Microstructure and Shape Evolution in Ti-10V-2Fe-3Al Alloy by Tempering

Solution-treated (STQ) materials of Ti-10Mo-7Al or Ti-15V-7Al alloys are known to have a β+α"_Mq microstructure and to exhibit peculiar phenomena during tempering. Commercially available Ti-10V-2Fe-3Al (Ti-1023) alloy STQ-treated materials are also known to have a similar β+α"_Mq structure. Therefore, the peculiar phenomenon associated with tempering of Ti-1023 alloy was investigated. The microstructure of STQ-treated Ti-1023 was found to change to β single phase after tempering at 300℃ for 3 min, and almost complete α"_Mt was reversibly generated after treatment at 550℃ for 5 sec. Cross-sectional observation revealed that α"_Mq in the STQ material tended to form in the interior of the specimen, while α"_Mt from tempering at 550℃ tended to form in the surface layer of the specimen. When a thin plate of STQ material was bent into a U-shape and heated, shape recovery was observed as in the case of Ti-10Mo-7Al, followed by shape evolution. Therefore, a peculiar phenomenon due to tempering also appears in Ti-1023, but the β reverse transformation temperature and α"_Mt transformation temperature are about 100℃ higher than those of Ti-10Mo-7Al, respectively. Phase decomposition associated with aging at 450℃ follows the process β + α"_Mq → β + α"_Mt → β → β + α, but no formation of α"_iso was observed.