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Surface Integrity and Oxidation of a Powder Metallurgy Ni-Based Superalloy Treated by Laser Shock Peening
摘要： Laser shock peening (LSP) is a mechanical surface treatment which can induce large compressive residual stresses and microstructural changes in a material by using repetitive shocks from laser pulses. In this work, the surface integrity (surface microstructure, topography, hardness and residual stress) of a LSP-treated powder metallurgy Ni-based superalloy was investigated for the first time. LSP treatment introduced large plastic deformation especially at a depth of about 100 lm from the surface, which increased the local hardness. The residual stress from the surface to the interior of the sample was investigated by synchrotron x-ray diffraction. The maximum compressive stress reached 400 MPa at the surface, while the depth of the compressive stress is about 0.7 mm. Lastly, the oxidation behavior of the treated and untreated samples was evaluated by thermal exposure at 700°C for 312 h. The LSP treatment decreased the thickness of the oxide layer, thereby showing improved oxidation resistance.
关键词： Oxidation resistance,Surface integrity,Powder metallurgy,Ni-based superalloy,Laser shock peening
更新于2025-09-23 15:19:57
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Effect of laser shock peening on high cycle fatigue characteristics of 316LN stainless steel
摘要： The influence of ‘laser shock peening’ (LSP) on fatigue behavior of 316LN stainless steel has been studied at 298 K by conducting fully reversed stress controlled fatigue tests in the range 200–300 MPa. A triangular wave form with a constant frequency of 5 Hz was employed for all the tests conducted below 107 cycles on the virgin and laser shock peened samples. The run out tests at 107 cycles were performed at a frequency of 60 Hz. The studies have clearly revealed that the fatigue life is dependent on surface condition of the material and stress amplitude employed. A comparison is made of cyclic stress-strain hysteresis loops and fatigue lives between virgin and peened material. The peened material showed better fatigue strength and life at low stress amplitudes pertaining to high cycle fatigue regime, and exhibited lower density of surface microcracks. The improved fatigue resistance of peened material is attributed to the presence of residual compressive stresses to a depth of ~100 μm from the surface. The beneficial effect of compressive stresses is perceived both in the reduction in number density of Stage-I microcracks and retarded stage-II crack growth in the initial stages (that revealed striations with lesser spacing compared to un-peened samples).
关键词： Laser shock peening,Stainless steel,High cycle fatigue,Compressive residual stresses
更新于2025-09-19 17:13:59
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Local deformation and macro distortion of TC4 titanium alloy during laser shock processing
摘要： Experimental investigation has been carried out to understand the local deformation, macro distortion, and residual stress distribution of TC4 titanium alloy thin plate with different thickness during laser peening processing. The results show that the geometry distortions generate different profile directions depending on the laser shock processing condition. The deformation coefficient λ based on laser power density and sheet thickness is used to predict the macro deformation mode. When λ < 0.212, no macro distortion is produced; when 0.212 < λ < 0.58, volume is transferred along the top surface, the geometric distortion direction is away the laser beam, compressive residual stress is induced on the surface, and convex deformation is produced; when 0.65 < λ, volume is transferred along the bottom surface, the macro distortion direction is toward the laser beam, tensile residual stress is induced on the surface, and concave deformation is produced; the threshold of concave and convex deformation is about 0.62. The deformation coefficient λ and the threshold of concave and convex deformation can be adopted to predict and control the geometry distortion of TC4 titanium alloy thin plate during laser shock processing.
关键词： Thin plate,Residual stress,Geometry distortion,Laser shock peening
更新于2025-09-19 17:13:59
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Fatigue Life Behavior of Laser Shock Peened Duplex Stainless Steel with Different Samples Geometry
摘要： Two different stress raiser geometries (fillet and notched) were treated by laser shock peening (LSP) in order to analyze the effect of sample geometry on fatigue behavior of 2205 duplex stainless steel (DSS). The LSP treatment was carried through Nd:YAG pulsed laser with 1064 nm wavelength, 10 Hz frequency, and 0.85 J/pulse. Experimental and MEF simulation results of residual stress distribution after LSP were assessed by hole drilling method and ABAQUS/EXPLICIT software, respectively. The fatigue tests (tensile-tensile axial stress) were realized with stress ratio of R = 0.1 and 20 Hz. A good comparison of residual stress simulation and experimental data was observed. The results reveal that the fatigue life is increased by LSP treatment in the notched samples, while it decreases in the fillet samples. This is related to the residual stress distribution after LSP that is generated in each geometry type. In addition, the fatigue crack growth direction is changed according to geometry type. Both the propagation direction of fatigue crack and the anisotropy of this steel results detrimental in fillet samples, decreasing the number of cycles to the fatigue crack initiation. It is demonstrated that the LSP effect on fatigue performance is influenced by the specimen geometry.
关键词： laser shock peening,residual stress,duplex stainless steel,fatigue life,sample geometry
更新于2025-09-19 17:13:59
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Healing cracks in selective laser melting by 3D laser shock peening
摘要： Selective Laser Melting (SLM) of Ni-based superalloys such as CM247LC is prone to weld-cracking. This paper investigates how to suppress cracks by repeatedly applying Laser Shock Peening (LSP) during the building phase of SLM. Samples made of CM247LC were processed with different LSP parameters, and the influence on bulk crack density has been quantified. It was observed that for all chosen conditions, a significant decrease of up to 95% could be achieved, demonstrating the potential of the new hybrid 3D LSP method in improving SLM processability of alloys sensitive to cracking.
关键词： Ni-based superalloy,CM247LC,Selective laser melting,Crack density,Laser shock peening,3D laser shock peening
更新于2025-09-16 10:30:52
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Effect of Laser Shock Peening on Fatigue Life at Stress Raiser Regions of a High-Speed Micro Gas Turbine Shaft: A Simulation Based Study
摘要： Fatigue failure due to stress raiser regions on critical rotating components in gas turbine engines, such as the shaft, is a crucial aspect. Methods to reduce these stresses and improve fatigue life are a source of ongoing research. Laser shock peening is a method where compressive residual stresses are imparted on the stress raisers of such components. However, numerical based studies on multiple laser shock peening applied to stress raisers is under-researched. Hence, this study will attempt to predict the fatigue life at fillet radii step induced stress raiser regions on a high-speed gas turbine engine shaft by utilization of laser shock peening. The objective of this study was achieved by developing a more computational efficient finite element model to mimic the laser shock peening process on the fillet radii step induced stress raiser regions of a shaft. A modified laser shock peening simulation method for effective prediction of the residual stress field was introduced. Furthermore, the fatigue life improvement due to laser shock peening was predicted by employing Fe-safe fatigue software. From the results, the modified laser shock peening simulation method provided accurate prediction of the residual stress field with a reduced computational time of over 68% compared to conventional methods. The fatigue life revealed an improvement of 553% due to laser shock peening, which is comparable to similar findings in the literature. Hence, from the findings and results achieved, the developed finite element model can be an appropriate tool to assist in the fatigue life estimation of laser shock peening applied to stress raisers.
关键词： Fatigue,laser shock peening,Fe-safe software,stress raiser regions,finite element model
更新于2025-09-16 10:30:52
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Crack closure mechanisms in residual stress fields generated by laser shock peening: A combined experimental-numerical approach
摘要： Laser shock peening (LSP) is successfully applied to retard fatigue cracks in metallic lightweight structures by introducing specific, in particular compressive, residual stress fields. In this work, experiments and a multi-step simulation strategy are used to explain the fatigue crack retarding and accelerating mechanisms within these LSP-induced residual stress fields. Crack face contact is identified as main mechanism to retard the fatigue crack as the stress distribution changes and the stress intensity factor range decreases. Crack face contact is experimentally detected by load vs. crack opening displacement (COD) curves and scanning electron microscopy (SEM) of the crack faces, as well as during numerical simulations. The convincing agreement between experiment and simulation, especially regarding the specific crack face contact areas, allowed the proper evaluation of the stress intensity factors depending on the crack length. It is found that crack closure is indeed one of the main reasons for the efficient application of LSP for fatigue crack retardation. Furthermore, the occurrence of crack closure does not indicate a zero value stress intensity factor in complex residual stress fields, as the areas of crack face contact depend strongly on the LSP-induced compressive residual stresses.
关键词： Stress intensity factor,Laser shock peening,Residual stress,Fatigue crack growth,Crack closure
更新于2025-09-16 10:30:52
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Enhancement of oxidation resistance of modified P91 grade ferritic-martensitic steel by surface modification using laser shock peening
摘要： In this paper, effect of laser shock peening (LSP) on high temperature oxidation behavior of P91 steel has been studied. P91 samples were subjected to single and triple LSP treatments at a constant laser power density of 3.9 GW.cm?2. Single and triple LSP treatment led to the formation of ultrafine subgrains of sizes ~300 ± 30 and ~105 ± 10 nm respectively at near surface comparing to unpeened P91 sample (~1200 ± 120 nm). Further, unpeened and LSP treated samples were oxidized at temperatures of 600, 650 and 700 °C for time 5 to 200 h in air. Compare to unpeened sample, single and triple peened samples exhibited two and five fold reduction in weight gain after 200 h of oxidation at highest test temperature (700 °C). Improvement of oxidation resistance in LSP treated samples is attributed to the formation of continuous layer of protective oxides such as (Fe,Cr)2O3, Cr2O3 and MnCr2O4 due to enhanced diffusivity of Cr and Mn from bulk during early stage of oxidation. The enhanced diffusivity Cr and Mn in LSP treated samples have been further supported by reduction in apparent activation energy of oxidation, which is evaluated by modelling the time-temperature dependence of weight gain data in purview of kinetics theory.
关键词： Kinetic energy,Laser shock peening,Oxidation resistance,Diffusivity,P91 steel
更新于2025-09-16 10:30:52
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Finite Element Analysis of Surface Roughness Generated by Multiple Laser Shock Peening
摘要： Laser shock peening (LSP) is a novel surface processing technique for improving the fatigue properties of metal parts, and surface roughness is a critical parameter when fatigue strength resistance is concerned. In this paper, a three-dimensional (3D) finite element model was developed in order to assess the surface roughness evolution induced by multiple LSP. A modified finite element analysis (FEA) method was used to compute the vertical displacements profiles, and discrete data obtained from the numerical simulations were subsequently input to the proposed discretized formula to calculate the surface roughness Ra. The results obtained from the numerical simulations are in good agreement with the experiment data from open literatures, which validates the proposed approach. After the validation of the numerical model, a parametric study was conducted in order to predict the effects of overlap rates, number of impacts, and pulse energy on surface roughness Ra.
关键词： laser shock peening,surface roughness Ra,numerical simulation
更新于2025-09-16 10:30:52
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Femtosecond laser shock peening of galvanized stainless steel
摘要： In this paper a SUS316L stainless steel was electroplated with metallic layers and coated with polymer films. A sub-100fs ultrashort laser pulse with a central wavelength of λ=800nm was utilized to process the layer. The aim was to generate shock waves due to ablation of the deposited sacrificial layers. Generated shockwaves propagate and penetrate the lower stainless-steel sample and increase its mechanical hardness (Laser Shock Peening). The sacrificial layer protects the sample from ablation damage and determines the shock wave coupling. To achieve maximal peening, we compare different sacrificial layers and laser processing parameters.
关键词： Ultrashort Laser Peening,Shock hardening,LIPSS,Laser Shock Peening
更新于2025-09-12 10:27:22