Effects of quasi-β phase forging plus duplex ageing process on microstructure evolution and mechanical properties of TC18 alloy

This study has systematically investigated the effects of unidirectional quasi-β forging deformation (20%, 40%, 60%) plus duplex ageing on microstructure and mechanical properties of TC18 titanium alloy. The alloy forged at 900 °C with the height reduction of 40% exhibits the optimal microstructure, with the β grain size of 47.7 μm, the dynamic recrystallisation volume fraction of 3.9%, and the geometrically necessary dislocation density of 0.48 × 10 14 m -2 . This microstructure provides favorable conditions for the uniform and fine precipitation of secondary α phase (α s ) during the subsequent ageing. After an optimized duplex ageing treatment (350 ℃/1 h + 600 ℃/4 h), the alloy achieves a favorable balance of strength and ductility, with ultimate tensile strength of 1577 MPa, yield strength of 1513 MPa and elongation to rupture of 6.6%, the ultimate tensile strength of which is approximately 77.2% higher than the as-forged state. The synergistic optimization of both strength and ductility in TC18 alloy can be ascribed to the adjustment of the size and the distribution of α s precipitates, which provide theoretical foundations and process guidance for the industrial production of high-performance titanium alloy components.