EFFECTS OF ENVIRONMENT ON HIGH-TEMPERATURE FATIGUE CRACK GROWTH IN A SUPER-ALLOY

Fatigue crack growth rate measurements were made on Inconel alloy 718 samples at 650°C in fourteen different gaseous environments. Minor amounts of either oxygen or sulfur bearing species in the environment produced large increases in crack growth rates. Aggressive environments promoted intergranular crack growth. Kinetic factors rather than thermodynamic ones appear to be the variables dominating the effects of an environment on crack growth. Environments that markedly increased the crack growth rate did not produce significant corrosion attack on unstressed samples. Thus conventional high temperature corrosion tests may not be useful for predicting service performance of stressed components. © 1979 American Society for Metals and the Metallurgical Society of AIME.