Tensile-hold effects on high-temperature fatigue-crack growth in nickel-based HASTELLOY® X alloy

The fatigue-crack growth behavior of HASTELLOY® X, a nickel-based superalloy, was studied at the temperatures of 816 and 927 °C under isothermal conditions. Various hold times were introduced at the maximum load. The fatigue tests were conducted under load and stress-intensity-factor control modes. The crack grew faster at a higher temperature. It was also noted that the introduction of a hold time at the maximum load led to an increase in the cyclic crack-growth rate. The longer hold time gave the faster crack-growth rate, which was related to the gradual transition from transgranular to intergranular cracking. The crack-growth rates in the fatigue and creep tests were correlated with the stress-intensity factor range, ΔK, and the stress-intensity factor, K, respectively. The crack-propagation rates in the hold-time tests were predicted from the crack-growth rates obtained from both the fatigue and the creep crack-growth tests, using a semi-empirical linear summation model. Crack-growth rate predictions reproduce most of the characteristics observed experimentally.