HIGH-TEMPERATURE DEFORMATION-BEHAVIOR OF PHYSICAL VAPOR-DEPOSITED TI-6AL-4V

A detailed study has been conducted of the high temperature creep and microstructural evolution accompanying the creep deformation of an ini tially nanocrystalline Ti-6-Al-4V alloy. For test temperatures of 600 and 680 degrees C the alloy transformed from an (alpha+alpha') to a si ngle phase alpha during creep testing and exhibited exceptionally low creep resistance. During testing between 760 and 900 degrees C, the al loy transformed to a conventional (alpha+beta) microstructure and exhi bited up to ten times the creep rates of conventional grain size (supe rplastic) Ti-6Al-4V. Creep models based on grain boundary sliding, dis location and diffusional creep were combined with relationships for ph ase evolution and grain growth to predict stress-strain rate relations hips at each test temperature. The analysis indicates that in the low temperature region dislocation accommodated GBS, in conjunction with d iffusional flow, are responsible for creep whilst in the high temperat ure region diffusion accommodated GBS is the dominant mechanism.