Effect of strength on environment-assisted cracking of Ti–8V–6Cr–4Mo–4Zr–3Al in aqueous NaCl: Part 1: Age hardening vs. work hardening

The objective of this research is to understand the effect of yield strength on the environment-assisted cracking (EAC) susceptibility of a β Ti alloy, Ti–8V–6Cr–4Mo–4Zr–3Al (Beta-C), precracked and stressed actively in aqueous NaCl. Isothermal aging renders immune, β-solution treated Beta-C susceptible to severe EAC coincident with strengthening by α precipitates. The threshold for EAC decreases to 40% of the air fracture toughness, subcritical crack growth rate approaches 100 μm s−1, and the crack path becomes fully intergranular for aging times in excess of several hours. In contrast, solution treated and cold-worked single-phase β Beta-C retains immunity to EAC for similar high strengths. For several levels of cold work, Beta-C cracks by transgranular microvoid processes, with equal values of EAC threshold stress intensity and air fracture toughness. Cold work reduces the air fracture toughness of β-phase Beta-C compared to values for β/α microstructures at similar strengths. The strength increase due to α precipitation does not uniquely promote EAC susceptibility.