Cyclic oxidation behavior of MoAlB in the temperature range 450–850 °C

Mo-Si-B alloys suffer from the materials disintegration below 800 °C due to the formation of a porous oxide scale and the evaporation of MoO3, known as Mo pesting. The nanolaminated ternary boride compound of MoAlB contains both Mo and B elements, hence, pesting is expected at temperatures below 800 °C as in Mo-Si-B alloys. However, the oxidation behavior of MoAlB at moderate temperatures has been less studied so far. This work reports on the cyclic oxidation behavior of MoAlB in air in the temperature range 450–850 °C over a time of up to 100 h. The results showed an excellent oxidation resistance of MoAlB at temperatures of 750 °C and 850 °C due to the formation of a dense and continuous Al2O3 scale, which acts as a barrier layer preventing oxygen inward diffusion and the evaporation of MoO3 and B2O3 oxides. No pesting was found in the MoAlB material during oxidation at temperatures below 850 °C. The phase composition and microstructure of the oxidized samples were characterized by x-ray diffraction and scanning electron microscopy techniques.