Constitutive analysis of the high-temperature deformation of Ti–6Al–4V with a transformed microstructure

Abstract The high-temperature deformation mechanisms of Ti–6Al–4V with a transformed microstructure were determined within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on samples with a lamellar structure containing different alpha-platelet thicknesses at temperatures of 715–900 °C. The flow stress-versus-strain rate curves for all the microstructures were well fit with an inelastic-deformation equation describing grain-matrix deformation (GMD) (dislocation glide+dislocation climb). However, for heavily pre-deformed specimens, grain-boundary sliding (GBS) as well as GMD was evident. The GBS rate was found to be most rapid for the microstructure with the thinnest alpha laths/platelets. Softening of heavily deformed material was attributed to a decrease in the internal-strength variable σ ∗ associated with reduced alpha–beta interface strength and to the occurrence of GBS.