Influence of temperature, stress intensity factor, and cold work on intergranular creep crack growth in TT Alloy 690

Creep crack growth tests were conducted on thermally treated (TT) Alloy 690 with 10–30% cold work in air over a temperature range of 360–475°C under applied stress intensity factors of 20–40 MPa√m. The creep crack growth rate (CGR) was evaluated primarily from post-test fracture-surface measurements, and the effects of temperature, applied stress intensity factor, and cold work on crack growth behavior were systematically examined. The results indicated that the CGR increased with increasing temperature, applied stress intensity factor, and cold work level. Fractographic and cross-sectional observations showed primarily intergranular crack growth accompanied by cavity formation. Arrhenius-type analysis of the CGR yielded apparent activation energies of 274, 250, and 241 kJ/mol for 10, 20, and 30% cold work, respectively, indicating thermally activated crack growth behavior. Steady-state displacement rates obtained from load-line displacement–time curves showed an overall correlation with the fracture-surface-based CGRs. The observed temperature dependence was also qualitatively similar to that reported for SCC crack growth in simulated PWR primary water, supporting the interpretation that long-term crack advance in cold-worked TT Alloy 690 involves thermally activated intergranular damage.