Powder Technology, Vol.321, 458-470, 2017
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. Nunierical 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 gamma-alpha phase transition at 1335 degrees C was used as marker of the temperature reached locally. More than 100 particle necks of several samples of 100 mu m 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. (C) 2017 Elsevier B.V. All rights reserved.