Effect of temperature on the initial reaction behavior of MAB phases (MoAlB powders) at 700–1000 °C in air

MoAlB suffers from degradation below 1000 °C owing to the formation of volatile oxides, which is critical for its application and has been less studied so far. In this work, the initial evolution of phase and morphology of MoAlB powders with the uniform size of about 50 μm reacted at 700-1000 °C for 5 h in air has been systematically investigated using thermogravimetric analysis in combination with XRD, SEM and HRTEM. The results show that the oxidation of MoAlB powders does not occur until 690 °C. The oxidation of MoAlB powders predominates at 700 °C, while the evaporation of rod-shape MoO3 and amorphous B2O3 gradually intensifies with the temperature increasing up to 950 °C. At 1000 °C, the well-developed plate-shape Al4B2O9 can hinder the further reaction to some extent. Based on this, the reaction mechanism of MoAlB powders at the initial stage is presented.