Laser Shock Peening Research Articles

Laser shock-induced gradient twinning microstructure in AZ31B alloy

Magnesium alloys are highly promising in biodegradable materials for medical applications. However, their applications are limited by weaknesses in mechanical strength and corrosion resistance. In recent years, advancements in a novel laser method, Laser Shock Peening (LSP), have been explored. Researchers suggest that LSP can induce surface compressive stresses and induce changes in residual stress and grain size gradients, thereby enhancing the material's fatigue resistance, corrosion resistance, and resistance to stress corrosion cracking. However, there is ongoing debate about whether LSP treatment can, in effect, create a gradient microstructure. In this study, we focused on the AZ31B alloy, notable for its dense hexagonal close-packed (HCP) crystal structure. This material is particularly interesting because, due to its low stacking fault energy, it is more prone to twinning deformation than to dislocation slip when it undergoes plastic deformation. To analyze the changes wrought by LSP, we employed optical microscopy (OM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) for examining the microstructures both before and after LSP treatment. Our findings revealed that LSP treatment refined the grain size, leading to a gradient distribution. In addition, we observed a direct correlation between the volume fraction of twinning and grain size. In contrast, the geometrically necessary dislocation (GND) density exhibited an inverse relationship. By measuring hardness and residual stress in the region affected by LSP, we determined that LSP could introduce a layer of plastic deformation up to a depth of 800–1000 μm. We also established a link between the gradient microstructure and hardness and provided a thorough discussion on the types of twinning and the mechanisms behind the induction of gradient microstructure on the surface.

Microstructure and high-temperature tribological properties of Ti–6Al–4V alloy treated by laser shock peening

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.

Effect of pulsed femtosecond laser shock peening surface modification on anti-wear failure properties of AISI 9310 gear steel

The wear resistance of gear components significantly influences operational reliability and lifespan of mechanical equipment. Compared with nanosecond time scale laser surface treatment, femtosecond laser shock peening (FLSP) has the advantage of no absorption layer and constraint layer in processing complex geometric structure parts. However, attempts at FLSP for gear materials are quite limited up to now. This paper introduces a methodology employing Pulsed FLSP to enhance the wear resistance of AISI 9310 gear steel. The research delves into the effects of FLSP on the surface morphology, mechanical characteristics, and wear performance of AISI 9310 steel under varying laser energy levels (50 μJ, 100 μJ, 150 μJ, 200 μJ) and pulse spacings (10 μm, 15 μm, 30 μm). The findings reveal that femtosecond laser surface treatment significantly augmented surface microhardness by 9.4 % to 17.4 % and induced a surge in surface residual compressive stress (RCS) by 30.5 % to 103.1 %. Moreover, it introduced a work hardening layer of 150–300 μm in depth direction, resulting in a wear rate reduction ranging from 10.1 % to 61.7 %. The sample treated with 15 μm pulse spacing and 150 μJ laser energy exhibited simultaneously the lowest wear rate and a minimum average coefficient of friction (COF) on 0.47. The advancement in wear resistance is attributed to the synergistic effects of markedly increased surface hardness, gradient hardness in depth direction, and reduced grain size induced by FLSP. A multiple linear regression (MLR) model indicates that deeper work hardening layers are most significant for improving wear resistance, which reduces risk of wear failure.

The effect of abrasive water jet peening and laser shock peening on the wear properties of direct metal laser sintered AlSi10Mg alloy

The present study explored the impact of laser shock peening (LSP) and abrasive water jet peening (WJP) on the physical, surface and wear properties of direct metal laser sintered (DMLS) AlSi10Mg alloy. The microstructure, phase composition, hardness, roughness, work of adhesion, residual stresses and wear properties of As-built AlSi10Mg, laser shock peened AlSi10Mg and water jet peened AlSi10Mg were evaluated. The results showed that both WJP and LSP could improve the hardness and wear resistance of DMLS AlSi10Mg alloy. Amongst, LSP was more effective than WJP in reducing the wear rate and coefficient of friction due to refined microstructure. Wear mechanisms were transformed from abrasive to fatigue after the LSP. Furthermore, the influences of roughness, residual stresses and hardness on the wear properties were discussed in detail.

Laser Shock Peening: Fundamentals and Mechanisms of Metallic Material Wear Resistance Improvement.

With the rapid development of the advanced manufacturing industry, equipment requirements are becoming increasingly stringent. Since metallic materials often present failure problems resulting from wear due to extreme service conditions, researchers have developed various methods to improve their properties. Laser shock peening (LSP) is a highly efficacious mechanical surface modification technique utilized to enhance the microstructure of the near-surface layer of metallic materials, which improves mechanical properties such as wear resistance and solves failure problems. In this work, we summarize the fundamental principles of LSP and laser-induced plasma shock waves, along with the development of this technique. In addition, exemplary cases of LSP treatment used for wear resistance improvement in metallic materials of various nature, including conventional metallic materials, laser additively manufactured parts, and laser cladding coatings, are outlined in detail. We further discuss the mechanism by which the microhardness enhancement, grain refinement, and beneficial residual stress are imparted to metallic materials by using LSP treatment, resulting in a significant improvement in wear resistance. This work serves as an important reference for researchers to further explore the fundamentals and the metallic material wear resistance enhancement mechanism of LSP.

Efficacy of Laser Shock Peening Post-milling: A Semi-numerical Study

Efficacy of Laser Shock Peening Post-milling: A Semi-numerical Study

Research on FSW Welds of Al-Alloy Modified by Laser Shock Peening Process

Research on FSW Welds of Al-Alloy Modified by Laser Shock Peening Process

High-temperature dry sliding friction and wear behavior of Ni60A coating on the 20CrNiMo alloy surface treated by laser shock peening and its bonding zone

To address the cracking issues that often occur between laser cladding coatings and substrates on brake disc surfaces, methods including microhardness testing, scanning electron microscopy (SEM), and X-ray stress testing were employed. These techniques were used to study the high-temperature dry sliding friction and wear behavior of Ni60A coating on the 20CrNiMo alloy surface treated by laser shock peening (LSP) and its bonding zone. The results indicate that LSP can significantly enhance the microhardness of the coating and bonding zone, refine the microstructure, and form residual compressive stress without generating new phases. The weight loss due to wear and the average coefficient of friction for the substrate, the cladding alloy, and the LSP-treated alloy demonstrate a trend of first decreasing and then increasing with the rise in temperature. The high-temperature friction and wear performance of the LSP-treated alloy is excellent. This is particularly true at 400 °C, where its wear resistance reaches its peak. Furthermore, after strengthening by LSP, the wear mechanism of the alloy at high temperatures transitions from spalling, oxidation, and adhesive wear to primarily oxidation and abrasive wear.

Application of Origami Engineering in the Formation of Complex Spring Shapes of Thin Steel Plates via Laser Quenching Forming

In this study, the controllability of the spring performance of complex sheet spring shapes was investigated to develop complex sheet spring shapes that are based on origami engineering, with the aim of integrating laser hardening formation with origami engineering. The number of forms generated during the same development was predicted from an origami engineering perspective, and two forms that agreed with the experimental results were generated. Consequently, the rigid-body origami simulation showed that the deformation behavior differs from that of the measured values, which is considered to be in accordance with elastic-body origami. Moreover, springs with arbitrary performances could be produced by varying the processing time and form.

Loss of functional and structural fatigue performance in Nitinol due to laser shock peening

Laser shock peening of austenitic Nitinol using a picosecond laser with 35 mJ laser energy resulted in compressive residual stresses in the surface. However structural fatigue experiments in stress-controlled mode revealed a reduction in fatigue life from 1, 86, 672 cycles in the unpeened condition to 89, 318 cycles in the peened condition. Functional fatigue experiments conducted in strain-controlled mode revealed a difficulty in complete strain recovery of the peened samples when compared to the unpeened samples. Differential scanning calorimetry experiments revealed a shift in the As and Af transformation temperatures to higher values in the peened sample. The deterioration in the structural and functional characteristics of the peened Nitinol was attributed to the enhancement in dislocation density brought about by the peening process, albeit enhancement in surface roughness from 0.25 μm to 0.31 μm could also be contributing towards the poor structural fatigue performance. This work reveals that for functional materials such as Nitinol, laser shock peening may not necessarily contribute to enhancement in fatigue performance. We also show in the work that PVC black tape is better than black paint as an ablation layer for generating compressive residual stresses during laser shock peening of Nitinol.

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

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

Effect of laser shock peening on the retention ability of surface roughness in forged Cr5 steel

The roughness retention ability of the work roll surface during the cold rolling process is of great significance, especially in the production of the high-quality rolling section. Laser shock peening (LSP) is an advanced and effective surface treatment technique to improve the fatigue life, wear resistance, and other mechanical characteristics of metal components. Current studies commonly examined the reinforcement effect of single and multiple LSP treatments on Cr5 steel samples through XRD analysis, hardness testing, and residual stress measurements of different parameters. In addition, the abrasion test is widely conducted to determine the wear resistance. Compared to unprocessed samples, LSP could promote grain refinement and thus significantly increase the hardness and residual stress. Furthermore, the slight decrease in surface roughness shows that LSP treatment is an effective approach to slowing down the roughness decline rate and prolonging the roller service life. It is also found that multiple LSP impacts could remarkably improve the surface roughness retention of Cr5 steel, in which the optimal laser power density was around 23 GW/cm2.

Mechanical properties and strengthening mechanisms of Ti-6Al-4V treated by electro-pulsing assisted laser shock peening

Laser shock peening (LSP) is an efficient surface treatment method used to improve the mechanical properties of materials. With the growing demand for high-performance components under extreme conditions, there is a need for further improvement in the effects of LSP. Recently, electro-pulsing assisted laser shock peening (EP-LSP) has emerged as a promising technique to enhance the effects of single-mechanical-field LSP. However, there has been limited systematic research on the effects of mechanical properties and strengthening mechanisms of material treating by EP-LSP. Herein, Ti‐6Al‐4V samples were subjected to synchronous treatment with electro-pulsing and LSP. The effects of EP-LSP on surface and subsurface characteristics, including surface morphology, hardness, residual stress and microstructure, were investigated and compared with both as-received and LSP-treated samples. Furthermore, the strength and ductility properties were carefully analyzed, and the strengthening mechanism was elucidated. It was observed that EP-LSP produced greater plastic deformation, inducing higher surface hardness and compressive residual stress. Tensile tests demonstrated that the EP-LSP-treated samples exhibited an increase of 7.5% in yield strength, 8.4% in ultimate tensile strength, and 19.7% in elongation compared to LSP-treated samples. Further analysis of the microstructure revealed significant phase transformation and recrystallization in the EP-LSP-treated sample. The increasing dislocation density, nano-twins and grain refinement had contributions to the strength, with nano-twins having the most significant contribution.

Improved rotating bending fatigue performance of laser directed energy deposited Ti6Al4V alloys by laser shock peening

A major challenge for additive manufactured titanium blades is to improve an unfavorable fatigue life. In this work, the rotating bending fatigue test was carried out on the laser direct energy deposited (L-DED) titanium alloy to simulate the service condition of the rotating blade, and the laser shock peening (LSP) post-processing was adopted to enhance the fatigue performance. The results showed that LSP induced gradient layer and phase transformation in L-DED Ti6Al4V alloy, and increased the fatigue limit to 570 MPa. The compressive residual stress dominated the crack source transfer confirmed by the finite element method, and its retention capacity under fatigue cycles reduced the semi-elliptical crack growth rate. A fatigue limit prediction formula was established to quantify the contribution of microstructure, residual stress and roughness changes.

The role of peening processes as a pre‐treatment to anodizing on fatigue behavior of aircraft aluminum alloy

AbstractIn this work, the possibility of employing shot peening and laser peening as pre‐treatments to a tartaric–sulfuric anodizing process on the fatigue behavior of 7050‐T7451 aluminum alloy components was investigated. The surface modifications and stress fields induced by the combination of the peening and anodizing processes were evaluated by scanning electron microscopy and residual stress assessment methodologies based on diffraction techniques, respectively. It was found that the anodizing process alone results in a significant reduction in fatigue life compared to the as‐machined condition especially in the high‐cycle fatigue (HCF) region of the S–N diagrams due to the presence of defects within the anodic layer that act as stress concentrators facilitating the initiation of fatigue cracks. The application of both shot and laser peening treatments is demonstrated to offset the negative effects induced by anodizing, offering greater safety margins useful for the design of critical aeronautical structures.

Improving Commercial Motor Bike Rim Disc Hardness Using a Continuous-Wave Infrared Fibre Laser

This study is focused on examining the feasibility of applying laser hardening to a commercial metallic bike rim, employing a CW IR fibre laser. The research comprises two main phases. The first phase involves an assessment of the impact of laser parameters on the metallic microstructure, while the second phase involves the actual laser hardening of the bike rim. A comprehensive evaluation encompassing hardness measurements, optical microscopy, and scanning electron microscopy was conducted on the samples. The microstructure type can be manipulated by skilfully adjusting the laser parameters, allowing for the creation of various microstructure variants within the laser-hardened zone for specific laser conditions. In this regard, multiple microstructure types were observed. The hardness of the laser-processed zones exhibited variations corresponding to the specific microstructure. Notably, the molten zone (MZ) and the second heat-affected zone (HAZ II) exhibited the highest levels of hardness. Furthermore, it was observed that a scan overlap of ≥ 75% led to an augmentation in hardness. This study sheds light on the intricate interplay between laser parameters, microstructure, and resultant hardness in the context of laser hardening of metallic materials.

Tensile properties and microstructural evolution of 17–4 PH stainless steel fabricated by laser hybrid additive manufacturing technology

Wire-based laser directed energy deposition (LDED) technology is an attractive and efficient additive manufacturing technology, which shows great potential in the process of manufacturing high-value engineering components. However, the thermal effect will lead to a large amount of residual tensile stress in the components, and the large crystal structures after solidification seriously affects the tensile performance. The pursuit of high mechanical properties in additive manufacturing components have prompted researchers to seek new strengthening process to produce high-strength components. Therefore, in this paper, laser shock peening (LSP) composite wire-based LDED were used for the additive manufacturing of 17–4 PH stainless steel under the specified experimental conditions, and the effects of LSP on microstructure evolution, microhardness, and tensile properties of wire-based LDED components were systematically studied. Results showed that uniform grains with an average size of 2.31 μm were generated on the top surface of specimen due to the ultra-high plastic strain induced by LSP shock wave. The size of hierarchical martensitic units shows varying degrees of reduction after LSP treatment, which is shown by the width decrease of packet, block and lath. Dynamic recrystallization caused by rearrangement and annihilation of high-density dislocations promoted the grain refinement. Meanwhile, the residual stress was completely converted from tensile state into compressive state with a maximum value of 425 MPa, and the microhardness was also enhanced to a peak value of 432 HV. In addition, we observed that the high-density dislocation environment created by LSP treatment promoted the further precipitation, and the aggregation phenomenon of precipitates was observed in the dense dislocation area. Furthermore, the tensile strength and elongation of LSP treated specimen were improved significantly, which was attributed to the combined effects of grain refinement, introduction of dislocation structures, precipitation strengthening and gradient residual compressive stress. In summary, laser hybrid additive manufacturing technology provides a new idea and method for the production of high-performance precipitation hardening stainless steel components.

The Effect of Laser Shock Peening (LSP) on the Surface Roughness and Fatigue Behavior of Additively Manufactured Ti-6Al-4V Alloy

Laser shock peening (LSP) uses plasma shock waves to induce compressive residual stress at the surface of a component which has the potential to improve its fatigue properties. For AM parts, the existence of internal defects, surface roughness, and tensile residual stresses leads to noticeably lower fatigue strength compared to materials produced through conventional processes. Furthermore, there is a tendency for greater scatter in the fatigue behavior of these parts when compared to traditionally manufactured components. In this study, the effect of LSP on the roughness and fatigue behavior of Ti-6Al-4V alloy constructed through Laser Powder Bed Fusion (L-PBF) technique was investigated. Two types of samples were designed and tested: as-built surface air foil samples for four-point bending tests and machined surface straight gage samples for uniaxial fatigue testing. Two sets of process parameters, optimized and non-optimized, were also used for the fabrication of each sample type. It was found that LSP had negative effects on the smooth (i.e., machined) surface samples, whereas for as-built surfaces the roughness was enhanced by decreasing the sharpness of the deep valleys and partially remelting the loosely bonded particles on the peaks. It was found that the scatter of the fatigue data decreased for optimized machined samples, while no clear improvement was observed in their lives. However, all non-optimized samples showed improvements in fatigue lives after the LSP process.

THE EFFECT OF HARDENING TECHNIQUES ON WEAR RESISTANCE AND FATIGUE LIFE OF DUCTILE CAST IRON

Many hardening methods have been developed and proposed as an effective technology to produce microstructural modification and improvement of mechanical properties of variety metallic materials. In this experimental study, the effects of applying laser peening (LP) and friction stir processing (FSP) methods on wear resistance and fatigue properties of selected cast iron ASTM A536, grade (80-55-06) with ferrite/pearlite microstructure were investigated. Microscopic study revealed evident refinement and crashing of graphite nodules as 50% of the basic size with FSP and 32% with LP within the processed surfaces hence improving average microhardness by 100% and 48% respectively. The wear resistance and fatigue life were increased by 33% and 122% after FSP whereas, the corresponding increments were 15% and 22% after LP in comparison with the basic ductile iron. These improvements were linked to surface hardening, compressive stresses and structural modification by the employed processes.

Comparative investigation on microstructure and mechanical properties of GH4169 superalloy after laser shock peening with and without coating

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.