Effects Of Laser Peening Research Articles

Effects of Laser Peening on Surface and Bending Fatigue Properties of Carburized Steel

Effects of Laser Peening on Surface and Bending Fatigue Properties of Carburized Steel

Comprehensive Analysis of Laser Peening Forming Effects on 5083 Aluminum Alloy.

In order to investigate the laws of the laser peening forming process and the effects of laser peening on the surface quality and tensile properties of 5083 aluminum alloy, experiments were conducted utilizing various laser peening paths, energies, and plate thicknesses. Subsequently, laser peening forming experiments were performed on S-shaped and different shapes of aluminum alloy substrates. The impact of different laser peening durations on surface morphology and tensile properties was then analyzed. Results indicated that the largest bending deformation perpendicular to the laser peening path reached 12.5 mm. In cases where the laser peening path was inclined relative to the horizontal direction, torsional deformations were observed in the aluminum alloy plate. For laser energy levels of 5 J, 6 J, and 7 J, deformation amounts were 3.8 mm, 4.9 mm, and 5.4 mm, respectively. Plates with thicknesses of 4 mm exhibited convex deformation, while those with 2 mm thickness showed concave deformation. Furthermore, following one and two laser peening cycles, the residual stresses in the alloy plates were -80 MPa and -107 MPa, the surface hardness increased by 16 HV and 31 HV, the roughness increased by 2.495 μm and 3.615 μm, and the tensile strength increased by 9.5 MPa and 18.5 MPa, respectively.

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/

Strengthening effect of laser peening on fatigue performance and life extension of laser cladded IN718 nickel-based alloy parts

Strengthening effects of laser peening (LP) on fatigue life extension of IN718 nickel-based alloy parts repaired by laser cladding (LC) were investigated. Special attention was paid on the microhardness, residual stress, microstructures and fatigue performance. The results show that LP increases the microhardness and compressive residual stress of LCed samples and the induced severe plastic deformation closes the metallurgical defect. In addition, LP changes the microstructure of LCed parts, transforms a large number of columnar dendritic structures into cellular dendritic structures. The grains in the subsurface were refined and a high-density dislocation structure is produced as well. As a result, while compared with the matrix sample, the fatigue life of LPed sample with laser power density of 11.30 GW/cm2 is increased by 54.9 %. Finally, synergistic strengthening mechanism of LP on LCed IN718 nickel-based alloy parts through defective pore closure effect, high-amplitude residual stress, and microstructure evolution was revealed.

Effect of laser peening without coating (LPwC) on retardation of fatigue crack growth in SM490 plates

Laser peening without coating (LPwC) is a well-known technique to improve high-cycle fatigue properties by introducing compressive residual stress (RS) near the surface of metal components. In this study, X-ray diffraction (XRD) and flexural fatigue tests were applied to pre-cracked 12 mm thick SM490A welding structural steel specimens that were subjected to LPwC nearly 20 years ago with a pulse energy of 200 mJ, a spot diameter of 0.8 mm and a pulse density of 36 pulse/mm2. XRD revealed that the compressive RS has remained stable to date, with approximately 400–500 MPa remaining at the surface and a compressive depth of approximately 0.9 mm from the surface, which is comparable to the data measured by XRD immediately after LPwC. In the flexural fatigue tests with a stress ratio of 0.1 and stress rages of 100, 150 and 200 MPa, LPwC extended the fatigue life by more than 1.6 times, depending on the stress range and individual specimens. Crack restarting cycles were significantly increased by a factor of at least 1.8, and the crack growth rate was suppressed by a factor of about 0.7 or less.

レーザピーニングが浸炭鋼の表面特性および曲げ疲労特性に及ぼす影響

To investigate the effects of laser peening (LP) on the surface and bending fatigue properties of carburized steel (JIS SCM420), surface roughness measurements, residual stress measurements, retained austenite measurements, and four-point bending fatigue tests were conducted. After LP, the compressive residual stress was introduced on the surface, with the effect extending to a depth of more than 1 mm. Due to the high compressive stress, the bending fatigue strength of LP specimen was 1.46 times higher than that of the as-heat-treated specimen even though the surface roughness was increased by LP. Notably, the amount of retained austenite was 10.9％ at the top surface of LP specimen, and high-density twins were observed in the lath martensite structure. This can be attributed to high strain rate deformation by LP.

Effect of Laser Peening on the Corrosion Properties of 304L Stainless Steel.

Dry canisters used in nuclear power plants can be subject to localized corrosion, including stress corrosion cracking. External and residual tensile stress can facilitate the occurrence of stress corrosion cracking. Residual stress can arise from welding and plastic deformation. Mitigation methods of residual stress depend upon the energy used and include laser peening, ultrasonic peening, ultrasonic nanocrystal surface modification, shot peening, or water jet peening. Among these, laser peening technology irradiates a continuous laser beam on the surface of metals and alloys at short intervals to add compressive residual stress as a shock wave is caused. This research studied the effect of laser peening with/without a thin aluminum layer on the corrosion properties of welded 304L stainless steel. The intergranular corrosion rate of the laser-peened specimen was a little faster than the rate of the non-peened specimen. However, laser peening enhanced the polarization properties of the cross-section of 304L stainless steel, while the properties of the surface were reduced by laser peening. This behavior was discussed on the basis of the microstructure and residual stress.

Effect of Laser Peening on Fatigue Properties of Butt-Welded Joints with Angular Distortion

Effect of Laser Peening on Fatigue Properties of Butt-Welded Joints with Angular Distortion

Microstructural response and surface mechanical properties of TC6 titanium alloy subjected to laser peening with different laser energy

In this paper, the main purpose was to investigate the effects of laser peening (LP) on the microstructural evolution and frictional wear resistance of TC6 titanium alloy. The surface topographic features, microhardness and residual stress distribution in the depth direction of differently treated specimens were measured using three-dimensional topography instrument, digital microhardness tester and residual stress instrument. The frictional wear test was carried out using a multifunctional friction wear tester. Meanwhile, X-ray diffraction (XRD), optical microscope (OM) and transmission electron microscopy (TEM) were utilized to investigate the effects of LP on the microstructural response of TC6 titanium alloy. The results indicated that the micro-pits induced by LP increased the surface roughness to a maximum of 6.94 μm. LP technique effectively improved the microhardness and frictional wear resistance of TC6 titanium alloy, and the wear form changed from abrasive wear, adhesive wear and fatigue spalling wear to abrasive wear at the laser energy of 8 J. Compared to the untreated specimens, the surface microhardness of the specimens treated by LP with 8 J increased from 356 HV to 442 HV, and the affected layer depth was approximately 500 μm. Moreover, the friction coefficient decreased from 1.2 to 0.5, the abrasion depth of the abrasion track was reduced by approximately 32 % compared to the untreated specimen. Additionally, the surface compressive residual stress induced by LP with 8 J reached about −510 MPa. The microstructural evolution of the specimens processed by LP was dominated by twin formation and dislocation slip, while the intercalation between multidirectional twins and the formation of sub-grain boundaries promoted grain refinement of TC6 titanium alloy. Refined grains, high density of dislocations, mechanical twins and the implantation of compressive residual stresses effectively improved the friction and wear resistance of TC6 titanium alloy.

Effect of laser peening without coating on mechanical and microstructural behaviour of SS 304 stainless steel

This present work investigates the influence of laser shock peening without coating (LPwC) of SS 304 stainless steel. To understand the effect of deformation behaviour, laser power densities of 3, 6 and 9 GW cm−2 were employed. The Residual stress and microhardness (HV) were investigated at surface and depth direction. The maximal value of compressive residual stress (−340 MPa) reached a depth of 50 µm for the laser intensity of 9 GW cm−2. Micro hardness significantly increased to 71.11% for 9 GW.cm−2 compared to the unpeened sample. To observe the mechanical twinning and grain refinement the Electron backscattered diffraction (EBSD) was carried out. A Transmission electron microscope (TEM) was also performed to know the nano twins and dislocation movement in the laser peened samples. Results showed that laser peening without coating process would cause a significant improvement on surface properties such as compressive residual stress, surface roughness, microhardness, and microstructure and grain refinement.

Investigations for improving fatigue strength by low energy laser peening via bending fatigue test

Laser peening can introduce compressive residual stresses on the surface of various materials, thereby effectively prolonging their fatigue lives. In this study, the effects of laser peening with pulse energies of 20 and 70 mJ on residual stress and fatigue life were investigated on two types of HT780 box-welded specimens of different sizes, considering the realization of a portable laser peening system equipped with a small laser device with low pulse energy. As a result of such low pulse energy laser peening, it was found that the depth of compressive residual stress becomes shallower compared to the current laser peening with a pulse energy of 200 mJ, while the residual stress on the surface remains at the same level. Bending fatigue tests were conducted with the stress ranges at 100 and 150 MPa, which revealed that the fatigue life of the specimens with low pulse energy laser peening was at least 50 times and eight times longer than that of the as-welded specimens, respectively. Comparing the fatigue test results of different size specimens, it is clear that laser peening with low pulse energy is effective in extending the fatigue life of HT780 box-welded specimen regardless of its size.

Effect of Laser Peening on Microstructural Changes in GTA-Welded 304L Stainless Steel.

The introduction of tensile residual stress has led to the induction of damage such as fatigue, corrosion fatigue, and stress corrosion cracking (SCC) in stainless steel in association with the influence of environments, components, surface defects, and corrosive factors during its use. Compressive residual stress can be achieved through various techniques. Among several methods, laser peening can be more attractive as it creates regularity on the surface with a high-quality surface finish. However, there is very little research on heavily peened surface and cross-section of stainless steel with very deep compressive residual stress. This work focused on welding and laser peening and the influence of Al coating on the microstructural changes in 304L stainless steel. The specimen obtained by laser peening had a very deep compressive residual stress of over 1 mm and was evaluated based on microstructural and hardness analysis. Therefore, a model for microstructural change by laser peening on welded 304L stainless steel was proposed.

Improving Fatigue Limit and Rendering Defects Harmless through Laser Peening in Additive-Manufactured Maraging Steel

Additive-manufactured metals have a low fatigue limit due to the defects formed during the manufacturing process. Surface defects, in particular, considerably degrade the fatigue limit. In order to expand the application range of additive-manufactured metals, it is necessary to improve the fatigue limit and render the surface defects harmless. This study aims to investigate the effect of laser peening (LP) on the fatigue strength of additive-manufactured maraging steel with crack-like surface defects. Semicircular surface slits with depths of 0.2 and 0.6 mm are introduced on the specimen surface, and plane bending-fatigue tests are performed. On LP application, compressive residual stress is introduced from the specimen surface to a depth of 0.7 mm and the fatigue limit increases by 114%. In a specimen with a 0.2 mm deep slit, LP results in a high-fatigue-limit equivalent to that of a smooth specimen. Therefore, a semicircular slit with a depth of 0.2 mm can be rendered harmless by LP in terms of the fatigue limit. The defect size of a 0.2 mm deep semicircular slit is greater than that of the largest defect induced by additive manufacturing (AM). Thus, the LP process can contribute to improving the reliability of additive-manufactured metals. Compressive residual stress is the dominant factor in improving fatigue strength and rendering surface defects harmless. Moreover, the trend of the defect size that can be rendered harmless, estimated based on fracture mechanics, is consistent with the experimental results.

Effects of Laser Peening with a Pulse Energy of 1.7 mJ on the Residual Stress and Fatigue Properties of A7075 Aluminum Alloy

Laser peening without coating (LPwC) using a palmtop-sized microchip laser has improved the residual stresses (RSs) and fatigue properties of A7075 aluminum alloy. Laser pulses with a wavelength of 1.06 μm and duration of 1.3 ns from a Q-switched Nd:YAG microchip laser were focused onto A7075 aluminum alloy samples covered with water. X-ray diffraction revealed compressive RSs on the surface after irradiation using laser pulses with an energy of 1.7 mJ, spot diameter of 0.3 mm, and density of 100–1600 pulse/mm2. The effects were evident to depths of a few hundred micrometers and the maximum compressive RS was close to the yield strength. Rotation-bending fatigue experiments revealed that LPwC with a pulse energy of 1.7 mJ significantly prolonged the fatigue life and increased the fatigue strength by about 100 MPa with 107 fatigue cycles. The microchip laser used in this study is small enough to fit in the hand or be mounted on a robot arm. The results may lead to the development of tools that extend the service life of various metal parts and structures, especially outdoors where conventional lasers are difficult to apply.

Effect of Laser Peening with a Microchip Laser on Fatigue Life in Butt-Welded High-Strength Steel

Laser peening introduces compressive residual stresses on the surfaces of various materials and is effective in enhancing fatigue strength. Using a small microchip laser, with energies of 5, 10, and 15 mJ, the authors applied laser peening to the base material of an HT780 high-strength steel, and confirmed compressive residual stresses in the near-surface layer. Laser peening with a pulse energy of 15 mJ was then applied to fatigue samples of an HT780 butt-welded joint. It was confirmed that laser peening with the microchip laser prolonged the fatigue life of the welded joint samples to the same level as in previous studies with a conventional laser.

Effects of Laser Peening on Various Aluminum Alloys

Effects of Laser Peening on Various Aluminum Alloys

Effect of Laser Peening on the Mechanical Properties of Aluminum Alloys Probed by Synchrotron Radiation and X-Ray Free Electron Laser

Synchrotron radiation (SR) and X-ray free electron laser (XFEL) are indispensable tools not only for the exploration of science but also for the evolution of industry. We used SR and XFEL to elucidate the mechanism and the effects of laser peening without coating (LPwC) which enhances the durability of metallic materials. X-ray diffraction (XRD) employing SR revealed that the residual stress (RS) in the top surface became compressive as the laser pulse irradiation density increased with appropriate overlapping of adjacent laser pulses. SR-based computed tomography (CT) was used to nondestructively reconstruct three-dimensional (3D) images of fatigue cracks in aluminum alloy, revealing that LPwC retarded crack propagation on the surface and inside of the sample. SR-based computed laminography (CL) was applied to friction stir welded (FSWed) aluminum alloy plates to visualize fatigue cracks propagating along the welds. The fatigue crack had complicated shape; however, it became a semi-ellipsoid once projected onto a plane perpendicular to the fatigue loading direction. Ultra-fast XRD using an XFEL was conducted to investigate the dynamic response of aluminum alloy to an impulsive pressure wave simulating the LPwC condition. The diffraction pattern changed from spotty to smooth, implying grain refinement or subgrain formation. Shifts in diffraction angles were also observed, coinciding with the pressure history of laser irradiation. The durations of the dynamic phenomena were less than 1 µs; it may be possible to use high-repetition lasers at frequencies greater than kHz to reduce LPwC processing times.

Improving the fatigue limit and rendering a defect harmless by laser peening for a high strength steel welded joint

The effects of laser peening (LP) on fatigue limit improvement and acceptable defect size of a high strength steel HT780 (JIS-SHY685) welded joint were investigated. Fatigue tests were performed, following the optimization of the LP conditions. The fatigue limit of the welded specimen without the defect increased by 45% via LP. The specimen containing 0.2 mm deep semicircular defect at the weld toe reached almost the same level of fatigue limit as that of the defect-free, LP-treated specimen. Therefore, a semicircular defect of less than 0.2 mm deep could be rendered harmless by LP. From the results, the fatigue strength and the reliability of HSS-welded joints can be significantly improved by LP. The dominant factor that contributed to fatigue limit improvement was the introduction of compressive residual stress by LP.

Influence of laser peening on the high-temperature fatigue life and fracture of Inconel 718 nickel-based alloy

High-temperature fatigue test was performed to study the effects of laser peening (LP) on the fatigue behavior of Inconel 718 nickel-based alloy at high temperature. Compressive residual stress (CRS) induced by LP was investigated at both room and high temperature. Microstructural evolution was also studied before and after LP process. The macro- and micro-fracture morphologies in fatigue crack initiation (FCI) region, fatigue crack growth (FCG) region and finial rupture (FR) region of LPed samples with different laser power densities at different temperatures were systematically analyzed. The results showed that LP process can enhance the fatigue life of IN718 nickel-based alloy at both room and high temperature. Excessively high temperature (e.g. 800 °C) may result in a sudden decrease in the fatigue life of LPed samples due to the weakening of grain boundaries and oxidation damage. The losing of coherent strengthen between γ″ phase and matrix was another reason for the rapid reducing of fatigue life. Compared to the untreated samples, the crack source transferred from the surface to deeper layer indicated that LP can retard the crack initiation on the metal surface, which is conducive to enhance the final fatigue life. Some direct evidence, such as the decreased distance between the parallel fatigue striations, the tortuous crack growth path in the LPed specimen confirmed the retarding effects of LP on the FCG. The mechanism of microcracking and the dynamic plastic behavior of LPed specimens during high-temperature fatigue test of IN718 nickel-based alloy were also discussed.

Effects of laser peening on tensile properties and martensitic transformation of AISI 316L stainless steel in a hydrogen-rich environment

Slow strain rate tensile test in a hydrogen-rich environment was performed to study the effects of laser peening (LP) on the tensile properties and martensitic transformation of AISI 316L stainless steel. Underlying physio-chemical processes involved in hydrogen embrittlement of 316L steel in the hydrogen-rich environment has been proposed. Results show that the grain refinement, mechanical twins and high-density dislocations were found in the laser peened specimens. The movement of hydrogen-carrying dislocations and martensite transformation were prevented by complex grain boundaries and high-density dislocations during tensile process. The ultimate tensile strength of the laser peened specimen were increased by 7.73% and 8.45% in air and hydrogen-rich environment respectively compared with that of non-laser peened specimen. What's more, the elongation loss of laser peened sample was far less than that of non-LP sample in a hydrogen-rich environment. LP induced compressive residual stress (CRS), grain refinement, high-density dislocations and a dense surface layer on the treated surface are beneficial for suppressing hydrogen penetration.