Hold-time effect on the elevated-temperature crack growth behavior of solid-solution-strengthened superalloys

The fatigue crack growth behavior of two solid-solution-strengthened superalloys, Ni-based HAYNES® 230 and HASTELLOY® X, was studied at 816 and 927 °C in laboratory air. The fatigue crack growth tests were conducted following a baseline triangular waveform of 0.33 Hz. Various hold times were introduced at the maximum load to study the hold-time effect. Fracture mechanics parameters, K, C∗, Ct, and (Ct)avg, were applied to correlate the crack growth rates at different temperatures for both HAYNES 230 and HASTELLOY X alloys. For both alloys, the fatigue cracking path was mainly transgranular at 816 and 927 °C. The cracking path became dominantly intergranular if the hold time increased to 2 min, indicating that the time-dependent creep damage mechanisms were in control. When the time-dependent damage dominated (temperature ⩾816 °C and hold time ⩾2 min), the crack growth rates can be correlated with Ct or (Ct)avg parameters. The Ct and (Ct)avg parameters were capable of consolidating data from different temperatures and different alloys.