A review on heat treatment efficiency in metastable β titanium alloys: the role of treatment process and parameters

Metastable β titanium alloys are widely used in the biomedical, automotive, and aerospace industry, due to their excellent corrosion resistance, fatigue strength, biocompatibility, and easy formability. Besides all these use areas, the suitable microstructure of the alloys for heat treatment increases the efficient usability day by day. In literature research, it has been found that heat treatment types such as cryogenic treatment and precipitation hardening can be applied efficiently to the alloys. Optimum strength/ductility, wear resistance, creep strength, and fatigue strength can be obtained with these heat treatments. For this reason, it has become important to understand the effect of heat treatments on the microstructural and mechanical properties of the alloys and parameters affecting this heat treatment efficiency. Precipitation hardening includes solution and aging treatment steps. The solution treatment can be applied at temperatures below and above the β transition temperature. While the aging treatment can be applied in four different ways, in the review article, the effects of single step and duplex aging treatment, which are applied with high efficiency, are emphasized. Precipitation hardening efficiency affects the chemical composition of the alloys, heat treatment steps, treatment temperature and times, and heating/cooling rate. The cryogenic treatment provides the formation of martensite α phases in metastable β titanium alloys cooled below the martensitic transformation temperature. Higher-strength and hardness have been obtained in the studies where aging treatment was applied after cryogenic treatment. Cryogenic treatment efficiency determines chemical composition of the alloys, treatment temperature and time, the heating/cooling rates, and heat treatments applied after cryogenic treatment.