Effect of starting powder particle size and heating rate on spark plasma sintering of Fe-Ni alloys

The effect of starting powder particle size and heating rate on spark plasma sintering of Fe-Ni alloys was investigated, with the particle powder size varying from 3 to 70 mm and heating rate from 50 to 150 degrees C/min. The effect of the starting powder particle size was more obvious when comparing 3-FeNi and 70-FeNi at all heating rates, with the former having better density and hardness than the latter. Sintered densities close to theoretical (>= 99%) were achieved for a heating rate of 50 degrees C/min for the different starting particle size powders, and decreased with increasing heating rate. The average grain size of alloys sintered at 150 degrees C/min was similar to 34% smaller than those sintered at 50 degrees C/min. The porosity content of the sintered samples increased with increasing heating for the same particle size. The shrinkage rate depends on both heating rate and particle size. At a particle size of 3 mm and a heating rate of 50 degrees C/min, three peaks were observed indicative of the phenomena responsible for good densification. As the heating rate increases, only two peaks and one peak are observed at heating rates of 100 and 150 degrees C/min, respectively. This suggests that, unlike high heating rates, the longer processing time at low heating rate allows the three phenomena to take place. The hardness measurement revealed a steady decrease with increasing heating rate. At a heating rate of 150 degrees C/min the particles were well packed but no typical dimple structure of a ductile material was observed. However, for samples sintered at 50 and 100 degrees C/min a typical dimple fracture morphology was observed. (C) 2016 Elsevier B.V. All rights reserved.