Comparative study of the effects of shot peening and electroless nickel coating on the fatigue strength of a metallic material

This article investigates the influence of surface treatments on the fatigue behavior of a low-carbon structural steel grade E235, used for pump rotors. Three surface conditions were considered: raw material, shot peened material and shot peened material followed by an electroless nickel coating. Fatigue specimens were extracted from critical areas of the rotor in order to reproduce the damage mechanisms as observed in real service. Fatigue tests were carried out under force-controlled loading at room temperature with a stress ratio of one tenth (R = 0.1). The results show that shot-peening significantly improves fatigue performance, with an increase in the fatigue limit of approximately 20 to 25% compared to the raw material condition. This increase of the fatigue limit is due to the introduction of compressive residual stresses and surface hardening. In contrast, the application of an electroless nickel coating after shot peening leads to a reduction in fatigue strength, probably related to tensile residual stresses and coating/substrate interface effects.