Effect of Cooling Rate on Superelasticity and Microstructure Evolution in Ti-10V-2Fe-3Al and Ti-10V-2Fe-3Al-0.2N Alloys

A Ti-10V-2Fe-3Al alloy with a small amount of nitrogen shows superelasticity. Controlling of the cooling rate from beta solution treatment temperature improves superelasticity in both Ti-10V-2Fe-3Al and Ti-10V-2Fe3-Al-0.2N alloys. In this study, a wider range of the cooling rate was examined and microstructure change during slow cooling was investigated through examining quenched and aged specimens by means of hardness and resistivity measurement and transmission electron microscopy. Although superelasticity is improved with a decrease in the cooling rate up to 22 K/s for the N-free alloy and up to 50 K/s for the 0.2N alloy, there is no obvious change in microstructure. It is clarified from the observation of specimens quenched and aged at the temperature range where superelasticity is improved that the beta phase decomposition occurs, through isothermal omega phase precipitation. Therefore, microstructure evolution during slow cooling is considered to be precipitation of isothermal beta phase or its precursor phenomena. [doi: 10.2320/matertrans.MA200909]