Influence of heat treatment on the microstructure and mechanical properties of TC25G-TiAl4822 titanium-based gradient materials

To achieve higher thrust-to-weight ratios in aero-engine high-pressure compressor blisks, this study employed laser additive manufacturing to deposit TiAl alloy onto a forged TC25G titanium alloy substrate, using AD30 (30% TiAl + 70% TC25G) as a transition layer. The effects of heat treatment on microstructure and mechanical properties at room temperature and 550℃ were systematically investigated. Results indicated that the stress-relief annealed gradient material exhibited a continuous microstructural evolution along the deposition direction, transitioning progressively from the (α + β) duplex microstructure of TC25G alloy to the (α₂ + γ) near-lamellar microstructure of TiAl alloy. After solution treatment at 950℃ (HT-950), the α-phase content in the TC25G alloy substrate decreased and became equiaxed. After solution treatment at 1200 ℃ (HT-1200), a basket-weave α/β microstructure appeared in TC25G and AD30 regions. In the TiAl alloy region, the HT-950 treatment led to the formation of a duplex microstructure consisting of γ-phase and α₂/γ lamellar colonies, while the HT-1200 treatment produced a near-γ microstructure dominated by coarse equiaxed γ-phase grains. Mechanical property analysis revealed that both the stress-relief annealed sample (SR) and the HT-950-treated sample exhibited good strength at room temperature, whereas the strength of the HT-1200-treated material decreased significantly. High-temperature tensile tests at 550 ℃ demonstrated that the SR sample possessed superior overall mechanical performance compared to the other heat-treated conditions. All specimens fractured within the TiAl alloy region.