Influence of prefatigue on the tensile strength and ductility of Ni-10at.%Cr alloys: Critical role of short range ordering

Abstract

To explore the effect of prefatigue deformation on the static mechanical behavior of face-centered cubic metals with high stacking fault energy and short-range ordering (SRO) degree, the quasi-static tensile properties of a Ni-10at.%Cr alloy were systematically investigated as a case study, after prefatigue deforming at a total strain amplitude of 1.5 × 10⁻³ up to different cycles. Dislocation structures at different stages are characterized using scanning electron microscopy-concentric backscattered electrons and scanning transmission electron microscopy. It is found that the static tensile properties of the prefatigued Ni-10Cr alloys exhibit non-monotonic changing tendency with the increasing of prefatigue cycles. At low prefatigue cycles (e.g., 200 cycles), SRO-induced planar slip causes strain concentrations, leading to a simultaneous degradation in ultimate tensile strength and elongation. As the precycle increases, SRO structures are significantly destroyed by moving dislocations, activating cross slip. Therefore, some typical wave slip dislocation structures, such as veins, labyrinths, cells, and persistent slip band (PSB) ladders, are found to form in the alloy prefatigued up to 20000 cycles that approach to the fatigue life. The increase in dislocation density enhances the tensile strength, while PSB ladders and labyrinths induced by prefatigue improve the compatibility of subsequent tensile deformation, thereby enhancing ductility.