Experimental investigation on dynamic phase transformation and texture evolution of Ti55531 high strength titanium alloy during hot compression in the α+β region

摘要

This work aims to study the flow behavior, dynamic phase transformation (DPT) and texture evolution of Ti55531 (Ti-5Al-5Mo-5V-3Cr-1Zr) alloy in the α+β region. Hot compression tests are carried out at temperatures from 730 to 820 ℃ and strain rates from 0.001 to 10 s~(-1) on the Gleeble-3800D simulator. Scanning electron microscope (SEM) and electron backscatter diffraction (EBSD) techniques are used to analyze the morphology, volume fraction and texture evolution of each phase (primary α_p and β phase). The measured stress is corrected for deformation heat, and an Arrhenius-type constitutive model is developed for the alloy in a whole strain range. The mechanisms of the DPT and texture evolution are explained by the grain boundary maps (GBMs), local orientation maps (LOMs), inverse pole figures (IPFs) and Schimid factor (SF). The softening fractions of deformation heat, DPT, and texture to the flow softening are determined according to the mixture law and Taylor theory. It is found that the maximum intensity of texture decreases with strain during initial stages, but it increases sharply with further straining. Orientation distribution function (ODF) shows that some texture components vanish and other new ones appear during deformation, but the texture intensity keeps unchangeable. The softening fraction due to the deformation is significant at strain rates higher than 1.0 s~(-1), it is in a range from 5.9% to 17.8%. The DPT plays a main role in the softening in strain rates lower than 0.1 s~(-1), its softening fraction is in a range from 14.7% to 20%.