Laser Shock Peening Research Articles

Multiscale simulation combined with experimental investigation on residual stress and microstructure of TC6 titanium alloy treated by laser shock peening

The evolution behavior of residual stress and microstructure of TC6 titanium alloy under laser shock peening (LSP) were investigated using finite element (FE) and molecular dynamics (MD) simulations combined with experiments. The propagation process of laser-induced stress wave and plastic deformation behavior of TC6 titanium alloy model were studied using FE software with ABAQUS. The FE simulation results showed that increasing laser energy and impact time could increase the amplitude of compressive residual stress (CRS) to a certain extent, while a higher overlapping rate improved the CRS uniformity. The experimental results of residual stress testing based on XRD technology were consistent with the FE simulation results. Based on the piston shock method, the microstructural evolution process of α phase of titanium alloy under different shock velocities was simulated using MD software with LAMMPS. Laser shock wave promoted the transformation of hexagonal close-packed (HCP) structure to body-centered cubic (BCC) and face-centered cubic (FCC) structures in titanium alloy, and the generated dislocation density increased with increasing shock velocity. The severe plastic deformation caused by laser shock wave induced the formation of mechanical twin, subgrain and stacking fault, which was consistent with the (transmission electron microscope) TEM characterization results.

Influence of double-side symmetric oblique laser shock peening on shape deviation, surface integrity, and fatigue properties of the blades in small-sized blisk

Double-sided symmetric oblique laser shock peening (DSOLSP) was adopted to experiment on a small-sized blisk with restricted space. The influences of different laser energies on the shape deviation, surface roughness, microhardness, and residual stress of the blades were studied. The optimum process parameters were selected based on the shape deviation results of the blades and the microstructural evolution of the surface layers was investigated. The strengthening effect of DSOLSP treatment on notched blades was evaluated by vibration fatigue tests. It was found that DSOLSP can effectively cover the fatigue vulnerable regions without interference. Two-way bending deformation was formed after DSOLSP, and the shape deviation of the blades could be controlled within ±0.02 mm. With the increase of laser energy, the surface roughness and the depth of work-hardened layer increased. The full-thickness compressive residual stress (CRS) field was induced. A gradient microstructure was generated on the surface of the blade, and the size of average nanograins on the topmost surface is approximately 36.5 nm. The fatigue strength of the DSOLSP treated blades with notches was increased by 25.9 %. The enhancement can be attributed to the synergistic strengthening of CRS and gradient microstructure.

Effect of laser shock peening on tribological properties of WC-Ni under seawater conditions: Anomalous behavior and solutions

This research investigated the effect of laser shock peening (LSP) on the tribological properties of WC-Ni under seawater lubrication. The experimental findings revealed an anomalous behavior, contrary to the existing literature, indicating that the LSP treatment actually deteriorated the tribological properties of WC-Ni. The mechanism and solutions for anomalous behavior were also examined, and the results indicated that the enhancement of material properties through LSP treatment cannot counterbalance the detrimental effects of increased surface roughness. For improved processes, the sample treated with LSP + Polish exhibits the highest residual compressive stress and the lowest surface roughness, thereby yielding the best comprehensive performance. Therefore, the experimental results demonstrate that LSP + Polish treatment can improve material performance and hydrodynamic effect, leading to reductions in friction and wear.

Effect of multiple laser peening on the wear resistance of 304 stainless steel

PurposeThe purpose of this paper is to investigate the effect of laser peening (LP) on mechanical and wear properties of 304 stainless steel sheet.Design/methodology/approachThree-dimensional morphology, micro-hardness and micro-structure of shocked samples were tested. The wear amount, wear track morphology and wear mechanism were also characterized under dry sliding wear using Al2O3 ceramics ball.FindingsThe LP treatment generates deformation twins that contribute to the grain refinement and hardness increase. The wear test displays that the wear mechanism of samples is mainly abrasive wear and oxidation wear at 10 N load. While at 30 N, the delamination and adhesion areas of treated sample are reduced visibly compared to untreated ones.Originality/valueThis study specifically investigates the mechanical and wear properties of 304 stainless steel after the direct action of LP on its surface, which shows an effective improvement on the wear resistance. For example, the wear loss of processed sample is reduced by 19% at 30 N, the friction coefficient decreases from 0.4714 to 0.4308 and the groove depth is reduced from 78.1 to 74.4 µm under same condition.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2024-0007/

Forming of monoaxially curved thin-walled T-section integral panels by double-sided laser peening

Thin-walled T-section integral panels are widely used in the aerospace industry for achieving lightweight and high performance, but their strict manufacturing requirements present challenges to current forming processes. This study proposes the double-sided laser peening (DSLP) process and develops corresponding models to achieve the forming of monoaxially curved T-section integral panels. An eigen-force model is derived to describe deformation behavior and reveal the underlying forming mechanism. The results indicate that bending deformation is driven by the moment originally induced by the in-plane eigen-force deviating from the neutral plane. Full-covered DSLP on the skin results in bending deformation towards the stiffeners, and vice versa. Additionally, DSLP on complementary regions induces identical bending deformations in opposite directions. The undesired bending distortion appeared in single-sided laser peening is eliminated by DSLP, as the action point of the eigen-force migrates to the neutral plane of the skin or stiffeners after DSLP, thereby preventing the generation of bending moments. Subsequently, drawing inspirations from topology optimization methods, a customized process planning model is developed for DSLP of monoaxially curved T-section panels. The globally convergent method of moving asymptotes is applied to solve the process planning model. The formed T-section panels, guided by the solution of the process planning model, exhibit good consistency with the objective shape. By unleashing the potential of double-sided laser peening in driving bending, this study provides a novel strategy for forming large-scale complex panels with stiffeners.

In-vitro fretting tribocorrosion and biocompatibility aspects of laser shock peened Ti-6Al-4V surfaces

Laser shock peening without coating (LSPwC), a prospective surface modification technique for improving the mechanical aspects of Ti-6Al-4V alloy for automotive/aerospace sector, is also expected to dictate the efficiency of this material class for implant application. Here we unravel the impact of LSPwC on Ti-6Al-4V material surface characteristics, in-vitro tribocorrosion and biocompatibility. Micrography shows the presence of nano and sub-micron sized pores after LSPwC process. The role of nano and sub-micron sized pores along with topography modification induced by LSPwC to serve as cues for controlling gene expressions, cell adhesion and activities offer novel insights in this research direction. A detailed X-ray photoelectron spectroscopy analysis detected local chemical non-stoichiometry with reduced number of oxygen diffusion channels. A crucial outcome of this oxide layer modification is the negative skewness (−0.55 ± 0.11) and reduced kurtosis (3.49 ± 0.14) of the surface, along with localized plastic deformation. These factors are correlated with the shift in potential during fretting tribo-corrosion from −800 to −250 mV after LSPwC, accompanied by a lower coefficient of friction of 0.4. Furthermore, the presence of well-spread cells and the up-regulation of beneficial genetic markers (Ki67) on LSPwC surfaces have the potential to form a better bone-material interface. The findings open new frontiers of the LSPwC-treated Ti-6Al-4V surface to synergistically modulate the tribocorrosion and biocompatibility aspects, with exciting possibilities for biomedical implants.

Insights into room- and elevated-temperature micro-mechanisms of laser shock peened M50 steel with superior tribological performance

M50 steel, commonly utilized in aircraft engine bearings, is susceptible to friction-induced failures, particularly in high-temperature service conditions. To address this issue, various strategies have been proposed, with laser shock peening (LSP) garnering significant attention due to its deeper residual stress penetration and excellent surface integrity, whereas the underlying strengthening mechanisms have not yet been fully elucidated. In this study, we systematically investigate the impact of LSP treatment on the tribological properties of M50 steel at temperatures of 25 and 300 °C, alongside elucidating the relevant micro-mechanisms. Microstructural analysis reveals that laser impact strengthening primarily arises from dislocation proliferation, resulting in a surface hardness increase of approximately 14 % and the formation of a substantial compressive stress layer reaching a maximum value of about 1200 MPa, with a depth of around 2 mm. Friction test results demonstrate reduced coefficients of friction and wear rates following LSP treatment at both temperatures. Notably, a more pronounced reduction is observed at 300 °C, with values decreasing by 41.4 % and 55.8 %, respectively. The enhanced performance is attributed to the synergistic interplay of compressive residual stresses, work-hardening layers, increased density of dislocations, and substantial microstructure refinement.

Microstructure, microhardness, tensile and fatigue investigation on laser shock peened Ti6Al4V manufactured by high layer thickness directed energy deposition additive manufacturing

Thin layer thickness in additive manufacturing (AM) has always been a hindering factor leading to long completion times. Increasing layer thickness is accompanied by a higher tendency of surface cracks and inferior mechanical properties. These can be improved with laser shock peening (LSP). Emphasizing on the high layer thickness, this paper elucidates the high-layer thickness laser directed energy deposition (LDED) AM and the effects of LSP on the fabricated parts. Primary focus was given to the investigation of surface microcracks, microstructures, tensile and fatigue properties. Ti6Al4V bulk sample was prepared using the LDED process. Tensile, fatigue, and other samples were extracted to investigate the above-mentioned properties using different characterization tools such as optical microscope, scanning electron microscope, Vickers microhardness tester, and universal testing machine. Results showed proper depositions without major defects despite the high-layer thickness. Micro-cracks were limited to the surface only, and typical Widmanstätten patterns with parallel α lath and mixed α+β microstructures are observed. Yield strength (YS) varied from 730 MPa to 940 MPa, while ultimate tensile strength (UTS) ranged from 799.5 MPa to 953.75 MPa. Even though laser peening significantly improved micro-hardness by 49.81 % on average, not all fatigue samples observed enhanced fatigue life. A maximum improvement of 40.34 % in fatigue performance was observed in the LDED+LSPed samples. The strain hardening, plastic deformation, and grain refinement during the LSP process contributed to the enhanced mechanical properties. Some samples’ reduced fatigue life may be due to the anisotropic nature of additively manufactured parts, internal defects, and surface cracks on the specific samples. Considering high layer thickness, vertical orientation of samples, and as-prepared samples, our research shows a promising high layer thickness additive manufacturing process. The current research can be used as a base for further study on other properties and characteristics.

Design and implementation of dynamic beam shaping in high power laser processing by means of a Deformable Mirror

Optimising the laser intensity distribution in high power laser processes, such as laser welding, laser cladding or laser hardening, can be used to tailor the local thermal fields and thermal cycles which, in turn, determine the final process results. Deformable Mirrors allow to dynamically shape the beam profile and previous studies showed their potential. However, only limited flexibility in achievable beam shapes is shown at higher power levels. In addition the relation between desired laser intensity profiles and required mirror surface profiles is nontrivial. In this work the design and implementation of a dynamic beam shaping system, capable of handling high laser powers (up to 1 kW), is presented and evaluated. To that end, several distinctly different laser intensity profiles are defined, corresponding mirror surfaces are determined and realised with the beam shaping system. Measurements of the laser intensity profiles were compared with laser intensity profiles simulated using a previously presented mathematical framework and showed a good agreement. From the measurements it was concluded that the setup is suitable for high laser powers (up to 1 kW) and is characterised by large depth of focus (<14% change in dimensions at a distance of 100 mm from the focal plane).

Improvement of fatigue life of Ti-6Al-4V alloy treated by double-sided symmetric oblique laser shock peening

To improve the anti-foreign object damage (FOD) ability of Ti-6Al-4V alloy blisk blades, a blade simulation specimen was designed and subjected to double-sided symmetrical oblique laser shock peening (DSOLSP) treatment. Surface roughness, residual stress distribution, and microstructural evolution of simulated specimens of Ti-6Al-4V alloy without and with DSOLSP were investigated, and the strengthening effect was evaluated by flexural fatigue test. The results showed that after DSOLSP treatment, surface roughness of simulated specimens was reduced from Ra0.97 µm to Ra0.6 µm. DSOLSP treatment generated a compressive residual stress (CRS) field along the entire thickness direction of the simulated specimen. Nanostructures with a depth of ∼500 nm was observed at topmost surface layer, and the average size of the nanograins was about 35.2 nm. Compared with the base material, the flexural average fatigue life of the simulated specimen was increased by 8.45 times. Moreover, mathematical statistical analysis confirms that DSOLSP has a significant effect on the fatigue life of simulated samples. The development of CRS fields throughout the entire thickness direction, the grain refinement on the surface, and the reduction of surface roughness are primarily responsible for the enhancement of the flexural fatigue life of the DSOLSP simulated specimen.

Measurement of laser shock peening induced residual stress by nanoindentation and comparison with XRD technique

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.

Improving mechanical properties of additively manufactured H13 steel through residual stress modulation by laser shock peening

Improving mechanical properties of additively manufactured H13 steel through residual stress modulation by laser shock peening

Improving the Abrasion Resistance of Nodular Cast Iron Castings by Remelting Their Surfaces by Laser Beam.

This paper presents the results of research conducted in the field of the technology of surface hardening of castings from unalloyed and low-alloy nodular cast iron using the laser remelting method. The range of studies included macro- and microhardness measurements using Rockwell and Vickers methods as well as metallographic microscopic examinations using a scanning electron microscope. Moreover, abrasive wear resistance tests were performed using the pin-on-disk method in the friction pair of nodular cast iron-SiC abrasive paper and the reciprocating method in the friction pair of nodular cast iron-unalloyed steel. Analysis of the test results shows that the casting surface layer remelting by laser for unalloyed nodular cast iron results in a greater improvement in its resistance to abrasive wear in the metal-mineral system, as compared to low-alloy cast iron. Additionally, carrying out the laser hardening treatment of the surface layer made of the tested grades of nodular cast iron is justified only if the tribological system of the cooperating working parts and allowable dimensional changes during their operation are known.

Effect of combined laser shock peening and nitrogen implantation on the microstructure and tribology of M50 bearing steel

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.

Study on crystal to amorphous transition of nickel-based alloy processed by ultra-short pulsed laser shock peening

The main purpose was to investigate the process of crystal to amorphous transition in nickel-based alloy subjected to ultra-short pulsed laser shock peening. A molecular dynamics model of laser shock peened nanopolycrystalline nickel-based alloy was established using LAMMPS. The influence of shock velocity on the amorphous transformation in nickel-based alloy was analyzed. The results indicated that ultra-short pulsed laser shock peening with ultra-high strain rate plastic deformation promoted the increase and accumulation of defect for nickel-based alloy, contributing to the formation of amorphous structures.

Real-time monitoring system for 100 mJ laser shock peening

A real-time monitoring system for laser shock peening(LSP) has been developed to measure temporal shape, spatial distribution, irradiated laser energy, and reflected plasma signal from a target. A laser peening head has also been designed and fabricated to enable this real-time monitoring. In this study, the correlation between the monitored data in our system and the peening specimens were analyzed.

Tailoring properties of directed energy deposited Al-Mg alloy by balancing laser shock peening and heat treatment

Wire arc-directed energy deposition (WADED) has shown great advantages and potential in fabricating large-scale aluminum (Al) alloy components. However, WADED Al alloys typically exhibit low strength and reliability due to pore defects and lack of work hardening or precipitation strengthening. This study utilized a combination of laser shock peening (LSP) and annealing to regulate the microstructure of WADED Al-Mg4.5Mn alloy and enhance mechanical properties. The effects of LSP and annealing on phase composition, pore distribution, and microstructures at multiple scales were systematically investigated to reveal the mechanical property improving mechanism. The results demonstrated that LSP-induced plastic deformation formed a defect-free zone by closing near-surface pore defects. LSP created the hardened layer with gradient mechanical properties by inducing gradient changes in grain size, the number of low-angle grain boundaries (LAGBs), and dislocation density along the depth direction. The annealing process promoted grain coarsening and reduced excessive dislocations and LAGBs, weakening the work hardening effect caused by LSP. Furthermore, the high-density dislocations and high stored energy generated by LSP accelerated the recrystallization, facilitating growth of near-surface grains. The defect-free zone, dislocation strengthening, and LAGBs strengthening were responsible for the increase in strength, while the synergistic deformation between hardened layers and soft core facilitated maintaining excellent elongation. The strength and elongation of WADED Al alloy can be synergistically improved by balancing the effects of LSP and heat treatment.

The effects of submerged laser peening, cavitation peening, and shot peening on the improvement of the torsional fatigue strength of powder bed fused Ti6Al4V produced through laser sintering

This study demonstrates the improvement in the fatigue strength of additive manufacturing (AM) metals such as laser-based powder bed fusion of metals by post-processing. Titanium alloy samples manufactured by powder bed fused (PBF) Ti6Al4V produced through laser sintering (LS), treated by submerged laser peening (SLP), cavitation peening (CP), and shot peening accelerated via a water jet (SPwj), were subjected to torsional fatigue testing and compared with the as-built specimen. At SLP, the samples were treated by laser ablation (LA) and laser cavitation (LC) which was developed following LA. A cavitating jet was used for CP. For comparison, conventional post-processing using SPwj was also performed. To characterize the microstructural modification caused by the three post-processing methods, the cross-section of the treated surface was observed by electron backscatter diffraction. The fatigue strengths at 107 cycles were found to be 217, 361, 313, and 285 MPa for the as-built, SLP, CP, and SPwj specimens, respectively. The primary factors contributing to fatigue strength improvement by post-processing were surface smoothing and the introduction of compressive residual stress. The experimental observations were used to derive correlation formulas to estimate the fatigue life improvement due to post-processing as the function of the surface roughness and surface residual stress.

Effects of sacrificial coating material in laser shock peening of L-PBF printed AlSi10Mg

ABSTRACT The 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.

Effect of Combined Laser Thermal and Shock Wave Effects on the Mechanical and Tribological Properties of Steels.

Herein, we present the results of an experimental study on the mechanical properties of Fe-C alloys with different carbon contents (0.2, 0.45, and 0.8%) in a wide range of deformation rates (10-3-103 s-1) and abrasive wear resistance, which underwent combined laser thermal (laser surface hardening-LSH) and laser shock wave (Laser Shock Peening-LSP) processing. The combined treatment modes included a different sequence of exposure to laser thermal and laser-induced shock pulses on the material. The amplitude and duration of laser-induced shock waves were measured using a laser Michelson interferometer. The mechanical properties of steel samples were studied under conditions of uniaxial tension under static loads on a standard universal testing machine, the LR5KPlus, and under dynamic loading, tests were carried out on a specialized experimental complex according to the H. Kolsky method using a split Hopkinson rod. The abrasive wear resistance of hardened surfaces was studied using the Brinell-Haworth method. Studies have shown that the use of a combination of LSH and LSP treatments leads to an increase in both the mechanical properties of steels and abrasive wear resistance compared to traditional laser hardening. It has been established that in the combinations considered, the most effective is laser treatment, in which LSP treatment is applied twice: before and after LSH. Thus, after processing steels using this mode, an increase in the depth of the hardened layer was recorded-by 1.53 times for steel 20, by 1.41 times for steel 45, and by 1.29 times for steel U8-as well as a maximum increase in microhardness values by 22% for steel 20, by 27% for steel 45, and by 13% for U8 steel. The use of this mode made it possible to obtain the maximum strength properties of the studied materials under static and dynamic loading, which is associated with an increase in the volume fraction of the strengthened metal and high microhardness values of the strengthened layer of traditional LSH. The dependences of abrasive wear of the studied steels after various combinations of LSP and LSH impacts were established. It is shown that the greatest wear resistance of the studied steels is observed in the case when the LSH pulse is located between two LSP pulses. In this case, abrasive wear resistance increases by 1.5-2 times compared to traditional LSH.