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

Laser shock peening (LSP) has been shown to promote a transition in the 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 for 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 superalloy at 600 °C, transitioning from adhesive wear to abrasive wear. Further examination of the cross-sectional microstructure of the worn subsurface reveals that the LSP-treated sample developed 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 via surface engineering.