Laser Shock Peening Research Articles

Laser surface treatment of Inconel 617 for next-generation nuclear reactors: A strengthening mechanisms study

With the recent acceptance of Inconel Alloy 617 (IN617) for use under the ASME boiler and pressure vessel nuclear code, there is significant interest in developing manufacturing methods that can further magnify its effectiveness in intense thermo-mechanical loading scenarios. In this work, one such method, known as laser peening, was utilized in tandem with thermal aging to determine the relationship between the dislocation-rich microstructure following laser peening and the precipitation behavior of the strengthening phases. Results show that surface hardness after laser peening alone increased to 226 HV over the as-cast value of 195 HV. Following an aging heat treatment, the microhardness of the entire specimen and the laser peened zone increased by an additional 20%. Microstructural investigations revealed no change in grain size or orientation, though the precipitation of carbides throughout the microstructure resulted in a more homogenous dispersion after aging. Transmission electron microscopy revealed a rich dispersion of nanoscale γ’ phases with an average area fraction of 12.5%, in addition to a high density of dislocations (3 × 1014 lines/m2) near the laser peened surface. The Jackson-Reed model of precipitate strengthening was used in tandem with the Taylor hardening relationship to determine the effects of γ’ strengthening and work hardening respectively. Both models were able to closely approximate the experimentally observed hardness data, leading to the conclusion that major surface strengthening effects result from (i) the precipitation of γ’, and (ii) work hardening effects, with minor strengthening effects coming from (iii) residual stresses, and (iv) carbide strengthening. The results outlined herein present a promising, proof-of-concept for the use of laser peening to introduce surface mechanical property enhancement for IN617, a prime candidate material for next-generation nuclear reactor applications.

Achieving isotropic microstructure in an additively manufactured Ti-6Al-4V alloy enabled by dual laser processing

With the development of science and technology and the popularization of intelligent manufacturing, laser additive manufacturing of titanium alloys is being attractive in industrial adoption due to its advantages of near-net shape and cost-saving features, and especially laser melting deposition is an effective additive manufacturing technique for large-scale and lightweight components such as TC4 alloy. However, inside the as-prepared alloy, large scale columnar crystals are formed along the forming direction, which will lead to anisotropic macroscopic properties of the alloy parts, further affecting their service life. In view of this, we report an innovative strategy of dual laser processing integrating laser melting deposition and laser shock peening, which can be used to achieve isotropic microstructure along three building directions in Ti-6Al-4V alloy. Interestingly, the isotropic microstructure is basket-weave structure of ultrafine α and nanometer β lamellar colonies together with abundant nanometer β fragments/particles distributed dispersedly inside ultrafine α matrix. Especially, the as-fabricated alloy exhibits approximately isotropy of mechanical properties along three building directions, and circumvents the strength–ductility trade-off of Ti-6Al-4V alloy with different microstructures reported so far. This study validates the feasibility of manufacturing high performance complex structural components by coupling technology of laser melting deposition and laser shock peening, for grain refinement and isotropic microstructure of additive manufactured titanium alloys in a low-cost and effective method. Impact statementThe proposed dual laser processing technology integrating additive manufacturing of laser melting deposition and synchronous laser shock peening, can provides insight into fabricating isotropic metal components with higher performance through additive manufacturing of one-step forming.

Optimization of microstructure and properties in U75V steel rail cladding layers manufactured by laser melting deposition and laser shock peening

Optimization of microstructure and properties in U75V steel rail cladding layers manufactured by laser melting deposition and laser shock peening

Surface stress monitoring of laser shock peening using AE time-scale texture image and multi-scale blueprint separable convolutional networks with attention mechanism

Surface stress monitoring of laser shock peening using AE time-scale texture image and multi-scale blueprint separable convolutional networks with attention mechanism

On the Degree of Plastic Strain during Laser Shock Peening of Ti-6Al-4V.

Laser shock peening (LSP) is an innovative technique that is used to enhance the fatigue strength of structural materials via the generation of significant residual stress. The present work was undertaken to evaluate the degree of plastic strain introduced during LSP and thus improve the fundamental understanding of the LSP process. To this end, electron backscatter diffraction (EBSD) and nano-hardness measurements were performed to examine the microstructural response of laser-shock-peened Ti-6Al-4V alloy. Only minor changes in both the shape of α grains/particles and hardness were found. Accordingly, it was concluded that the laser-shock-peened material only experienced a small plastic strain. This surprising result was attributed to a relatively high rate of strain hardening of Ti-6Al-4V during LSP.

High energy laser shock peening of Ti6Al4V alloy without any protective coating

Industrial laser shock peening (LSP) is gradually moving away from using protective overlay as it is tedious and time-consuming making the whole process inefficient for a production run. However, the peening of titanium alloys is still performed with the protective coating to protect the surface from thermal exposure to the laser. In this work, we study the effect of uncoated LSP (without protective coating) of Ti6Al4V alloy on its surface microstructure and mechanical performance. Our results show that uncoated LSP produces a thin oxide layer consisting of TiO2 and Al2O3 due to oxygen diffusion facilitated by the thermal effect of the laser. A brittle alpha layer around 5–8 µm thick is also generated on the surface. We find that similar compressive residual stress conditions as that in coated LSP can be generated beneath the surface by increasing peak power density in uncoated LSP. Despite this, the fatigue performance of the peened alloy does not improve, which is attributed to the presence of several microcracks in the alpha layer. On the other hand, the removal of the alpha layer by abrasive grinding is found to increase the fatigue life by almost 9 times compared to that from uncoated LSP. The findings indicate that the uncoated LSP of Ti6Al4V alloy must be combined with a post-cleaning step to reap the significant improvement in fatigue life.

The Finite Element Analysis on the Effects of Overlapping Rate in Low-Energy Laser Shock Peening

Laser shock peening has been widely studied and pioneeringly applied in aerospace industry as a life-extension technology for structured mechanical components. However, in other promising fields such as nuclear power industry, little has been studied concerning such critical issues as long-distance transmission of the laser beam by optical fiber and optimized parameters of typically low pulse energy with micrometer-sized beam spots. In such scenario, the overlapping rate between adjacent small spots plays a critical role in obtaining homogenous residual stress and surface morphology. In this study, a three-dimensional finite element model in AISI 420 martensitic stainless steel has been developed to correlate the residual stress as well as surface morphology with varying overlapping rates. Multiple laser spots are loaded with VDLOAD user subroutine in Abaqus. The residual stress distribution is analyzed with respects of laser shocking and in-depth planes. And the surface morphology is evaluated in terms of depression depth as well as surface roughness. Combined results suggest that the overlapping rate of 61% as an optimized value, which can be used as a basis for future experimental studies and industrial applications.

Investigating the applicability of the layered average eigenstrain method in laser shock peening

The eigenstrain model is widely used to predict residual stress and deformation resulting from laser shock peening (LSP). However, most existing eigenstrain models rely on the input of layered average eigenstrain (LAE), which has not been fully verified, particularly considering the non-uniform eigenstrain distribution in the workpiece. To address this issue, a modified eigenstrain model is proposed that uses periodic array eigenstrain (PAE) as input to verify the accuracy of the LAE method. First, a dynamic LSP model is developed to obtain the initial eigenstrain, which is then used in both the LAE and PAE models. The effects of overlapping rate and laser energy of LSP are analyzed by comparing the results of residual stress and displacement predictions. The results show that although the LAE model accurately predicts the displacement induced by LSP, it has errors in predicting residual stress. Although the LAE model has errors in predicting residual stress, its results can still be used to predict the stress intensity factor (SIF) of laser shock peening with some fluctuations. Therefore, we conclude that the LAE method is applicable under high overlapping conditions in LSP, while the proposed PAE-based eigenstrain model provides a more accurate approach for predicting residual stress and deformation during LSP. This has practical implications for the design and optimization of LSP processes.

Cavitation Erosion Prevention Using Laser Shock Peening: Development of a Predictive Evaluation System.

Marine flow-passing components are susceptible to cavitation erosion (CE), and researchers have worked to find ways to reduce its effects. Laser Shock Peening (LSP), a material strengthening method, has been widely used in aerospace and other cutting-edge fields. In recent years, LSP has been used in cavitation resistance research. However, the current LSP research does not realize a comprehensive predictive assessment of the material's CE resistance. This paper uses m stresses to develop a comprehensive set of strengthening effect prediction models from LSP to CE using finite element analysis (FEA). Results show that the LSP-1 sample (4 mm spot, 10 J energy) introduced a compressive residual stress value of 37.4 MPa, better than that of 16.6 MPa with the LSP-2 sample (6 mm spot, 10 J energy), which is generally consistent with the experimental findings; the model predicts a 16.35% improvement in the resistance of LSP-1 sample to water jet damage, which is comparable to the experimental result of 14.02%; additionally, interactions between micro-jets do not predominate the cavitation erosion process and the final CE effect of the material is mainly due to the accumulation of jet-material interaction.

Ti6Al4V Bone Implants: Effect of Laser Shock Peening on Physical, Mechanical, and Biological Properties

Ti6Al4V Bone Implants: Effect of Laser Shock Peening on Physical, Mechanical, and Biological Properties

Plastic deformations of 42CrMo4 under LSPwC and subsequent cyclic stresses

42CrMo4 steel used as connecting rods is generally encountered with fatigue damage during service. Enhancing its fatigue behavior is therefore required to ensure the structural safety. In this work, the high cycle fatigue performances of 42CrMo4 steel subjected to laser shock peening without coating (LSPwC) are studied, and its plastic deformation mechanisms are revealed during the LSPwC processes and fatigue tests. The results show that 50.62% increase in fatigue lives of 42CrMo4 steel are achieved after 5 LSPwC cycles. The LSPwC triggers a hierarchical gradient structure, including a top-most thermal layer of ∼100 μm, an intermediate severe plastic deformation (SPD) layer of ∼200 μm and an inner substrate. They are formed as a result of competitive effects between the mechanical strain and thermal circulations at different depth. Under these incentives, some transformations occur at carbides and martensitic lath. The original cementite clusters are mechanical split into short-rod counterparts in the SPD layers, while turning into long-lamellar ones in the thermal layer. Compared with others, the long-lamellar cementite has stronger competence to establish intricate dislocation configurations to refine the martensitic lath, due to larger accommodation to collect mobile dislocation. However, thermal circulation raises the range of lath width. During cyclic deformation, LSPwC-induced compressive residual stress mitigates lath coarsening at SPD and thermal layers. As cycle proceeds, plastic deformation energy focuses on the broad decompositions of carbide debris predominantly, which further leads to a turbulence of lath boundaries (LBs) and subsequent LB network collapse. Instead, it contributes to defect initiations associated with carbide cluster and causes premature failure of substrate. Therefore, the fatigue properties 42CrMo4 steel are greatly ameliorated. Finally, the strength contributions of the gradient materials are estimated by applying a modified gradient strengthening strategy coupled with Williamson-Hall approach, proving that dislocation devotes most to the enhanced mechanical performance and SPD layer possesses higher strengthening contribution as compared to thermal layer.

Influence of laser hardening modes on the properties of 40X13 steel

We have studied the dependence of the characteristics, strength and plasticity, as well as the microhardness of specimens made of corrosion-resistant steel 40X13 on the modes of laser surface hardening by a fiber laser. Depending on the size of the scanning spot and the scanning speed, 3–5 tracks were applied on opposite planes of the sample with overall dimensions of 20 × 200 mm. Samples were tested for static fracture and the microhardness of the material of the samples was studied in terms of the depth of the changed structure. It was found that the fracture of the treated samples in all cases was of a brittle nature with a low level of destructive deformations at stresses below the tensile strength of the original material. The plotted tension diagrams indicate an insignificant effect of laser processing on the value of the elastic modulus of the material. Studies of the hardness of the material of the laser-hardened track and the microhardness of the material along the depth of the zone of the changed structure showed their increase up to 3–4 times compared with the initial characteristics. The results obtained can serve as a basis for studying the relationship between the modes of heating by a laser beam and the properties of the material of the hardened zone.

Assessment of residual strain in laser shock peened additive manufactured Inconel 718 using synchrotron X-ray diffraction

The through-thickness residual strain profile due to laser shock peening (LSP) of an additively-manufactured IN718 sample is shown for the first time. The results provide tantalising insight into the potential of fatigue life extension of additive-manufactured samples using LSP. Residual strains were measured in as-manufactured and peened samples using state-of-the-art synchrotron radiation. Significant beneficial compressive in-plane residual strains, extending to 1.0 mm depth, were observed due to the peening process. No phase changes were observed due to LSP. A periodic strain variation was observed arising from the layer-by-layer manufacturing strategy of the samples. The peened sample showed no increase in diffraction peak width in the near-surface regions. This is contrary to reported studies using wrought laser shock peened alloys and suggests less grain disruption in additively-manufactured peened samples. The results are timely given a current drive to adopt additive-manufacturing for a step-change in efficiency of aero-engine component production.

Reliability prediction of high‐cycle fatigue behavior of parts treated by laser shock peening

AbstractThe purpose of this paper is to develop a global approach to predict the reliability of the high‐cycle fatigue behavior of mechanical components treated by laser shock peening (LSP). Most works that exist in the literature have introduced experimental and numerical studies. The originality of our investigation is to predict and validate the reliability of high‐cycle fatigue of the workpieces treated by LSP treatment by using the modified Crossland criterion. Based on previous works made by our team that shows the finite element simulation of the LSP process, this approach will be based on the integration of probabilistic fatigue criteria adapted to the superficially treated parts using ABAQUS software. After the validation of this approach, it will allow design engineers to optimize the operating conditions of the LSP process.

Tailoring precipitation of directed energy deposited Al-Cu alloy via laser shock peening

Wire-arc directed energy deposition (DED) has become a promising method to fabricate large-sized metallic components. The mechanical properties of the directed energy deposited Al-Cu alloy usually can be improved by fine precipitates formed during subsequent heat treatment. In this study, a novel hybrid post-treatment method (HPTM) with laser shock peening (LSP) introduced between heat treatment was proposed. The results indicate that the yield and tensile strength of Al-Cu alloy treated by the HPTM were 38% and 13%, respectively, higher than those of the T6 counterparts. Based on the atomic scale characterization of spherical aberration transmission electron microscopy, the influencing mechanism of LSP on the precipitation process was investigated. The quantification of various strengthening mechanisms shows that the improvement of precipitation strengthening is the main reason for the excellent strength. This HPTM route provides a promising way for the post-treatment of complex additively manufactured precipitation strengthening alloy components.

A study on the effects of laser shock peening on the microstructure and substructure of Ti–6Al–4V manufactured by Selective Laser Melting

A study on the effects of laser shock peening on the microstructure and substructure of Ti–6Al–4V manufactured by Selective Laser Melting

Effect of Laser Hardening and Gas Nitriding on Wear Resistance of Steel P20: A Comparative Study

Effect of Laser Hardening and Gas Nitriding on Wear Resistance of Steel P20: A Comparative Study

Разработка конструкции индуктора для закалки детали сложной формы

Due to active process of import substitution, domestic industry starts producing the parts previously purchased abroad. These parts are necessary for stable and reliable operation of various technical objects and systems. Thus, the development of a technological installation for hardening a metal profile is topical. The task is complicated by the fact that the profile has very thin irregularly shaped walls, which should be hardened only from the inside, while the outer wall of the profile should be heated minimally to maintain strength. The studies have been carried out on simulation models of electromagnetic and thermal fields, which make it possible to reproduce the process of induction heating of the research object. Since the part has the same shape along the entire length, the simulation of the process of its induction heating is performed in two-dimensional space. The authors have developed a simulation model of the process of induction heating of a part of a non-standard shape, which includes calculations of thermal and electromagnetic fields. The design of the inductor is proposed, supplemented with ferrite inserts, which makes it possible to achieve the temperature regime necessary for the hardening process. The developed simulation model makes it possible to evaluate the distribution of the thermal and electromagnetic fields of the part, thereby predicting getting the temperatures required for its hardening when using various designs of inductors. The results of numerical experiments are consistent with the physical concepts of induction heating and prove the possibility to use induction hardening for thin-walled parts of complex shape instead of laser hardening used for this type of parts. The proposed model can be used in engineering practice to design inductors of non-standard parts.

Influence of pulse energy on surface integrity of AZ31 magnesium alloy processed by femtosecond laser shock peening

Compared with traditional laser shock peening by nanosecond pulse laser, femtosecond laser shock peening (FLSP) exhibits superior flexibility and efficiency since it can be carried out directly in air without any ablative or confinement layers. In this work, FLSP was successfully performed on AZ31 magnesium alloy sheet. The influence of pulse energy on surface morphology and roughness, microstructure, surface residual stress and hardness was investigated in details. The results show that varying the laser pulse energy could effectively improve the surface integrity of the material. Regular dents are produced at the material surface with relatively low pulse energies, and the regular dent morphology disappears gradually with increasing pulse energy, suggesting an increased surface roughness. Surface microhardness and residual compressive stress are increased significantly after FLSP. The surface microhardness increases from the untreated 58.13 HV to the maximum value of about 69.58 HV at 37 μJ, by an increase of 19.7%. At 73 μJ, the residual compressive stress rises to a maximum value of approximately 59.6 MPa from an untreated 16.3 MPa. Moreover, the nano-hardness near the surface at the cross section is 1.68 GPa at 37 μJ, with an increase of 46% compared to the untreated 1.14 GPa. Particularly, twins and grain refinement layers are observed near the surface after FLSP, also indicated by the XRD analysis. The plastic deformation and grain refinement with low pulse energies contribute to the surface strengthening while the thermal effect and surface oxidation with increasing pulse energy may inhibit the enhancement of surface integrity.

Fatigue crack initiation and growth of laser shock peened 2Cr13 martensitic stainless steel as a function of the coverage layer

Fatigue properties and plastic deformation-induced gradient nanostructures of 2Cr13 martensitic stainless steel subjected to laser shock peening (LSP) were investigated. Combining the residual stresses and microstructural evolution of 2Cr13 martensitic stainless steel before and after three-point bending fatigue test, the influences of LSP on fatigue crack initiation and growth are systematically analyzed. Results showed that massive LSP treatments with one and two coverage layers caused obvious improvements of 13% and 37.6% in the fatigue crack initiation life, 19.3% and 34.9% in the fatigue lives of 2Cr13 stainless steel, respectively. Typical in-depth microstructures for two kinds of LSP-treated specimens were described by transmission electron microscopy characterization. Results showed that dynamic recrystallization (DRX) process at room temperature may be activated and accelerated by LSP-induced atom collision, and then a nucleation equation by ultrahigh-strain-rate plastic deformation was developed, which depended strongly on LSP-induced ultrahigh strain rate. Moreover, the basic improvement mechanism of LSP on fatigue properties was analyzed in detail.