Search Results (199)

To address the severe wear of the hole wall and orifice in ejector pin guide holes of injection molds caused by frequent hole-shaft sliding, this study proposes a composite strengthening method that combines nitriding with oblique laser shock peening (N-OLSP). The strengthening uniformity in both circumferential and axial directions was evaluated by defining a laser shock peening uniformity coefficient ($k$). By strictly controlling the uniformity coefficient ratio of two adjacent spots to be no less than 0.98, the optimal step angles for circumferential and axial directions were determined. Comparative experiments were conducted on three types of samples: Untreated, Nitrided, and N-OLSP treated. The results demonstrate that N-OLSP significantly enhances both surface hardness and residual compressive stress of the guide hole, and the degree of improvement increases with a higher value of $k$. Among the tested samples, N-OLSP exhibited the best wear resistance at the orifice, reducing the wear rate to 0.60 μm/h. Compared with the untreated and nitrided samples, the wear rate reduction achieved by N-OLSP was 66.85% and 16.67%, respectively. Full article

This study investigates the effects of multiple laser shock peening (LSP) treatments on the low-cycle fatigue performance and fracture mechanisms of laser-melted, additive-manufactured Ti-6.5Al-1Mo-1V-2Zr (TA15) titanium alloy. The primary objective is to systematically evaluate how different LSP impact numbers (0, 1, and 2 impacts) enhance fatigue life and alter fracture behavior. Low-cycle fatigue life was determined via tensile-compression fatigue testing. Microfracture morphology was examined using scanning electron microscopy (SEM), surface residual stresses were measured by X-ray diffraction (XRD), and microhardness tests were conducted concurrently. Results indicate that LSP significantly enhances fatigue life: fatigue life increased by 2.34 times and 2.56 times after one and two LSP impacts, respectively, compared to the untreated state. As impact cycles increased, the microhardness of the material surface rose by 8.51% and 14.53%, respectively, with residual compressive stresses reaching −145 MPa and −183 MPa. Concurrently, LSP-2 treatment formed a refined microstructure featuring coexisting lamellar α and acicular martensite in the surface layer. This strengthening effect is attributed to LSP-induced surface residual compressive stress, grain refinement, and the resulting migration of fatigue crack initiation from the surface to subsurface regions. These findings provide critical insights for optimizing fatigue-resistant designs of additively manufactured titanium alloy components. Full article

Mg alloys show great potential in biomedical fields due to superior biocompatibility and biodegradability. Additive manufacturing (AM) provides opportunities in fabricating metallic implants with complex geometries while inherent defects during AM limit its further applications. In this work, laser shock peening (LSP) was employed as a post-processing technique to tailor the surface integrity and corrosion resistance of additively manufactured AZ91 Mg alloy by selective laser melting (SLM). The surface morphology, microstructure and porosity, surface hardness and residual stress, and corrosion resistance of the SLMed alloy before and after LSP were examined. The results show that a gradient structure is formed along the depth direction after LSP and high-density dislocations and high-fraction low-angle grain boundaries are induced. The porosity is gradually reduced in number and size and the highest density of 1.794 g/cm³ is obtained after two impacts of LSP. The surface hardness and residual compressive stress both increase with LSP number and the highest values of 135.26 HV and 40.13 MPa after four impacts, respectively. All of the SLMed alloy samples show improved corrosion resistance after LSP. This work provides a promising route for enhancing the performance of additively manufactured Mg alloys through laser materials surface modification. Full article

Aluminum alloys require improved surface performance to satisfy the demands of today’s aerospace, automotive, marine, and structural applications. This paper compares three key surface hardening methods: diffusion-assisted microalloying, thermomechanical deformation-based treatments, and composite/hybrid reinforcing procedures. Diffusion-assisted Zn/Mg enrichment allows for localized precipitation hardening but is limited by the native Al₂O₃ barrier, slow solute mobility, alloy-dependent solubility, and shallow hardened depths. In contrast, thermomechanical techniques such as shot peening, surface mechanical attrition treatment (SMAT), and laser shock peening produce ultrafine/nanocrystalline layers, high dislocation densities, and deep compressive residual stresses, allowing for predictable increases in hardness, fatigue resistance, and corrosion performance. Composite and hybrid reinforcement systems, such as SiC, B₄C, graphene, and graphite-based aluminum matrix composites (AMCs), use load transfer, Orowan looping, interfacial strengthening, and solid lubrication effects to enhance wear resistance and through-thickness strengthening. Comparative evaluations show that, while diffusion-assisted procedures are still labor-intensive and solute-sensitive, thermomechanical treatments are more industrially established and scalable. Composite and hybrid systems provide the best tribological and load-bearing performance but necessitate more sophisticated processing approaches. Recent corrosion studies show that interfacial chemistry, precipitate distribution, and galvanic coupling all have a significant impact on pitting and stress corrosion cracking (SCC). These findings highlight the importance of treating corrosion as a fundamental design variable in all surface hardening techniques. This work uses unified tables and drawings to provide a thorough examination of strengthening mechanisms, corrosion and fatigue behavior, hardening depth, alloy suitability, and industrial feasibility. Future research focuses on overcoming diffusion barriers, establishing next-generation gradient topologies and hybrid processing approaches, improving strength ductility corrosion trade-offs, and utilizing machine-learning-guided alloy design. This research presents the first comprehensive framework for selecting multifunctional aluminum surfaces in demanding aerospace, automotive, and marine applications by seeing composite reinforcements as supplements rather than strict alternatives to diffusion-assisted and thermomechanical approaches. Full article

In the present paper, the fatigue performance of a TC6 titanium alloy with a microstructure gradient and residual stress gradient produced by laser shock peening (LSP) is investigated. After LSP, a 1 mm thickness gradient compressive residual stress layer with a maximum surface compressive residual stress of −708 MPa is introduced into the materials. Electron back-scattering diffraction (EBSD) and transmission electron microscopy (TEM) techniques are used to characterize the microstructural evolution of the TC6 titanium alloy subjected to LSP. The results show that a nanostructured layer forms on the surface of the TC6 titanium alloy. At a depth of 20 μm, high dense dislocation and nanocrystalline are observed on the top surface. Based on the results of the microstructural characterization, it is found that dislocation movement is the main reason for the formation of nanocrystalline on the top surface. A high-cycle fatigue test showed that the fatigue limit of the TC6 titanium alloy treated by LSP improves from 431 ± 10 MPa to 486 ± 14 MPa, increasing by 12.8%. Full article

The internal surfaces of hot-working dies are prone to wear and fatigue fracture during service, often necessitating surface modification and strengthening. Among available techniques, laser shock peening (LSP) is an effective surface strengthening method. However, when treating internal surfaces, achieving perpendicular laser incidence is difficult, and irradiation must often be applied at an angle. To clarify the relationship between the laser incidence angle and the strengthening effect, this study applied laser shock peening to H13 steel at various incidence angles(0°, 15°, 30°, 45°) with a spot diameter of 3 mm, using laser energies of 8 J, 8.2 J, 9.2 J, and 11.3 J, respectively, and maintaining a fixed power density of 1.41 GW/cm². By maintaining a consistent power density through laser energy compensation, the influence of the incidence angle on surface integrity and wear resistance of the hole structure was systematically investigated. The results show that as the impact angle increases from 0° to 45°, the depth of the affected material layer gradually decreases. Surface microhardness and residual compressive stress peak at a 30° impact angle, reaching values of 633.5 HV1 and 517.4 Mpa, respectively. Wear tests indicated that the friction coefficient was lowest at 30° (0.542), with the dominant wear mechanism shifting from abrasive to adhesive wear. Under controlled power density conditions, oblique laser impact improves surface properties at the expense of a reduced thickness of the affected layer. Full article

DH36 high-strength steel is widely used in shipbuilding and other fields due to its excellent strength, low-temperature toughness, wear resistance, and corrosion resistance. However, the harsh deep-sea environment seriously reduces the service life of welds. In this study we subjected DH36 welded joints to laser shock peening at three different energy levels (5 J, 7 J, 9 J) to investigate its effects on microhardness, microstructure, high-cycle fatigue, and residual stress of the DH36 welded joints. Results indicate that LSP can significantly enhance the surface microhardness of welded joints. Notably, the 7 J energy treatment increased the weld zone microhardness from 195 HV_0.2 to 231 HV_0.2 (18.5% improvement) and the heat-affected zone microhardness from 194 HV_0.2 to 234 HV_0.2 (20.6% improvement). Residual tensile stress on the specimen surface was offset and replaced by residual compressive stress after LSP. Concurrently, the high-cycle fatigue limit of the specimens was significantly improved, with the most pronounced improvement observed in specimens subjected to 5 J energy—increasing from 258 MPa to 295 MPa, representing an increase of 14.34%. Full article

The mechanical integrity of shipbuilding steel under demanding maritime service conditions is a pivotal factor for ensuring the structural safety and operational longevity of vessels. This research employs laser shock peening (LSP) to augment the surface performance of AH32 steel and carries out a comprehensive analysis of the influence and underlying mechanisms of LSP on both the microstructural evolution and mechanical properties of the material. The results indicate that the LSP treatment successfully introduced a high magnitude residual compressive stress (−162 MPa) at the surface of AH32 steel. Additionally, the surface hardness of LSP-1 and LSP-2 increased by 7.3% and 14.7%, respectively. The tensile test results indicate that Sample LSP-2 achieved a 25.8% improvement in elongation while exhibiting only a 5.9% reduction in ultimate tensile strength. Friction and wear tests demonstrated that the average coefficient of friction for the samples treated with LSP decreased by approximately 18%, while the wear rate reduced significantly by over 40%. Full article

Ferroelectric oxides, such as Pb(Zr,Ti)O₃ (PZT), have been shown to maintain stable ferroelectricity even in ultrathin film configurations. However, achieving controllable modulation of microstructure and physical responses in these ultrathin films remains challenging, limiting their potential applications in modern nanoelectronics and optoelectronics. Here, we propose a single-pulse femtosecond (fs) laser micromachining technique for high-precision engineering of microstructure and ferroelectric/piezoelectric responses in ultrathin PZT films. The results show that various microstructures can be selectively fabricated through precise control of fs laser fluence. Specifically, nano-concave arrays are formed via low-fluence laser irradiation, which is mainly attributed to the fs laser peening effect. In contrast, nano-volcano (nano-cave) structures are generated when the laser fluence is close to or reaches the ablation threshold. Additionally, applying an fs laser pulse with fluence exceeding a critical threshold enables the formation of nano-cave structures with controlled depth and width in PZT/Pt/SiO₂ multilayers. Piezoresponse force microscopy measurements demonstrate that the laser peening process significantly enhances the piezoelectric response while exerting minimal influence on the coercive field of PZT thin films. This improvement is attributed to the enhanced electromechanical energy transfer and concentrated compressive stresses distribution in PZT thin films resulting from the laser peening effect. Our study not only offers an effective strategy for microstructure and property engineering in ferroelectric materials at the nanoscale but also provides new insights into the underlying mechanism of ultrafast laser processing in ferroelectric thin films. Full article

A systematic investigation was conducted on the laser shock forming (LSF) process of carbon steel Q355ME sheets and practical skin components, focusing on the influence of absorption layer types, laser energy, and impact cycles on forming capacity and surface properties. Three kinds of absorbing layers were compared in the experiment: no absorbing layer, 0.1 mm aluminum foil and 0.12 mm black tape. The results show that when the black tape is used as the absorbing layer, the forming effect is the best, the arc height value reaches 2.63 mm, and the radius of curvature is 1066 mm. Using 0.1 mm thick black tape as the absorption layer and laser parameters of 10% overlap rate, 15 ns pulse width, 4 mm spot, and 1064 nm wavelength, the single impact of 13 J, 15 J, and 17 J, and one, two, and three impacts of 15 J energy were carried out on the plate. It was found that the increase in laser energy and impact times resulted in increases in deformation, surface roughness, microhardness, and residual stress of the plate. The surface work hardening phenomenon of Q355ME plate after laser shock slowed down the increase in these performance parameters. The experimental results show that the laser energy is linearly positively correlated with the residual stress in a certain energy range. Under the optimized laser process parameters, the forming error of the actual skin parts is controlled within ± 0.4 mm, the surface residual stress increases by 368.9%, and the surface microhardness increases by 10.4%. The ultra-high strain plastic deformation and grain refinement on the surface of the sheet were caused by multiple laser shock peenings, which confirmed that LSF technology can improve the formability of carbon steel skin parts and improve its surface properties. Full article

To accurately assess the residual stress distribution on the superficial layer of the weld for a pure copper butt-welded joint after laser shock peening (LSP), a coupled model was established by integrating experimental measurements with numerical simulations. This model simulates both the tungsten inert gas (TIG) welding process of pure copper and the subsequent LSP treatment applied to the weld. On this basis, the effects of the spot overlapping rate, number of impact layers, and pulse width on the weld residual stress profile were evaluated via multi-point LSP simulations. The findings imply that LSP converts the weld’s superficial residual stress from tensile to compressive, which verifies the accuracy of the simulations through the experimental data. Multi-point LSP numerical simulations demonstrate that elevating the spot overlapping rate and number of impact layers enhances the amplitude and affected depth of the surface compressive residual stress (CRS). A slight decrease in the CRS on the superficial layer of the weld was observed with an increase in pulse width. Compared with increasing the overlapping rate and pulse width, increasing the number of impact layers has a more significant strengthening effect. When the impact layer reached 3 times, the surface CRS reached −219.4 MPa, and the influence depth was 1.3 mm. Full article

316L stainless steel offers attractive characteristics for hydrogen applications, including low hydrogen diffusivity and high hydrogen solubility. However, its use is limited by relatively low strength and resistance to hydrogen embrittlement (HE) under prolonged hydrogen exposure. Laser-directed energy deposition (L-DED) can not only increase the strength of 316L, but also induce significant tensile residual stresses that promote HE. In this study, 316L stainless steel samples produced by L-DED were post-processed by laser shock peening (LSP) to release the tensile residual stresses and refine the near-surface microstructure. LSP-treated samples showed refined grains, higher hardness, and the introduction of compressive residual stress, which led to improved tensile performance in hydrogen. Notably, after seven passes of LSP, the HE index (reduction in elongation due to hydrogen) was 12.5%, compared with 36.1% for the unpeened material. These results demonstrate that LSP is an effective approach to simultaneously increase strength and significantly improve HE resistance in additively manufactured 316L stainless steel. Full article

This study investigated the effect of laser shock peening (LSP) treatment on the fatigue performance of Q355D steel butt-welded joints. The results demonstrate that LSP sig-nificantly enhances joint fatigue resistance through gradient hardening in surface lay-ers, introduction of high-magnitude residual compressive stress fields, and micro-structural refinement. Specifically, microhardness increased across all joint zones with gradient attenuation of strengthening effects within an approximately 700 μm depth. LSP effectively suppressed residual tensile stress concentration in regions beyond 4 mm on both sides of the weld. Fatigue tests confirmed that LSP substantially extended joint fatigue life: by 113–165% in the high-stress region (250–270 MPa) and 46–63% in the medium-low-stress region (230–240 MPa). Fractographic analysis further revealed reduced fatigue striation spacing and lower microcrack density in LSP-treated speci-mens, reflecting the synergistic effect of residual compressive stress fields and micro-structural refinement in retarding crack propagation. This work substantiates LSP as an effective method for enhancing fatigue resistance in Q355D steel welded joints. Full article

In this paper, the different effects of laser shock peening (LSP) and laser shock peening without coating (LSPwC) on the morphology, microhardness and fretting-wear behavior of DD6 Ni-based single-crystal superalloy are investigated. The results show that the surface roughness of DD6 decreases slightly after LSP, while it increases after LSPwC due to surface remelting. Shock wave strengthening during LSP and LSPwC results in plastic deformation of the surface layer of DD6 samples. However, besides work hardening from shock wave, dispersion strengthening of oxide particles also occurs during LSPwC. Therefore, after LSPwC, the microhardness of the DD6 surface layer increases by 38.8%, higher than the increase of 27.7% after LSP. The fretting wear resistance of DD6 increases by about 42.8% and 58% after LSP and LSPwC, respectively. The surface roughness only affects the friction coefficient at the initial stage of fretting wear. The hardness increase caused by work hardening and the dispersion strengthening of surface oxides after laser strengthening is the key to the improvement of fretting wear resistance. The main wear mechanisms of untreated and LSP sample are oxidation wear, abrasive wear and adhesive wear, while the main wear mechanisms of LSPwC sample are oxidation wear and adhesive wear. Full article

To accurately assess the effect of different plate thicknesses on the residual stress field of laser shock peened GH3039 superalloy, residual stress measurements were performed on GH3039 alloy plates with thicknesses of 2 mm and 5 mm after laser shock peening (LSP) treatment. Both quasi-static and high strain rate mechanical tests of GH3039 were conducted, and the Johnson-Cook (J-C) constitutive equation for GH3039 alloy at specific strain rates was fitted based on the experimental results. To obtain the parameter C in the J-C constitutive equation of GH3039 alloy under ultra-high strain rates, a modified method was proposed based on LSP experiment and finite element simulation results. Using the modified GH3039 alloy J-C constitutive equation, numerical simulations and comparative analyses of the residual stress field of GH3039 alloy plates of different thicknesses under LSP were carried out using ABAQUS software. The simulated residual stress fields of laser-shocked GH3039 alloy plates of different thicknesses were in good agreement with the experimental measurements, indicating that the modified GH3039 alloy J-C constitutive equation can accurately predict the mechanical behavior of GH3039 alloy under ultra-high strain rates. Based on the modified GH3039 alloy J-C constitutive equation, the effect of different plate thicknesses on the residual stress distribution of laser-shocked GH3039 alloy was studied, along with the underlying mechanisms. The unique distribution characteristics of residual stresses in laser-shocked GH3039 plates with varying thicknesses are primarily attributed to differences in plate bending stiffness and the detrimental coupling effects of reflected tensile waves. Full article