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 60%, 75%, and 90%. Then, the cold-rolled samples were annealed at different temperatures of 500°C-700°C, for various time ranges of 5 to 60 minutes. The evolution of the microstructure of the samples was studied using X-ray diffraction analysis and optical microscopy. The hardness of the 90% cold-rolled sample was about 82% 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 90% cold-rolled sample were calculated as about 179 kJ/mol and 0.75, 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 90% cold-rolled sample, these values improved by about 160% and 117% 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 415 MPa and 36.4%, respectively. These values were varied to 558 MPa and 29.15% for the 90% cold-rolled sample annealed at 700°C for 1 h. To study the fracture behavior of the different samples, scanning electron microscopy (SEM) was used.