Deterioration effect of creep on fatigue properties in QCr0.8 alloy: Damage mechanism and fatigue-creep life evaluation

The QCr0.8 alloy used in the thrust chamber liner wall of the reusable liquid rocket engine is subjected to high-temperature fatigue and high-temperature creep loading. This work investigates the effect of fatigue-creep interaction (FCI) on the fatigue life of QCr0.8 alloy. Experimental results reveal accelerated cyclic softening and decelerated stress relaxation in the alloy under FCI conditions, attributed to creep deformation and stress amplitude growth. The damage evolution mechanism of FCI is revealed by the results of the energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The decrease in fatigue-creep life of the QCr0.8 alloy is attributed to the fracture of the outer surface oxide layer, as well as the coupling development of creep voids and secondary cracks. Finally, a new fatigue-creep life prediction model has been developed, taking into account the increase in plastic strain energy resulting from stress relaxation and creep deformation behaviors. The study results provide substantial theoretical justification for the utilization of QCr0.8 alloy in the thrust chamber wall of reusable liquid rocket engines.