Study On High-efficiency Superplasticity Deformation Mechanism Base On The M Value Of Titanium Alloy

Titanium alloy is a very important lightweight structural material; it has good high temperature performance, high specific strength and excellent corrosion resistance. Therefore, it has wide range applications in the aerospace industry, automotive industry and chemical industry areas. With superplastic forming, the force of forming can reduce, the size of deformation can increase, and precision parts can be produced, so studying on superplasticity of titanium alloys not only can solve some of the titanium alloy processing problems, but also can reduce the manufacturing costs of components to expand the use of titanium alloys, it has very important practical significance. The theory of High-efficiency Superplasticity Deformation base on the m value is based on the Maximum m (Strain rate sensitivity index, hereafter referred to m values) and Strain Rate Cycling superplasticity method, to explore a new experimental method that the process of superplastic deformation in the titanium alloy can not only get good superplastic deformation, but also greatly enhance the efficiency of superplastic deformation, the theory has broad application prospects.Some subprograms were compiled and debugged under Visual Basic environment for the controlling system of High-efficiency Superplasticity base on the m value, the program could fulfill the task of controlling the drawing machine, acquiring, analyzing and processing data generated during the experiment, and can even draw real time supervising curves, thus a complete, effective method of superplastic research was formed after the subprograms were integrated.Subsequently, the superplastic deformation behavior of TC6 alloy has been studied. Different microstructure of TC6 alloy have taken high temperature tensile test by adopting the High-efficiency Superplasticity Deformation base on the m value, Maximum m and Strain Rate Cycling (SRC) method respectively at the temperature range 850℃to 950℃. The results show that the method of High-efficiency Superplasticity Deformation base on the m value greatly improves the efficiency of superplastic deformation and obtain a good elongation. At 900℃, while the smallest m value is set to 0.3, the elongation of fine-grained sample reaches 1696%, the tensile time is only 57.6 minutes, deformation efficiency is improved 1029%, the elongation of coarse-grained sample reaches 604%, the tensile time is only 45.1 minutes, and deformation efficiency is improved 246%.Finally, Systematic study on High-efficiency Superplasticity Deformation base on the m value in TC6 alloy. Study the influence of m value, temperature, grain size and other parameters on the efficiency of deformation and superplasticity, and the relation of flow stress and temperature, strain rate in deformation as well as the microscopic structure after deformation were studied. The results show that:(1) TC6 alloy by adopting the method of High-efficiency Superplasticity Deformation base on the m value, m value is change constantly between the minimum m value in setting and 0.9, and the minimum m value is set higher, tensile test time is longer, elongation slightly better. (2)Temperature and grain size have a significant impact on superplasticity. As the temperature increased, the elongation showed the first increase after decreasing trend, moreover under the same temperature, the finer the grain, the smaller the maximum flow stress, the slower the rate of strain hardening, the longer the stress reaches its peak.(3)The main superplastic deformation mechanism of the method of High-efficiency Superplasticity Deformation base on the m value is grain boundary sliding(GBS).In the early deformation, strain hardening effect significantly, flow stress increased rapidly to peak, and then accompanied by dynamic recovery and recrystallization from occurring, flow stress fluctuate constantly and gradually reduced to specimen fracture. In the deformation, strain rate constant fluctuations in the changes over time and showed a falling trend, the corresponding speed displayed a increasing trend.(4)Temperature and deformation have a significant effect on the microstructure, the temperature is higher and the deformation is greater the grain growth more obvious. The dynamic recrystallization occurred during the deformation made the grain became equiaxed.