The effect of partial vacuum on the fatigue crack growth of nickel base superalloys

The effect of a partial vacuum environment, simulative of a typical spin-pit test atmosphere, on the high temperature crack growth behavior of two nickel-base superalloys was examined. Under constant amplitude loading, the partial vacuum typically reduced the crack propagation rate in one alloy while an increase in growth rate was found for the other. Cycling with a superposed tensile dwell period increased the crack growth rates at low levels of Delta K relative to those found in air for both alloys. This anomalous behavior was heretofore not recognized and raises doubt as to our understanding of the environmental drivers on fatigue crack propagation.