Effect of Microstructural Continuity on Room-Temperature Fracture Toughness of ZrC-Added Mo–Si–B Alloys

Abstract

The room-temperature fracture toughness of ZrC-added Mo–Si–B alloys prepared using an arc-melting technique was investigated. The constituent phases of the heat-treated alloys were mainly molybdenum solid solution (Mo_ss), Mo₅SiB₂ (T₂), and ZrC, with a small amount of Mo₂B in a few alloys. Four-point bending tests with a Chevron-notch were performed, and the average fracture-toughness values ranged from 12.4 to 20.3 MPa(m)^1/2 depending on alloy composition. Here, the effects of the volume fractions of the constituent phases and the continuity of Mo_ss on the fracture toughness are discussed. The fracture toughness improved with an increase in the volume fractions of the Mo_ss and ZrC phases. Alloys with a higher Mo_ss continuity exhibited higher fracture toughness, for example, the fracture toughness of 64.5Mo–3.2Si–6.5B–12.9Zr–12.9C (mol.%) was 19 MPa(m)^1/2; the alloy contained a >95%-continuous Mo_ss phase, even though it also contained 16 vol.% T₂ and 23 vol.% ZrC.