. The addition of a commercial inoculant decreases eutectic cell size and increases the number of cells, while iron powder almost only changes cell size.

  • 5.
    Ghassemali, E.
    et al.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Jarfors, A. E. W.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Tan, M. -J
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Lim, S. C. V.
    Singapore Institute of Manufacturing Technology (SIMTech).
    Chew, M.
    Singapore Institute of Manufacturing Technology (SIMTech).
    Investigation of microstructure and hardness in microfoming of pure copper pins2010In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 447-448, p. 381-385Article in journal (Refereed)
    Abstract [en]

    Microforming is defined as the process of production of metallic micro-parts with sub-millimeter dimension. There is as strong interaction between the scale of the microstructure and the size of the part affecting material flow, the so-called "size effect" in microforming processes. Conventional forming rules cannot be directly applied to the micro-scale forming. To better understand the implications for part geometry and properties, further investigation of the material flow related events is necessary. The aim of this work is to investigate microstructural evolution of pure copper during a micro-extrusion process - for production of micro-pins with diameters varying from 300 to 800Όm - by means of optical microscope (OM). Qualitative strain gradient distribution could be observed by those pictures. The results showed that change of micro-pins diameter and die angle affect the microstructure and strain distribution of the final product remarkably, that affect the mechanical properties of the pin formed. Furthermore, microhardness results were consistent with the microstructural observations. © (2010) Trans Tech Publications.

  • 6.
    Ghassemali, Ehsan
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Investigation of Microstructure and Hardness in Microforming of Pure Copper Pins2010In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 447-448, p. 381-Article in journal (Refereed)
  • 7.
    Goh, C. S.
    et al.
    Singapore Institute of Manufacturing Technology.
    Gupta, M.
    Department of Mechanical Engineering, National University of Singapore.
    Jarfors, A. E. W.
    Singapore Institute of Manufacturing Technology.
    Tan, M. J.
    School of Mechanical and Aerospace Engineering.
    Wei, J.
    Singapore Institute of Manufacturing Technology.
    Magnesium and Aluminium carbon nanotube composites2010In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 425, p. 245-261Article in journal (Refereed)
    Abstract [en]

    Carbon nanotubes are one of the most exciting discoveries of nanosized materials in the 20th century. Challenges to create materials applicable for industrial applications involve both the incorporation of the carbon nanotubes into the material and to ensure that they do not agglomerate. Aluminium and magnesium based materials are among the metals that can benefit from the incorporation of carbon nanotubes. The fabrication of Aluminium carbon nanotube composites has challenges from reactivity and degradation of the carbon nanotube additions; hence the powder metallurgy route is preferred. Magnesium based materials on the other hand do not have this limitation and both the powder metallurgical route and the casting route are viable. Among the benefits of adding carbon nanotubes are increased yield strength and stiffness. Here is important that the effect is significant already at very low addition levels. This makes it possible to increase strength without having a significant detrimental effect on ductility. In fact, for magnesium alloys ductility can be improved due to the activation of additional slip planes improving the normally low ductility of HCP structure materials. © (2010) Trans Tech Publications.

  • 8. Jørgensen, O.
    et al.
    Horsewell, A.
    Sørensen, B.
    Leisner, Peter
    Technical University of Denmark.
    Effect of Inhomogeneous Intrinsic Stresses on the Cracking of Layered Brittle Coatings1996In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 116-117, p. 351-370Article in journal (Refereed)
  • 9.
    Liu, J.
    et al.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Tan, M. -J
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Castagne, S.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Aue-u-lan, Y.
    Singapore Institute of Manufacturing Technology.
    Fong, K. -S
    Singapore Institute of Manufacturing Technology.
    Jarfors, A. E. W.
    School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore.
    Investigation of process parameters in superplastic forming of mechanical pre-formed sheet by FEM2010In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 447-448, p. 437-441Article in journal (Refereed)
    Abstract [en]

    Conventional superplastic forming has been applied in automotive and aerospace industries for a few decades. Recently, superplastic forming combined with mechanical pre-forming process has been reported to be capable of forming non-superplastic AA5083 at 400°C to a surface expansion of 200 % [1]. In this paper, finite element modeling (FEM) was used to develop the combined forming process by using the non-superplastic material AA5083-O. The simulation follows the experimental sequence and was divided into two phases (mechanical pre-forming and superplastic forming). A conventional creep equation based on tensile test data was adopted as a material model for the simulation. The pressure cycle and forming time was simulated according to the actual process route. The thickness distributions obtained from simulation validated the capability of the model to be used for this case. The influence of different parameters, such as holder force, friction, and punch depth was investigated by comparing the final sheet thickness and level of material draw-in. It was found that the punch depth played a significant effect on the uniformity of thickness distribution, from which a more uniform formed part can be obtained by using the punch with higher depth during mechanical pre-forming phase. © (2010) Trans Tech Publications.

  • 10.
    Selin, Martin
    Jönköping University, School of Engineering, JTH. Research area Materials and manufacturing – Casting.
    Using Regression Analysis to Optimize the Combination of Thermal Conductivity and Hardness in Compacted Graphite Iron2010In: Key Engineering Materials, ISSN 1013-9826, E-ISSN 1662-9795, Vol. 457, p. 337-342Article in journal (Refereed)
    Abstract [en]

    In cast iron there is a contradictory relationship between thermal conductivity and strength. In many applications it is desirable to optimize the material properties to obtain both sufficiently high thermal conductivity and sufficiently high strength. The aim of this paper is to investigate how various microstructure parameters and alloying elements affect thermal conductivity and hardness in compacted graphite irons. It was found that the fraction of ferrite, the fraction of cementite, nodularity and content of carbon and silicon are parameters that influence the thermal conductivity and hardness the most. Based on these five key parameters linear regression equations were created for calculation of thermal conductivity and hardness. Ferrite and carbon have a positive influence on the thermal conductivity, while silicon, cementite and nodularity have a deleterious effect. All parameters except ferrite have a positive influence on the hardness. This is because the thermal conductivity is dependent on the movement of free electrons, and therefore unfavourable growth directions and grain boundaries which impede the electron movement will reduce the thermal conductivity. Ferrite has quite high thermal conductivity, while cementite has poor thermal conductivity, due to an unfavourable crystal structure. Nodular shaped graphite has a lower thermal conductivity than compacted graphite which explains the deleterious influence of nodularity. The soft ferrite phase will reduce the hardness value, while increasing the fraction of harder graphite nodules and harder cementite phase will increase the hardness. To investigate how these five parameters affect the combination of hardness and thermal conductivity, values for hardness and thermal conductivity were calculated for all combinations of key parameters in given intervals, using two linear regression equations. From these it is possible to predict the combination of parameters which gives a particular combination of hardness and thermal conductivity in compacted graphite iron.

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