The Sintering Behavior and Microstructure Evolution of W-11.4 Wt. % Cr Alloys by Field-Assisted Sintering Technology

Abstract

Self-passivating metal alloys with reduced thermo-oxidation (SMART) have been considered as promising candidates for the first wall armor in fusion plants to suppress the sublimation of radioactive substance in loss-of-coolant accident (LOCA). However, how to optimize the sintering processing to improve the microstructure as well as mechanical properties are vital issues for the industrial application of SMART. In this paper, the sintering behavior of W-11.4 wt.% Cr binary alloys, as well as its microstructure evolution are studied for the microstructure optimization of the SMART systems. Field-assisted sintering technology (FAST) was undertaken at the temperatures from 1400 °C to 1700 °C to suppress the spinodal decomposition of Cr-rich phase. It is found that the fast densifying of the powders starts form around 900 °C and ends at around 1400 °C. The Cr-rich phases, considered as the harmful phases to the mechanical behavior as well as oxidation resistance, could be suppressed by sintering above 1500 °C. Moreover, at higher sintering temperature, the grains become larger and the activation energy of grain growth is calculated to be 380 kJ/mol. And Hall-Petch relationship of binary W11.4Cr alloys as well as ternary W-11.4Cr-0.6Y alloys is obtained to present the relationship between grain size and hardness, which could serve for further microstructure improvement and for optimizing of mechanical properties of SMART materials.

Keywords: Self-passivating metal alloys, field-assisted sintering technology, tungsten-based alloys