Creep failure mechanisms of a Ti-6Al-4V thick plate

The creep failure operating mechanisms of a 17-mm thick plate of a Ti-6Al-4V alloy in various heat treating conditions have been investigated. Specimens in the as-received, mill-annealed, condition (50 min maintenance at 720°C and air cooled as the final step of the thermomechanical process) showed the lowest creep resistance and their metallographic analysis revealed that the temperature-activated dislocation climb was the mechanism responsible for the failure and that observed holes were generated by plastic deformation, rather than by creep cavitation. Conversely, maximum times to failure were recorded in beta-annealed specimens (1030°C for 30 min, air cooled and aged for 2 h at 730°C). The fracture surfaces of these broken specimens exhibited an intergranular morphology that was attributed to grain boundary sliding along the former beta grains. Finally, alpha-beta field-annealed samples (940°C 4 h, and furnace cooled at 700°C) possessed intermediate lives between those of mill-annealed and beta-annealed specimens and the failure operating mechanism was diffusional creep by the nucleation and coalescence of the creep cavities generated at the alpha-beta interfaces and the triple points.