Microstructure and mechanical properties of Ti-6Al-4V alloy sheets via room-temperature rolling and cryorolling

Ti-6Al-4V alloy sheets were rolled at room temperature (293 K) and various cryogenic temperatures (173, 123, and 83 K). The microstructures of the specimens were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. In addition, the hardness and tensile properties of the rolled sheets were systematically investigated. The results showed that under identical specimen thickness reductions, the grains became gradually refined, and dislocation densities increased with decreasing cryorolling temperature, furthermore, the beta phase broke and became refined due to shear stress, while the hardness and strength values of the specimens increased. A hardness value of 383 HV was achieved when the rolling temperature was 83 K, and with a thickness reduction of 75%. In addition, we obtained a maximum tensile strength of 1329 MPa at 4.4% elongation, at a rolling temperature of 123 K and 75% thickness reduction. Thus, the increased dislocation density, grain refinement, and the high-density of the fine beta phase were contributed to the improved mechanical properties of the specimens. In addition, the cryorolled sheets had good thermostability when the annealing temperature was not higher than 773 K.