High temperature deformation behavior of physical vapor deposited Ti-6Al-4V

Abstract

A detailed study has been conducted of the high temperature creep and microstructural evolution accompanying the creep deformation of an initially nanocrystalline Ti-6Al-4V alloy. For test temperatures of 600 and 680°C the alloy transformed from an ( α + α′) to a single phase α during creep testing and exhibited exceptionally low creep resistance. During testing between 760 and 900°C, the alloy transformed to a conventional ( α + β) microstructure and exhibited up to ten times the creep rates of conventional grain size (superplastic) Ti-6Al-4V. Creep models based on grain boundary sliding, dislocation and diffusional creep were combined with relationships for phase evolution and grain growth to predict stress—strain rate relationships at each test temperature. The analysis indicates that in the low temperature region dislocation accommodated GBS, in conjunction with diffusional flow, are responsible for creep whilst in the high temperature region diffusion accommodated GBS is the dominant mechanism.