Microstructure and mechanical properties of lanthanum oxide-doped Mo-12Si-8.5B(at%) alloys

Mo-12Si-8.5B alloys with different mass fraction (0, 0.6 wt%, 12 wt%) lanthanum oxide(La₂O₃) additive were fabricated by using arc-melting and spark plasma sintering (SPS) techniques. The doped Mo-12Si-8.5B alloys are consisted mainly of α-Mo, Mo₃Si and Mo ₅SiB₂(T2) phases. It is found that the grains are reduced and the intermetallics particles are dispersed more homogeneously after the addition of La₂O₃. The optimization in microstructure induces corresponding improvements in both compression strength and breaking strain of the alloys. The predominant strengthening mechanisms are fine-grain strengthening and particles dispersion strengthening. In addition, fracture toughness test shows that the addition of La₂O₃ can improve the toughness of Mo-12Si-8.5B alloys, for which the toughening mechanism involves crack trapping by α-Mo phases and extensive small second phase particles in the alloys.