Microstructure, mechanical properties and oxidation behavior of a hot-extruded TiAl containing Ta

The microstructure, the mechanical properties and the oxidation behavior of a novel Ti-46.5Al-3Ta-2Cr-0.2W (at%) alloy after hot extrusion were investigated. The results show that the alloy is mainly composed of γ and α₂ phases, which has fine near lamellar microstructure with colony sizes of 50~70 μm after hot extrusion. The different microstructures after hot extrusion were obtained by different cooling rates, and a great amount of massive phase were found at grain boundaries by oil quenching. Tensile test results exhibit that the yield strength (YS) and ultimate tensile strength (UTS) of the alloy after hot extrusion decrease from 807 and 846 MPa at room temperature to 620 and 760 MPa at 800 °C, respectively, and the elongation (EI) of the alloy increases from 2.16% at room temperature to 3% at 800 °C which means that the alloy still keeps higher strength at elevated temperature. The observation of fracture surfaces shows that the crack length of the present alloy is smaller, and the additive of Ta increases the ductility of Ti-46.5Al-3Ta-2Cr-0.2W alloy at room temperature. The oxidation behavior of the novel TiAl based alloy in the experimental range was discussed. It is found that the addition of Ta can reduce the oxygen solubility into the TiAl alloy and suppress TiO₂ growth at elevated temperature due to the low diffusivity.