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The phenomena of stress-corrosion cracking and corrosion fatigue have been investigated assuming that a thermally activated process (diffusion) acts in conjunction with mechanical energy to produce subcritical extension of a flaw. Associated with this diffusion process is an apparent activation energy which is shown to be dependent on the stress-intensity level indicating that the rate limiting diffusion step is associated with the material rather than the environment. A characteristic activation energy associated with the diffusion process is obtained by plotting apparent activation energy versus mechanical energy input required for crack extension and extrapolating to zero mechanical energy input. The characteristic activation energy associated with the stress-corrosion differs fram that associated with the corrosion-fatigue process. Thus, a linear superposition model for corrosion fatigue employing stress-corrosion data is not valid for the material studied. Also from this plot it can be seen that the toughness of the material at the crack tip is inherently degraded by the diffusion process.
titanium alloy, stress corrosion, cracking (fracturing), corrosion fatigue, activation energy, stress intensity, hydrogen embrittlement
metallurgist, Wright-Patterson Air Force Base, Ohio
Professor, University of Cincinnati, Cincinnati, Ohio