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

In this study, U ₃Si ₂ pellets were fabricated by spark plasma sintering (SPS) of U ₃Si ₂ 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 U ₃Si ₂ phase, grain size and shape) of U ₃Si ₂ pellets were analyzed. The density of U ₃Si ₂ 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 U ₃Si ₂ phase in the pellets, and low-temperature annealing at 300 °C effectively released the residual stress and eliminate the lattice distortion of U ₃Si ₂. The U ₃Si ₂ grain size increased with increasing dwell temperature and showed an opposite trend with increasing pressure. The grain growth mechanisms of the SPS-sintered U ₃Si ₂ pellets involved temperature-dependent surface diffusion and pressure-induced grain growth inhibition. The evolution of the U ₃Si ₂ grain morphology from equiaxed to columnar grains was due to plastic strain under SPS conditions.