Compressive Residual Stress Layer Research Articles

Investigation into the cavitation erosion of rolled Ti6Al4V titanium alloy strengthened by the ultrasonic-assisted laser shock peening process

The novel process known as ultrasonic-assisted laser shock peening (ULSP) is conducted on hot rolled Ti6Al4V titanium alloy with polished surface to improve its cavitation erosion (CE) resistance. The microstructure and phase structure were investigated by transmission electron microscope and X-Ray diffractometer. The microhardness and residual stress were measured by microhardness tester and X-Ray residual stress analyzer. After that, the CE mass loss and morphology were analyzed through high-precision analytical balance and scanning electron microscope to reveal the CE resistance mechanism of ULSP. The results show that ULSP treatment causes plastic deformation at the surface layer, resulting in refined grains and complex dislocation structures. The aforementioned process produces a hardened layer and compressive residual stress (CRS) layer with notable amplitude and deep influence. The surface microhardness of the ULSP-9J specimen is 410 ± 4 HV, which is a 14.8 % increase compared to the LSP-9J specimen. The CRS of the ULSP-9J specimen is −329 ± 6 MPa. As a result, it is vital in preventing the formation and propagation of CE cracks, strengthening the material's resistance to CE damage, reducing mass loss, and enhancing the overall morphology of CE.

Microstructure and mechanical properties of wire and arc additive manufactured 2319 aluminum alloy treated by laser shock peening

The components manufactured by Wire and Arc Additive Manufacturing (WAAM) have some problems to be solved urgently, such as uneven microstructure, numerous pore defects, and residual tensile stress. Laser Shock Peening (LSP) is an innovative and advanced surface modification technology that improves mechanical characteristics by inducing significant plastic deformation and high compressive residual stress on metal surfaces. Therefore, combining LSP with WAAM is expected to solve its existing problems. In this work, LSP with different energy parameters was used to post-process the WAAM 2319 aluminum alloy. The results indicated that LSP could improve the microstructure, eliminate near-surface pores, harden the surface layer, and induce a residual compressive stress layer, and the effect was more effective with the increase of laser energy applied. The yield strength of the peened specimens significantly increased by 60.73 %, and the ultimate tensile strength also increased by 16.03 %. The hole fatigue life of the peened specimens was significantly improved, increasing by 179.8 % and 261.7 %, respectively, applying laser energies of 5 J and 10 J. Therefore, the engineering industry may benefit from a combination of LSP and WAAM technology.

Effect of laser shock peening on tribological properties of 55SiMoVA bearing steel

Wear is an important factor limiting the service life of 55SiMoVA bearing steel. In this work, laser shock peening (LSP) technology is used to improve the tribological properties of 55SiMoVA bearing steel, and the corresponding underlying mechanism is systematically discussed. After LSP, the kurtosis (Sku) of surface roughness asperities reduced from 10.355 to 5.488, and no new phase was generated. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) analysis suggested LSP induced the generation of dislocation structures and deformation twins, leading to a decrease in the average grain size and an increase in the fraction of high-angle grain boundaries. Due to the work-hardening and fine-grain strengthening, the microhardness increased by 16.6 %, the maximum residual compressive stress amounted to −793.1 MPa, and the coefficient of friction (COF) and wear volume were significantly reduced. Scanning electron microscopy (SEM) results indicated that the wear mechanism of 55SiMoVA bearing steel before and after LSP was not transformed. However, the abrasive wear and delamination wear of the LSPed specimens were significantly improved, which was mainly attributed to grain refinement, increasing microhardness and constructing a residual compressive stress layer in the subsurface layer of 55SiMoVA bearing steel. During the sliding process, the increase in microhardness limits micro-plowing on the wear surface, and the residual compressive stress inhibits the crack formation and expansion, improving the wear resistance of 55SiMoVA bearing steel.

Dual skin effect and deep heterostructure of titanium alloy subjected to high-frequency electropulsing-assisted laser shock peening

Laser shock peening, an advanced technology for severe surface plasticity peening, encounters challenges such as shallow hardened layers and surface spalling when dealing with difficult-to-machine materials. In this study, we introduced a high-frequency electropulsing-assisted laser shock peening (HFEP-LSP) technique that coupled laser shock peening with high-frequency electric pulses to achieve a significant and deeper plastic deformation layer. In the HFEP-LSP technique, we first considered the dual “skin effect”, which coupled the skin effect of high-frequency electric pulses with the “skin effect” of the mechanical effect induced by the laser shock wave. An integrated experimental platform comprising an electric pulse generator, laser shock peening equipment, and a control system was built. A >1.6 mm deep compressive residual stress layer was obtained, and the depth of the plastic deformation layer increased by 83.3 %. Furthermore, we elucidated the dual “skin effect”-induced complex heterostructure and βm phase transition. A comprehensive analysis revealed the factors contributing to the deeper strengthening layer induced by HFEP-LSP, including the compressive residual stress and plastic deformation layers. In addition, the effects of laser shock peening and HFEP-LSP on the mechanical properties were investigated. Compared to the annealed samples, the ultimate tensile strength and elongation of the HFEP-LSP-treated samples were increased by 12.3 % and 57.1 %, respectively, with a fatigue life improvement of 176.4 %. The mechanism of synergistic improvement in strength and ductility was demonstrated.

Numerical simulation study of combined shot peening and laser shock peening on surface integrity of Ti-6Al-4V titanium alloy

Combined shot peening and laser shock peening (CSP) can introduce high surface compressive residual stress (CRS) and deep CRS layer, and reduce the high surface roughness caused by shot peening. The relationship between CSP sequences and surface integrity, including CRS and surface roughness, is far from satisfying the actual demand. In this paper, we construct a finite element model considering initial surface profile features. The experimental results agree with the simulated results. Based on the simulation results, axial and longitudinal stress wave transfer effects on surface CRS and depth CRS are investigated. Compared with shot peening (SP) and laser shock peening (LSP) alone, CSP treatment can increase CRS depth and CRS magnitude by 1060 μm and 50 ∼ 80Mpa, respectively. In addition, the roughness following CSP treatment is lower than that observed after SP treatment alone, and the roughness varies depending on the sequence of CSP treatment. Specifically, the roughness values for SP, SP + LSP, and LSP + SP are 0.938 ± 0.031 μm, 0.982 ± 0.11 μm, and 1.168 ± 0.093 μm, respectively. The surface morphology, hardness, and simulation results are combined to reveal the reasons for the reduction of surface roughness after CSP treatment. The changes of peaks and valleys after CSP treatment compared with single SP treatment were studied, and the variation trend of surface roughness was further explained.

The effects of stress ultrasonic rolling on the surface integrity and fatigue properties of TiB2/7050 Al composite

In the present work, a new surface mechanical strengthening (SMS) technique named stress ultrasonic rolling (SUR), which is ultrasonic rolling (UR) assisted with a uniaxial tensile elastic stress field, was reported and successfully conducted on 5 % wt TiB2/7050Al composite. Based on the experimental analysis and numerical simulation, the effects of SUR on surface integrity and fatigue performance of the composite were comprehensively investigated. Compared with ordinary UR, SUR further enhanced the fatigue strength at 106 cycles of the composite by 5 % and prolonged the fatigue life of the composite under the stress level of 532.8 MPa by 1.8 to 3.3 times, which are attributed to the comprehensive effect of excellent surface finish, larger and deeper compressive residual stress (RSc) layer, dispersed TiB2 particles distribution in the surface, and superficial nanocrystalline structures. Besides, the assistance of uniaxial tensile elastic stress field did not increase the amount of surface plastic deformation, which indicates the RSc generated by SUR should have similar mechanical and thermal stability to that produced by ordinary UR treatment.

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.

Mathematical Modeling and Finite Element Analysis of Residual Stress (RS) Field after Multipass Ultrasonic Surface Rolling

In order to achieve the change rule of the induced residual stress (RS) field after multipass ultrasonic surface rolling (USR), a mathematical model of the induced residual stress (RS) field after multipass ultrasonic surface rolling is first established. Then, the coupling mechanisms of the RS field after dual-pass USR and multipass USR are analyzed, respectively. Subsequently, a finite element (FE) model is established, and the influence of the interval between two adjacent rolling paths LS is investigated. Finally, both the mathematical model and the FE model are experimentally verified. The results show that both the mathematical model and the FE model can predict the RS field after multipass USR. Two adjacent RS fields will couple with each other in their overlapping regions. For a relatively small interval LS, the RS field after multipass USR can be fully coupled, so as to form a uniform compressive RS layer. In this study, when LS = 0.05 mm, the values of the surface compressive RS, the maximum compressive RS, the depth of the maximum compressive RS, and the depth of the compressive RS layer reach 426.71 MPa, 676.54 MPa, 0.05 mm, and 0.54 mm, respectively.

Effect of contact stress and slip amplitude on fretting fatigue behaviour of ultrasonic surface nanocrystallized TC11 titanium alloy

In this paper, combined experimental and numerical methods are applied to investigate the effect of different contact stress and slip amplitude on the fretting fatigue (FF) behaviour of TC11 titanium alloy with gradient nanostructure introduced by ultrasonic surface rolling process (USRP). The properties of gradient nanostructure are characterized using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray residual stress tester, microhardness tester. As evidenced by the FF experimental results, USRP can significantly improve the FF life of TC11 by introducing large compressive residual stress and work hardening layer. The dominant parameters in improving the FF resistance under different loading conditions are investigated. In addition, the simulated results from Abaqus show that contact stress plays a more important role in influencing FF life compared to fretting bridge span, which is attributed to the change in slip amplitude and stress concentration. Fretting fatigue life initially increases and then decreases with contact stress and there is a contact stress threshold that leads to minimum lifetime. This threshold of USRP specimens is greater than that of untreated specimens. The transition of fretting mode along with contact stress is observed and discussed.

Enhancing the fracture toughness and hardness of sapphire by high‐temperature rolling

AbstractAlthough the hardness of sapphire is very high, in some applications, for example, working as panels in mobile phones and watches as well as optical windows in various military optical sensors, it still suffers from the destruction of being scratched and marked as well as mechanical failure by fracture. Here we reported that the technique of high‐temperature rolling we developed recently could be exploited to sapphire to enhance its hardness and fracture toughness. After rolling at 1200°C, Vickers’ hardness and fracture toughness of sapphire increase by 4%–6% and 13%–27%, respectively. The enhancement of fracture toughness was explained by the residual compressive stress layer that was introduced in sapphire during rolling. The improvement of hardness was thought to be related to the hardening effect of dislocations. This work provides a new strategy for the mechanical property enhancement of sapphire in further applications.

Effect of supersonic fine particle bombardment on microstructure evolution and tribological properties of GCr15SiMn bearing steel

The surface of GCr15SiMn bearing steel was strengthened by supersonic fine particle bombardment (SFPB), and the effects of different impact times on the microstructure, mechanical properties and friction and wear properties of the material were studied. The results show that the surface roughness of GCr15SiMn steel samples increases and the grain is refined after SFPB. As the impact time prolongs, the grain size gradually decreases. When the bombardment time is 180 s, the surface grain size of the sample reaches 12.7 nm. The microhardness of the sample gradually increases and tends to stabilize with the increase of the impact time. The residual compressive stress layer is produced on the surface of the sample after SFPB and the residual compressive stress shows a trend of first increasing and then decreasing with rising the impact time. The friction coefficient and wear rate of GCr15SiMn bearing steel decreases after SFPB. The wear mechanism of the sample changes from mixture of adhesive wear and oxidation wear, accompanied by slight abrasive wear (before SFPB) to the abrasive wear, supplemented by adhesive wear (after SFPB). The wear resistance is improved by the of the grain refinement and the formation of a high residual compressive stress layer.

Development of Maximum Residual Stress Prediction Technique for Shot-Peened Specimen Using Rayleigh Wave Dispersion Data Based on Convolutional Neural Network

Shot peening is a surface treatment process that improves the fatigue life of a material and suppresses cracks by generating residual stress on the surface. The injected small shots create a compressive residual stress layer on the material’s surface. Maximum compressive residual stress occurs at a certain depth, and tensile residual stress gradually occurs as the depth increases. This process is primarily used for nickel-based superalloy steel materials in certain environments, such as the aerospace industry and nuclear power fields. To prevent such a severe accident due to the high-temperature and high-pressure environment, evaluating the residual stress of shot-peened materials is essential in evaluating the soundness of the material. Representative methods for evaluating residual stress include perforation strain gauge analysis, X-ray diffraction (XRD), and ultrasonic testing. Among them, ultrasonic testing is a representative, non-destructive evaluation method, and residual stress can be estimated using a Rayleigh wave. Therefore, in this study, the maximum compressive residual stress value of the peened Inconel 718 specimen was predicted using a prediction convolutional neural network (CNN) based on the relationship between Rayleigh wave dispersion and stress distribution on the specimen. By analyzing the residual stress distribution in the depth direction generated in the model from various studies in the literature, 173 residual stress distributions were generated using the Gaussian function and factorial design approach. The distribution generated using the relationship was converted into 173 Rayleigh wave dispersion data to be used as a database for the CNN model. The CNN model was learned through this database, and performance was verified using validation data. The adopted Rayleigh wave dispersion and convolutional neural network procedures demonstrate the ability to predict the maximum compressive residual stress in the peened specimen.

Effects of discrete laser surface melting on the fatigue performance of 20CrMnTi steel gear

Bionics research has revealed the remarkable fatigue resistance exhibited by intertidal zone shellfish, attributed to their radial ribs and multi-layered microstructure. Leveraging the analogous stress and working conditions shared by shellfish and gears, we adopted the discrete laser surface melting (DLSM) technology to create discrete laser surface melted (DLSMed) units on gear tooth surfaces. This paper aimed to scrutinize the influence of discrete laser surface melting on the fatigue performance of 20CrMnTi steel gears. In terms of laser selection, we opted for the Nd: YAG pulsed laser. Across various laser parameters, the proportion of DLSMed units on gear tooth surfaces varied. Scanning Electron Microscopy (SEM) facilitated the observation of microstructures and fatigue morphology of the DLSMed gear. X-ray Diffraction (XRD) measurements gauged residual stress along both the surface and cross section of the DLSMed unit, unveiling the residual stress distribution. Microhardness and surface roughness were assessed through a microhardness tester and a surface profilometer, respectively. Fatigue tests were conducted using both the Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine and a high-frequency fatigue testing machine. Experimental findings disclosed that the DLSMed unit comprised a melting zone and a heat-affected zone. The depth of the residual compressive stress layer increased alongside current intensity, albeit with the unexpected emergence of residual tensile stress. Enhanced current intensity corresponded to a noticeable elevation in the DLSMed gear's hardness value. Differing fatigue behaviors were evident between the as-received gear and the DLSMed gear. The DLSMed gear exhibited reduced fatigue damage compared to the as-received gear. The DLSMed units effectively curbed crack initiation and propagation, markedly enhancing gear fatigue performance. A direct relationship between the DLSMed unit's area proportion on the gear surface and gear fatigue strength was established. Finally, we delved into the anti-fatigue mechanism underlying the DLSMed gear's performance.

High-temperature fatigue life improvement of small-deep holes by using a novel cold expansion process in a nickel-based superalloy

Cold expansion of holes is a typical strengthening technology widely used in aviation parts and can effectively improve the fatigue life of hole structures. In this paper, a novel hole strengthening technology called the multi-annular convex hull rotating cold expansion process (MCR-CEP) for small-deep holes (diameter 1.72 mm, depth 10 mm) is proposed. After application of MCR-CEP at different expansion degrees (δ= 20–50 μm), the hole walls exhibit a lower surface roughness (Ra from 0.152 μm to 0.296 μm), higher microhardness (HV from 465 to 510), an obvious plastic deformation layer (depth of 15–35 μm) and a compressive residual stress layer. Under the optimal expansion degree (δ= 40 μm), the average fatigue life of the MCR-CEP specimens increased by 1.06–3.18 times at different thermal loads (300–700 °C) and mechanical loads (700–1000 MPa). The results of scanning electron microscopy (SEM) examination of fatigue fractures show that the possibility of crack initiation can be effectively reduced by the existence of a low surface roughness and plastic deformation layer in the top layer of the hole wall when the tested temperature is lower than 600 °C. The higher the mechanical loads are, the closer the crack initiating source is to the surface of the hole wall.

Fatigue crack propagation behavior in Ti−6Al−4V alloy with surface gradient structure fabricated by high-energy shot peening

A gradient structure was successfully fabricated on the surface of Ti−6Al−4V alloy by high-energy shot peening (HESP), and its effect on fatigue crack propagation was investigated. Optical microscope, scanning electron microscope, transmission electron microscope and X-ray diffractometer were used to characterize the microstructure and residual stress evolution during HESP. The results show that a gradient nanostructure with residual compressive stress layer of 220 μm in depth is formed. The generation of gradient nanostructures improves the strength−ductility combination of the alloy. Maximum residual compressive stress is generated on the subsurface, which gradually increases with the increase of shot peening time. HESP treatment effectively reduces the crack propagation rate and increases the fatigue crack propagation life. The residual compressive stress reduces the effective stress intensity factor range at crack tip, thereby generating the crack closure effect and delaying the crack propagation. At the same time, the synergy effects of increase in grain boundaries, decrease in effective slip length and the plastic zone at the crack tip caused by the refinement of the surface grains can increase the crack propagation resistance as well.

A tribological study of shot peening process on stainless steel

The goal of this study is to figure out how to use the microstructure, friction, and wear parameters of a shot-peened stainless steel 316L surface to study tribology. Tribology is the study of how moving parts rub against each other, wear out, and are oiled. Tribology looks at all of these things from a mechanical point of view. Improves the surface and frictional properties of materials, making them less likely to break and giving them a longer life. Because of this, it can make materials smoother and less likely to stick together. This is possible because it can improve the properties of many different materials. Shot peening is a type of cold working technique that can change the mechanical properties of materials like metals and composites. Because shot peening is a part of the peening process, this improvement is possible. Also, as a direct result of the result, a layer of compressive residual stress will form in the material. Before the process can be finished, the surface of the SS316L needs to be honed with abrasive sheets and a double-disc polishing machine. Next, a Vickers hardness test is done on the material, and then a pin-on-disc tribometer is used to study how the material wears. At the end of the process, a trinocular microscope is used to look at the structure of the substance being studied on a small scale.

A comprehensive investigation on the effect of controlling parameters of ultrasonic peening treatment on residual stress and surface roughness: Experiments, numerical simulations and optimization

This paper aims to study the effect of controlling parameters of ultrasonic peening treatment (UPT), including the pin diameter, the vertical velocity of the pin, friction coefficient etc. on the residual stress, PEEQ and surface roughness. A method was promoted to simulate the UPT process using the ability of the ABAQUS scripting interface and transferring results between ABAQUS analyses. The finite element results of the proposed method were consistent with the UPT simulation. Moreover, the finite element results agreed well with experimental measurements of residual stress, surface roughness and surface deformation. The results revealed that increasing the pin diameter, the vertical velocity of the pin and also the number of impingements increased the depth of the compressive residual stress layer. Decreasing the vertical and horizontal velocity of the pin and increasing the pin diameter and the distance between two adjacent impingements resulted in a decline of surface roughness parameters (Ra and Rq). A combination of finite element model and multi-objective optimization technique was implemented to determine the optimum controlling parameters of UPT for reaching the maximum compressive residual stress and the minimum surface roughness. For the optimum proposed controlling UPT parameters, the values of −386 MPa, 16.7 μm and 20.9 μm were obtained for the surface residual stress, Ra and Rq, respectively.

An investigation on the effect of change in experimental sequence of warm laser shock peening and laser shock peening on the performance of DD6 nickel-based single-crystal superalloy

Incorporated with the benefits of dynamic strain aging (DSA) and laser shock peening (LSP), warm laser shock peening (WLSP) is able to induce a compressive residual stress (CRS) layer with high thermal stability on the near-surface of the material. It has been widely used in recent years as a new surface modification technique to prolong the fatigue life of aero-engine turbine blades. Single WLSP has limited effect on material modification, while multiple WLSP when the confining layer is quartz glass will affect the thickness and thermal stability of the CRS layer during replacement of the confining layer, absorbing layer, and cooling and heating. To address this issue, this study investigates the mechanism of the CRS response, mechanism of strengthening, mechanism of action, and change of electrochemical corrosion performance of DD6 superalloy samples to different surface treatments after double LSP, single WLSP plus single LSP and double WLSP surface treatments by changing the experimental sequence of WLSP and LSP.The experimental results show that all three surface treatments deform the sample by inducing 〈110〉 cross-slip bands on the sample surface. Also all three surface treatments strengthen the sample surface by pipeline diffusion of elements to form a dislocation network similar to the γ/γ′ substructure.Meanwhile, single WLSP plus single LSP treatments can effectively prevent the thermal relaxation of the previously induced CRS layer. The final induced CRS layer thickness, dislocation distribution and dislocation density are better than those of double LSP and double WLSP. Pipeline diffusion of elements can improve the electrochemical and thermal corrosion resistance of the single-crystal superalloy.

Numerical Simulation on Laser Shock Peening of B4C-TiB2 Composite Ceramics.

The introduction of residual stresses using laser shock peening (LSP) is an effective means of improving the mechanical properties of ceramics. Numerical simulations offer greater convenience and efficiency than in-lab experiments when testing the effects of different processing techniques on residual stress distribution. In this work, a B4C-TiB2 ceramic model based on the extended Drucker-Prager model was established to investigate the effects of laser power density, the number of impacts and laser spot overlapping rate on the residual stress distribution, and the reliability of the simulation method was verified by experimental data. The following results are obtained: increasing the laser power density and the number of impacts can increase the surface residual compressive stress and reduce the depth of the residual compressive stress; the presence of multiple impacts will significantly reduce the depth of the residual compressive stress layer; with the increase in the laser spot overlapping rate, the compressive residual stress in the processed area gradually increases and is more uniformly distributed; the best processing effect can be achieved by using a spot overlapping rate of 50%.

Influence of ultrasonic impact treatment on stress corrosion of 7075 aluminum alloy and its welded joints

The effects of ultrasonic impact treatment (UIT) on stress corrosion cracking (SCC) of 7075 aluminum alloy and its welded joints have been investigated. The microstructural evolution, corrosion behavior, and mechanical properties of the UITed and untreated specimens were studied. The results showed that UIT can refine the grains dramatically and induce a compressive residual stress layer with a depth of 50–75 µm on the material surface. The corrosion resistance was also improved, exhibiting that the SCC factors Iσ, Iδ, and SSI of the specimens with double-side treatments decreased by 37 %, 68 %, and 46 %, respectively. The improved SCC resistance of 7075 aluminum alloy and its welded joints subjected to UIT was mainly attributed to the residual compressive stress and grain refinement, which not only enhanced the pitting corrosion resistance but also effectively inhibited the initiation and growth of corrosion cracking.