Shot Peened Surface Research Articles

Correlation between shot peening coverage and surface microstructural evolution in AISI 9310 steel: An EBSD and surface morphology analysis

In this study, martensitic high-strength steel serves as the subject of investigation, with both conventional and severe shot peening experiments being conducted. The coverage levels for conventional shot peening (CSP) are set at 100 % and 200 %, while severe shot peening (SSP) sees levels of 800 % and 1200 %. For the first time, the use of kernel average misorientation (KAM) enables the calculation of geometrically necessary dislocation (GND) density after peening, facilitating the study of GND density distribution across different coverage and offering a method for the visual assessment of peening degree. Results reveal that, under CSP, the gradient distribution of grain size is relatively uniform, whereas SSP leads to a pronounced gradient in grain size distribution. Taking into account the heterogeneous distribution of the initial material microstructure, a gradient in grain size from the surface to the interior of the material will appear after the coverage reaches a certain value, which is 400 % for AISI 9310 steel. Compared with CSP, SSP will further reduce the surface roughness Sa and improve the surface quality. The research presented further understands the relationship between shot peening process parameters and martensitic steel microstructure, providing an important reference for revealing the strengthening mechanism and selecting reasonable process parameters.

Effect of surface high-density twinned structure on the fatigue crack initiation of Ti–6Al–4V

Fatigue crack initiation sites would transfer from surface to subsurface of metal specimens through shot peening (SP) or laser shock surface strengthening. This phenomenon is typically attributed to the introduction of compressive residual stress on the surface of the specimen during the surface strengthening process. In this study, Ti–6Al–4V specimens featuring a high-density twinned structure on their surfaces, which eliminated compressive residual stress, were fabricated. Fatigue test result revealed that fatigue crack initiation sites in specimens with twinned structures were predominantly located in the subsurface, near the junction area between the twinned structure and the matrix. This phenomenon was accompanied by an increase in fatigue life. The microstructural features in the fatigue crack source were analyzed using focused ion beam (FIB) coupled with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). It was observed that primary crack formed in badly oriented grains that are difficult to initiate dislocation slip according to the Schmid factor (SF). Nonetheless, TEM observations revealed the activation of basal <a> dislocations in these grains, potentially leading to crack nucleation along basal slip bands and subsequent propagation along the basal plane. Our results suggest that a high-density twin structure on the surface can enhance the fatigue strength of Ti–6Al–4V by transferring the fatigue crack source to the subsurface.

Oxidation behaviour of austenitic stainless steel 304HCu in Advanced Ultra Supercritical (AUSC) steam and the efficacy of shot-peening treatment

Effect of shot-peening on the oxidation behaviour of alloy 304HCu in controlled advanced ultra-supercritical (AUSC) steam at 650 ◦C, 31 MPa for 600 h was investigated. Non-shot peened surfaces form thick Fe-rich oxides, undergo internal oxidation, and suffer oxide spallation sooner than those reported in literature. Shot-peened surfaces form a thin, external chromia scale with Mn(Cr,Fe)2O4 and MnCr2O4 spinels growing above and below it respectively. Shot-peening enhances Cr and Mn diffusivity through grain refinement and increased dislocation density, which aids in resisting chromia scale breakdown, eliminating iron oxides, and preventing oxide spallation. Oxide growth mechanism in AUSC steam is discussed.

Microstructure Evolution, Hardness, and Tribological Behaviors of Ti-50.8Ni SMA Alloy with Ultrasonic Surface Shot Peening Treatment.

To explore a new method to improve the wear resistance of TiNi shape memory alloy (SMA), Ti-50.8Ni alloy was treated by the method of ultrasonic surface shot peening. The microstructure evolution, hardness, and tribological behaviors have been further investigated to evaluate the effect of ultrasonic surface shot peening (USSP). The surface microstructure can be refined to some extent while the basic phase composition has little change. USSP can facilitate the martensitic transformation in the surface layer, which benefits improving the surface hardness. Additionally, the hardness of Ti-50.8Ni alloy increases first and then decreases with the increase of applied load, but the USSP-treated alloy tends to be more sensitive to load. USSP treatment can improve the wear resistance and reduce the coefficient of friction (COF) in case of a low sliding wear speed of 5 mm/s. However, the tribological properties of USSP-treated alloy are reversely worse in the case of 10 mm/s. This is mainly attributed to the combined effect of stress-induced martensite transformation and degeneration resulting from the frictional heating during the dry sliding wear process.

Preparation of the gradient nanostructured layer in uranium by surface shot peening treatment

The gradient nanostructured layer in uranium prepared by surface shot peening treatment has been systematically characterized. The evolution of the ultrafine grains within the surface layer of uranium was derived. The results show that the gradient microstructures from the surface to the matrix could be divided into four zones including ultrafine grains, high density deformation twins, low density deformation twins, and coarse grain matrix. The deformed microstructures in the four zones were characterized in detail. Twinning and dislocation activities were found to be the main plastic deformation mechanisms for grain refinement in uranium. Four types of twinning and dislocation slip modes were distinguished. The formation of fine equiaxed grains on uranium surface should be attributed to the combined action of the twinning, dislocation activities, and the subgrain rotation driven by mechanical-thermal coupling. The surface microhardness and the natural oxidation corrosion performance were improved in uranium prepared by shot peening treatment.

Comparison of the effects of induction heating composite shot peening and conventional shot peening on residual stress, microhardness, and microstructure of 20CrMnTi gear steel

As a commonly used surface strengthening technology, shot peening, which can significantly improve the fatigue strength of mechanical parts, is widely used in the fields of vehicles and aviation. To obtain a larger residual compressive stress and further refine the grain size under normal shot peening intensity and coverage, this study proposes an induction heating composite shot peening (IHCSP) surface strengthening method, aiming to utilize the coupling effect of temperature and stress fields to promote the shot peening strengthening effect. An IHCSP test plan was designed and an IHCSP test bench was created to achieve simultaneous induction heating and shot peening. This study compares the surface integrity parameters and microstructures under three processes: un-peened, conventional shot peening, and IHCSP. The results show that the maximum axial and radial compressive residual stresses increase by 72.41 and 75.4 MPa respectively; the depth of the hardened layer increases by 0.3 mm, the martensitic transformation more complete, the grain size decreases by 483 nm, the dislocation density increases significantly, and nanocrystals are obtained on the surface of the material. These results verify the superiority of IHCSP surface strengthening.

A numerical method for generation of shot peened surfaces

Shot peening is a widely utilized surface modification technique, and the surface morphology of the treated materials plays a crucial role in determining their friction and fatigue properties. Surface morphology generation is a pivotal process in simulating shot-peened surface friction and other performance characteristics. However, there are limited available methods for shot-peened surfaces until now. In this paper, we present a method that directly specifies the height probability distribution and power spectrum to generate shot-peened surfaces. Compared to methods that specify height parameters, this method has more flexibility. This approach replaces the traditional Johnson transformation method with an optimization algorithm to generate height data that follows a high probability distribution, while the power spectrum is derived from the Fourier transform of an exponential autocorrelation function. The results show that this approach can generate shot-peened surfaces using any conventional height parameters, with a maximum difference in height parameters between the reconstructed surface and the original surface of no more than 18.63%. Compared to the Johnson transformation method, this method significantly reduces the errors in skewness and kurtosis of the generated surface. It offers rapid surface generation for shot-peened surfaces, leading to significant time and cost savings in experiments.

Shot peening of AZ31 magnesium alloy: role of surface microstructure and iron diffusion on corrosion behaviour

ABSTRACT In the present work, surface grain refined AZ31 magnesium (Mg) alloy was produced by shot peening (SP). X-ray diffraction analysis demonstrated iron diffusion into the surface of AZ31 Mg alloy during SP. Higher hardness, increased surface energy and decreased corrosion resistance were observed for the shot-peened surface due to nanostructured grains resulted from SP. From the immersion studies in a simulated physiological solution carried out for 3 days, higher level of biomineralization was observed for the shot peened AZ31 compared with the base alloy that dominated the adverse effect of iron diffusion in resisting the biocorrosion. The results suggest that the nano-structuring of AZ31 Mg alloy surface helps to enhance the biomineralization to control the degradation. However, the selection of processing medium is crucial to eliminate the effect of chemical composition change during the process in tailoring the corrosion behaviour of AZ31 Mg alloy for biomedical implant applications.

Surface shot peening of cast SiCw/Al composites

ABSTRACT The surface shot peening treatment was carried out on the as-cast SiCw/Al composites, and the distribution of the residual stresses in the surface matrix was measured, the X-ray diffraction method for the yield strength of the surface matrix of the composites was established to explore the strengthening effect of the surface shot peening. The results show that the surface matrix of the composites after shot peening shows a large compressive residual stress state, and the FWHM, that is, the microstructure strengthening effect, is significantly increased., resulting in an increase in the yield strength of the surface matrix of the composites.

Enhancement in interfacial bonding quality of CoCrFeMnNi high-entropy alloy vacuum hot-compression bonding via surface shot peening

Vacuum hot-compression bonding (VHCB) is an advanced solid-state bonding technique. To expand its application in high-entropy alloys (HEAs), a new strategy to enhance the interfacial bonding quality of CoCrFeMnNi HEA VHCB joints by surface shot peening (SP) was proposed, and the effects of SP treatment on the interfacial bonding behavior and mechanical properties of VHCB joints were investigated. The results revealed that SP treatment introduced a nanocrystalline layer and plastic deformation layer with non-uniform strain on the specimen bonding surface, and a hierarchical grain size gradient fine microstructure was formed by a static recrystallization process under the thermal activation condition before VHCB. During the bonding process, the fine microstructure of the SP-treated layer was retained and provided a large number of grain boundaries and dislocations, which facilitated atomic diffusion and plastic flow in the interfacial region and promoted the closure of interfacial voids and the dissolution of interfacial oxide particles. Additionally, interfacial crystallographic and tensile test analyses indicated that the SP treatment induced a multiple interfacial grain boundary (IGB) migration mechanism in the VHCB joints, which dramatically improved the IGB migration level and ultimately led to a complete recovery of the mechanical properties of the CoCrFeMnNi HEA VHCB joints.

Effect of ultrasonic shot peening on microstructure and mechanical properties of GH3230 superalloy during selective laser melt solution heat treatment

Additive manufacturing (AM) is widely used because of its well-known advantages, but there are some disadvantages including microstructure inconsistencies and harmful residual stresses, which can lead to premature part failure. In this study, the microstructure, and mechanical properties of GH3230 alloy processed by AM are changed by a new post-treatment method, which combines thermal solution treatment (ST) and ultrasonic shot peening (USP). The microstructure evolution of GH3230 after ST and USP after ST is investigated experimentally. The experimental results show that equiaxed crystals and M23C6 carbides appear after solution treatment. After ST, USP is performed, and the gradient microstructure is formed perpendicular to the shot peening surface. Dislocation entanglement and grain refinement occur in the plastically deformed layer. In addition, the carbide interacts with the dislocation. After ST, USP can produce a high level of residual compressive stress in the plastic deformation layer. This combination of ST and USP helps to improve the mechanical properties of additive manufactured parts by changing their microstructure and residual stress distribution.

Shot Peening Effect on Sliding Wear in 0.9% NaCl of Additively Manufactured 17-4PH Steel.

The growing demand for modern steels showing corrosion and tribological resistance has led to their increased use in the production of medical devices. This study analyzed the effect of shot peening on wear resistance in 0.9% NaCl solution of 17-4PH steel produced by direct laser metal sintering (DMLS) technology. The study's novelty relies on revealing the effect of shot peening (SP) surface treatment on the wet sliding wear resistance of 17-4PH steel produced with DMLS. Moreover, in the context of 17-4PH steel application for medical devices, the 0.9% NaCl tribological environment were selected, and SP processes were conducted using steel CrNi shot and ceramic (ZrO2) beads. The up-to-date scientific literature has not identified these gaps in the research. DMLS technology makes it possible to obtain products with complex architectures, but it also faces various challenges, including imperfections in the surface layer of products due to the use of 3D printing technology itself. The chemical and phase composition of the materials obtained, Vickers hardness, surface roughness, and microscopic and SEM imaging were investigated. Tribological tests were carried out using the ball-on-disc method, and the surfaces that showed traces of abrasion to identify wear mechanisms were subjected to SEM analysis. The XRD phase analysis indicates that austenite and martensite were found in the post-production state, while a higher martensitic phase content was found in peened samples due to phase transformations. The surface hardness of the peened samples increased by more than double, and the post-treatment roughness increased by 12.8% after peening CrNi steels and decreased by 7.8% after peening ZrO2 relative to the reference surfaces. Roughness has an identifiable effect on sliding wear resistance. Higher roughness promotes material loss. After the SP process, the coefficient of friction increased by 15.5% and 20.7%, while the wear factor (K) decreased by 25.9% and 32.7% for the samples peened with CrNi steels and ZrO2, respectively. Abrasive and adhesive mechanisms were dominant, featured with slight fatigue. The investigation showed a positive effect of SP on the tribological properties of DMSL 17-4PH.

Study of the shot peening surface roughness in fretting

Fretting fatigue manifests in mechanical systems exposed to contact forces that vary over time, resulting in premature cracks that can lead to component failure. Shot peening treatment is one of the palliatives to mitigate fretting fatigue problems. Recent studies have noted that the fretting fatigue is also extended by exclusively applying SP to the contact pad surface. This suggests that the improvement in the fatigue live produced by SP comes not only from the compressive residual stresses but also due to the characteristic surface roughness from the SP treatment. For this reason, the main goal of this work is to analyse how the shot peened roughness affects the fretting fatigue life. To do so, a confocal microscope was used to measure various profiles of shot peened pads. Using these profiles, and under fretting loads combination, the contact stress and strain field are calculated, followed by the application of a fatigue model. Finally, the estimated fatigue life is contrasted with empirical data derived from a research published by the authors. The study reveals that the fretting fatigue life is influenced by the surface roughness, although to a lesser extent with respect to residual stresses. Besides, the Smith-Watson-Toper parameter and stress intensity factor were analysed, suggesting that the rough surface primarily affects the initiation phase rather than the propagation phase, as it was expected.

Ex-situ observation of the short crack initiation and propagation behaviour of nickel-base wrought alloy Inconel 718 for critical rotating components under fatigue conditions at elevated temperatures

In this paper, the initiation and propagation behaviour of short fatigue cracks in nickel-base alloy Inconel 718 is studied extensively in the fatigue loading regime by ex-situ scanning electron microscopy on component-near notched specimens in the temperature range between 400°C and 600°C. To investigate the influence of different surface treatments, both specimens with polished and shot-peened surfaces were tested. For polished specimens, most fatigue cracks initiated at oxidised non-metallic inclusions, whereas for shot-peened specimens, the process-induced surface roughness also served as crack starters. It was found, that the observed scatter in lifetime for repetitive tests is mainly caused within the short crack fatigue regime below 50μm, while cracks larger than 100μm showed similar growth characteristics.

High-precision simulation and experimental verification of residual stress and surface topography of cylindrical surface shot peening

Shot peening is commonly employed for surface deformation strengthening of cylindrical surface part. Therefore, it is critical to understand the effects of shot peening on residual stress and surface topography. Compared to flat surface, cylindrical surface shot peening has two significant features: (i) the curvature of the cylindrical surface and the scattering of the shot stream cause distributed impact velocities; (ii) the rotation of the part results in a periodic variation of the impact velocity component. Therefore, it is a challenge to quickly and accurately predict the shot peening residual stress and surface topography of cylindrical surface. This paper developed a high-precision model which considers the more realistic shot peening process. Firstly, a kinematic analysis model was developed to simulate the relative movement of numerous shots and cylindrical surface. Then, the spatial distribution and time-varying impact information was calculated. Subsequently, the impact information was used for finite element modeling to predict residual stress and surface topography. The proposed kinematic analysis method was validated by comparison with the discrete element method. Meanwhile, 9310 high strength steel rollers shot peening test verified the effectiveness of the model in predicting the residual stress and surface topography. In addition, the effects of air pressure and attack angle on the residual stress and surface topography were investigated. This work could provide a functional package for efficient prediction of the surface integrity and guide industrial application in cylindrical surface shot peening.

Effect of shot peening with different peening intensity and coverage on surface integrity of Inconel 718 alloy

Shot peening, which usually serves as a final treatment on the components’ surface, greatly alters the surface geometrical and mechanical states. In this study, shot peening experiments using ceramic beads with a diameter of 0.3 mm are performed on the Inconel 718 alloy with varied peening intensity and coverage. The surface roughness, microhardness, and residual stress from shot peening and turning are characterized by a laser scanning confocal microscope, Vickers hardness tester, and X-ray diffraction to evaluate the influence of peening parameters. The results show that the shot peening treatment decreases the surface roughness of the specimens, and the roughness decreases with increasing intensity in the range of 0.13-0.17 mmA. Moreover, the shot peening intensity has a greater influence on the microhardness and residual stress of the shot peening surface compared with coverage. A surface with a large compressive residual stress profile (-1221 MPa in the axial direction) and a high hardness gradient (538.3 HV0.2 at a depth of 50 μm) is formed after the TPI3C3 process (shot peening with the peening intensity of 0.17 mmA and coverage of 300% after turning). The results of this research will provide guidance for developing more effective shot peening strategies.

Effect of Shot Peening and Nitriding on Toughness and Abrasive Wear Resistance of Powder Metallurgic Steels Highly Alloyed with Vanadium

Böhler K390 steel is used for cold work tools, with 9% of V, made by using powder metallurgy. In this work, it has been studied the effect of shot peening and nitriding surface treatments on wear resistance and impact toughness of this type of steel. For this purpose, previous changes in several thermal processing factors related to quenching and tempering were carried out. The results allow for an increase in the hardness, impact toughness, and abrasive wear resistance of these steels. An austenitizing treatment at 1100 °C with air cooling and 3 tempering processes at 550 °C is suggested. These conditions foster a lower weight percentage of retained austenite, up to 3%, a higher carbide percentage, up to 15–16% in weight, and a greater impact toughness with no notch, of above 40 J/cm2. If this treatment is combined with further ion nitriding, the maximum level of abrasive wear resistance is reached. The only carbide type present in the microstructure is the MC type. Most of the V, Cr, and Mo contents are present in said carbides. The Co and the W tend to remain in solid solution in the matrix constituent. Both the shot peening treatment as well as ion nitriding offer a considerable increase in hardness, with values of up to 1500–1600 HV. Nevertheless, it has been confirmed that shot peening does not offer any abrasive wear resistance improvement. Such resistance may only be considerably improved by the application of an ionic nitriding treatment. The thickness of the nitrided layer fluctuates between 150 and 175 µm. The carbides are affected by nitriding, reaching levels that are higher than the atomic 10%, at an intermediate depth of the nitrided layer. These values are higher in the matrix constituent, as they are even higher than the atomic 20% in N.

Effect of ultrasonic shot peening surface alloying on microstructure and tribological behavior of Inconel 718 superalloy

Ultrasonic shot peening (USP) surface alloying can enhance the surface strength and achieve the microstructure modification concurrently. In this paper, Inconel 718 superalloy was subjected to USP surface alloying with Nb powder, followed by post-annealing treatment. The microstructure and tribological behavior of the samples were investigated. After USP alloying and subsequent annealing, a Nb alloying layer with a thickness of ∼7 μm was fabricated on substrate surface, and a grain refinement layer with a depth of 100 μm was formed. The introduced alloying layer promoted the precipitation of additional reinforcing phases through thermal activation, thereby engendering heightened hardness values within the sub-surface layer as compared to samples treated only by USP. The frictional test results showed that the lowest friction coefficient and smallest wear rate were obtained in sample treated by USP alloying and annealing, which was closely related to the highest hardness in the near-surface layer. Moreover, the wear mechanisms of these samples were subsequently discussed.

Microstructural characteristics and enhanced mechanical properties of 2024 aluminum alloy resulting from shot-peening treatment

Microstructural characteristics and enhanced mechanical properties of 2024 aluminum alloy associated with shot-peening treatment were investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction technology (EBSD), X-ray diffraction (XRD) and tensile test. The results showed that the shot-peening treatment induces a severe plastic deformation within the surface area of alloys and the depth of the affected area caused by the shot-peening treatment is measured to be 600 ± 20 μm. Within the affected area, the formation of twins, curved grain boundaries and the fragmentations of grains were detected. In addition, the microstrain of the shot-peened surface increased to 0.5769% (±0.00215) from 0.2181% (±0.01084) after the shot-peening treatment. Correspondingly, the yield strength, the tensile strength and the uniform elongation were improved to 410.3 MPa (increased by about 11%), 519.4 MPa (increased by about 15.8%) and 19.7% (increased by about 81%), respectively, after the shot-peening treatment. Microstructural characteristics and the variation of microstrain within the affected area mainly account for the enhanced mechanical properties of the shot-peened 2024 aluminum alloys. The results of this work indicate that the shot-peening process is one of the effective ways to simultaneously improve the strength and ductility of alloys.

A computational model of wear evolution for shot peened surfaces of gear steel

In mechanical engineering, shot peening is frequently used to reinforce the surfaces of some crucial components. Currently, there are no models available which can accurately predict the long-term wear behavior of surfaces treated with shot peening. This research proposes a computational model and technique for simulating the evolution of wear on gear steels with shot-peened surfaces in a ball-on-flat contact. Based on the fundamental Archard’ s equation, a wear equation is derived from the perspective of a contacting point on the static flat to represent the wear loss. The model takes into account the effects of abrasive particles and variations in hardness along the vertical direction by introducing a scaling factor in the wear equation and stratification of the flat material, respectively. The proposed model and developed method are validated through experiments and can be utilized to predict the wear evolution of shot peened surfaces on gear steels under the application of various loads and friction duration. Furthermore, the model and method can be easily extended to other materials as well.