Evolutions of the microstructures and mechanical properties of Ti-2.8 wt%Cu alloy during heat treatment

Abstract

The evolutions of the microstructures and mechanical properties of Ti-2.8Cu (wt%) alloy during heat treatment were investigated in this study using X-ray diffraction and electron microscopes. Three typical microstructures including α + Ti2Cu, α + α′ and single α′ were obtained after solution treatment at 780 ℃ for 4 h, 850 ℃ for 2 h and 950 ℃ for 1 h, respectively. With an increase in the solution temperature, the mechanical strength of the alloy was enhanced while the elongation was decreased. When the alloy with different microstructures was isothermally aged at 450 ℃ for 15 h or 550 ℃ for 15 h, a few of precipitates were observed in α phase that has a low Cu content and a large number of disk-shaped Ti2Cu precipitates were detected in α′ martensite that has a high Cu content. Most of the Ti2Cu precipitates lie on {11̅01}α′ except that a few of them can be occasionally detected on {11̅03}α′ in samples aged at 450 ℃ for 15 h, while all of the Ti2Cu precipitates lie on {11̅03}α′ in samples aged at 550 ℃ for 15 h. The Ti2Cu precipitates lying on {11̅01}α′ are thinner and denser than that lying on {11̅03}α′, which can cause a better precipitation strengthening effect in the alloy. For this reason, the sample solutionized at 950 ℃ for 1 h and then aged at 450 ℃ for 15 h has the highest yield strength of 907.8 MPa.