Effects of Solution Temperature in Two-phase Region on Microstructure and Mechanical Properties of TB18 Titanium Alloy

TB18 titanium alloy is a metastable β titanium alloy independently researched and developed by China. It has excellent matching ability of strength and toughness, and is the preferred material for the new generation of unmanned aerial vehicles. The relations between microstructure and properties of the TB18 alloy subjected to different solution temperature and aging treatments are investigated. Results indicate that under the conditions of aging temperature of 550 °C and aging time of 8 h, as the solution temperature elevates from 750 ℃ to 790 ℃, the primary α phase dissolves, with its fraction volume decreasing, and the thickness and length of lamellar αs phase declines, leading to the gradual increase of the tensile strength and ductility and toughness of the titanium alloy. According to the fracture morphologies of tensile specimens and fracture toughness specimens after heat treatment in the two-phase region with different solution aging temperatures, all the fractures are ductile fracture, and the lower the primary αp phase, the more easily the fracture occurs. The optimum overall performance is achieved with the heat treatment conditions of 770 ℃/2h,AC+550℃/8h, AC, and the tensile strength, yield strength, elongation and percentage reduction of area of alloy are 1 353 MPa, 1 282 MPa, 12.0% and 61.5 MPa·m^1/2, respectively.