The effect of creep and oxidation on high-temperature fatigue crack propagation in 〈001〉-loaded CMSX-2 superalloy single crystals

Fatigue crack propagation (FCP) behaviour of 〈001〉 axially oriented single-edge notch tension specimens (R = 0.05) of CMSX-2 single-crystal superalloy has been examined in the 650–950 °C temperature range. Secondary orientations of the specimens, i.e. the crack propagation directions, are mainly 〈100〉 or 〈110〉. The increase of the test temperature from 650 °C to 750 °C leads, at 4 Hz, to an increase of the FCP rates. A further increase of the temperature up to 950 °C causes a FCP rate decrease. ependent FCP mechanisms are explored at 950 °C performing triangular (4 Hz) and trapezoidal (0.19 Hz) load wave-shape tests. Tests in air reveal much slower FCP rates than tests in vacuum, especially at low ΔK and when 5 s hold time is added. Oxide closure at the crack tip can explain the drastic environmental effect on FCP at low ΔK values while creep mechanisms can explain the acceleration of FCP at high ΔK when hold time is added in vacuum.