Tensile Deformation Behavior Of Fine-Grained TC4 Titanium Alloy At High Temperature

Titanium alloy is a structural metal material which is widely used in aircraft industry. Because the microstructure and performance of titanium is relatively sensitive to the processing parameters in hot deformation processes, the optimal process parameters are in a relatively narrow range. Therefore ,the studying of plastic deformation behaviors and microstructure evolution during hot forming can provide scientific foundation and theoretic direction in determining the process parameters and controlling the service quality of work pieces.The tensile deformation behaviors of fine-grained TC4 titanium alloy have been studied by tensile test at room temperature and that at high temperature. The true stress-true strain curves of fine-grained TC4 alloy under different conditions of tensile test are discussed and the influences of processing parameters on flow stress and elongation during plastic deformation are studied.The original microstructure is discussed with the aids of optical microscope (OM), scan electrical microscope (SEM), transmission electron microscope (TEM). The transformation temperature fromαphase toβphase is tested by DSC. The influences of heat-treatment on fine-grained TC4 are discussed and the relationship between tensile test condition and the deformation microstructure are studied. The experimental results show that the original microstructure is fine (α+β) equiaxed microstructure phase. The temperature in heat-treatment has notable influence on microstructure of TC4 titanium alloy. The volume of the firstα-phase ?declines with the increase of deformation temperature. Strain rate has little influence on volume of the firstα-phase, but has a distinct effect on the shape ofα-phase.Fracture surface analysis by SEM revealed that fine-grained TC4 titanium exhibits ductile fracture and brittle fracture during tensile test at room temperature. At elevated temperatures, too many dimples could be observed on the fracture surfaces of the fine-grained TC4 titanium alloys. It implied that the tensile fracture of the alloys occurred basically in a ductile mode. The fracture mechanism of fine-grained TC4 titanium alloys at high temperature can be explained by the theory of cavity growth and connection.