Effect of Hot Isostatic Pressing Temperature on Microstructure and Properties of TC21 Titanium Alloy

Powder metallurgy combined with hot isostatic pressing (PM-HIP) enables the fabrication of near-net-shape titanium alloy components with near-theoretical density, yet the HIP temperature fundamentally determines the densification behavior, phase constitution and mechanical properties of the consolidated alloy. In this work, TC21 pre-alloyed powder is consolidated by HIP at 890 °C, 920 °C, 950 °C, 980 °C and 1010 °C under 140 MPa for 3 h, followed by furnace cooling, and all the as-HIPed compacts are subsequently subjected to a two-step heat treatment (900 °C/1 h/air cooling + 590 °C/4 h/air cooling). The microstructure in both the as-HIPed and heat-treated states is characterized by SEM (scanning electron microscope), XRD (X-ray Diffraction), EBSD (Electron Back Scatter Diffraction) and TEM (transmission electron microscope), and the room-temperature tensile properties are evaluated. The results show that increasing the HIP temperature coarsens the primary α (α_p) and secondary α (α_s) phases while promoting the precipitation of α_s in the β matrix. The competition between the precipitation strengthening of α_s and microstructural coarsening governs the strength–ductility balance, and the alloy HIPed at 950 °C attains the optimum properties after heat treatment, with an ultimate tensile strength of 1259.5 ± 3.63 MPa, a yield strength of 1195.5 ± 3.5 MPa, an elongation to fracture of 13 ± 2.82% and a reduction of area of 35.5 ± 2.12%. The superior performance is attributed to the high volume fraction of fine α_s lamellae, which provides pronounced precipitation strengthening, together with an appropriate amount of α_p phase, which preserves strain-hardening capacity and ductility. These results clarify the HIP-temperature-dependent microstructure–property relationship of PM-HIP TC21 alloy and provide guidance for optimizing HIP parameters of powder-metallurgy titanium alloys.