The effect of plastic deformation on martensite decomposition process in Ti-6Al-4V alloy

Microstructure and mechanical properties of heat treated martensitic two-phase α+β titanium alloys are in major perspective determined by results of martensite decomposition during tempering. The process of martensitic α’(α”) phase decomposition in titanium alloys, although utilized in industry for years, has not been sufficiently characterized in the scientific literature. Especially aspects of plastically deformed martensite decomposition is poorly described. Preliminary research results of water quenched Ti-6Al-4V alloy, subsequently cold deformed in compression and tempered at the temperature range of 600-900ºC for 1 and 2 h indicated that α’(α”) martensite undergoes strain hardening and deformed martensite laths exhibit tendency towards fragmentation and spheroidization during tempering at 900ºC. In the present paper, also α’(α”) martensite decomposition under compressive load applied at the temperature range of 600-900ºC is considered too. Based on light and scanning electron microscopy observations, thermal analyses and XRD measurements, the effect of plastic deformation on kinetics of martensite decomposition and morphology of α phase formed in the process is analysed.