The Effects of the Thermo-Mechanical Process Variables on the Microstructure, Mechanical Properties, and Recrystallization Behavior of the Commercially Pure Titanium

Commercial pure titanium sheets were thermo-mechanically treated to investigate the effects of the treatment variables on the microstructure, mechanical properties, and recrystallization behavior. The as-received sheets were initially cold-rolled up to different reduction percentages of ۶۰%, ۷۵%, and ۹۰%. Then, the cold-rolled samples were annealed at different temperatures of ۵۰۰°C-۷۰۰°C, for various time ranges of ۵ to ۶۰ minutes. The evolution of the microstructure of the samples was studied using X-ray diffraction analysis and optical microscopy. The hardness of the ۹۰% cold-rolled sample was about ۸۲% higher than that of the as-received sheet. Increasing the time and temperature of the annealing process caused a decrease in the microhardness values of the samples. The recrystallization activation energy and Avrami’s exponent of the ۹۰% cold-rolled sample were calculated as about ۱۷۹ kJ/mol and ۰.۷۵, respectively. The results of the uniaxial tensile tests revealed that the cold-rolling process significantly improved the yield strength (YS) and ultimate tensile strength (UTS) of the specimens. In the case of the ۹۰% cold-rolled sample, these values improved by about ۱۶۰% and ۱۱۷% with respect to the as-received metal, respectively. However, the elongation of the cold-rolled samples dropped sharply. Moreover, annealing had a positive effect on the elongation of the cold-rolled samples. The UTS and elongation percentage of the as-received sheet were ۴۱۵ MPa and ۳۶.۴%, respectively. These values were varied to ۵۵۸ MPa and ۲۹.۱۵% for the ۹۰% cold-rolled sample annealed at ۷۰۰°C for ۱ h. To study the fracture behavior of the different samples, scanning electron microscopy (SEM) was used.

Keywords:

Commercially pure titanium , Cold-rolling , Annealing , recrystallization , Mechanical properties