Influence Of Laser Shock Peening Research Articles

Effects of Laser Shock Peening on the Mechanical Behaviors and Microstructure of Friction Stir Processed 2A14 Aluminum Alloy

The influence of laser shock peening (LSP) on the microstructures and mechanical behaviors of the friction stir processed (FSPed) 2A14 aluminum alloy was investigated. Microhardness and tensile measurements, as well as wear test, were taken to analyze the changes in mechanical characteristics. The vibration fatigue experiments were also conducted, while the vibration fatigue life of the specimens with different treatments was compared and the fracture morphologies were observed by scanning electron microscopy. The microstructures before and after LSP were observed with electron backscattered diffraction and transmission electron microscopy. The analysis results evidenced that LSP significantly improved the mechanical properties of the FSPed specimens. Meanwhile, LSP increased the dislocation density and promoted the precipitation of the second phases on the surface layer of the FSPed 2A14 aluminum alloy, while their interactions improved the stability of the dislocation structures, which contributed to the improvement of the mechanical behaviors.

Influence of laser shock peening on surface integrity and tensile property of high strength low alloy steel

Laser Shock Peening (LSP) is a well-established surface treatment commonly used to improve mechanical properties of material's surfaces. To further understand the relationship between tensile property and fatigue life improvement of high strength low alloy steel in the LSP process, LSP treatment of 32CrNi high strength low alloy steel was carried out by YAG laser with pulse energy of 15 J, and tensile property was tested by electronic universal material testing machine. Surface morphology, residual stress and tensile fracture of the specimens before and after LSP were observed by white light interferometer (WLI), X-ray measuring apparatus and scanning electron microscope (SEM). Result shows that LSP did not change tensile strength of 32CrNi steel but cause yield characteristic transform from obvious yield point to no yield phenomenon which is the only factor benefiting fatigue life, indicating that the increment of fatigue life was probably related to the disappearance of yield phenomenon. Formation mechanisms of tensile fractures and yield phenomenon induced by LSP at room temperature were also discussed and completely revealed. Deeper compressive residual stress and flat grains contributed to the transition of yield characteristic and lower elongation rate of 32CrNi steel subjected to LSP.

Influence of laser shock peening on the surface energy and tribocorrosion properties of an AZ31B Mg alloy

The present study investigates the influence of laser shock peening (LSP) on surface energy (SE) of AZ31B Magnesium alloy and its resilience to corrosion and tribocorrosion. AZ31B alloy was treated at different laser intensities. The SE and its interfacial components of treated surfaces were analyzed. The SE was found to be least at low laser intensity LSP. Lower interfacial SE showed decreased wettability, providing enhanced tribocorrosion resistance with respect to untreated surface. However, higher laser intensities increased the surface roughening effect, causing an increase in the interfacial SE and wettability of the surfaces, decreasing the tribocorrosion resistance. The study finds LSP can enhance tribological properties and mitigate the effects of corrosion and tribocorrosion.

Improvement of Wear Resistance in Laser Shock-Peened Copper Contacts

This study investigated the influence of laser shock peening without coating (LSPw/oC) on the degradation of copper electrical contacts. A theoretical calculation of the plastic-affected depth (PAD) induced by LSPw/oC was performed, based on the laser-induced plasma pressure along with the Hugoniot elastic limit of our LSPw/oC experimental conditions. The theoretical PAD was obtained approximately 650 µm from the surface for the LSPw/oC at the laser energy density of 5.3 GW/cm2. Various characterization methods such as the Vicker’s hardness test, residual stress test, and electron backscattered diffraction (EBSD) mapping indicated the PAD may play a significant role in laser induced effective depth for LSPw/oC. At a laser energy density of 5.3 GW/cm2, the laser shock-peened copper showed approximately double the surface hardness as compared to the pure copper. This was attributed to grain refinement, which was confirmed by measuring average grain sizes, and by observing mechanical twin structures from the EBSD analysis. Additionally, a compressive residual stress was induced down to the PAD but gradually switched to a tensile residual stress below PAD. The surface hardening effect conferred by LSPw/oC to the pure copper surface resulted in excellent wear resistance, i.e., a low coefficient of friction and wear loss. As a result, the contact exhibited lower electrical resistance following the fretting friction test compared to pure copper; this would result in a significant delay in electrical contact failure.

Influence of laser shock peening on the coefficient of thermal expansion of Al (7075)-based hybrid composites

Integration of laser shock peening (LSP) and friction stir welding (FSW) was conducted for TiC strengthening on 7075 aluminum (Al) alloys. During FSW, TiC nanoparticles were mixed by using a stir pin to obtain TiC coating with FSWed joints. Nanocrystallines on the surface of Al-based hybrid composites with high-density dislocation were generated through LSP. Microstructural variables, including dislocations and precipitates of the different treatment specimens, were characterized through transmission electron microscopy and X-ray diffractometry. Thermal expansion of cylindrical treated samples was measured from room temperature to 300 °C. The coefficient of thermal expansion (CTE) value of the LSPed samples with TiC decreased by approximately 30% compared with that of the as-FSW sample. Differential scanning calorimetry (DSC) provides insights into the thermal expansion and strengthening mechanisms of LSP. These conditions were mainly caused by the acceleration of precipitated phase transformation from metastable η′ to stable η, resulting in the negative growth of the lattice constant of Al matrix and a decrease in CTE. In addition, the low CTE and dislocation pinning are important in providing a significant synergistic contribution to retard the thermal expansion of Al (7075)-based hybrid composites.

Influence of laser shock peening on fatigue performance of LZ50 axle steel for railway wheel set

AbstractLaser shock peening (LSP) is a surface treatment technique that forms a strengthened layer on the metal surfaces. In this study, the LSP was applied on the locomotive LZ50 axle steel surface which was interference fitted with the wheel. The microstructures, fracture morphologies and fatigue performances of LSP‐treated and untreated axle steels were explored. The results indicated that after the LSP treatment, a strengthened layer was generated on the axle steel surface. The surface hardness was increased by 25%, that is, from around 204 to around 255 HV0.3. The residual compressive stresses were improved from 260 to 345 MPa along the axial direction and from 165 to 225 MPa along the radial direction. The fatigue limit was increased by 30%, that is, from around 130 to around 170 MPa. The fracture surfaces could be divided into three regions: crack initiation, crack propagation, and short‐break regions. In the crack initiation region, the fatigue striation of the LSP‐treated steel was denser than the untreated steel. In the crack propagation and short‐break regions, the fracture morphologies of the LSP‐treated and the untreated axle steels were similar.

The Influence of Laser Shock Peening on Fatigue Properties of AA2024-T3 Alloy with a Fastener Hole

The objective of the present study was to estimate the influence of laser shock peening on the fatigue properties of AA2024-T3 specimens with a fastener hole and to investigate the possibility to heal the initial cracks in such specimens. Fatigue cracks of different lengths were introduced in the specimens with a fastener hole before applying laser shock peening. Deep compressive residual stresses, characterized by the hole drilling method, were generated into the specimens by applying laser shock peening on both sides. Subsequently, the specimens were subjected to fatigue tests. The results show that laser shock peening has a positive effect regarding the fatigue life improvement in the specimens with a fastener hole. In addition, laser shock peening leads to a healing effect on fatigue cracks. The efficiency of this effect depends on the initial crack length. The effect of laser shock peening on the fatigue life periods was determined by using resonant frequency graphs.

Effects of laser shock peening on microstructure and fatigue behavior of Ti–6Al–4V alloy fabricated via electron beam melting

Laser shock peening (LSP) is a post-treatment process that is widely used to modify the surface microstructure and mechanical properties of parts constructed by additive manufacturing (AM). In this study, the influence of LSP on the microstructure and fatigue behavior of Ti–6Al–4V alloy manufactured via electron beam melting (EBM), a popular method of AM, was investigated. The microstructure of the EBM sample consisted of the β phase (~6 vol%) and α lamellar phase. Grain refinement of the α phase occurred via both dislocation evolution and deformation twinning during LSP. A theoretical description of the microstructural evolution, particularly the distribution of deformation twins, was developed. The fatigue strength and micro-hardness of the EBM samples increased by approximately 17% and 11% after LSP treatment, respectively. The fatigue fracture morphologies at three defined damage stages (crack initiation, crack propagation, and instantaneous rupture) were examined for EBM samples before and after LSP. The dominant mechanism of fatigue strength enhancement by LSP was discussed. The effects of residual compressive stress assistant with adiabatic temperature increase and grain refinement of the α phase produced by LSP reduced the pre-existing crack size, suppressed crack initiation, and increased the required work for fatigue fracture.

Effect of Laser Shock Peening on the Microstructure and Properties of the Inconel 625 Surface Layer

The aim of this work was to investigate the influence of laser shock peening on the topography, microstructure, surface roughness and the mechanical properties of the Inconel 625 nickel alloy. Examination of the topography and microstructure of the nickel alloy after laser treatment was carried out by means of scanning electron microscopy as well as atomic force microscopy. The roughness of the surface was measured by WYKO NT9300 equipment. Nanohardness test was carried out using a nanoindenter NHT 50-183 of CSM Instruments equipped with a Berkovich diamond indenter. Additionally, transmission electron microscopy was used to examine the microstructural changes on the surface layer after laser treatment. The investigations showed that the laser process produced an ablation and melting of the surface layer and, hence, increased the surface roughness of the Inconel 625. On the other hand, the presence of the slip bands on the surface and on the cross section of the treated material, a high density of dislocations and a higher hardness of the treated region indicated that the laser shock processing caused severe plastic deformation of the surface layer. Additionally, due to the high plastic deformation, cracking of the carbide precipitates was observed.

Effect of laser shock peening on tribological properties of magnesium alloy ZK60

The influence of laser shock peening (LSP) on tribological properties of magnesium alloy ZK60 was investigated adopting different laser power density. Surface wear morphology, elemental composition and content in wear debris were observed and analyzed using SEM and EDS. Meanwhile, surface roughness, profiles, microhardness, and microstructure were also characterized. It was proven that the roughness increased from 0.32 μm to 9.3 μm, microhardness improved by 39%, the number of grains augmented from 1045 to 1461, and wear rate decreased by 17.6% in maximum. Adhesive wear and oxidation wear were the main mechanisms of the original sample, and the wear mechanism of modified specimens was dominated by abrasive wear. In conclusion, LSP can improve wear resistance under the higher normal force.

Effects of laser shock processing and shot peening on 253 MA austenitic stainless steel and their consequences on fatigue properties

A comparative study of the influence of laser shock peening without coating (LSPwC) and shot peening (SP) treatments on the low cycle fatigue life of 253 MA austenitic stainless steel was investigated. LSPwC treatments were performed with 2500 pulse/cm2 and 5000 pulse/cm2. To evaluate the effects of each treatment, residual stress, roughness, hardness, and microstructure were analyzed. It is of particular interest the correlation of the fatigue performance with the dislocation microstructure evolution. The results reveal that all the surface treatments increase the surface hardness, induce compressive residual stresses (CRS) and a high density of mechanical twins and dislocations. The stability of the workhardened near surface microstructure results in the improvement of the fatigue life of peened 253 MA. Moreover, the best improvement of fatigue life reached for SP is mainly due to the highest number of twins and the more superficial CRS.

Electrochemical stability of laser shock peened 17-4 PH stainless steel

In this study influence of laser shock peening without protective coating (LSPwC) on electrochemical stability of 17-4 PH martensitic stainless steel was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. For this purpose room-temperature LSPwC was performed with laser pulses of 10 ns duration at two pulse densities (2500 and 6250 pulses cm−2). LSPwC increased the surface roughness to a maximum of 1.1 μm, influenced by material-ablation during peening and the peened surfaces showed slight enhancement in oxidation. Corrosion behavior in 3.5% NaCl solution was found to be insignificantly influenced by peening induced surface roughness. On the peened surfaces due to melted/re-solidified layer no deleterious inclusions were found and thereby the charge transfer resistance was improved. Peening did not suppress the secondary δ-ferrite phase in the martensite matrix, which acted as strong pit initiators. Pitting corrosion occurred preferentially at the regions where δ-ferrite phase present both at unpeened and peened conditions. Morphology of the pits formed on peened conditions is discussed.

High temperature wear performance of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy subjected to laser shock peening

ABSTRACTThis paper investigates the influence of laser shock peening (LSP) parameters on surface integrities and high temperature wear performances of Ti–6.5Al–3.5Mo–1.5Zr–0.3Si alloy. Surface integrities include surface roughness, residual stress and micro-hardness are measured. High temperature wear performance of TC11 alloy with and without LSP are investigated. The results indicate that multiple LSP impacts can improve surface micro-hardness and induce compressive residual stress in the surface layer. Moreover, the friction coefficient and wear rate of TC11 alloy significantly decrease after LSP with optimised parameters. The improved wear performance is ascribed to the low surface roughness, higher surface micro-hardness and compressive residual stress induced by multiple LSP impacts in the surface layer.

激光冲击强化对激光增材TC4钛合金组织和抗氧化性的影响

激光冲击强化对激光增材TC4钛合金组织和抗氧化性的影响

Influence of laser shock peening on irradiation defects in austenitic stainless steels

The laser shock peening process can generate a dislocation network, stacking faults, and deformation twins in the near surface of austenitic stainless steels by the interaction of laser-driven shock waves with metals. In-situ transmission electron microscopy (TEM) irradiation studies suggest that these dislocations and incoherent twin boundaries can serve as effective sinks for the annihilation of irradiation defects. As a result, the irradiation resistance is improved as the density of irradiation defects in laser-peened stainless steels is much lower than that in untreated steels. After heating to 300 °C, a portion of the dislocations and stacking faults are annealed out while the deformation twins remain stable, which still provides improved irradiation resistance. These findings have important implications on the role of laser shock peening on the lifetime extension of austenitic stainless steel components in nuclear reactor environments.

激光冲击强化对316L不锈钢熔覆层微观结构和性能的影响

激光冲击强化对316L不锈钢熔覆层微观结构和性能的影响

Influence of laser shock peening pulse density and spot size on the surface integrity of X2NiCoMo18-9-5 maraging steel

Abstract Maraging alloys are a special class of steels with exceptional mechanical properties, suitable for critical and added value applications in aeronautical, aerospace engineering, and the tooling industry. Researchers have been studying several surface engineering techniques to enhance surface characteristics of maraging and tool steels with the aim of extending service life. The goal of the research presented in this paper was to investigate the influence of laser shock peening (LSP) pulse density and spot size on the surface integrity of X2NiCoMo18-9-5 maraging steel. Different pulse densities and spot sizes were chosen for this purpose. Surface integrity was analysed through roughness, residual stress, and microhardness measurements. The influence of each processing parameter was statistically evaluated using the analysis of variance (ANOVA) confirming a significant influence. LSP without the use of an absorbent coating generated high compressive residual stresses in the surface layer with relatively low surface roughness, a combination of characteristics which may have a beneficial influence on mechanical properties of 18% Ni maraging steel. According to the measurements taken in this research, maximal compressive residual stresses were not achieved using the smallest laser beam spot while maintaining constant pulse energy.

Influence of laser shock peening on morphology and mechanical property of Zr-based bulk metallic glass

Laser shock peening (LSP) is a promising surface treatment technology which has been extensively employed to improve the fatigue life of many metallic components. Our works focused on LSP with Nd: glass laser system and circular laser spot diameter of 4mm for Zr41.2Ti13.8Cu10Ni12.5Be22.5 (vit1) bulk metallic glass (BMG). LSP changed the surface morphology and mechanical properties of vit1. Optical profiles indicated that micro-indent would generate on the surface of BMG under the treatment of the higher intensity laser pulse. Detailed observation demonstrated that the surface roughness increased after laser treatment. Surface hardness decreased by up to 13% on the central region of micro-indent. The softening effect was attributed to the high density shear bands induced by the LSP technology.

Improving Anti-Reflection MgF2 Thin Films by Laser Shock Peening and Investigation of its Laser Damage Threshold

This study is divided into two parts. In the first part, the influence of laser shock peening (LSP) on the surface properties of MgF2 thin films is studied. The MgF2 monolayer films with thickness of 100 nm were prepared on a BK7 glass substrate by physical vapor deposition (PVD). An ArF excimer laser with 110 mJ energy, 53 J/cm2 power density, 20 ns pulse duration and wavelength of 193 nm in TEM00 mode was used for the LSP experiments at different (20, 50, 90, and 120) number of the pulses. Transmittance of MgF2 thin films, before and after the LSP treatment, was evaluated by a spectrophotometer and the surface morphology of samples was examined by scanning electron microscope. In the second part, the effect of the LSP treatment on the laser induced damage threshold of a sample irradiated by 90 pulses of the ArF excimer laser was examined.

Comparison Research on Mechanical Properties of High Temperature Alloy after Laser Peened and Ultrasonically Peened

For comparative study of the influence of laser shock peening and ultrasonic shot peening on the mechanical property of superalloy K403, untreated, ultrasonic shot peening with 850°C heat preservation, laser shock (heat preservation, Hp), the fatigue testing of samples under four states were conducted at room temperature, and the analysis of two techniques’ influence on the mechanical properties of K403 was done by hardness tester, profile tester, scanning electron microscopy (SEM). The results indicated that LSP with Hp, LSP, USP with Hp can improve the fatigue life of K403 respectively for 2.4, 2.25, 1.4 times more longer than untreated sample; the increase of micro-hardness gradient after LSP were smaller than after USP. The SEM studies showed that the γ' phase distortion was elongated and the plastic deformation of samples by LSP was larger than by USP.