Densification mechanism of U3Si2 consolidated by spark plasma sintering

Abstract

The high uranium density and good thermal conductivity at high temperature render U3Si2 an excellent candidate for accident tolerant fuels (ATF). Spark plasma sintering (SPS) is a convenient method to produce U3Si2 fuel and U3Si2-X fuels. However, the densification mechanism of U3Si2 by SPS has been rarely investigated. In this work, U3Si2 pellets were fabricated by SPS with 2 sets of different sintering parameters (the soak samples and the ramp samples). The grain size of U3Si2 pellets sintered by SPS persisted ∼25 μm when soaked at 900–1300 °C and increased to ∼35 μm at 1400 °C. The morphology of the 900 °C soak sample was supposed to be due to spark plasma and plastic deformation. Utilizing the Helle-Granger model, the apparent activation energy (Q) and the stress exponent factor (n) can be determined. The soak samples exported n as 2.88, 3.16, and 3.55 (average 3.20) at 900, 1000, and 1100 °C, respectively. The ramp samples exported Q as 355.57, 325.48, 343.04, and 377.04 kJ/mol (average 350.28 kJ/mol) and n as 4.67, 4.22, 4.04, and 3.52 (average 4.11) at 65, 70, 75, and 80%TD, respectively. The n values of the two set of samples were both consistent with the suspected deformation hints in SEM. These results suggest that densification of SPS-sintered U3Si2 occurred via plastic deformation controlled by dislocation motion.