Effect of hot isostatic pressing on the microstructure and fracture toughness of laser additive-manufactured MoSiBTiC multiphase alloy

MoSiB-based alloys are extremely promising ultrahigh–temperature materials, owing to their high melting points, good thermal stability, and excellent elevated-temperature mechanical properties. However, their fabrication is limited to conventional manufacturing techniques. In this work, a MoSiBTiC multiphase alloy, mainly consisting of Mo solid solution (Mo_ss), Mo₅SiB₂ (T₂), and TiC phases, was fabricated by laser powder bed fusion (L-PBF) using ball-milled alloy powders; subsequently, the effect of hot isostatic pressing (HIP) on its microstructure and fracture toughness was investigated. Due to the non-equilibrium metallurgical characteristics of L-PBF, the as-built alloy included uniform and fine-grained structures, as well as internal microcracks. The length of microcracks was effectively reduced with the assistance of the TiC bridging effect during HIP. As revealed by a high-resolution transmission electron microscope, the TiC was uniformly dispersed and was in close contact with the Mo_ss or T₂ phase. Consequently, the MoSiBTiC multiphase alloy exhibited a high fracture toughness of 9.0 MPa(m)^1/2 after HIP at 1973 K. This work could be an important step towards the fabrication of high-performance refractory components with advanced properties in ultrahigh–temperature use.