Effect of heat treatment on the microstructure and mechanical properties of TiAl alloys

In this work, a Ti45Al45Nb5Mo5 alloy was prepared by non-self-consuming vacuum arc melting furnace. The effects of heat treatment on the microstructure and mechanical properties of the alloys were investigated. The alloy was heat treated in a vacuum at temperatures of 1150 °C, 1200 °C, 1250 °C and 1300 °C with a holding time of 30 min and then cooled in a furnace. The microstructure of the alloy after heat treatment showed a coarsening phenomenon. The bright linear precipitated phases in the α2/γ lamellar structure diffused along the lamellar orientation. However, the lamellae exhibited significant deterioration after heat treatment at 1300 °C. The microhardness of the alloy improved by the heat treatment and the alloy had the highest microhardness of 414.4 HV after heat treatment at 1250 °C. At the same time, the heat treatment also significantly improved the plasticity of the TiAl alloy. The alloy exhibited the highest compressive strength and elongation at break of 2220 MPa and 39.9% after heat treatment at 1250 °C. The increase in microhardness was primarily attributed to the reduction in interlamellar spacing and the increase in strength due to solid solution. All variations in matrix phases, interlamellar spacing and grain size significantly affected the compressive properties of the alloy.