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

The creep failure operating mechanisms of a 17-mm thick plate of a Ti-6-Al- 4V alloy in various heat treating conditions have been investigated. Specim ens in the as-received, mill-annealed, condition (50 min maintenance at 720 degreesC and air cooled as the final step of the thermomechanical process) showed the lowest creep resistance and their metallographic analysis revea led that the temperature-activated dislocation climb was the mechanism resp onsible for the failure and that observed holes were generated by plastic d eformation, rather than by creep cavitation. Conversely, maximum times to f ailure were recorded in beta-annealed specimens (1030 degreesC for 30 min, air cooled and aged for 2 h at 730 degrees C). The fracture surfaces of the se broken specimens exhibited an intergranular morphology that was attribut ed to grain boundary sliding along the former beta grains. Finally, alpha-b eta field-annealed samples (940 C 4 h, and furnace cooled to 700 degrees C) possessed intermediate lives between those of mill-annealed and beta-annea led 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.