Design of high strength titanium alloy through finding a critical composition with ultra-fine α phase

This study presents the design of a high strength titanium alloy based on the idea that the β titanium alloy with critically stable composition could precipitate ultra-fine α phase. An efficient method was used to find the composition of TC21-xV alloy in which ultra-fine α phase could be obtained. It is found that TC21-5V alloy containing ultra-fine α phase and possessing highest hardness could be obtained after solution treatment in the β single-phase region and subsequent aging. The morphology of primary and secondary α phases can be controlled by changing the solution treatment and aging temperatures. Calculation results of driving force and growth rate of secondary α phase show that the growth rate may be a decisive factor for the final size of secondary α phase after solution and aging treatments in the two-phase region. Finally, when the alloy was solution treated at 820 °C and aged at 500 °C, the highest strength of 1540 MPa was obtained. The alloy was solution treated at 820 °C and aged at 600 °C exhibited high strength of 1210 MPa with 11.4% elongation.