Effect of Third-Stage Heat Treatments on Microstructure and Properties of Dual-Phase Titanium Alloy

Abstract

Two-phase TC21 titanium alloy samples were solution-treated at 990 °C (β phase zone) and cooled by furnace cooling (FC), air cooling (AC), and water quenching (WQ), respectively. The second solution stage treatment was carried out at 900 °C (α + β phase zone), then aging treatment was performed at 590 °C. The influence of the size and quantity of the α phase on the properties of the sample were studied. The experimental results showed as the cooling rate increased after the first solution stage treatment, wherein the thickness of primary layer α gradually decreased, and the tensile strength and yield strength gradually increased. After the second solution stage treatment, the tensile properties of samples increased due to the quantity of layers α increased. The aging treatment promoted the precipitation of the dispersed α phase and further improved the tensile strength. After the third solution stage treatments, the FC samples with more β-phase had the best comprehensive mechanical properties.

β-Phase-Induced Quasi-Cleavage Fracture Mechanism by Dual-Phase High-Strength Titanium Alloy at Elevated Temperature

“…Generally, α-phase titanium alloys are mainly solution-strengthened by adding Al, Mo, V and other alloy elements, so as to obtain a near-α-phase structure [10]. Although solution strengthening significantly improves the strength of titanium alloy, the strength of α-phase titanium alloy is still lower than that of ordinary steel for oil pipe strings because it cannot be strengthened by heat treatment, which makes it difficult to meet the actual use needs [11,12]. The microstructure of β-phase titanium alloys is usually a metastable β-phase, and only the β-phase is contained after air cooling above its transition temperature.…”