Grain growth and densification of uranium mononitride during spark plasma sintering

Abstract

With the aim of investigating the spark plasma sintering behavior of uranium mononitride synthesized by the hydride-nitride process, several pellets were prepared using a wide range of fabrication temperatures (1500-1800 degrees C) and dwell times (5-180 min) under 70 MPa. The collected data in the grain size-density trajectory revealed that the spark plasma sintering process of uranium mononitride was divided into two regimes according to the sintering temperature. In particular, at low temperatures up to 1700 degrees C, the pellet density increased with increasing temperatures until it reached a maximum value (similar to 97 %TD), while the grain growth was not significant (average grain size < 3.5 mu m). In contrast, at a temperature of 1800 degrees C, the maximum density was rapidly achieved (<5 min) with a slightly larger average grain size (4.3 mu m), and a significant grain growth (up to 8 mu m) continued for 180-min dwell time.