Effects of Double-Ageing Heat Treatments on the Microstructure and Mechanical Behaviour of a Ti-3.5Al-5Mo-4V Alloy

Abstract

In this work, the effect of double-ageing heat treatments on the microstructural evolution and mechanical behaviour of a metastable β-titanium Ti-3.5Al-5Mo-4V alloy is investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The double-ageing treatments are composed of low-temperature pre-ageing and high-temperature ageing, where the low-temperature pre-ageing is conducted at 300 °C or 350 °C for different times, and the high-temperature ageing is conducted at 500 °C for 8 h. The results show that the phase transformation sequence is altered with the time spent during the first ageing stage, the isothermal ω phase is precipitated in the pre-ageing process of the alloy at 300 °C and 350 °C with the change in the ageing time, and the ω phase is finally transformed into the α phase with the extension of pre-ageing time. The existence time of the ω phase is shortened as the pre-ageing temperature increases. The microhardness of the alloy increases with increasing pre-ageing time and temperature. Compared with single-stage ageing, the ω phase formed in the pre-ageing stage changes the response to subsequent high-temperature ageing. After the two-stage ageing treatment, the precipitation size of the α phase is obviously refined after the double-ageing treatment. A microhardness test shows that the microhardness of the two-stage aged alloy increases with extended pre-ageing time.

Microstructure, Texture Evolution, and Aging Behavior of a Cold‐Rolled Ti–B20 Alloy

“…The specimen was cut into plates required for cold rolling by a wire‐cut electrical discharge machine (EDM). Based on previous research on the Ti–B20 alloy, [ 25,26 ] the specimen was solution treated (ST) at 850 °C/1 h to eliminate forging stress, obtaining a uniform single β ‐phase; afterward, the specimen was cooled to room temperature by water quenching (WQ). Furthermore, the plates were subjected to deformation degrees of 10%, 30%, 50%, and 70% of CR at room temperature by taking a correctly sized specimen and performing an aging treatment for different times at 500 °C in the salt bath furnace.…”

“…However, recent investigations on the new β ‐Ti alloy Ti–B20 chiefly focus on a single heat treatment; there are few studies on the microstructure and texture evolution characteristics that form during cold deformation and the effect of cold rolling on the aging behaviors of Ti–B20 alloys during aging treatment. [ 25,26 ] To enhance the mechanical properties of Ti–B20 alloys, the objective of this work is to investigate the microstructure and texture evolution characteristics and aging behavior of CR Ti–B20 alloys using X‐ray diffraction (XRD), scanning electron microscopy (SEM), electron back scattering diffraction (EBSD), and transmission electron microscopy (TEM). The relationship between the microstructures and mechanical properties of the Ti–B20 alloy is analyzed.…”

Precipitation behaviour of single and duplex aged metastable β-Ti alloy, Ti–5Al–5Mo–5V–3Cr

“…Therefore, it is important to see whether this difference in the microhardness values is observed at every aging condition or is limited to certain aging conditions. Salvador et al [12] and Ji et al [13] also studied the duplex aging response of metastable β-Ti alloys, but they did not study the response of slow heating rate to obtain the extremely refined microstructure. Also, the high-temperature aging was restricted to only 500 °C, however, the α-phase precipitation takes place over a wide temperature range of 500 °C to 700 °C.…”