Aluminizing mechanism on a nickel-based alloy with surface nanostructure produced by laser shock peening and its effect on fatigue strength

A nanocrystalline surface layer with grain sizes ranging between 30 and 150 nm was fabricated on a K417 nickel-based cast alloy by means of laser shock peening (LSP). The effect of the surface nanostructure on the gas aluminizing process was investigated through microstructure characterizations, carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that, following the LSP treatment, a higher amount of Al diffused into the matrix and a thicker-aluminizing layer was produced. The diffusion mechanism was that the thermal stability of surface nanostructure and high-density dislocation induced by LSP increased its surface activity and made more channels available for element diffusion during the high temperature gas aluminizing processing. The specimens in different surface treatments (aluminizing and LSP + aluminizing) were then subjected to vibration fatigue load. The fatigue strengths of the aluminizing specimens and LSP + aluminizing specimens were 226 MPa and 335 MPa, respectively. All the results indicated that LSP-induced surface nanostructure increased the efficiency of the aluminizing process and the fatigue resistance.