Effect of solution-aging treatment on microstructure and high temperature fracture toughness of Ti60 alloy rolled sheet

In this study, the Ti60 alloy rolled sheet was solution-aging treatment at different temperatures, and then the high temperature fracture toughness test was carried out on the samples after solution-aging treatment. The microstructure morphology and crack propagation behavior were studied. The original microstructure of the Ti60 alloy rolled sheet is composed of primary α phase and flocculated α phase. The microstructure of Ti60 alloy rolled sheet after solution-aging treatment is a typical bimodal structure. It is mainly composed of acicular α_s phase, equiaxed α phase and lamellar α phase. The proportion of equiaxed α phase gradually increases from 46 % to 82 % with the increase of solution treatment temperature. After 1080 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment and 1090 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment, lamellar α appears inside the equiaxed α grains. After 1100 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment, the lamellar α will be transformed into acicular α_s. The average K_IC value of the original Ti60 alloy rolled sheet is 46.35 MPa·m^1/2. The K_IC values of the samples after 1070 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment, 1080 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment and 1100 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment is approximately in the range of 44.15 MPa·m^1/2–51.33 MPa·m^1/2. But the average K_IC value after 1090 °C/2 h/AC + 700 °C/2 h/AC solution-aging treatment is increased to 74.56 MPa·m^1/2. This may be due to the appearance of lamellar α, which makes the fracture toughness of Ti60 alloy rolled sheet increase significantly.