Effect of duplex aging on microstructure and mechanical properties of near-β titanium alloy processed by isothermal multidirectional forging
(1. College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China;
2. Department of Chemical and Materials Engineering, the University of Auckland, Private Bag 92019, Auckland 1142, New Zealand)
2. Department of Chemical and Materials Engineering, the University of Auckland, Private Bag 92019, Auckland 1142, New Zealand)
Abstract: The effects of sub-transus (α+β) annealing treatment (ST), followed by single aging (SA) or duplex aging (DA) on the microstructural evolution and mechanical properties of near-β Ti-4Al-1Sn-2Zr-5Mo-8V-2.5Cr (mass fraction, %) alloy were investigated using optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show that the finer secondary α phase precipitates in the alloy after DA than SA (e.g., 149 nm for SA and 69 nm for DA, both after ST at 720 °C). The main reason is that the pre-aging step (300 °C) in the DA process leads to the formation of intermediate ω phase nanoparticles, which assist in the nucleation of the acicular secondary α phase precipitates. In addition, the strength of the alloy after DA is higher than that of SA at the specific ST temperature. A good combination is achieved in the alloy subjected to ST at 750 °C, followed by DA (UTS: 1450 MPa, EL: 3.87%), which is due to the precipitation of nanoscale secondary α phase by DA. In conclusion, DA is a feasible process for this new near-β titanium alloy.
Key words: new near-β titanium alloy; multidirectional forging; annealing treatment; duplex aging; ω-assisted α nucleation; microstructure; mechanical properties