Effect of prestraining on high-temperature fatigue behaviour of two Ni-base superalloys

Abstract Isothermal cyclic deformation tests were carried out on two nickel-base alloys (Nimonic 105 and Nimonic 75) after monotonic tensile predeformation to various strains at room temperature. The effect of predeformation was found to lose importance for the fatigue behaviour with increasing temperature, increasing plastic strain amplitude, decreasing prestrain and decreasing influence of particle strengthening. Appreciable changes in the crack initiation mechanisms and the steady-state dislocation arrangements established during cyclic loading resulted from predeformation. However, the change in the cyclic stress–strain response was identified to be the main reason for the effect of predeformation on fatigue life. Consequently, a predeformation parameter SP_SWT was introduced which combines the Smith-Watson-Topper damage parameters obtained in fatigue tests on predeformed and not predeformed samples. It was shown that SP_SWT is suitable to quantitatively describe the effect of loading conditions on th...