Wear mechanism transition in laser shock peened GH4169 superalloy achieved via <i>in situ</i> formation of a compound gradient structure

Laser shock peening (LSP) has been shown to promote a transition in wear mechanisms of nickel-based superalloys during elevated-temperature fretting wear. However, the intrinsic relationship between LSP-induced microstructural features and the resulting wear mechanisms has not been fully elucidated, particularly with regard to the adoption of in-situ techniques. In this study, the mechanism underlying this transition is clarified in detail from a microstructural perspective through quasi-in-situ experimental efforts and state-of-the-art characterization techniques. Fretting wear test results demonstrate that LSP can significantly shift the wear mechanism of GH4169 at 600 °C, transitioning from adhesive wear into abrasive wear. Further examination of the cross-sectional microstructure of the worn subsurface reveals that the LSP-treated sample develops a compound gradient structure, consisting of an amorphous-crystalline oxide layer and a nanocrystalline grain structure on the surface. In contrast, this structure is absent in the untreated sample. The in-situ formation of this compound gradient structure, coupled with the plastically deformed gradient nanostructure beneath it, results in the LSP-treated sample predominantly exhibiting an abrasive wear mechanism during fretting wear at 600 °C. This contrasts with the adhesive wear mechanism observed in the untreated sample. This work provides valuable insights into the fundamental understanding of plastic deformation in LSP-treated superalloys during fretting wear at elevated temperatures, and offers guidance for the design of wear-resistant alloys using surface engineering.