Abstract
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 μm and heating
rate from 50 to 150 °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°C/min for the different starting particle size powders, and
decreased with increasing heating rate. The average grain size of alloys sintered at 150°C/min
was ~34% smaller than those sintered at 50°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 μm and a heating rate of
50oC/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 150oC/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°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°C/min a typical
dimple fracture morphology was observed.