Effects of residual stress and surface roughness on the fatigue life of nickel aluminium bronze alloy under laser shock peening

Abstract

The surface properties of alloy materials have a significant influence on the overall strength and fatigue properties of the materials. In this study, the effects of laser shock peening (LSP) on the residual stress distribution and variation in surface roughness and its correlation to the resulting high-cycle fatigue properties of a treated nickel aluminium bronze (NAB) alloy were investigated. The residual stress, surface roughness, and microhardness of NAB specimens subjected to various laser pulse energies were tested and analysed. In addition, the fatigue stress concentration factor considering the combined effect of the residual compressive stress and surface roughness induced by LSP was derived to explain the fatigue characteristics gain mechanism of the treated NAB alloy. Furthermore, axial tension–tension fatigue tests on the NAB specimens were conducted and the fatigue fracture morphologies were analysed in detail to establish the response mechanism between the LSP process parameters and the resulting fatigue life. The results indicated that the high-cycle fatigue life variation trend of the NAB specimens under different laser pulse energies agreed well with the fatigue stress concentration factor, and the beneficial surface roughness and compressive residual stress induced by LSP were considered the main factors that contributed to the improvement of the fatigue properties.