Micromechanics of fatigue, creep-fatigue interaction and thermo-mechanical crack growth of XH73M nickel alloy

This study presents interpretation and evaluation of a range of isothermal experimental crack growth data on polycrystalline XH73M nickel-based alloy generated by two type tests carried out by stress-controlled pure fatigue and creep-fatigue interaction conditions. The tests have been carried out using cycles with a triangular and trapezoidal waveform and a temperature range of 23-750°C. It was found that from the crack growth rate point of view, the following order of arrangement of fatigue fracture diagrams is formed: isothermal creep-fatigue interaction, isothermal pure fast (f=10 Hz) and slow (f=1 Hz) fatigue. The ordering of the crack growth rate curves is supported by detailed fractographic analysis which shows transgranular or intergranular mechanism of fatigue crack growth depending on thermo-mechanical test conditions. The regularities of fatigue crack propagation were established by fractographic analysis. It was found for example that the intergranular crack growth mechanism become dominant at 750°C for the pure fatigue and at 550°C for creep-fatigue interaction conditions. The secondary crystals on the grain boundary of primary grain at intergranular fracture of specimen tested at 650°C under creep-fatigue interaction conditions appeared.