Search

This paper investigates the fatigue behavior prediction of Ti‐6Al‐4V thin‐leading‐edge turbine blade specimens treated with laser shock peening (LSP) using two advanced artificial intelligence (AI) methods: artificial neural networks (ANNs) and adaptive network‐based fuzzy inference system (ANFIS). The study aims to estimate the endurance under high cycle loading conditions. First, using ABAQUS and MATLAB software, the modified Crossland criterion for uniaxial loading is applied to recalibrate endurance limit values based on modifications induced by the LSP process. Then, these techniques are employed to predict the modified Crossland criterion profile and endurance limit values influenced by the LSP treatment. Specifically, numerical values are used as training and testing data for these AI models. As a result, these AI methods provide highly accurate prediction and optimization of the modified Crossland criterion and endurance limits, demonstrating their reliability and effectiveness. Highlights: The studied samples are processed using the LSP treatment.The fatigue behavior is based on Modified Crossland criterion.The fatigue behavior based on the Crossland diagram is predicted using the FEM analysis.The ANNs and the ANFIS approaches are used to predict the endurance limit values. [ABSTRACT FROM AUTHOR]

Nickel alloys are widely used in aerospace and defense industries due to their excellent high-temperature characteristics. In order to increase fatigue resistance and oxidation corrosion resistance, aerospace curved surface parts always need to be strengthened using laser shock peening technology on five-axis machines. However, it is easy to generate dense laser spots in certain regions during the process, which might lead to an uneven distribution of residual stress on surfaces of the component. To address this issue, the study investigates the problem of excessive spot overlap rate at large curvature positions caused by a mismatch between the surface curvature of curved components and the dynamic performance of equipment, then proposes an optimization algorithm for motion control based on linear interpolation principles. By analyzing the relationship between the feed rate of the program segment and the actual feed rate, the speed of each axis of the machine tool is confirmed and adjusted, and the control flow of the optimization algorithm is established. The feasibility of the algorithm is preliminarily verified by comparing the changing trend of feed rate before and after optimization through simulation. In actual laser shock peening experiments on nickel alloy spherical shell elements, the laser spot distribution on the surface of the component is uniform, and the relative error range between the actual overlap ratio and the theoretical value can be controlled within 5%, demonstrating the correctness of the optimization algorithm. This study can significantly improve the surface machining quality of curved components and have practical applications. [ABSTRACT FROM AUTHOR]

Ti48Al2Cr2Nb high-temperature alloy consisting of γ and α 2 phases, whose room-temperature brittleness limits its use in other lower temperature ranges, has been laser shocked to improve its surface properties. The study of the shock response and plastic deformation behaviour of material then provides further insight into the laser shock peening mechanism. In this paper, the molecular dynamics method and piston impact method are used to simulate laser shock peening of lamellar two-phase TiAl alloys to study the shock response and plastic deformation of material at different shock velocities, as well as the effects of shock velocity and two-phase interface on them. The results show that, in terms of shock response, the location of elastic–plastic wave separation as well as the atomic velocity and stress magnitude are affected by the shock velocity, elastic strain energy and interfacial energy, and some of stresses change significantly at the semi-coherent interface. At lower shock velocities, it is mainly stacking faults and twin boundaries in γ phase that initiate phase transitions across the interface to the α 2 phase, whereas at higher velocities, in addition to earlier α 2 phase transitions, clustered amorphous atoms and intermediate phases are also observed. The dislocations at the semi-coherent interfaces are affected by both interface type and shock velocity. The mechanical properties of lamellar two-phase TiAl are improved by the effect of laser shock at different shock velocities. These results provide experimental and theoretical guidance for improving the room-temperature properties of two-phase TiAl alloys. [ABSTRACT FROM AUTHOR]

This article explores the use of deep learning, specifically artificial neural networks, to optimize the parameters of laser shock peening in the Ti-6Al-4V alloy. Laser shock peening is a technique that introduces compressive residual stresses to improve the fatigue properties of materials. The authors develop a neural network model that accurately predicts residual stresses and depth of the modified layer. The model can be used to identify optimal processing parameters for achieving maximum depth and compressive stresses. The study concludes that the neural network predictions align with experimental results. [Extracted from the article]

As a crucial high-performance material, nickel-based superalloys inevitably generate residual stresses during processing, manufacturing, and usage. The mechanical properties of nickel-based superalloys are significantly reduced by residual stress, which becomes one of the important factors restricting material reliability. The systematic analysis of residual stresses in nickel-based superalloys throughout the entire manufacturing and usage processes is insufficient. The residual stress generation factors, measurement methods, prediction models, and control methods in nickel-based superalloys in recent years are summarized in this paper. The current challenge and future development trends in the research process of nickel-based superalloy residual stress are also presented. A theoretical reference for further research on residual stresses in nickel-based superalloys can be provided in this review. [ABSTRACT FROM AUTHOR]

This study focuses on the effect of a plasma nitriding (PN) process on the thermal stability of nanocrystalline on the surface of Ti-6Al-4 V (Ti64) titanium alloy, which is printed by selective laser melting (SLM) and subsequently treated by laser shock peening (LSP). The microstructure evolution of SLM-Ti64 titanium alloy treated sequentially by LSP and PN at different annealing temperatures was observed by X-ray diffraction, differential scanning calorimeter, scanning electron microscope, and transmission electron microscope. The results show that the average size of SLM-Ti64 alloy treated by LSP is 49.7 nm, even at 600 °C nanocrystals maintain thermal stability, which is attributed to the strong hinder effect of high-density dislocations on grain boundary migration. The microstructural characterization indicates that the nitrided layer is mainly composed of nanostructured TiN phase by PN at 600 °C, and the thermal stability of nanocrystals was further increased to 700 °C compared without nitriding, which is attributed to dispersed nanoscale TiN precipitates hindering the migration of grain boundaries by Zener pinning effect. Our work provides a method of preventing nanocrystalline coarsening in Ti64 alloy by PN. [ABSTRACT FROM AUTHOR]

In this study, the effect of electro-pulsing combining laser shock peening (EP-LSP) treatment on the microstructure and corrosion resistance of Ti-6Al-4V alloys was investigated, and the hardness, surface roughness, microstructure, and electrochemical properties of Ti-6Al-4V alloys after EP-LSP treatment were studied and compared with those of single EPed and LSPed samples. Also, to investigate the effect of the number of laser impacts on microstructure and corrosion resistance, changes in samples after one and three laser impacts were compared. The results showed that all treatments improved the hardness of as-received sample and three EP-LSPed (3 EP-LSP) samples had the maximum hardness which increased 24.3% compared with the as-received sample. As the number of laser impacts increased from one to three, the surface hardness increased, but the surface quality decreased, and the surface showed periodic protrusions. The one EP-LSPed (1 EP-LSP) sample showed the best corrosion resistance, with a 73.2% reduction in corrosion current density compared to the as-received sample. This is due to the grain refinement and the transformation of the α to β phase in the EP-LSPed samples. It has a beneficial effect on the formation of dense passive film. In addition, the sample surface with one impact has lower surface roughness and better surface quality compared to that of three impacts. [ABSTRACT FROM AUTHOR]

The high‐temperature fretting fatigue damage characteristics of dovetail specimens strengthened by nanosecond laser (NL) and nanosecond combined femtosecond laser (F‐NL) were investigated. The results show that the fretting fatigue life of the NL strengthened sample (NL sample) is improved by 211.2% compared to the base metal samples (BM sample). The lifetime of the nanosecond combined femtosecond strengthened sample (F‐NL sample) was increased by 319.6%. It was attributed to the strengthening introducing hardened layers, residual compressive stress field, and high density of dislocations. The combined strengthening process reduces the surface roughness of the NL strengthened surfaces, while the strengthening influence layer is further increased. The fracture morphology shows that the crack source of the strengthened specimen has changed from multi‐source sprouting to single‐source sprouting, and the crack source sprouted on the subsurface. The fatigue strip morphology similarly confirms that a reduction in the crack propagation rate occurs. [ABSTRACT FROM AUTHOR]

The fatigue crack kinetics in the residual stress field is investigated in the specimens of TC4 titanium alloy after their laser shock peening (LSP). Following this treatment, the fatigue tests are carried out. The fatigue life of the specimens after LSP is found to increase. The maximum applied force in the fatigue cycle, which compensates for the residual stress effect, is determined by a numerical simulation. This determines the range of applied forces within which the compressive residual stress field generated by LSP remains effective. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) is a formidable cold working surface treatment that provides high-energy precision to enhance the mechanical properties of materials. This paper delves into the intricacies of the LSP process, offering insights into its methodology and the simulation thereof through the finite element method. This review critically examines various points, such as laser energy, overlapping of shots, effect of LSP on residual stress, effect of LSP on grain refinement, and algorithms for simulation extrapolated from finite element analyses conducted by researchers, shedding light on the nuanced considerations integral to this technique. As the significance of LSP continues to grow, the collective findings underscore its potential as a transformative technology for fortifying materials against mechanical stress and improving their overall performance and longevity. The discourse encapsulates the evolving landscape of the LSP, emphasizing the pivotal role played by finite element analysis in advancing our understanding and application of this innovative surface treatment. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) is a relatively novel and promising surface hardening method. An absorbing layer, which is needed to protect the specimen surface from undesirable thermal effects caused by laser irradiation, should be considered as one of many varying parameters. The physical characteristics of the coating and its adhesion to the specimen surface can significantly influence the result of LSP. In this study, three commonly used absorbing coatings, namely black polyvinylchloride tape with a sticky layer, aluminum foil, and black alkyd paint were used to cover three-millimeter-thick plates of the Ti-6Al-4V titanium alloy with globular or lamellar microstructures. LSP of one side of the plates was carried out with a power density of 10 GW/cm2. The hole drilling method was used to evaluate residual stresses. The aluminum foil was found to be the optimal option for LSP of the Ti-6Al-4V titanium alloy. Microstructural investigations carried out using EBSD analysis suggested that no significant reduction in grain size, twinning, or dislocation density growth occurred as a result of LSP irrespective of the initial structure. [ABSTRACT FROM AUTHOR]

The present study reports the effect of laser shock peening (LSP) on stress corrosion cracking (SCC) behavior of the shear cut surfaces of type 304L stainless steel. The LSP is carried out on as shear cut surface of SS 304L steel at a fixed laser power density of 3.53 GW cm−2 with multiple passes, i.e., double and triple. The preliminary investigation showed that as shear cut surfaces of SS 304L possess a very high tensile residual stresses of the order of 450-700 MPa and hardness 400 HK0.1. The LSP treatment with double and triple pass led to the generation of high compressive residual stress of the order of − 200, and − 250 MPa as compared to as cut shear surfaces. Microscopic analysis revealed that the shear cut surfaces, after double and triple LSP treatment exhibited significantly reduced susceptibility to the SCC in chloride environment after 8-hour test. The results of the present study recommend that LSP treatment can acts as protector of the product and components of austenitic stainless steel with sheared cut surfaces stored for long time in susceptible corrosive environment. This way a huge loss to the nuclear and process industries can be minimized. [ABSTRACT FROM AUTHOR]

Laser peen forming (LPF) is an appealing technique for forming metal sheets using high-energy, short-duration laser pulses. The deformation of the target metal plate is closely related to the magnitude and distribution of laser-induced residual stress. Consequently, the relationship between process parameters and residual stress is worth researching. In this research, two process parameters in LPF, laser energy and coverage ratio (spot distance essentially), and one workpiece parameter, plate thickness, were examined through an element method (FEM) of multiple square-spot laser shock peening (SSLSP). Corresponding experiments of SSLSP on aluminum alloy 2024-T351 test blocks were conducted, together with an X-ray diffraction (XRD) residual stress measurement and a surface morphology observation. The FEM simulation and experimental results show that congested laser spots had a significant influence on the magnitude of compressive residual stress; higher laser energy was beneficial to the depth of the compressive stress layer but could decrease its magnitude. Therefore, for better forming ability, higher laser energy and a higher coverage ratio are beneficial; for surface strengthening, laser energy should not be too large, and the coverage ratio should be larger than 100% to ensure that the residual stress on the treated surface is compressive, resulting in better surface integrity.

High-strength titanium alloy TC21 is often used to make aircraft load-bearing components in the aviation field. However, due to vibration, load-bearing components often suffer from fretting fatigue (FF), which greatly reduces their actual service life. Nowadays, laser shock peening (LSP) is being recognized as an effective strengthening process for many materials. Therefore, in this study, the effectiveness of LSP on the strengthening of high-strength titanium alloy TC21 is studied, in terms of surface integrity and FF properties. TC21 fretting specimens and tests are designed. Before fretting tests, the specimens are processed by LSP with varying laser pulse energies, number of shocks and overlap rate, and their surface integrity and FF properties are analyzed. It is found that the greater the laser pulse energy and number of shocks, the higher the surface hardness and compressive residual stress, the more the grain refinement, the greater the improvement in FF life. Under 32J-50%-T1, the FF life is improved by 191.3% compared with BM. But the overlap rate has little effect on surface integrity and FF life. Meanwhile, there forms amorphous structures, which tended to be transformed into nanograins during fretting process. This transformation is helpful for prolonging FF life due to its action of energy absorption. This study reveals the strengthening mechanism of LSP on TC21 and its effect on the FF properties of TC21 specimens.

In this study, the effects of surface treatment namely electro-pulsing followed by laser shock peening (EP-LSP) on wear resistance properties of Ti–6Al–4V alloy are investigated. It was compared with samples treated solely with laser shock peening (LSP) and electro-pulsing treatment (EP) to investigate the effects of different processes on the friction and wear properties of Ti–6Al–4V alloy. In addition, the friction coefficient, wear rate, wear morphology were also investigated. Finally, the wear mechanism was described in detail. The results demonstrated a significant reduction in grain size for the samples after EP-1-LSP treatments. Furthermore, compared with the as-received samples, the maximum hardness of EP-1, LSP and EP-1-LSP treated samples increased by 6.5%, 5.9%, and 19.6%, respectively, and the compressive residual stress on the surface increased by 2.4%, 15.0%, and 37.2%, respectively. Under the same friction conditions, the depth of wear scar of the samples after EP-1, LSP, and EP-1-LSP treatments decreased by 7.2%, 10.6%, and 18.5% than that of the as-received sample. The as-received samples mainly exhibited severe oxidative and adhesive wear, and the LSP and EP-1 treated samples showed slight adhesive and oxidative wear. The EP-1-LSP treated samples predominantly showed signs of abrasive wear.

Titanium alloy Ti6Al4V is widely used in the production of bone implants due to its favorable mechanical properties and biocompatibility. However, implant failures still occur due to lack of osseointegration, tissue infection, and fatigue. Laser shock peening (LSP) is a surface treatment method that can improve the physical, mechanical, and biological properties of Ti6Al4V implants. This method enhances the fatigue life of implants by inducing compressive residual stress on their surface region. In this study, Ti6Al4V samples were subjected to LSP treatment using different laser power densities (9.6 and 14.9 GW / cm 2 ) and with (vinyl tape and commercial black color) and without a protective layer. LSP-treated samples with higher power density exhibited maximum compressive residual stresses. Furthermore, hydrophobicity increased in all samples with increasing laser power density. Notably, the surface roughness results demonstrated significant improvement where the roughness increased with increasing the laser power density. The sample without a protective layer exhibited the highest surface roughness, followed by the black color coated and vinyl tape surface protected samples. The residual stress, surface roughness, and hydrophilicity of the samples were evaluated to determine the optimal LSP parameters. Fatigue tests revealed a remarkable enhancement in the fatigue life of the LSPed samples compared to untreated samples (3 and 2.9 times longer life for black-color coated and without coating samples, respectively). Moreover, the microstructure of laser peening samples and the fracture surface of the fatigue samples were characterized using field emission scanning electron microscopy (FE-SEM). To evaluate the biological characteristics of the optimal LSP-treated samples, a hydroxyapatite coating was applied, and their biological characteristics, including cell viability and adhesion, were investigated. Furthermore, the combination of LSP with hydroxyapatite coating offers a potential solution to promote osseointegration and reduce implant failures. [ABSTRACT FROM AUTHOR]

7-Series aluminum (Al) alloys have been widely used in aircraft and high-speed train manufacturing owing to its excellent mechanical properties and fracture toughness. However, surface problems of corrosion, wear and fatigue failure of Al alloy parts seriously affect the service life. In the present study, the noncontact laser shock peening (LSP) was applied to improve the fatigue life of the substrate before the coating deposited by cold spraying (CS). The effect of LSP on the interfacial bonding behavior between CS Al with 50 vol.% Al2O3 composite coatings and 7075 Al alloy substrate was comprehensively investigated. Results showed that after LSP treatment, the tensile strength is reduced from 47 to 34 MPa and 32 MPa when the laser shock energy was 2 and 3 J, respectively. Under the condition of shear strength, it decreases from 41.5 to 30 MPa and 26 MPa, respectively. In addition, numerical simulations were conducted on LSP and CS processes, and the results showed that with the increase of laser shock energy, the plastic deformation dissipation energy of Al particles increases gradually, while the plastic deformation dissipation energy of the matrix decreased. Therefore, the surface hardening caused by LSP treatment is the main reason for the decrease of interfacial bonding strength. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) is a technique similar to shot peening that improves the mechanical properties, such as fatigue performance of metallic structures, by introducing compressive residual stresses. This study aims to present a 3D finite element simulation for simulating residual stress field after laser shock peening without absorbent coating (LSPwC) in real applications. Also, the residual stress distribution induced by LSPwC in a Rene 80 Ni-based superalloy was obtained via X-ray diffraction and hole drilling measurements. The excellent correlation between the simulated residual stress values and experimental test results proved this model reliable. Laser peening Rene-80 superalloy samples with single LSP impact at a laser power density of 6 GW/cm2 led to a significant increase in the compressive residual stress (-405 MPa) compared to the unpeened sample. The yield strength of laser-peened samples was improved by ~ 16% and a reduction of ~ 12% in the failure strain compared to the baseline sample. Similarly, the laser peening increased microhardness by 26% compared to the untreated samples. Scanning electron microscopy (SEM) was also utilized to interpret the failure mechanism of samples examined before and after LSP. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Drainage & Irrigation Machinery Engineering / Paiguan Jixie Gongcheng Xuebao is the property of Editorial Department of Drainage & Irrigation Machinery Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laser shock peening (LSP) is a powerful technique for improving the fatigue performance of metallic components by customizing compressive residual stresses in the desired near-surface regions. In this study, the residual stress distribution characteristics of 6061-T6 aluminum alloy induced by LSP were identified by the X-ray diffraction method, and their dependent factors (i.e., LSP coverage, LSP energy, and scanning path) were evaluated quantitatively by numerical simulations, exploring the formation mechanism of LSP residual stresses and the key role factor of the distribution characteristics. The results show that LSP is capable of creating anisotropic compressive residual stresses on the specimen surface without visible deformation. Compressive residual stresses are positively correlated with LSP coverage. The greater the coverage, the higher the residual stress, but the longer the scanning time required. Raising LSP energy contributes to compressive residual stresses, but excessive energy may lead to a reduction in the surface compressive residual stress. More importantly, the anisotropy of residual stresses was thoroughly explored, identifying the scanning path as the key to causing the anisotropy. The present work provides scientific guidance for efficiently tailoring LSP-induced compressive residual stresses to improve component fatigue life. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the strengthening mechanism of laser shock peening on the interfacial bonding properties between TiN coatings and TC4 titanium alloy substrates. The different surface textures were induced by LSP on a TC4 titanium alloy substrate. Subsequently, titanium nitride (TiN) coatings were deposited on the surface texture. A scratch test and reciprocating sliding wear assessment were conducted to evaluate the impact of LSP on the interfacial bonding properties and wear performance of the coatings. The experimental results demonstrated that the adhesion of TiN coatings deposited on the surface texture formed by laser shock peening was significantly enhanced. The efficacy of laser shock treatment in reducing wear rates was found to be significantly enhanced in cases of both increased spot overlapping rate and increased laser power density. The surface texture created using laser parameters of 6.43 GW/cm2 and a 50% overlapping rate was found to have the most significant effect on improving the adhesion and anti-wear properties of the coating. The laser shock texture was identified as the main contributor to this improvement, providing a large interfacial contact area and a mechanical bond between the coating and the substrate. This bond inhibited the initiation and propagation of micro-cracks caused by the concentration of internal stress and interfacial stress of the coating. [ABSTRACT FROM AUTHOR]

The high tensile residual stresses in the laser powder bed fusion (LPBF) manufactured H13 steel lead to severe cracks and low mechanical properties. To solve this problem, the laser shock peening (LSP) was applied to H13 steel manufactured by LPBF to eliminate tensile residual stress and improve mechanical property. The evolution mechanism of defects and residual stress during LPBF-LSP process were accounted for using the finite element method. The numerical results indicate that the compressive residual stress induced by LSP shock was beneficial for pores and cracks closure. A single shock cannot completely eliminated the tensile residual stress generated in LPBF process, and the mechanism of tensile residual stresses elimination by shock wave and rarefaction wave was proposed. The LSP process parameters of LPBF manufactured h13 steel were optimized by single point impact tests, and the effects of residual stress induced by LSP on defect, microstructure, and nano-hardness were experimentally studied. The experimental result shows that the defect closure zone depth increases with the number of laser impacts. The nano-hardness near the surface was increased by 31% than the LPBF sample after double LSP treatment. The strengthening mechanism of LSP-H13 was clarified as dislocation strengthening. This work verifies the feasibility of tensile residual stress elimination and mechanical properties improvement of the LPBF manufactured H13 steel by LSP treatment. [ABSTRACT FROM AUTHOR]

Surface texturing is a promising sustainable technique to get better the machining performance of cutting tools. Laser surface texturing and micro-EDM are the most commonly used fabrication techniques and the textured tools exhibit better tool performance as compared to conventional tool. However, these processes involve resolidification of material surface which makes the surface softening and reduction in the surface hardness. In the present work, cutting performance of the high-speed steel (HSS) tool is studied by fabricating hybrid (microgrooves with dimples) textures on its rake face using both laser ablation and micro-EDM methods followed by laser shock peening without ablative coating (LSPWAC) process. Hybrid textured with shock peened HSS tools are used in orthogonal dry turning of 316 L stainless steel. It has been observed that hybrid textures with shock peened HSS tool exhibits higher tool life of up to 255 and 85% than the conventional and the hybrid textured (HT) tools respectively. The results shown that surface texturing followed by shock peening is an innovative method to improve the sustainability in machining process than only surface texturing method. Moreover, analysis of chip is studied by finite element analysis. [ABSTRACT FROM AUTHOR]

In the present study, the effect of laser intensity on the microstructure, residual stress, microhardness, and corrosion resistance property of laser shock peened Ti6Al4V using an Nd: YAG laser has been investigated. The applied laser intensity varied from 1 to 8 GW/cm2. During the processing, the pulse density was 574 pulses/cm2, and water was used as a confining layer. Due to laser shock peening, there is refinement of microstructure and presence of oxides on the surface. The residual stress on the surface was found to vary from + 130.12 to − 138.16 MPa and varied with process parameters. There is an increase in microhardness which also varied with process parameters. Due to laser surface processing, there is a significant improvement in corrosion resistance. A detailed structure–property correlation has been established. [ABSTRACT FROM AUTHOR]

In this work, the effect of laser shock peening (LSP) on the electrochemical behavior of HSLA steel (ASTM A 588 Grade D) in 3.5 wt.% NaCl solution was investigated. The microstructural evolution, micro-texture development, surface roughness, residual stress development, microhardness, dislocation density, potentiodynamic polarization, and electrochemical impedance spectroscopy were studied in depth. The corroded surfaces (with and without LSP) were characterized using scanning electron microscopy and Raman spectroscopy for understanding the nature of the passive film formation and its stability. The results revealed that LSP treatment marginally refines the near-surface microstructure from 9.1 to 7.4 μm and generated high compressive residual stress (CRS) of about 500 MPa on the top surface; such variation happened due to severe plastic deformation during LSP. The micro-texture analyses of the laser-peened specimens (on the surface) revealed that {011} <111> texture components were significantly increased while the γ-fiber weakened after laser-peening. Dislocation density was obtained ~ 9.266 × 1012 on the unpeened and ~ 1.158 × 1013 on the laser-peened surfaces, indicating that higher pressure shock waves plastically deformed the top layer of the peened specimen. The corrosion studies indicated about 4 times improvement in the corrosion resistance of the peened specimens—the combined effects of LSP-induced gradient CRS and refined microstructure improved the corrosion resistance. The EDS and Raman spectroscopy results demonstrated the persistence of a compact and continuous passive oxide film/layer, primarily made of Fe2O3, on the surface of the laser-peened specimens. [ABSTRACT FROM AUTHOR]

Micro-geometrical errors, surface roughness, and surface integrity (microstructure, residual stresses, microhardness) play an important role in defining the quality of the gears as they directly affect their noise, vibration characteristics and service life during their use. In the present work, underwater laser shock peening (LSP) is employed to improve the quality of the laser powder bed fusion built 17-4 PH small-size spur gears (12 mm outside diameter). LSP was employed near the spur gear root, and effects were measured in terms of residual stresses, variation in microgeometry errors, surface roughness, porosity, microstructure, and microhardness. It was observed that LSP could impart compressive residual stresses up to 0.4 mm of measured depth, while the surface roughness has improved by 32%. Microgeometry and microhardness of gears showed minor variations. Additionally, LSP has shown an impact on the microstructure as the grain orientation was altered and grain size reduced by 15.6% due to shock wave transmission. The study paves the way to use LSP as a post-processing technique to modify the surface characteristics of LPBF-built miniature spur gears with minimal impact on the gear microgeometry.

To investigate the surface integrity of 17-7PH stainless steel welded structural components used in aviation, laser shock peening (LSP) with different power densities was applied to stainless steel welded joints. The microstructural morphology, structural features, full-width at half-maximum, microhardness, and surface roughness of the stainless steel welded joint specimens before and after LSP were characterized and measured using SEM, TEM, XRD, a microhardness tester, and a high-resolution confocal microscope. The effects of different laser power densities on the microstructure and properties of the stainless steel welded joints were explored. Results indicate that the stainless steel welded joints exhibit a typical BCC phase. Laser shock peening promotes grain refinement in the welded joints, leading to the phase transformation of residual austenite into martensite. The surface roughness of the specimen is positively correlated with laser power density. At a power density of 5.17 GW/cm2, the surface roughness increased to 1.919 μm, which is 117.08% higher than that of the non-peened specimen. The microhardness of the specimens shows a decreasing trend with increasing power density. When the power density is 2.79 GW/cm2, the microhardness of the specimen significantly increases to 462.94 HV0.5, which is 22.26% higher than that of the non-peened specimen.

Laser shock peening (LSP) is an innovative surface treatment technique successfully used to improve fatigue performance of metallic components. It is based on the application of high intensity laser and suitable overlays with the aim to generate high pressure shock waves on the surface of the mechanical part to be treated. Shock waves generate severe plastic deformations and, consequently, compressive residual stresses (RS). An accurate measurement of these latter is crucial for predicting the resistance of treated parts under service loads and to assess the effectiveness of LSP process.In this paper, a non-destructive method, based on the nanoindentation technique and finite element analysis (FEA), was developed to measure the RS generated by LSP process on AA-7050-T451 samples. In particular, the methodology is based on the analysis of the nanoindentation peak load variation generated by the presence of residual stresses on a component. Obtained results were compared, for validation, with the measurements carried out by the most consolidated X-ray diffractometer (XRD) technique. The results showed a satisfactory agreement between the two techniques, revealing nanoindentation as a promising and reliable method for characterizing RS induced by LSP.

The M50 bearing steel underwent a combined treatment of laser shock peening (LSP) and nitrogen ion implantation. The microstructure, surface mechanical properties and tribological behaviors were evaluated. Comparative analysis with the untreated sample revealed significant improvements in surface nano-hardness, increasing from 7.51 GPa to 11.35 GPa, 11.51 GPa, and 12.62 GPa for samples subjected to LSP, ion implantation, and combined strengthening, respectively. Correspondingly, surface compressive residual stress showed notable increases from −15.55 MPa to −1043.76 MPa, −451.34 MPa, and −1276.13 MPa, respectively. The improved surface mechanical properties observed in the combined strengthened sample are likely due to the synergistic effects of the combined strengthening. In friction tests, the combined strengthened sample exhibited the lowest friction coefficient, attributed to the presence of a metal nitride layer and a thicker amorphous layer. Wear mechanisms transitioned from fatigue spalling for the untreated specimen to slight wear and the formation of an oxidative adhesion layer after LSP and ion implantation. Remarkably, the surface of the combined strengthened specimen demonstrated minimal wear, with only an oxidative adhesion layer present.

Stress corrosion cracking (SCC) of welded joints is a significant issue that affects the widespread application of multimetal welded structures in aerospace, transportation, and other fields. This paper investigates the effect of laser shock peening (LSP) on the SCC of TC4/2A14 friction stir welded (FSW) joints with dissimilar metals. The microstructural evolution, mechanical properties, and corrosion behavior with and without LSP treatment were investigated using optical microscopy, transmission electron microscopy, X-ray analysis, electrochemical testing, and slow strain rate tensile testing (SSRT). The results showed that the LSP significantly refined the grains and induced work-hardening on the near-surface of the material. After LSP, the compressive residual stresses on the surface of the titanium and aluminium sides were −817.6 MPa and −153.6 MPa for the joint, respectively. Corrosion resistance was also improved, with the self-corrosion current density on the Al side of the joints reduced by 77% and the SCC susceptibility index (Issrt) reduced from 0.140 to 0.121. The enhanced SCC resistance of the LSP-treated TC4/2A14 dissimilar metal FSW joints is primarily due to grain refinement, work-hardening effect, and high-level compressive residual stress. These factors not only enhance the material strength and improve the pitting resistance of the joints but also prevent the initiation and propagation of SCC.

The high-temperature wear resistance plays an important role for Ti–6Al–4V alloy components working in extreme environments, especially vital for avoiding unexpected failure. However, the reasonable method of surface modification should meet the requirement of improving in wear resistance and less decreasing in mechanical properties simultaneously, which brings a great challenge. In the present research, the laser shock peening (LSP) technique was applied to optimize the superficial layer of Ti–6Al–4V alloy by different processing. The microstructure, elastic modulus, nano-hardness and high-temperature tribology properties of the LSP processed Ti–6Al–4V were investigated to reveal the improving effect. The results demonstrate the LSP processing transforms the dual-size grain structure to relative homogeneous grain structure and forms the gradient nano-structure in superficial layer. With the increasing of LSP processing numbers, the density of geometrically necessary dislocation (GND) decreases obviously, but the density of statistically stored dislocation (SSD) rises significantly, which promotes the increase of total dislocation density compared with the as-received (AR) alloy. Due to the crystal evolution, the Ti–6Al–4V alloy with three-times LSP processing has the lowest wear rate which is less than half of the as-received state. The observations on worn surface and adjacent cross-sectional microstructure reveal the severe scratching and many inner microcracks in the AR sample but the slight scraping and few inner microcracks in the three-times LSP processed sample. Considering the elevated nano-hardness and elastic modulus, the improved tribological properties should be mainly attributed to the optimized microstructure and dislocation state by LSP processing. The present research provides a more reasonable method to improve the high-temperature wear properties of Ti–6Al–4V alloy.

To cater to the diverse requirements of industrial applications, it is crucial to conduct a comprehensive investigation into the influence of laser shock peening (LSP) with and without coating (LSPwC) on the microstructure and mechanical properties of materials. This study employs various methods to compare and analyze the effects of LSP and LSPwC on the microstructure and mechanical properties of GH4169 alloy. One notable contrast between LSP and LSPwC lies in the formation of oxide layers and microcracks on the surface of LSPwC-treated samples. Tensile tests subsequently reveal that LSP enhances the tensile strength, whereas LSPwC diminishes it. The reduced strength in LSPwC-treated samples can mostly be attributed to the oxide layer and microcracks resulting from laser-induced heat, as determined through failure analysis. After the removal of the oxide layer, the strength undergoes a significant improvement with LSPwC treatment, surpassing both the strength and ductility levels observed in GH4169 treated with LSP alone. These improvements can be attributed to a combined effect involving the removal of the oxide layer and microcracks, the formation of a gradient hardened layer, and the presence of dense slip bands.

It is challenging to maintain decent plasticity while increasing strength in laser powder bed fusion (LPBF) manufactured Haynes 230 alloy. The fundamental issue of both inadequate affected depth and deteriorated plasticity exists for laser shock peening (LSP). To address this problem, the treatment method of heat treatment plus laser shock peening (HT-LSP) was proposed. After heat treatment, dispersive M23C6 carbides were precipitated, and dislocation was predominately decreased inside grains but increased at grain boundaries. The junction of three imperfect dislocations was identified at M23C6 after HT-LSP treatment, indicating the novel phenomenon of twin formation via the polar-axis mechanism of dislocation proliferation, given the inhibition of intergranular transfer of dislocations and adequate clean rooms without dislocation clusters inside grains. Grain rotation occurred after HT-LSP derived from dynamic recrystallisation and twin distortion. The hardness along depth direction of the sample demonstrated the increased effective affected depth of LSP from 900 to 1400 μm after heat treatment. The shear strength of the HT-LSP sample was increased to 662 MPa. The elongation of the sample reaching 13.4% was also higher than that with LSP. The mechanical performance improvement was mainly due to the gradient twin layer, carbides’ precipitation and high-density dislocation.

Heat treatment free aluminum alloys have been developed for wire arc directed energy deposition (DED) large thin-walled components, but their further performance enhancement methods remain unexplored. In this study, laser shock peening (LSP) treatment was performed on wire arc DED Al-6Mg-0.3Sc components. The results show that LSP creates a gradient microstructure with submicro-grains near the surface. The effects of LSP on defects were quantified by quasi-in-situ CT, demonstrating a reduction in porosity by over 68% together with decreased size. Simultaneously, tensile strength increases by 39.5% to 295.8 ± 6.4 MPa with only a marginal loss of elongation, as compared to the as-deposited (AD) state. This was due to the accumulation of dislocations and continuous dynamic recrystallization lead to grain refinement, as well as the appearance of a triple heterogeneous microstructure. Therefore, this study offers a novel solution for manufacturing of high-performance heat treatment free large thin-walled components.

ABSTRACTThe objective of this work is to study the effects of different coating materials (black paint, thermoplastic elastomers, black vinyl tape and uncoated surfaces) in Laser Shock Peening (LSP) processing of laser powder bed fusion (L-PBF) printed thin AlSi10Mg tubes. The investigations were carried out with pre-identified optimal LSP parameters for the AlSi10Mg material. The study was performed using an analysis of surface residual stresses, where a maximum compressive stress of −85 MPa has been reached, while the depth of the compressive regime stays till 2 mm. The microstructural study reveals the multifold dislocation of the grains and formation of new sub-grains, thus changing the grain boundaries in all experiments due to lattice strain development by LSP. Microhardness has also shown alteration after LSP and accounted for a 5–15% increase in it after LSP. Surface properties, such as roughness and volumetric parameters, have also shown changes after LSP processing.

Additive manufacturing (AM) has shown advantages to fabricate complex components in an efficient way. However, it has some limitations related to imperfections on the as-built parts that may limit its mechanical behavior and performance. The aim of this paper is to investigate the effect of laser shock peening (LSP) as a post-processing technique of components produced by AM. Porosity, microstructure, residual stresses, and fatigue life of Inconel 718 samples manufactured by laser powder bed fusion (LPBF) and then treated by LSP have been evaluated. For the laser shock peening (LSP) treatment, a Nd:YAG pulsed laser operating at 10 Hz with 1064 nm of wavelength was used; pulse density was 2500 pulses/cm2. The LSP setup was the waterjet arrangement without protective coating. Residual stress distribution as a function of depth was determined by the hole-drilling method. Fatigue specimens were LSP treated on both sides and then cyclic loading was applied with R = 0.1. Residual stress profiles of as-built specimens showed tensile residual stresses while specimens with LSP exhibited compressive residual stresses. Fatigue life in specimens with stress relief heat treatment plus LSP showed an increase of 18–22% with respect to that of as-built specimens. Porosity levels were lower than 1% in the tested specimens, while surface microhardness increased due to LSP. It is shown that LSP is a viable alternative to improve the performance of IN718 components processed with AM. [ABSTRACT FROM AUTHOR]

The role of the initial residual stresses (IRS) induced by the milling on the efficacy of laser shock peening (LSP) was investigated numerically on IN718 specimens. Three milling conditions exhibiting high (3.5 μm), medium (1.1 μm), and low (0.6 μm) surface roughness were considered for LSP. Experimentally measured (from XRD) milling-induced sub-surface (up to 60 μm depth) residual stresses were introduced into the simulations of LSP as predefined fields. The role of spot diameter with the IRS on the LSP-induced residual stress was studied systematically. For most cases, the tensile IRS from milling caused a significant decrease in the magnitude of maximum compressive residual stresses induced by LSP. [ABSTRACT FROM AUTHOR]

The stainless-steel weld joints of dry storage canisters (DSC) used for storing spent nuclear fuel are highly susceptible to stress corrosion cracking (SCC). This is a serious safety concern in the nuclear industry as it releases nuclear radiation from interim storage locations. To mitigate this issue, the present study utilizes laser shock peening without protective coating (LSPwC) on austenitic stainless steel (ASS) weld joints. LSPwC is performed on the ASS weld joints with two intensities (7 and 9 GW/cm2) and two overlap ratios (30 and 50%). The results showed that LSPwC induced high magnitude and in-depth residual compressive stress (RCS), work-hardened layer, and plastic strain in the weld joints. The remarkable enhancement in SCC resistance of LSPwC'ed ASS weld joints can be attributed to grain refinement and RCS. The underlying mechanism of improved SCC resistance of the LSPwC'ed ASS weld joints was elucidated using x-ray diffraction (XRD) and scanning electron microscope. These findings demonstrate that LSPwC is a viable surface modification technique to mitigate the SCC in DSCs. [ABSTRACT FROM AUTHOR]

Laser cladding (LC) is a versatile additive manufacturing process where strands of metallic material are deposited and melted by a laser. However, there are some limitations associated with this process that may affect the performance of the final manufactured parts. In the present work, the influence of laser shock peening (LSP) on the fatigue life of 304 stainless steel flat specimens with a cobalt-based alloy (Stellite 6) coating applied by LC was investigated. The analysis was carried out both experimentally and numerically. In the LSP simulation, the ABAQUS/Explicit code was used to determine the residual stress distribution of specimens with double central notches with a radius of curvature of 5, 10, 15, and 20 mm. From the numerical results, an improvement was found regarding fatigue life up to 48% in samples with LSP. Experimentally, 14% in fatigue life enhancement was observed. The residual stress, determined by the contour method, showed good agreement with the LSP simulation. The SEM images revealed that the fatigue failure started at the Stellite 6 coating and propagated towards the center of the specimen. LSP has been shown to be a suitable postprocessing alternative for laser-cladded parts that will be subjected to fatigue loading since it led to fatigue improvement through the introduction of compressive residual stresses on clad coatings. [ABSTRACT FROM AUTHOR]

To select the optimal treatment mode of Ti64 alloy specimens with a stress concentrator, several laser shock peening (LSP) modes are studied. The effectiveness of the modes was determined by two criteria: indirect, based on the residual stress (RS) profile formed immediately after LSP (the depth of the layer with compressive RS and its maximum value), and direct, based on the number of cycles to failure during fatigue testing of Ti64 alloy flat specimens after hardening by LSP. The most effective LSP mode, which improves the fatigue properties of the specimens with the concentrator of the studied geometry, has been determined. To study the physical RS generation mechanisms, structural studies of the specimens after LSP have been carried out using the Electron Backscatter Diffraction (EBSD) method. The obtained data include the spread of the grain orientation, the average grain misorientation, and the change in the number of defects in the grains under different LSP modes. The results of the microstructure studies correlate with the profiles of the residual stresses caused by LSP. [ABSTRACT FROM AUTHOR]