Speaker
Description
Spark Plasma Sintering (SPS) is a powder metallurgy technique used for the elaboration of dense materials with a fine-grained microstructure [1]. In this process, a pulsed electric current and a uniaxial pressure are applied simultaneously, leading to high heating and cooling rates, thus limiting the grain growth [2]. The powder is placed into a graphite die and the pressure is applied by two graphite punches. A graphite foil is inserted between the punches and the powder and between the die and the powder to ensure a good electrical, physical and thermal contact [3]. In the case of the SPS sintering of metallic powders, one of the major drawbacks is the carburization of the powder in contact with the graphite tooling. This phenomenon is particularly pronounced in the case of Fe-based powders. The length of the carburized area could reach some hundred microns, depending on the powder composition, then affecting the integrity of the sintered material. In this study, a PVD coating of a carbide element (Ti) was applied on the graphite foils in contact with the metallic powder (pure iron), in order to limit the carburization phenomenon. Several coatings’ thicknesses were tested ranging from few hundreds of nanometers to more than one micron. The contact zones between the coated graphite foils and the metallic powder were analysed by optical microscopy and scanning electron microscopy coupled with EDX. The results showed that a Ti PVD coating is effective to prevent carburization of the metallic sintered sample. The effect of the PVD layer thickness on the diffusion mechanisms is also compared and discussed.
[1] Y. Zhang et al., Mater. Trans., 46 (9) (2005) 2015-2019.
[2] Z.A. Munir et al., J. Mater. Sci. 41 (3) (2006) 763-777.
[3] K. Vanmeensel et al., Acta Mater. 53 (2005) 4379–4388.
| Speaker Country | France |
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