Effects of spark plasma sintering parameters on the microstructure of U3Si2 pellets

In this study, U3Si2 pellets were fabricated by spark plasma sintering (SPS) of U3Si2 clinkers generated by a high-temperature solid reaction between U and Si powders. The influences of SPS operating parameters (dwell temperature from 1000 to 1300 °C and pressure from 30 to 90 MPa) on the microstructure (porosity, normal and distorted U3Si2 phase, grain size and shape) of U3Si2 pellets were analyzed. The density of U3Si2 pellets enhanced with increasing temperature and pressure and it reached of the 97.9% theoretical density (TD) at 1300 °C/60 MPa. The residual stress caused the generation of a distorted U3Si2 phase in the pellets, and low-temperature annealing at 300 °C effectively released the residual stress and eliminate the lattice distortion of U3Si2. The U3Si2 grain size increased with increasing dwell temperature and showed an opposite trend with increasing pressure. The grain growth mechanisms of the SPS-sintered U3Si2 pellets involved temperature-dependent surface diffusion and pressure-induced grain growth inhibition. The evolution of the U3Si2 grain morphology from equiaxed to columnar grains was due to plastic strain under SPS conditions.