Insights into ultrasonic surface rolling induced hierarchical structure in Ni-based single crystal superalloy for enhanced tribological performance

Ni-based single crystal (NBSC) superalloys are extensively deployed as crucial hot end components such as turbine blades of aeroengines, where wear failures are indispensable at elevated temperature. To extending longevity, ultrasonic surface rolling (USR) was employed on NBSC in this work, and the tribological behavior was systematically investigated at 650 °C. Result demonstrates that USR creates a spatial slip trace network on NBSC surface via a/2 < 110 > pairs cutting. Anti-phase boundary strengthening and dislocation strengthening synergistically dictate the work hardening of the treated alloy, raising hardness by 54 %, inducing compressive residual stress (CRS) of 969 MPa, thus diminishing wear rate by 55 %. Owing to γ dislocation cutting stages during early wear, the asynchronous continuous dynamic recrystallization (cDRX) of γ/γ’ in pristine NBSC arouses the formations of chain-like ultra-fine grains. The size disadvantages of these chains deprive their dislocation storage capabilities, leading them vulnerable to microcrack initiations. Ultimately, the encompassed nanograin bulks are more likely discharged and evolve into large third-bodies, incurring serious abrasive wear. In contrast, USR-produced γ terminals create the direct entrances for the exchanges of solutes and dislocations between γ/γ’ during elevated temperature sliding, accelerating local rafting and promoting synchronous cDRX, respectively. Without ultra-fine chains, microcracks, confined by CRS, just originate from uppermost surface at later period of wear, thereby releasing tiny debris outside that is responsible for lower wear volume and contributes to alleviate wear damage of fresh surface. The findings provide some new insights to understand the wear mechanisms of NBSC and guide their anti-wear designs.