A high temperature W$_2$B cermet for compact neutron shielding

Abstract

We have developed a new material for neutron shielding applications where space is restricted. W$_2$B is an excellent attenuator of neutrons and gamma-rays, due to the combined gamma attenuation of W and neutron absorption of B. However, its low fracture toughness (~3.5 MPa$\cdot$m$^{0.5}$) and high melting point (2670 {\deg}C) prevent the fabrication of large fully-dense monolithic parts with adequate mechanical properties. Here we meet these challenges by combining W$_2$B with a minor fraction (43 vol.%) of metallic W. The material was produced by reaction sintering W and BN powders. The mechanical properties under flexural and compressive loading were determined up to 1900 {\deg}C. The presence of the ductile metallic W phase enabled a peak flexural strength of ~950 MPa at 1100 {\deg}C, which is a factor of 2-3 higher than typical monolithic transition-metal borides. Its ductile-brittle transition temperature of ~1000 {\deg}C is typical of W-based composites, which is surprising as the W phase was the minor constituent and did not appear to form a fully continuous network. Compression tests showed hardening below ~1500 {\deg}C and significant elongation of the phase domains, which suggest that by forging or rolling, further improvements in ductility may be possible.