Abstract
The effect of the precipitation of α2 (Ti3Al) particles on the stress corrosion cracking (SCC) susceptibility of Ti-7Al binary alloy in sea water was determined by the notched, cantilever beam, stress corrosion test. This alloy was aged in the α + α2 region up to 500 hrs following alpha, beta, and alpha-beta solution annealing treatments. Aging of the alpha annealed material caused an increase in stress corrosion susceptibility for aging times up to 120 hrs at 1200 F (649 C). Aging for 500 hrs produced a significant recovery of SCC resistance, indicating dependence of SCC on the size of the α2 precipitate particles. The extent of susceptibility was increased by increasing grain size of the alloy. The stress corrosion fracture path was found to be transgranular for both equiaxed and Widmanstätten microstructures with cracking primarily by cleavage. Mixed ductile and cleavage fracture was observed in the fast fracture (air) zone. A correlation is shown between impact toughness in air and fracture stress in sea water.