Study On The Superplasticity Of TC4 Titanium Alloy

TC4 is a kind of two-phase titanium alloy. Due to high ductility, high strength, good heat resistance, excellent corrosion resistance et al, it is widely applied in the aviation, warship, chemical and other industries. Compared with the traditional forming process, the superlastic forming of titanium alloy can not only decrease deformation resistance, but also produce complex components with high dimensional accuracy and compact structure. Therefore, it is important to theoretical and practical for titanium alloy exploring a new superplastic technology.In this paper, the 2 mm thick of TC4 titanium alloy sheet was selected as experiment materials, and its superplastic was studied. Firstly, TC4 titanium alloy sheet was heat-treated, through analyzing the mechanical property to get the optimal process parameters. Then, in order to get the elongation of specimens, the high-temperature tensile test of contant strain rate and strain induced were carried out with heat-treated specimens.In the strain induced experimental, specimens were stretched to the pre-strain under the condition of constant strain rate, then unloading insulation 10 min,and stretched to fracture with the previous period of strain rate. This process not only can improve the superplastic, but also is very simple, and easy to be used in industrial production. The optical microscopy, scanning electron microscopy(SEM) and electron probe micro analyzer(EDS) were used to analyze the fractured tensile sample. Therefore, the mechanical behavior of superplastic deformation, microstructure evolution during the deformation, mechanism of the deformation and fracture of TC4 titanium alloy can be explored in depth. From above tests and analysis, the conclusions as follows:(1). The superplasticity of TC4 Titanium alloy is the best conditions when the heating temperature is 820 ? and holding time is 1 hour.(2). The grain size of TC4 titanium alloy is 2.41?m by stretched with constant strain rate. The superplastic deformation is best conditions when the heating temperature is 850?, and strain rate is 1 × 10-3 s-1. Otherwise, the elongation of sample is 901 % at this time.(3). The superplasticity is best conditions when the ?? is 1.5, the strain rate is 5 × 10-4s-1, and the heating temperature is 850 ?, and the elongation of sample can reach 1270.8 % in this condition.(4). The microstructure evolution which is the specimens from the original materials to be stretched fracture, and its true stress- strain curve of specimens results show that superplastic deformation mechanisms of TC4 Titanium alloy are the slide of grain boundary, dynamic recovery of the microstructure and dynamic recrystallization.(5). The fracture morphology shows a typical characteristic of ductile fracture, including shear zone,dimple fracture, vein-like patterns. Therefore, indicating that TC4 titanium alloy has good ductility.