Fatigue crack growth behavior of a newly developed Ni–Co-base superalloy TMW-2 at elevated temperatures

Fatigue crack growth (FCG) rates of a new superalloy TMW-2 in air was studied by a fracture mechanics test method. Compact tension specimens were tested under load control with a triangular wave form to investigate the effects of temperature (400, 650, and 725 °C) and load ratio (0.05 and 0.5) on FCG rates. The results showed that the FCG rates increased significantly with increasing the temperature. Compared with the creep effects, the results showed that the degradation of mechanical properties and the oxidation assisted crack growth may dominate the FCG rates of TMW-2 at elevated temperatures. Load ratio had a little (at 400 °C) or moderate (at 650 and 725 °C) influence on the FCG rates, which increased as the load ratio increased. The load ratio effects were successfully accounted for by applying the Walker model. The fractographic observations showed that the fracture mode was transgranular at 400 °C and was mixed transgranular and intergranular at 650 and 725 °C.