Theoretical and experimental investigations of local overheating at particle contacts in spark plasma sintering

This paper analyzes the heating of TiAl powders at particle scale in spark plasma sintering (SPS). During SPS processing, the powder particles are subjected to uniaxial pressing and small contact areas are formed between particles. Numerical simulations are performed on a representative cell of the material and qualitatively compared to experiments. In order to understand the heating mechanisms involved in SPS, two models are analyzed. The first one considers only heat diffusion in the material. The second one associates local Joule heating due to current concentration and heat diffusion. In TiAl alloys, the γ-α phase transition at 1335°C was used as marker of the temperature reached locally. More than 100 particle necks of several samples of 100μm diameter Ti48Al48Cr2Nb2 powders processed by SPS were investigated to detect overheating marks. Simulations clearly show high current concentration in and close to the necks, but both simulations and experiments show that there is no heat concentration close to the necks for this size of particles. Simulations show that this is due to fast heat dissipation in small particles: centimetric or higher size particles would be required to observe significant overheating.