Densification of nanocrystalline Y2O3 ceramic powder by spark plasma sintering

Nanocrystalline Y2O3 powders with 18 nm crystallite size were sintered using spark plasma sintering (SPS) at different conditions between 1100 and 1600 °C. Dense specimens were fabricated at 100 MPa and 1400 °C for 5 min duration. A maximum in density was observed at 1400 °C. The grain size continuously increased with the SPS temperature into the micrometer size range. The maximum in density arises from competition between densification and grain growth. Retarded densification above 1400 °C is associated with enhanced grain growth that resulted in residual pores within the grains. Analysis of the grain growth kinetics resulted in activation energy of 150 kJ mol−1 and associated diffusion coefficients higher by 103 than expected for Y3+ grain boundary diffusion. The enhanced diffusion may be explained by combined surface diffusion and particle coarsening during the heating up with grain boundary diffusion at the SPS temperature.