The high temperature tensile properties and microstructural analysis of Ti–40Al–15Nb alloy

This research investigates the relationship between microstructure and high temperature mechanical properties of the Ti–40Al–15Nb alloy. Alloy specimens under different heat treatment conditions, including as-cast Ti–40Al–15Nb, homogenized Ti–40Al–15Nb and as-rolled Ti–40Al–15Nb alloys, have been studied to determine their phases and tensile properties at elevated temperatures. The phase, microstructure and precipitation temperatures of the Ti–40Al–15Nb alloy were obtained from the experiments and compared with previous literature. Experimental data indicate that the structure of the Ti–40Al–15Nb alloy at 1200 °C is dual phases of α and β. The microstructure analysis shows β is the single phase above 1290 °C but α2 phase precipitates below 1290 °C. Furthermore, γ phase appears below 1150 °C, and ω phase is observed below 950 °C. It is also found that γ phase is a very brittle phase which leads titanium aluminide alloy to fracture. The ultimate tensile strength of the as-rolled and homogenized Ti–40Al–15Nb alloys exhibits a positive temperature dependence at temperatures below 800 and 850 °C, respectively. The ultimate tensile strength (666.4 MPa) of the homogenized Ti–40Al–15Nb alloy at 850 °C is extremely high. The superior effect is explained by the stress anomaly phenomenon which is due to the frequent interactions of screw dislocations in γ phase.