Research On Globularization Behavior Of Lamellar Microstructure Of Titanium Alloy TC21

Titanium alloy TC21 as a new type of tolerant titanium alloy with high strength,and high toughness, it can be widely used in the aerospace industry and civilian industry.Because of the high structural stability at elevated temperature, there are several problems for the deformation in alpha and beta phase field, it is difficult to be obtained ideal work piece resulting from poor thermal conductivity of the lamellar titanium alloys. Therefore, large plasticity deformation in alpha and beta phase field is necessary to obtain the globular microstructure. In this paper, lsothermal constant strain rate compression experiment of titanium alloy TC21 has been carried out in the temperature range of 760℃~920℃ and strain range of 0.16~0.91 and strain rate range of0.001s-1~10s-1, by analyzing the stress-strain curves at different deformation parameters.The microstructure of titanium alloys TC21 was described; the globularization mechanism for titanium alloy TC21 was studied, the dynamic model of globularization for titanium alloy TC21 was established.Flow stress has been peaked when the strain of small, with increasing strain, the stress decrease, temperature and strain rate also has been influence, from analysis of stress-strain curves of titanium alloy TC21. The large influence of deformation parameters on globularization behavior of titanium alloy TC21 by metallographic observation. With increasing temperature, globularization percentage of alpha and diameter of globularization alpha phase were increase. But alpha phase transition and volume reduce for high temperature. The effect of strain rate on alpha phase globularization percentage and shape, flow localization and adiabatic shear bands and other defects produce at high strain rate, but that defects were disappeared and lamellar alpha phase was globularization obvious at low strain rate. Strain was the main factors of globularization, with increasing strain, lamellar alpha phase shape has changed, to become long strips or lamellar kinking separation and globularization at the end.Temperature range of 880℃~920℃ and strain rate range of 0.001s-1~0.01s-1 and strain range of 0.59~0.91 were the more reasonable parameters.The globularization mechanism of TC21 titanium alloy has analysis showed that the globularization procedure of TC21 titanium alloy with lamellar microstructure by the combined action of diffusion and deformation mechanisms by scanning and transmission electron microscopes. Dislocation slip can arising defects from hot deformation, and the lamellar was divided to form subgrain microstructure in the lowstrain rate. The penetration of beta phase into the interface of alpha and alpha phase caused by deformation twin plays an important role in the globularization procedure, and the kinking separation and parallel separation of the lamellar alpha phase also important. The penetration of beta phase into the interface of alpha and alpha phase caused by deformation twin plays an important role in the globularization procedure,and the kinking separation and parallel separation of the lamellar alpha phase also important. The diffusion process runs through that whole processing, The diffusion happened at this position where the atoms are arranged irregularly and the structure of complex at the grains boundaries and dislocation and other defects.The establishment of a dynamic model of the globularization for the lamellar TC21 titanium alloy by globularization regular and globularization mechanism. In this model the experimental and calculated values fit well, accordingly it can represent the dynamic process of globularization for TC21 titanium alloy.