Microstructure refinement and oxidation behavior improvement in Mo modified TiAl4822 alloy prepared by vacuum sintering

In this paper, mechanical milling and vacuum hot-pressing sintering were used to fabricate TiAl4822 and TiAl4822-4 wt%Mo alloy. Hot compression and high temperature oxidation behavior at 800 °C and 900 °C were investigated respectively. Microstructure of the as sintered sample, morphology and composition of the oxidized surface was analyzed by SEM, TEM and EDX. The result shows that a refined microstructure with multi-scaled α₂ lamella is exhibited in TiAl4822-4 wt%Mo alloy. The size of both equiaxed γ phase and α₂/γ colony is finer in Mo modified alloy. Mo addition results in ∼6% lattice misfit by SAED analysis. Obvious improvement of hot compression properties and retardation of high temperature oxidation is displayed in Mo modified alloy. The compressive yield strength at 800 °C of TiAl4822-4 wt%Mo reaches 554.6 MPa which is higher than the Mo free counterpart. The weight increment and oxidation rate of TiAl4822-4 wt%Mo alloy after 900 °C/250 h is 3.74 mg/cm² and 0.060 mg²cm⁻⁴h⁻¹ which is 32.97% lower than TiAl4822 alloy. The increase of hot compressive strength is originated from grain refinement effect and solid solution strengthening effect introduced by lattice misfit. The decrease of oxidation rate in Mo modified alloy is probably attributed to the lower vacancy density of oxygen.