Study On The Strain-Induced Superplasticity Of TC6Titanium Alloy

TC6is 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 theaviation, chemical, shipbuilding and other industries. Compared with the traditionalforming process, the superplastic forming of titanium alloy can not only decreasedeformation resistance, but also produce complex components with high dimensionalaccuracy and compact structure. Therefore, It is theoretical and practical for titaniumalloy to explore a new superplastic forming technology.The method of strain-induced superlasicity was proposed to improve thesuperplasticity of TC6titanium alloy in the paper, which is based on the research ofmaximum m-value method and strain rate cycling method. The principle of themethod is that the grains are refined because of dynamic recrystallization induced bythe distortion energy, which was generated during pre-strain deformation.The superplastic deformation behaviors and microstructure evolution of TC6alloy have been systematically studied by three superplastic tensile methods, such asconstant velocity, maximum m-value superplasticity and strain-induced superlasicity.The law of the true stress-true strain under various processing parameters was alsostudied. The influences of temperature on flow stress and elongation duringsuperplastic deformation were analyzed. Compared with other two methods, thecharacteristics of the strain-induced superplasticity are described as follows.1. When the temperatures range from850to950℃, with increasing of thetemperature, the elongation increases firstly and then decreases. TC6alloy is quitesensitive to temperature, and the optimum temperature is850℃.2. During superplastic deformation, the engineering strain which caused criticalrecrystallization is1.5, and the optimum engineering strain is2.0, which improved thesuperplasticity of TC6alloy.3. The main deformation mechanism of strain-induced superplasticity method isgrain boundary sliding, and the auxiliary mechanism of deformation is dynamic recovery and recrystallization.4. In the process of superplastic deformation, the grains were refined and keptequiaxed. Because the time of deformation is longer, the grains grow slightly.Whereas the driving force of recrystallization is produced continuously with increaseof the deformation amounts, leading to dynamic recrystallization in the wholesuperplastic deformation, which restrain the growth of grains. It is inferred that thetime of deformation has little effect on the superplasticity of TC6titanium alloy.5. The method of strain-induced superplasticity is superior to other two methods.It can not only refine the grains of TC6alloy, but also keep the optimum proportionbetween α and β phase, inducing the high elongation of2053%, but the elongationsonly can reach1347%and754%when maximum m-value method and constantvelocity method were applied respectively.