Effect of microstructure on high cycle fatigue behavior of brass processed by laser shock peening

In this paper, fatigue behavior and microstructure response of laser shock peening (LSP) brass during high cycle fatigue (I-ICF) test are systematic investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that broadening, shifting and intensity decreasing of diffraction peaks can be attributed to grain refinement and increase of micro-strain after HCF test. The new grain boundaries in initial grains imply the increase of low angle grain boundaries and the decrease of grain size. The mode of fatigue crack growth is determined by the grain orientation and the grain boundary characteristics. Due to different grain sizes in LSP layers and sub-surface layer, the deformation mechanisms of these layers lead to different microstructural changes. In addition, fracture morphologies indicate that the fatigue crack initiation (FCI) of LSP brass is transferred from surface to subsurface relative to untreated brass. Based on the investigation above, the fatigue fracture mechanism accompanied by grain evolution is proposed in detail.