Effect of Ta on the high temperature oxidation behavior of Mo-based bulk metallic glasses

Mo-based bulk metallic glasses (BMGs) exhibited very high thermal stability and showed promising applications in high-temperature fields. However, their high-temperature oxidation resistance remains unsatisfactory. In this work, the effect of Ta (0-6 at.%) on the high-temperature oxidation behavior of MoCoB BMG was systematically investigated. The oxidation kinetics of MoCoB BMG and Ta-bearing Mo-based BMGs generally followed a parabolic law at 873-973 K, and the rate constants increased with the increasing temperature. The oxidation products of MoCoB BMG were primarily composed of CoMoO4 and MoO3, and the oxides of Ta-bearing Mo-based BMG were mainly CoMoO4, MoO3, CoTa2O6, and Ta2O5. The addition of Ta can significantly promote adhesion between the substrate and the external oxide layer, forming a dense spinel layer with a diffusion barrier that provides good oxidation resistance to the Mo-based BMG. The thin oxidation layer of Mo44Co34Ta6B16 was only about 13 mu m after oxidation at 973 K for 120 h.