Features of evolution of TI-6AL-4V submicrocrystalline titanium alloy structure under superplastic deformation

Abstract

The aim of the study is to determine the correlation between the structure evolution and features of submicrocrystalline VT6 alloy deformation behavior under superplastic deformation. in the alloy was obtained by the multi-directional pressing method changing the deformation axis and gradual decrease of deformation temperature in the interval of 823-1073 К. Deformation behavior of VT6 alloy submicrocrystalline state was studied under tensile tests of 10-2 Pa in vacuum with the initial stretching rate of 6,9 10-3 sec.-1 and in the temperature range of 773-1073 К. The TEM method has been used to investigate the alloy structure in the initial state as well as in the submicrocrystalline state after the elongation of 40, 60 and 200 %. Submicrocrystalline structure formation in the alloy is found to lead to decreasing the temperature interval of superplastic flow beginning from 1173 to 873 K. It was shown that the increase in temperature of superplastic deformation of submicrocrystalline VT6 alloy samples from 873 to 973 K results in appearance of strain hardening stage in the stress-strain curves in the coordinates of the "true stress - true strain". Structure evolution of the submicrocrystalline VT6 alloy during superplastic deformation depends on the test temperature. At 973 K one can observe the change in the character of size distribution histogram of grain-subgrain structure elements from unimodal to bimodal. The strain hardening of the alloy under superplastic flow is caused by bimodal structure formation in it and growth in volume fraction of relatively large grains at deformation.

Keywords

• titanium alloy
• submicrocrystalline structure
• superplastic deformation
• "stress-strain" curves
• structure evolution
• grain size