Stress-corrosion cracking of Ti-8Al-lMo-lV in aqueous environments: 1. The kinetics of subcritical crack propagation

Abstract

Precracked specimens of Ti-8Al-lMo-lV were tested in salt-water, and the subcritical crack velocity was measured as a function of applied stress-intensity. The minimum applied stress intensity which produces subcritical cracking,K _Iscc, varies inversely with the average chloride-ion concentration of the environment, butK _Iscc does not vary significantly with temperature. Plots of subcritical crack velocity,a, against applied stress intensity,K _I, reveal two types of cracking behavior. At low stress intensitiesa is approximately proportional toK _I (Stage I crack propagation). At high stress intensities,a is approximately constant, independent ofK _I (Stage II crack propagation). The apparent activation energy for subcritical crack propagation is 5600 cal-(g-mole)^-1, anda ∞ [Cl^-]^1/6. It is suggested that the instantaneous subcritical crack velocity is limited by the rate of production or by the diffusion of some embrittling species.