Effect of annealing temperature on microstructure and mechanical properties of Ti-55511 titanium alloy

The microstructure of Ti-55511 alloy in a wide annealing temperature range of 600−900 °C was obtained by gradient heat treatment. The annealing microscopic mechanism map reflecting phase composition and the homogeneity of grain size was constructed. When the temperature exceeds 875 °C, the annealing microstructure is a single-phase structure of β phase. When the annealing temperature is 800−875 °C, a small amount of α lamellar structure is precipitated in the β grains. When the annealing temperature is 650−800 °C, the α GB phase precipitates at the β grain boundary. When the annealing temperature is 600−650 °C, the content of the α phase is high but there is no α GB phase. The sample annealed at 750 °C for 120 min has good matching of strength and plasticity, with a yield strength of 1197 MPa and a true fracture strain of 0.31. The annealing microstructure has the best homogeneity degree of β grain size. The α lamellar structure can hinder the dislocation movement, and its grain boundary strengthening effect contributes 207 MPa to strength.