Microstructural evolution for enhanced high temperature fretting fatigue resistance in GH4169 via laser assisted ultrasonic surface rolling process

Laser assisted ultrasonic surface rolling process (LA-USRP) was applied to GH4169 superalloy to improve its high temperature fretting fatigue resistance. Conventional USRP increased the fretting fatigue life under axial tension–tension cyclic loading (stress ratio R = 0.1, frequency of 131 ± 2 Hz, maximum stress of 800 MPa, and contact pressure of 85 MPa) at 600 °C by a factor of 3.3, whereas LA-USRP achieved a 14.7-fold enhancement compared to the base material. This superior performance is primarily attributed to advantageous microstructural evolution, including a thicker gradient nanostructured surface layer (average surface grain size around 25 nm), higher compressive residual stresses (surface −2079 MPa, maximum −2443 MPa at around 35 μm depth), and the formation of refined nanotwins and stabilized 9R phase. These features significantly improve cyclic stability of compressive residual stresses (relaxation reduced from 89.6 % in USRP to 35.9 % in LA-USRP after fatigue) and impede dislocation motion at elevated temperatures. These findings offer a promising approach for enhancing the high temperature fretting fatigue performance of critical aero-engine components.