Effects of lanthanum oxide content on mechanical properties of mechanical alloying Mo-12Si-8.5B (at.%) alloys

Mo-12Si-8.5B alloys with different mass fraction (0 wt.%, 0.3 wt.%, 0.9 wt.%, 1.5 wt.%, 2.5 wt.%) lanthanum oxide (La₂O₃) additive were fabricate by using mechanical alloying and hot pressing sintering techniques. XRD results indicate that the doped Mo-12Si-8.5B alloys are consisted mainly of α-Mo, Mo₃Si and Mo₅SiB ₂ (T2) phases. It is found that addition of La₂O ₃ has little effect on both the grains and intermetallic sizes. The intermetallic particles are more homogeneously dispersed within α-Mo matrix by increasing the La₂O₃ content. Compression test and three-point bending test showed that both compression and flexure strength of alloys were obviously improved by the addition of La₂O ₃. The predominant strengthening mechanisms are fine-grain strengthening and particles dispersion strengthening. In addition, fracture toughness tests showed that the fracture toughness values of all alloys were on the order of 9 MPa·m^1/2 that revealed the addition of La ₂O₃ had little effect on improving the alloys toughness.