Effect of Initial α-Phase Morphology on Microstructure, Mechanical Properties, and Work-Hardening Instability During Heat Treatment of TC21 Ti-Alloy

Abstract

The effect of initial α-phase morphology on the microstructure, mechanical properties, and work-hardening instability was studied during the heat treatment of Ti-6Al-3Mo-2Sn-2Zr-2Nb-1.5Cr-0.1Si (TC21) alloy. In addition, the surface texture of TC21 Ti-alloy aircraft components in acidic environments by an Abbott-Firestone curve was investigated, based on MATLAB software. The samples were heated to 925 °C for 20 min before cooling at varying rates of furnace cooling (FC), air cooling (AC), and water quenching (WQ). The samples were then aged at 600 °C for 4 h. The microstructure is composed of primary α-phase (αp), retained β-phase (βr), and secondary α-phase (αs). In the case of solution treatment with AC and aged samples, the αs-phase precipitated within the βr-phase. The exploitation zone for the AC sample is two times the value of the FC and WQ samples. After the aging process, the exploitation zone increased in the FC + Aging and WQ + Aging samples and decreased in the AC + Aging sample. Therefore, the FC, WQ, and FC + Aging samples are highly prone to failure in an etch environment. However, the AC, AC + Aging, and WQ + Aging samples all have a reasonable level of safety. The optimum combination of strength and elongation was found for the AC + Aging and WQ + Aging samples. Finally, the elongation (23%) can reach the highest value for the WQ sample. However, the best ultimate tensile strength (1621 MPa) can be achieved for the WQ + Aging sample. All the samples have a high initial work-hardening exponent (ninitial = 0.50–0.66) because of relatively high yield tensile strength (YTS/UTS = 0.87–0.96).