Investigation of Globularization and Mechanical Behavior of Ti-۸Al-۱Mo-۱V Alloy During Post-Deformation and Heat Treatment

In this study, the effect of hot compression and subsequent heat treatment on α globularization and mechanical properties of Ti-۸Al-۱Mo-۱V (Ti-۸۱۱) alloy with an initial lamellar microstructure was investigated. Heat treatment was performed on hot-deformed samples (at ۱۰۰۰ °C and ۰.۰۰۱ s-۱), at temperatures of ۸۰۰, ۸۵۰, and ۹۰۰ °C for durations ranging from ۱ h to ۵ h. The results showed that the microstructural changes depended on the temperature and time of heat treatment and globular α phase fraction increased with increasing time and temperature. By increasing the heat treatment temperature from ۸۰۰ °C to ۹۰۰ °C for ۵ h, the volume fraction of globular α phase increased from ۶۸% to ۷۹% and the aspect ratio decreased from ۷.۲ to ۶.۲. Microstructural studies showed that the globularization mechanism was controlled by boundary splitting, interface migration, and Ostwald growth. At lower temperatures of ۸۰۰ °C and ۸۵۰ °C, the dominant mechanism was boundary splitting by the shearing of α layers, which depended on the amount of pre-strain. At the higher temperature of ۹۰۰ °C, globularization was controlled by interface migration and Ostwald growth, which were diffusion processes and dependent on heat treatment time. The static globurization kinetics of Ti-۸۱۱ during heat treatment was well modeled by the modified JMRE equation, with a correlation coefficient (R) of ۰.۹۷ and the mean absolute relative error (MARE) of ۷.۱۹%. A punching test was applied to evaluate the mechanical properties of the deformed and heat-treated samples. The maximum shear strength and elongation were obtained at ۹۰۰ °C and a holding time of ۲ h, which were equal to ۶۹۵ MPa and ۱.۱, respectively.

کلیدواژه ها:

Ti-۸۱۱ alloy ، Hot compressive test ، Heat treatment ، Globularization ، Mechanical properties