Effects of doping nano-la₂O₃ on the microstructure and mechanical properties of Mo9Si18B alloys

The refractory Mo9Si18B (at%) alloy doped with different mass fractions of nano-La₂O₃ were prepared by combining arc-melting, mechanical alloying and vacuum hot-pressing sintering techniques. The microstructures and mechanical properties of the alloys were systematically investigated. The results showed that the doped alloys presented finer grains than that of the non-doped alloys. Interestingly, most of the La₂O₃ particles dispersed in the grains interior rather than gathered in the grain boundaries by this combining process. This optimal microstructure had led to corresponding improvement in the compression strength (both at room temperature and 1200°C) and room temperature fracture toughness of the Mo9Si18B alloys. Among these alloys, the 0.6 mass% La₂O₃ doped alloys exhibited the best mechanical properties. The predominant strengthening mechanisms are particles dispersion strengthening and fine-grain strengthening. And the toughening mechanism mainly involves particle toughening.