Shot Peening Research Articles

Effect of surface strengthening by ultrasonic shot peening on TC17 alloy

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.

Copper Coatings for Antibiotics Reduction in Fattening Livestock

In the current work, twin-wire arc-sprayed copper coatings are investigated to reduce the spread of pathogenic germs in broiler farming. Compressed air and nitrogen are used as process gasses, while the coating torches are varied. The results demonstrate a reduction of 99% pathogenic load due to the presence of coatings in comparison with the uncoated nickel-chromium-steel. This accounts especially for the bacterial strains E.coli, S.aureus and E.cecorum, which are the predominant bacteria in broiler farming. Moreover, posttreatment processes like cold plasma, tungsten inert gas arc processing and shot peening are investigated to further increase the bactericidal properties and abrasion resistance characteristics of the coatings. Further investigations involve the microstructure and the electrical conductivity of the coatings. In this work, it is demonstrated that copper-coated surfaces have an inhibitory effect on bacterial growth of the three investigated bacterial strains compared to the uncoated bulk nickel-chromium-steel material.

Non-synchronous deformation under shot peening post-treatment of SUS304 bar-plate rotary friction weld generates non-monotonic evolution on material and fatigue property

Shot peening post-treatment was conducted at SUS304 austenite steel bar-plate rotary friction welding joint with fatigue property deterioration from welding flash. along the shotting intensity increasing, non-synchronous deformation of the plate and flash resulted in non-monotonically evolution of local microstructure, residual stresses, and make the fatigue life increased to flash-removed joint level.

Microstructure Evolution and Numerical Modeling of TC4 Titanium Alloy during Ultrasonic Shot Peening Process

Ultrasonic shot peening (USP) is a surface treatment technology used in the mechanical properties strengthening of the engineering material and components during manufacturing. TC4 titanium alloy is a commonly used engineering material in the aerospace industry. In this study, a gradient nanostructured surface layer was successfully fabricated on the TC4 titanium alloy via USP technology at room temperature. The microstructure evolution of TC4 titanium alloy during USP was investigated. The surface microhardness was elevated from 330 HV to 438 HV with a penetrating depth of around 900 μm after USP with the duration of 8 min. EBSD characterization results confirmed the presence of high-density grain boundaries within the gradient structure in the region of 0–200 μm, accompanied by proliferation of dislocation density. TEM characterization indicated a substantial amount of nanograin with an average size of 74.58 nm. Furthermore, the USP process was also investigated by the finite element method to evaluate the surface-strengthening effect. The calculated maximum residual stress reached 973 MPa after multi-ball impact. The impact behavior of the shots during the USP process was studied. The effect of the parameters on the USP strengthening intensity was explored based on the validated model. This work provided a clearer understanding of the USP strengthening process of TC4 titanium alloy through an effective method of evaluating the process parameters.

Simulations of the effect of shot peening backstress on nanoindentation

Shot peening is a mechanical surface treatment that can introduce compressive residual stress and work hardening simultaneously. This work hardening, considered as a modification of the elastic region with plastic strain, can be modeled with two types of contributions: isotropic hardening and kinematic hardening. In order to characterize the mechanical properties of the treated surface using the instrumented indentation technique, the effect of the backstress associated with kinematic hardening should be studied, especially for works related to fatigue loading. In this paper, the distribution of three backstress components is obtained by shot peening simulations on a nickel-based alloy, Inconel 718, commonly used in the aerospace industry, and a series of indentation simulations are carried out using a spherical tip with different equivalent backstress levels. For Inconel 718, the third backstress component, which has the slowest evolution rate, is found to have the most significant influence on the response. However, compared to the effect of residual stress and cumulated plastic strain, the effect of backstress can be neglected.

Ultrastrong gradient M50 bearing steel with lath-shape nano-martensite by ultrasonic shot peening and its enhanced wear resistance at elevated temperature

This investigation delves into the intricacies of the process mechanism for generating a gradient nanostructured surface (GNS) layer on M50 bearing steel, with the aim of augmenting its surface hardness and wear resistance under elevated temperature. The electron backscatter diffraction and transmission electron microscopy substantiate the successful formation of a GNS layer, surpassing 200 µm in thickness, on the M50 bearing steel treated by Ultrasonic shot peening (USP) technology. The severe plastic deformation (SPD) induced by the USP process resulted in a significant refinement of the martensite in M50 bearing steel, leading to a remarkable 32.25 % increase in surface hardness compared to its untreated coarse-grained (CG) counterpart. Pin-on-Disk wear tests were conducted at an elevated temperature of 300 °C on both the as-received CG-M50 and USP-treated M50 bearing steel samples to evaluate the impact of USP treatment on the wear resistance of M50 bearing steel. Experimental results reveal that the volume loss of the USP-treated M50 bearing steel is 94.9 % less than that of the untreated CG-M50 bearing steel after 4 h of wear tests. The improved wear resistance of the USP-treated M50 bearing steel can be attributed to the creation of an ultrastrong and stable GNS layer facilitated by USP.

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.

Studies on residual stress and surface topography after pneumatic shot peening using discrete element method–finite element method coupled model

After pneumatic shot peening, compressive residual stress is induced on the surface of the target, which will improve the fatigue life. During the process, surface roughness is also induced, which may reduce the fatigue life. To achieve the optimum compressive residual stress with the smallest surface roughness, the formation mechanism of the residual stress field and the surface topography are revealed. Then, pneumatic shot peening is simulated by using a discrete element method–finite element method coupled model. Based on the effects of four variables (the incident angle θ, the initial shot velocity v0, the shot radius R) and the mass flow rate rm on five parameters (the equivalent plastic strain, the equivalent stress, the surface compressive residual stress, the maximum compressive residual stress), the surface roughness is investigated. The results show that it induces a residual elastic–plastic strain after the impact of a single shot, which can form a crater and a hemispherical residual stress field. After the impact of many random shots, scattered craters connect with each other, therewith a rough and continuous surface topography is formed. Scattered residual stress fields couple with each other, and a constant residual stress layer with the compressive residual stress in the surface and the tensile residual stress in the subsurface are formed. All five parameters are determined by the residual elastic–plastic strain, which increases as the augment of the normal impact velocity, the shot mass, and the coverage rate. Along with the increase of θ and rm, these five parameters firstly increase and then decrease; with the increase of v0 and R, these five parameters increase. Therefore, reasonable values of θ, v0, R, and rm should be chosen to obtain the optimum compressive residual stress with as small surface roughness as possible.

Optimization of shot peening parameters for blades based on the constraint of equivalent residual stress-induced deformation

Optimization of shot peening parameters for blades based on the constraint of equivalent residual stress-induced deformation

Surface modification and enhanced wear performance through severe shot peening treatment in 316L stainless steel manufactured by metal injection moulding

This study investigates the micro-to nanostructural evolution, hardness, and linear reciprocating wear resistance, using Al2O3 ball as a counterpart of 316L stainless steel fabricated by the metal injection moulding (MIM) process, with and without severe shot peening treatment (SSP). SSP treatment led to a slight increase in Ra but a decrease in Rz and the formation of nanocrystalline surface, α′-martensite and mechanical twin. The subsurface hardness increased significantly. Surprisingly, the coefficient of friction remained constant (0.37–0.56) and depended solely on the testing load, despite alterations in surface roughness and subsurface microstructure due to SSP treatment. Furthermore, wear resistance notably improved under 10 N and 20 N loads, attributed to the surface modification by SSP treatment, but showed no significant difference at 30 N. The wear mechanisms, including abrasive, adhesive wear, and oxidative wear, remained similar, with adhesive and oxidative wear dominating at lower testing loads (10–20 N). However, with a testing load of 30 N, the strengthening effect of SSP treatment was surpassed, leading to the dominance of severe adhesive and oxidative wear. Consequently, the wear resistance exhibited insignificant differences between specimens before and after SSP treatment.

Evolution and anti-fatigue mechanism of surface characteristics of Ti60 alloy induced by ball burnishing and shot peening during tensile-compression fatigue

To clarify the evolution of surface characteristics of Ti60 alloy induced by ball burnishing and shot peening and their anti-fatigue mechanism during tensile-compression fatigue, room temperature and 450℃ elevated temperature fatigue tests were conducted on burnished and shot peened round bar Ti60 samples. Residual stresses, microhardness, and microstructures were analyzed during fatigue, and the fracture mechanism was investigated through fractography. The results show that the residual stress relaxation rate of the burnished sample is lower than that of the shot peened sample. After fatigue, the strengthened samples showed reduced microhardness and fewer low angle grain boundaries. The strengthened samples are both subsurface initiation, and the depth of initiation of the burnished sample is greater than that of the shot peened sample. The fatigue initiation mode at room temperature and 450℃ high temperature is quasi cleavage. No fatigue striations are observed at room temperature fatigue propagation zone, but they can be observed at 450℃ elevated temperature. The dimples can be observed at room temperature fatigue transient fracture zone. However, at 450℃ elevated temperature fatigue transient fracture zone, the dimples and quasi-cleavage can be observed simultaneously, indicating a mixed fracture mode. In addition, the crack shape of the strengthened sample is a wide top and narrow bottom shape due to the compressive residual stress layer.

Effect of Laser Scanning Speed and Fine Shot Peening on Pore Characteristics, Hardness, and Residual Stress of Ti-6Al-4V Fabricated by Laser Powder Bed Fusion

There is a concern regarding sub-surface pores within laser powder bed fusion of Ti-6Al-4V, which can initiate cracks and reduce mechanical properties, especially after machining for surface finishing. This study investigated the effect of laser scanning speed and fine shot peening on the pore characteristics, hardness, and residual stress of Ti-6Al-4V fabricated by laser powder bed fusion using scanning electron microscopy, X-ray micro-computed tomography, Vickers hardness, and X-ray diffraction. As the laser scanning speed increased, the number of pores and pore size increased, which reduced the hardness of Ti-6Al-4V. Most pores were less than 20 µm in size and randomly distributed. The fine shot peening generated plastic deformation and compressive residual stress on the surface, leading to higher hardness, with similar surface properties at all scanning speeds. The depth of compressive residual stress by fine shot peening varied corresponding to the scanning speeds. Increasing the scanning speed accelerated the rate of conversion between the compressive and tensile residual stresses, and decreased the depth of the maximum hardness by the fine shot peening from initial tensile residual stress within Ti-6Al-4V fabricated by laser powder bed fusion, thus reducing the enhancement achieved by the fine shot peening.

Effects of Shot Peening and Electropolishing Treatment on the Properties of Additively and Conventionally Manufactured Ti6Al4V Alloy: A Review.

This literature review indicates that the basic microstructure of Ti6Al4V is bimodal, consisting of two phases, namely α + β, and it occurs after fabrication using conventional methods such as casting, plastic forming or machining processes. The fabrication of components via an additive manufacturing process significantly changes the microstructure and properties of Ti6Al4V. Due to the rapid heat exchange during heat treatment, the bimodal microstructure transforms into a lamellar microstructure, which consists of two phases: α' + β. Despite the application of optimum printing parameters, 3D printed products exhibit typical surface defects and discontinuities, and in turn, surface finishing using shot peening is recommended. A literature review signalizes that shot peening and electropolishing processes positively impact the corrosion behavior, the mechanical properties and the condition of the surface layer of conventionally manufactured titanium alloy. On the other hand, there is a lack of studies combining shot peening and electropolishing in one hybrid process for additively manufactured titanium alloys, which could synthesize the benefits of both processes. Therefore, this review paper clarifies the effects of shot peening and electropolishing treatment on the properties of both additively and conventionally manufactured Ti6Al4V alloys and shows the effect process on the microstructure and properties of Ti6Al4V titanium alloy.

Enhancement of fatigue properties of selective laser melting fabricated TC4 alloy by multiple shot peening treatments

This study investigated the impact of multiple shot peening (SP) treatments on the surface morphology, microstructure, residual stress and fatigue performance of TC4 alloy manufactured by selective laser melting (SLM). The multiple SP treatments were conducted sequentially using cast steel beads, ceramic beads and glass beads at different peening intensities. In comparison to the conventional single SP process, multiple SP treatments reduced surface roughness and stress concentration coefficient while further increasing the residual compressive stress on the alloy surface. SP significantly enhanced the fatigue life of the alloy by 6.4 to 9.6 times, with a more pronounced improvement observed with multiple SP. Fatigue fracture analysis revealed that the untreated alloy showed multiple fatigue sources which all located on the surface, with surface printing defects acting as potential sites for crack initiation. After SP treatments, all fatigue cracks were initiated beneath the surface. The improved fatigue performance of SLM-formed TC4 alloy could be mainly attributed to the SP-induced surface microstructure refinement and residual compressive stresses. Furthermore, results indicated that, for subsurface crack initiation, the initial cracks primarily stemmed from the fracture of α/α' martensite in the primary β columnar grains.

Effect of surface contamination on electrochemical corrosion behavior of ultrasonic shot peened TA2 alloy

Ultrasonic shot peening (USSP) is a technique to tune the performance of metallic materials by generating gradient nanocrystalline structure (GNS) as well as residual compressive stress. However, surface contamination can also be introduced during USSP. The nature of this surface contamination layer and how it influences the corrosion behavior of alloy require further investigation. In this work, we found that a Fe-rich oxide layer with a thickness of around 50 nm, mainly in an amorphous state, was introduced on the topmost surface layer of TA2 alloy during USSP treatment. Electrochemical corrosion results indicate that this Fe-rich oxide significantly decreases the corrosion resistance of TA2 alloy. By polishing off this surface contamination layer, the corrosion resistance of the peened sample becomes superior compared to the untreated counterpart, indicating that the introduction of the Fe-rich oxide layer conceals the beneficial effect of GNS caused by USSP. Additionally, the corrosion resistance of TA2 alloy after USSP treatment exhibits a downward trend with the increasing repeated use of steel shots. The corrosion mechanism and potential use of this surface contamination layer are also briefly discussed.

Microstructural characterization and wear performance of shot-peened TA15 titanium alloy fabricated by SLM

Ti-6Al-2Zr-1Mo-1 V (TA15) is a kind of near-α titanium alloy widely used in the aerospace industry, known for its excellent thermal strength and weldability. However, its low thermal conductivity and high deformation resistance make traditional machining methods challenging. Despite some researchers have manufactured TA15 alloy using SLM, the issue of tensile residual stresses on component surfaces remains prominent. This study aims to investigate the impact of shot peening on the surface residual stresses, microstructure, and wear performance of SLM-formed TA15 alloy. Experimental results demonstrate the successful introduction of surface compressive residual stresses through shot peening, with a maximum value of -897 MPa (at 0.45mmA intensity). Shot peening reduces the grain size within the deformation layer, resulting in a significant presence of dislocation entanglement and dislocation cells. When the intensity reaches 0.35mmA, the emergence of nanocrystals is observed, attributed to the influence of dislocation activity and dynamic recrystallization. Additionally, shot-peened samples exhibit notably improved wear resistance compared to their non-peened counterparts. However, excessive shot peening intensity may compromise surface quality. Therefore, under specific load conditions, higher intensity is not necessarily better. In conclusion, shot peening proves to be an effective technique for enhancing the surface stress state and wear performance of SLM-formed TA15 alloy.

Effect of stress shot peening on the microstructure and residual stress of Al18B4O33 whisker reinforced aluminum matrix composite

This work systematically studied the effects of stress shot peening (SSP) on the microstructure, residual stress and hardness of the ultrafine-grained Al18B4O33 whisker reinforced Al-Mg-Si matrix composite (Al18B4O33w/Al-Mg-Si) by the modified Warren-Averbach method, X-ray diffraction stress equipment, transmission electron microscopy and hardness tester. The results showed that conventional shot peening generated a gradient deformation layer of the Al18B4O33w/Al-Mg-Si with ultrafine grains (200–400 nm) near the surface layer. By contrast with conventional SP, SSP effectively induced superior microstructures at the deformed zone with finer crystalline size and more dislocations. In parallel, SSP effectively enhanced the compressive residual stress (CRS) distribution with a higher magnitude of surface CRS (−83 MPa) and maximum CRS (−152 MPa) value and deeper affected depth along the loading direction. The fragmentized whisker during SSP acted as the pinning role on the dislocation movements, which was beneficial for grain refinement and CRS improvement. It is concluded that SSP technique can be regarded as an effective process of improving the surface properties of ultrafine-grained Al18B4O33w/Al composite.

Ultrasonic horn material dependence of shot dynamics and target property induced by ultrasonic shot peening

Ultrasonic shot peening (USP) is a surface strengthening method used to improve the surface and service properties. In this paper, assembled ultrasonic horns with vibration bolts made of 304 stainless steel (SS), TC4 alloy, and SKD11 steel were developed to investigate the shot dynamics and target property as a function of horn material, the hardness and yield stress of which vary. The impact detection experiments and FEM results demonstrated that the SKD11 horn produced the largest maximum impact velocity and effective impact frequency, followed by TC4 and 304SS horns. This finding was related to the varying degrees of plastic deformation of the horns and the kinetic energy consumption. As the plastic deformation of the horn became more severe, the impact velocity and frequency on the target decreased. Moreover, material testing results indicated that the use of SKD11 horn resulted in the highest surface hardness, highest residual compressive stress, and maximum amount of martensite in 304SS targets within the shortest time, which could be attributed to the highest impact velocity and frequency. Finally, the relationships between the horn material and shot dynamics, and between the horn material and target properties were clarified, providing valuable insights into the optimization of USP parameters in industrial applications.

Effect of laser shock peening on fretting wear behaviour of AISI 304 stainless alloy

Unlike many other surface treatment techniques, such as shot peening (SP), low plasticity burnishing (LPB), ultrasonic surface rolling process (USRP), ultrasonic nanocrystal surface modification (UNSM), laser shock peening (LSP) is a non-contact process. This means that LSP achieves surface modification without direct physical contact, thereby eliminating the risk of media contamination and undesired wear on the peening equipment. As a surface hardening technology, LSP tends to produce a hardened layer with a high gradient of residual stress (RS) in the near-surface, significantly enhancing wear resistance. The well-known wear theories applied for numerical prediction, whether Archard model or dissipated frictional-energy model, contain a multiplier for contact pressure and relative slip amplitude p·ds or shear stress and relative slip amplitude q·ds, respectively. These multipliers are sensitive to the mechanical properties near the surface. Additionally, the wear profile is governed not only by the wear effect but also by the deformation of materials. Therefore, to accurately evaluate the wear performance for surface-hardened materials, the influence of RS is hard to be overlooked. In this work, the finite element method (FEM) is utilised to construct a 3D numerical model, which ignores and considers RS, for both as-received and LSP-treated samples. Two distinct RS distributions induced by different scanning strategies (one- and five-time), are introduced in the finite element (FE) model. The numerical simulation results are then compared with the experimental data to verify the accuracy of the fretting wear model built in this study. On this basis, the impact of different RS distributions on fretting wear characteristics, including wear profile and volume, is extensively investigated. The findings reveal that higher amplitude RS can reduce the degree of fretting wear to a greater extent, highlighting the beneficial role of RS in enhancing wear resistance. Furthermore, the numerical models incorporating RS demonstrate superior predictive accuracy compared to those that omit RS. This naturally underscores the importance of integrating RS in numerical simulations of LSP and other surface-hardened materials.

Accurate superposition modeling method of grinding-shot peening surfaces

Abstract The coexistence of initial surface texture features and shot peening texture features in the final surface topography is a significant feature of shot peening. After the initial surface topography is strengthened by shot peening, the wave peak will produce more substantial deformation relative to the wave valley, which has not been considered in the existing superposition modeling methods. And this will affect the correlation study between surface topography and performance. Taking the surface generated by the grinding-shot peening process as the research object, based on the feature extraction of measured topography, the concept of ‘Shot peening texture depth distribution surface’ is put forward. And the proposed precise superposition method uses the texture depth distribution surface to optimize the characteristic baseline of shot peening based on the existing theory. The measured grinding-shot peening surfaces verify the given method. It is found that the topographical and spatial features of the surfaces superimposed by this method are consistent with those of the measured surfaces, and the error of roughness parameters defined by ISO25178 are all less than 8%. Among them, the percentage errors of the critical parameters Spd, Sdq, and Sdr related to friction and lubrication are significantly reduced to 5%.