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.

This research presents a quantitative analysis of TC17 alloy subjected to ultrasonic shot peening (USP) treatment. The effects of USP treatment under different Almen intensities on surface roughness, microstructure, plastic strain range, microhardness, residual stress, fatigue behavior and strain gradient of TC17 alloy were analyzed. Results show that increasing Almen intensity from 0.15 mmA to 0.25 mmA leads to a 27% increase in surface roughness, a 12% increase in surface compressive residual stress value, a 29% increase in the depth of compressive residual stress layer, and a 6.7% increase in the maximum value of compressive residual stress. Microstructural analysis reveals material stacking, pores, and microcracks on the specimen surface and grain refinement characteristics in the surface and subsurface layers. Strain gradient analysis shows that the deformation layer depth is uniformly distributed. An increase in Almen intensity leads to a higher degree of plastic deformation and work hardening, and the increase in compressive residual stress layer depth counteracts early fatigue failure caused by high roughness.

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 paper employs in situ Electron Backscatter Diffraction (EBSD) tensile technology to thoroughly consider the evolution of microstructure, grain size, grain boundary characteristics, orientation differences, and dislocation density of H13 steel during the elastic and plastic stages of room temperature tensile testing. The study unveils the deformation mechanisms of inclusions, carbides, and the matrix in H13 steel during the various stages, providing a comprehensive explanation for the slightly superior tensile properties of H13 steel when refined by Vacuum Induction Melting combined with Vacuum Arc Remelting (VIM + VAR) over those when refined by Electroslag Remelting (ESR). This discrepancy is primarily attributed to the differences in inclusions and carbides present in the two refining processes. The quantity and size of inclusions and carbides are closely related to material fracture. Large-sized carbides and inclusions were shown to be more likely to cause dislocation pile-ups and stress concentration. This, in turn, leads to faster crack initiation and propagation during plastic deformation. Conversely, the formation of micro-pores within these fine inclusions and the matrix is contingent on greater plastic deformation, resulting in a gradual and incremental linkage of these micro-pores to form dimples beneath the influence of slip.

This paper investigates the effects of ultrasonic shot peening (USP) on surface morphology, microstructure, and residual stress field distribution of TC17 alloy under different process parameters. The aim is to reveal the surface strengthening mechanism of TC17 alloy caused by USP. The results suggest that the use of the 2.5 mm projectile diameter leads to an increase in surface roughness, plastic deformation, and a deeper grain refinement layer compared to the 1.5 mm projectile diameter. Additionally, it results in a greater depth of the compressive residual stress layer and maximum compressive residual stress. The crack initiation sites under two projectile diameters are located below the compressive residual stress layer. The USP treatment introduces compressive residual stress on the surface, inhibiting the initiation of surface cracks, and the deeper compressive residual stress layer offsets the early fatigue failure caused by higher roughness.

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.