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 env ironment-assisted cracking (EAC) resistances of three microstructures of Ti-8V-6Cr-4Mo-4Zr-3A1 (Beta-C) in aqueous NaC1 through variation in crack tip strain rate. The single-phase beta microstructure of Beta-C cold worked to high strength, as well as a beta/alpha structure from short-term aging at 500 degrees C, are immune to EAC in aqueous NaC1 f or a range of crack tip strain rates that should allow varying levels of atomic hydrogen production and accumulation. Intergranular EAC occu rs in underaged Beta-C, but only if driven by high crack tip strain ra te from rapid loading or stable crack growth. Increased process-zone h ydrogen from increased crack tip strain rate promotes this embrittleme nt. The severity of EAC in ST/A Beta-C increases with aging time for c onstant crack tip strain rate. These results strengthen the Part I fin ding that increased strength does not uniquely promote intergranular E AC; rather, crack tip strain rate as well as grain boundary characteri stics that change during alpha-precipitation hardening govern the EAC severity of beta-Ti alloys. (C) 1998 Published by Elsevier Science S.A . All rights reserved.