Effect of high strain rate hot compression on the microstructure evolution and subsequent α precipitation of TC17 alloy during single-step and duplex aging

Abstract

The modified α precipitation based on severely deformed β phase and optimized aging treatments is essential to the strengthening of titanium alloys. This study investigated the β phase features of high strain rate (20 s−1) hot compressed (810–900 °C) TC17 alloy coupled with the precipitation behavior and mechanism of α phase during single-step and duplex aging. The dynamic recovery (DRV) dominated the microstructure evolution of alloy and the low compression temperature resulted to high flow stress, strong β texture and dense low angle boundaries (LAGBs). The α precipitation of un-compressed alloy was dominated by homogeneous nucleation mechanism and the intragranular α laths in duplex aged alloy changed from lamellar to skeletal with pre-aging temperature increased from 320 °C to 380 °C. The α precipitates in compressed alloy however were coarsened a lot and the duplex aging at 350 °C/2.5 h + 600 °C/3.5 h caused finer and more uniform α distribution compared with the single-step aging. Generally, the high strain rate hot compression dramatically promoted the nucleation and growth of α phase during both two aging treatments due to its introduction of dense dislocations/sub-structures, whereas the duplex aging is more beneficial to the refinement of α precipitates as the pre-aging can inhibit the rapid growth of local intragranular α lamellas.