Novel design of Mo-Si-B + La₂O₃ powder with multi-shell structure for ideal microstructure and enhanced mechanical property

In this study, the multi-shell structured Mo-Si-B powder with La₂O₃ particles (MSB + L powder) was designed to obtain the ideal microstructure of sintered body, and the effects of the La₂O₃ addition on the microstructural and mechanical characteristics were investigated. Mo-Si-B powder (MSB powder) was prepared via mechano-chemical powder metallurgy methods, and MSB + L multi-shell powder was fabricated via chemical methods such as mixing and calcination processes. Using this powder, MSB + L alloys were prepared under cold isostatic pressing followed by pressureless sintering. Our unique powder's architecture allows us to fabricate the ideal microstructure of MSB + L alloys which consist of isolated intermetallic compound phases and uniformly dispersed La₂O₃ particles in continuous α-Mo matrix. This ideal microstructure contributes to the enhancement of fracture toughness of MSB + L alloys by changing fracture behavior, compared to MSB alloys without La₂O₃ particles. For example, intergranular fracture mode in MSB alloys changed to intragranular fracture mode in MSB + L alloys. In addition, the fracture toughness was enhanced around 26% in MSB with 0.3 wt% La₂O₃ particle at room temperature (17.0 MPa·m^1/2) while MSB alloys have around 13.50 MPa·m^1/2. The addition of La₂O₃ particles in MSB alloys highly affect the fracture behavior at room temperature through the grain refinement and oxide particle strengthening.