Low-temperature superplasticity of cryorolled Ti-6Al-4V titanium alloy sheets

To investigate the superplastic deformation behavior of cryorolled Ti-6Al-4V titanium alloy,tensile tests were carried out at760 ℃ and 830℃ with different strain rate.The evolution of grain and micro structure has been studied using transmission electron microscopy and electron backscatter diffraction.When the tensile temperature was 760℃（<0.5Tm,Tm is absolute melting point of alloy.） and the strain rate was 5 × 10-4 s-1,the fracture elongation of the sample reached 385%,showing good low-temperature superplasticity.Compared with the tensile temperature of 760 ℃,the fracture elongation of the s ample at 830 ℃ was lower due to grain coarsening and oxidation.The strain rate sensitivity value m of all samples was larger than0.3,which confirmed that the cryorolled Ti-6A1-4V titanium alloy with a non-equiaxed grains structure can achieve high superplasticity at a temperature lower than 0.5Tm,and indicated that the main deformation mechanisms in the tensile test at760-830 ℃ were grain rotation and grain boundary sliding.After the tensile test,the average grain size of all samples was less than 5 μm,in which significant dynamic recrystallization and recovery occurred.