Oxidation mechanisms of lanthanum-alloyed Mo–Si–B

• 0.2 and 2 at.% La-alloyed Mo–9Si–8B were prepared using spark plasma sintering.
• Superior oxidation resistance of 2La-alloyed Mo–9Si–8B in 750–900 °C is observed.
• Formation of lanthanum–molybdate oxides prevents evaporation loss of MoO3.
• Lanthanum reduces the inward diffusion of oxygen in protective silica-rich scale.

High temperature oxidation behavior of a Mo–9Si–8B (at.%) alloy containing 0.2 and 2 at.% La was studied between 750 and 1400 °C in static air. Isothermal thermogravimetric analysis for up to 72 h indicated a significant improvement in the oxidation resistance of the 2La-alloyed material in the 750–1000 °C temperature range. The oxide layers characterized by XRD, SEM, EDS, and FIB-TEM revealed the formation of more stable lanthanum–molybdates (xLa2O3⋅yMoO3), which reduces the evaporation of MoO3 below 1000 °C. The thickness data obtained for the external scale and the inner oxidation layers indicated a reduction of inward diffusion of oxygen with higher La concentrations.