This work focuses on the effects of ultrasonic shot peening (USP) on grain refinement and orientation behavior in the surface region of GH4151 superalloy. The microstructure evolution of the alloy under USP durations were studied. The effects of USP-induced grain refinement, orientation, and dislocation motion behavior were analyzed. The results indicated that during the USP process, the plastic deformation of the surface layer of superalloys is accompanied by changes in grain size and orientation. The random impact of the spheres on the surface area promotes grain refinement and grain rotation, enhancing the randomness of grain orientations and reducing the texture strength and the proportion of “soft” orientation distribution. Over a long period of treatment, a large number of spheres cause the slip planes and slip directions of each grain to rotate due to the additional shear stress from the impact, resulting in relatively consistent plastic deformation on the surface and the enhanced randomness of grain orientations, thus reducing the high texture strength introduced by previous machining processes. The understanding of dislocation pile-up behavior and the relationship between externally applied shear stress, pile-up characteristics, and grain refinement is essential for optimizing the USP process and achieving the desired material properties.

The study evaluated and compared the surface morphology, roughness, and coating structure of ultrasonic shot peening (USP)-treated samples of the NiCrAlYSi-coated GH4169 alloy used for turbine blades and discussed the influence of blade-surface roughness and coating thickness on aerodynamic performance. The NiCrAlYSi coating was deposited on the surface of the alloy using electron beam-physical vapor deposition (EB-PVD), and the NiCrAlYSi bond coat was subsequently surface treated at Almen intensities of 0.1 A, 0.15 A, and 0.2 A by USP. The results following USP treatment indicated that the bond coat becomes denser with a smoother surface and a porosity reduction ranging from 12.5% to 50%, accompanied by localized enrichment of Cr elements near the substrate. Additionally, the study examined the influence of coating thickness and roughness on turbine blade aerodynamic performance, validating the effectiveness of USP in reducing these factors, thereby potentially enhancing the aerodynamic efficiency of coated turbine blades.

This study investigates how ultrasonic shot peening (USP) influences compressive residual stress (CRS) in the material surface layer. By combining experimental and simulation analyses, the research explores the distribution and variability of CRS. The results suggest that the residual stress (RS) curve from shot peening may not always conform the typical ‘√’ shape. The experimental results show that, compared to the unpeened specimens, each group curve of the USP specimens exhibits a deeper CRS depth. Notably, within a 30 μm surface layer, certain data points exhibit CRS relaxation, which deviates from the expected behavior. Further research was conducted to simulate the mutual effects of the spheres impact on the material surface, using parameters from the USP treatment experimental. Simulations with a small number of spheres and a model of multiple-shot USP both indicate that higher velocities intensify RS accumulation and accentuate mutual influence between pit locations. Strong interactions among spheres during impact can extend from the surface to the subsurface. The stress vectors of adjacent craters exert compression and tension effects on each other, leading to the formation of tensile residual stress (TRS) in certain local areas. This TRS is often observed at the stacking regions. However, relaxation of CRS at the crater locations can also occur due to the influence of stress vectors. This may potentially cause relaxation in the subsurface RS field due to sphere interactions and pit stress vectors, although this relaxed state is not consistently observed.