Microstructure and Mechanical Properties of Ultrafine-Grained TC4 Titanium Alloy Prepared by Severe Hot Rolling

The ultrafine-grained TC4 titanium alloy was produced by severe hot rolling for 2-4 passes at start rolling temperature of 1 100℃ with 70 t rolling mill, and the effects of rolling reduction (60%-90%) on the microstructure and mechanical properties of the alloy were investigated. The results show that the lamellar structures of α and β phases in TC4 titanium alloy were deformed to ultrafine structures by dynamic recrystallization during hot rolling, and dislocations were retained in the microstructures because of the incompletion of dynamic recrystallization. With the reduction increasing, the number of ultrafine grains increased, the grain size decreased, the tensile strength of the alloy increased, the plasticity was kept well, and the tensile fracture occurred by ductile mode. After 90% severe hot rolling, the high-strength high-ductile ultrafine-grained TC4 titanium alloy was produced, with average grain size of 150 nm, tensile strength of 1 135 MPa and elongation above 9%.