Transmission electron microscopic investigation of hot-salt cracking in titanium alloys

New dislocation structures in Ti-8Al-1Mo-1V were observed after exposure to hot salt at 440 °C for 1 h in a vacuum at 10−6mm Hg. Dislocation sources were found to be associated with salt crystals or stain sites formerly occupied by salt. These dislocation sources are believed to be capable of generating a sufficient number of dislocations during dislocation pileup to nucleate cracks at grain boundaries, inside the grain or grain boundary precipitate. A stacking fault energy for Ti-8Al-1Mo-1V was calculated to be 15.4erg cm−2. This value indicated that the alloy had low stacking fault energy. This energy is consistent with the pileups, stacking faults, and complex networks observed. Dislocation structures observed for Ti-8Al-1Mo-1V and Ti-6Al-4V were similar at room temperature but not after exposure to hot salt. Metallurgical processing to control grain size and grain boundary precipitation could be beneficial in reducing hot-salt-cracking susceptibility of the titanium alloys investigated.