Microstructure, mechanical properties and oxidation resistance of bulk W-B-Fe-Cr for fusion shielding

In this work, a bulk W-B-Fe-Cr shielding material with lower boron content (9.6 at.%) has been fabricated by hot isostatic pressing (HIP) for potential engineering applications in compact fusion reactors. The microstructure, mechanical properties and oxidation resistance of W-B-Fe-Cr were systematically investigated. By HIP sintering at 1250 °C, the uniform, dense and crack-free microstructure of W-B-Fe-Cr was obtained. The results of the phase analysis show that W-B-Fe-Cr is mainly composed of W, (Fe,Cr)WB and (Fe,Cr)7W6. In the range of 500 °C–1000 °C, the low-boron W-B-Fe-Cr possesses higher flexural strength than the reported high-boron (16 ∼ 30 at.%) W2B-W owing to its W-rich composition, which can more effectively exploit both the toughness of the W phase and the hardening effect of the boride phase. The results show that although the neutron shielding property is degraded by the reduction of the boron content, conversly the strength is enhanced. Therefore, for W-B based shielding reactive sintered borides (RSBs), prudent balancing between shielding capability and mechanical performance is essential for the design of the boron content. To evaluate the oxidation resistance of W-B-Fe-Cr, the bare specimen and its Si-coated counterpart were subjected to oxidation tests in air at 1000 °C. The underlying WSi2-(FeWCr)Six dual-phase reaction layer was formed by coating Si, which was transformed into the dense SiO2 protective film at high temperature to effectively prevent exposure of the substrate. The scientific discoveries and constraints of the low-boron W-B-Fe-Cr research are systematically summarized, and the prospective strategies for mechanical performance optimization in high-boron derivatives are reviewed.