Microstructure and oxidation resistance behavior of lanthanum oxide-doped Mo-12Si-8.5B Alloys

Mo-12Si-8.5B (at.%) alloys doped with different mass fraction of lanthanum oxide (La₂O₃) were fabricated by using arc-melting and spark plasma sintering techniques. Composition and microstructures of the samples were examined with XRD and optical microscope, respectively. Oxidation resistance behavior of the alloys at 800 °C and 1000 °C was investigated using TGA, XRD and SEM-EDS. Experimental results show that the Mo-12Si-8.5B alloys are mainly composed of α-Mo, Mo₅SiB₂ (T ₂) and Mo₃Si phases and the grain sizes of alloys doped with La₂O₃ were finer than the undoped ones. At 800 °C and 1000 °C, the alloys doped with La₂O₃ have good oxidation resistances because the protective borosilicate scale is quickly formed and adhered with the substrate. The oxide scales consist of outer boronsilicate glass scale and inner reaction zone consists of molybdenum dioxide. The oxidation mechanisms of the La₂O₃-doped Mo-12Si-8.5B alloys were also discussed in light of the experiments results.