Microstructure and mechanical properties of HIP-ZTC4 during thermal exposure and tensile deformation

Casting titanium alloy TC4 (ZTC4) after hot isostatic pressing (HIP) is one of the preferred materials in the field of aerospace manufacturing. In this paper, HIP-ZTC4 after a long-term thermal exposure was investigated. In order to evaluate the variation of mechanical properties with service time, the tensile properties of this alloy after exposure at 400 °C for 100, 500, and 1,000 h were investigated. Microstructure of samples was observed by the means of optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Tensile test was carried out under different test temperatures and fracture appearance was studied. The results show that the strength increases with exposure time due to the harder α₂ (Ti₃Al) phase precipitated in the α phase and superficial oxygen layer formed, which results in the fact that the resistance of crack propagation could be increased and cracks first initiate between surface oxidation and the matrix. Besides, the tensile temperature also has a significant effect on the mechanical properties of HIP-ZTC4. The yield strength and tensile strength decrease with the increase of tensile temperature, while the total elongation increases.