Effect of strength on environment-assisted cracking of Ti–8V–6Cr–4Mo–4Zr–3Al in aqueous NaCl: Part II: Crack tip strain rate

The objective of this study is to critically examine the intrinsic environment-assisted cracking (EAC) resistances of three microstructures of Ti–8V–6Cr–4Mo–4Zr–3Al (Beta-C) in aqueous NaCl through variation in crack tip strain rate. The single-phase β microstructure of Beta-C cold worked to high strength, as well as a β/α structure from short-term aging at 500°C, are immune to EAC in aqueous NaCl for a range of crack tip strain rates that should allow varying levels of atomic hydrogen production and accumulation. Intergranular EAC occurs in underaged Beta-C, but only if driven by high crack tip strain rate from rapid loading or stable crack growth. Increased process-zone hydrogen from increased crack tip strain rate promotes this embrittlement. The severity of EAC in ST/A Beta-C increases with aging time for constant crack tip strain rate. These results strengthen the Part I finding that increased strength does not uniquely promote intergranular EAC; rather, crack tip strain rate as well as grain boundary characteristics that change during α-precipitation hardening govern the EAC severity of β-Ti alloys.