Massive Laser Shock Peening Research Articles

Fatigue crack initiation and growth of laser shock peened 2Cr13 martensitic stainless steel as a function of the coverage layer

Fatigue properties and plastic deformation-induced gradient nanostructures of 2Cr13 martensitic stainless steel subjected to laser shock peening (LSP) were investigated. Combining the residual stresses and microstructural evolution of 2Cr13 martensitic stainless steel before and after three-point bending fatigue test, the influences of LSP on fatigue crack initiation and growth are systematically analyzed. Results showed that massive LSP treatments with one and two coverage layers caused obvious improvements of 13% and 37.6% in the fatigue crack initiation life, 19.3% and 34.9% in the fatigue lives of 2Cr13 stainless steel, respectively. Typical in-depth microstructures for two kinds of LSP-treated specimens were described by transmission electron microscopy characterization. Results showed that dynamic recrystallization (DRX) process at room temperature may be activated and accelerated by LSP-induced atom collision, and then a nucleation equation by ultrahigh-strain-rate plastic deformation was developed, which depended strongly on LSP-induced ultrahigh strain rate. Moreover, the basic improvement mechanism of LSP on fatigue properties was analyzed in detail.

The role of annealing heat treatment in high-temperature oxidation resistance of laser powder bed fused Ti6Al4V alloy subjected to massive laser shock peening treatment

The role of annealing heat treatment (AHT)in high-temperature oxidation resistance at 700 ℃ of the laser powder bed fused (LPBFed) Ti6Al4V alloy subjected to massive laser shock peening treatment (MLSPT) was investigated. AHT transformed the acicular martensitic α′ phase into stable α and β phases and released the tensile residual stresses, significantly improving the isotropy of the LPBFed specimens. The excellent gradient compressive residual stresses, gradient microhardness, dislocation structures, nanocrystalline, and nanotwins on the obtained dense plastic deformation layer after AHT-MLSPT contributed decisively to the high-temperature oxidation resistance of the LPBFed specimens.

Enhancement of corrosion resistance of 304L stainless steel treated by massive laser shock peening

The effects of laser shock peening (LSP) on the pitting corrosion behaviour of austenite stainless steel in an acid chloride environment are investigated in this work. The results reveal that LSP treatment improves the pitting corrosion resistance of 304L stainless steel, resulting in a higher pitting potential and a lower metastable pitting nucleation rate of larger pits. However, the augmented effect is only significant in the case of massive LSP impacts. The effects of LSP on microstructure, surface morphology, residual stress, and chemical composition of the surface are studied and analyzed. The significant compressive residual stress and grain refinement on the surface of 304L stainless steel treated by massive LSP impacts are attributed to the enhancement of pitting corrosion resistance, as the former helps minimize microcracks between the intermetallic and matrix metals, and the latter allows for forming a thicker inner layer supplied by Cr2O3 in the passive film.

Improvement mechanism in stress corrosion resistance of the X70 pipeline steel in hydrogen sulfide solution by massive laser shock peening treatment

The effects of massive laser shock peening treatment (MLSPT) on the microstructural evolution and stress corrosion behavior of the X70 pipeline steel in hydrogen sulfide solutions with different concentrations were investigated by residual stress measurement, microstructural observation and slow strain rate tension test. The results revealed that MLSPT generated nanocrystallines, refined martensite-austenite constituent and nanocarbides in the near-surface layer. The combined effects of MLSPT-induced gradient compressive residual stress and refined microstructures significantly improved the stress corrosion crack (SCC) resistance. Furthermore, the influence mechanism of MLSPT on SCC resistance of the X70 pipeline steel was presented in detail.

Delamination in titanium-based carbon-fibre/epoxy laminates under laser shock peening

Surface modification of titanium-based carbon-fibre/epoxy laminates (Ti-CF FMLs) is a challenging topic due to its multilayer structure. This paper investigates the delamination behavior of the Ti-CF FMLs under laser shock peening (LSP) based on experimental and numerical methods. The results show that the onset of the delamination of the Ti-CF FMLs depends on LSP treated area and the delamination width along the thickness direction increases with LSP area. The direct effect of LSP is to degrade the scalar stiffness of the interface between metal and CFRP layers in the Ti-CF FMLs instead of inducing delamination. As massive LSP are performed, the compressive residual stress produces reverse bending, thus delamination occurs at the damaged interface. The damage of the adhesive layer can be effectively prevented by reducing the laser spot size.

Cavitation erosion behaviour of AISI 420 stainless steel subjected to laser shock peening as a function of the coverage layer in distilled water and water-particle solutions

Influences of the coverage layer on cavitation erosion (CE) behaviour, cavitation-silt erosion (CSE) behaviour and damage morphologies of AISI 420 steel subjected to massive laser shock peening treatment (MLSPT) was studied through mass loss measurement, scanning electron microscopy observation, microstructure characterization, and residual stress measurement. Results showed that original martensitic laths with an average width of 450 nm were refined into fine equiaxed grains of 94–220 nm under the mechanical effect of ultra-strong laser shock wave. Moreover, MLSPT induced a compressive residual stress layer up to 1 mm deep, and the surface residual stress was up to −400 MPa. In addition, the average cumulative mass losses of LSPed specimens were respectively 42.2% and 26.5% lower than that of the non-treated specimen in distilled water and water-particle solution, and the erosion resistance was significantly improved with increasing the coverage layer due to the MLSPT-induced grain refinement and compressive residual stresses in the surface layer.

Effects of laser shock peening on microstructural evolution and wear property of laser hybrid remanufactured Ni25/Fe104 coating on H13 tool steel

• LSP was combined with LC to realize the hybrid additive remanufacturing. • MLSPT generated compressive residual stress in surface layer of LCed coating. • The wear resistance of LCed coating was obviously improved by MLSPT. • MLSPT-induced wear mechanisms of LCed coating were proposed. H13 tool steel is often damaged by wear, erosion and thermal fatigue, and laser hybrid additive remanufacturing is an effective method to repair damaged locations to extend their service lives. In this study, the Fe-based layer with Ni-based transitional layer is fabricated in the surface layer of H13 tool steel by laser cladding (LC). Subsequently, massive laser shock peening treatment (MLSPT) is applied to improve the mechanical properties of the LCed coating. Meanwhile, the effects of MLSPT on the residual stress, micro-hardness, microstructure and wear performance are systematically investigated. Results indicate that after MLSPT, the residual stress is transformed from tensile to compressive state, and high-density dislocations and a large number of mechanical twins are generated in the coating. MLSPT-induced surface nanocrystallization contributes to the improvement of micro-hardness and wear resistance of the LCed Ni25/Fe104 coating, and the grain refinement and wear property enhancement mechanisms are also revealed.

Laser shock peening-induced surface gradient stress distribution and extension mechanism in corrosion fatigue life of AISI 420 stainless steel

Surface gradient stress distribution was prepared on AISI 420 martensitic stainless steel (MSS) by massive laser shock peening treatment (MLSPT) with different pulse energies, and effects of MLSPT on residual stress and corrosion fatigue properties in NaCl solutions with different pH values were investigated by microstructural observation, residual stress measurement, corrosion fatigue test, and fractural morphology. Results showed that the coupling effect of MLSPT-induced surface microstructural evolution and gradient stress distribution effectively contributed to an extension in corrosion fatigue properties. Furthermore, the corrosion fatigue crack growth rate equation considering both gradient compressive residual stress and pH value was developed.

High-performance integrated additive manufacturing with laser shock peening –induced microstructural evolution and improvement in mechanical properties of Ti6Al4V alloy components

High-performance integrated additive manufacturing with laser shock peening (LSP), is an innovative selective laser melting (SLM) method to improve mechanical properties, and refine microstructure in the surface layer of metallic components. Phase, residual stress distribution, surface micro-hardness, tensile properties and microstructural evolution of SLMed and SLM-LSPed specimens in horizontal and vertical directions were examined. In particular, typical microstructural features in the surface layer were characterized by transmission electron microscopy (TEM) observations. Results indicated that surface micro-hardness subjected to massive LSP treatment had significantly improved, tensile residual stress was transformed into compressive residual stress by LSP-induced plastic deformation, and both SLMed specimens in two directions exhibited a good combination of the ultimate tensile strength (UTS) and ductility. Meanwhile, high-density dislocations and a large number of mechanical twins were generated in the coarse α′ martensites by laser shock wave (LSW), and gradually evolved into refined α′ martensites. Furthermore, according to the included angle between LSW and the deposited plane, two kinds of LSW-induced atomic diffusion processes at the interfaces between both adjacent deposited layers were presented, and the influence mechanisms of the included angle between LSW and the deposited plane on tensile properties of both SLM-LSPed specimens were revealed. The hybrid additive manufacturing technology combined SLM with LSP realizes the high-efficiency and high-quality integrated manufacturing of the formed metallic components for practical applications.

Strengthening mechanism of Nd: Yag laser shock peening for commercially pure titanium (CP-TI) on surface integrity and residual stresses

Abstract In the present work, an attempt has been made to investigate the effect of generating shock waves through direct and confined ablation modes of plasma method of massive laser shock peening (MLSP) on surface integrity of cast dumbbell shaped and cylindrical cast specimens of commercially pure titanium (CP-Ti) and to compare with those of untreated CP-Ti. The MLSP is usually performed in a massively peening mode to induce uniform compressive residual stress and surface deformation across the entire specimens. After MLSP, tensile testing was carried out to obtain the tensile strength, modulus of elasticity and percentage elongation. The microstructural and surface topography investigations of the laser shock peened material were carried out using digital, optical microscopy and SEM equipped with an energy dispersive spectrometer (EDS) and XRD. The results show that laser shock peened with confined ablation make the surface of CP-Ti with improved change in microstructure, increase in tensile strength, microhardness (73.08%), surface roughness and compressive residual stresses (−420 MPa) which prolongs the mastication ability and dimensional stability of dental implant restorative materials.

Effects of scanning path and overlapping rate on residual stress of 316L stainless steel blade subjected to massive laser shock peening treatment with square spots

The effects of different scanning paths and overlapping rates on the residual stresses distribution in a 316L stainless steel blade subjected to massive laser shock peening treatment with square spots were investigated. Special attention was paid to the surface and in-depth residual stress distributions at 30%, 50% and 70% overlapping rates. Results showed that there were similar residual stress profiles for two scanning paths at 30% overlapping rate. At 50% overlapping rate, the induced surface compressive residual stresses along the width direction (Path 1) was larger than those along the length direction (Path 2), but the latter was more uniform than that of the former. When the overlapping rate increased to 70%, the former was more uniform and larger than the latter. Simulated residual stress profiles were in an agreement with the measured data in all cases. The calculated residual stresses by finite element model analysis were smaller compared with the measured residual stresses.

Effects of coverage layer on the electrochemical corrosion behaviour of Mg-Al-Mn alloy subjected to massive laser shock peening treatment

Effects of coverage layer on electrochemical corrosion behaviour and pitting morphologies of Mg-Al-Mn alloy subjected to massive laser shock peening (LSP) treatment were investigated by potentiodynamic polarisation test, electrochemical impedance spectroscopy (EIS), and scanning electron microscope (SEM) observations. Microstructures of Mg-Al-Mn alloy subjected to massive LSP treatment were also characterized. Results showed that LSP induced an obvious improvement in electrochemical corrosion resistance with increasing coverage layer. Even in a higher corrosive solution concentration, LSP could still prevent corrosion to some extent. The improvement in electrochemical corrosion resistance was due to the grain refinement and compressive residual stress induced by massive LSP treatment. Finally, the influence mechanism of the coverage layer on electrochemical corrosion behaviour of Mg-Al-Mn alloy was revealed.

Effects of laser shock peening with different coverage layers on fatigue behaviour and fractural morphology of Fe-Cr alloy in NaCl solution

Effects of massive laser shock peening (LSP) treatment as a function of coverage layer on surface residual stress, microstructure, and corrosion fatigue (CF) resistance of Fe-Cr alloy were studied by X-ray diffraction technique, scanning electron microscope observations, and corrosion fatigue crack growth (CFCG) testing. Special attention was paid to the details of compressive residual stress and fracture morphology, and the influence mechanism of coverage layer on CF behaviour was also determined. Results indicated that LSP generated deeper compressive residual stress and effectively decreased the CFCG rate, and increased coverage layers further improved the corrosion fatigue life of notched specimens.

Surface EBSD analysis and strengthening mechanism of AISI304 stainless steel subjected to massive LSP treatment with different pulse energies

The effects of massive laser shock peening (LSP) treatment with different pulse energies on surface roughness and microstructural evolution in the surface layer of AISI304 stainless steel were investigated. The deformation-induced grain subdivision processes under two LSP treatment conditions of 3 and 6J pulse energies were characterized and presented, respectively. Subsequently, EBSD characterization was conducted to analyze the peaks of misorientation angle for as-machined sample and LSPed samples with different pulse energies. Furthermore, a novel MT–MT intersection with four directions was found for the first time in the plastic deformation layer of AISI304 stainless steel, and the generation mechanism was completely presented according to the inherited crystal structure of austenite stainless steel. The formation process of the surface roughness and the formed microstructure subjected to massive LSP impact treatment with different pulse energies were compared and revealed.

Microstructural evolution in the welding zone of laser shock peened 316L stainless steel tube

Typical microstructure morphologies in the near-surface layer of the welding zone of gas tungsten arc welded 316L stainless steel tube with and without laser shock peening (LSP) were characterized by optical microscopy and transmission electron microscopy observations. Experimental results and analysis indicated that massive LSP treatment has an important influence on microstructures in the welding zone and heat-affected zone of the welded stainless steel tube. Special attention has been paid to the grain refinement mechanism induced by massive LSP treatment is proposed in the near-surface layer of the welding zone, consisting of the formation of dislocation tangles and dislocation walls due to the pile up of dislocation lines, the development and formation of subgrain boundaries, and the evolution from subgrain boundaries to new grain boundaries. Meanwhile, under laser shock wave, the coarse grain in the near-surface layer in heat-affected zone of the welded specimen was also divided by dislocation movement.

Electrochemical and pitting corrosion resistance of AISI 4145 steel subjected to massive laser shock peening treatment with different coverage layers

The effects of massive laser shock peening (LSP) treatment with different coverage layers on residual stress, pitting morphologies in a standard corrosive solution and electrochemical corrosion resistance of AISI 4145 steel were investigated by pitting corrosion test, potentiodynamic polarisation test, and SEM observations. Results showed massive LSP treatment can effectively cause an obvious improvement of pitting corrosion resistance of AISI 4145 steel, and increased coverage layer can also gradually improve its corrosion resistance. Massive LSP treatment with multiple layers was shown to influence pitting corrosion behaviour in a standard corrosive solution.

Characterization and analyses on micro-hardness, residual stress and microstructure in laser cladding coating of 316L stainless steel subjected to massive LSP treatment

The effects of massive laser shock peening (LSP) treatment on micro-hardness, residual stress and microstructure in four different zones of laser cladding coating was investigated. Furthermore, micro-hardness curves and residual stress distributions with and without massive LSP treatment were presented and compared, and typical microstructure in different zones of both coatings were characterized by transmission electron microscope (TEM) and cross-sectional optical microscope (OM) observations. Results and analyses showed that massive LSP treatment had an important influence on micro-hardness and residual stress of the cladding coating. Special attempt was made to the effects of massive LSP treatment on microstructure in three zones of the cladding coating. In addition, the underlying mechanism of massive LSP treatment on microstructure and mechanical properties of the cladding coating was revealed clearly.

Investigation and microstructural analyses of massive LSP impacts with coverage area on crack initiation location and tensile properties of AM50 magnesium alloy

The influence of massive laser shock peening (LSP) impacts with coverage area on tensile properties of AM50 magnesium alloy was investigated using MTS880-10 servo-hydraulic material testing machine system. Microstructure in the surface layer and fracture morphologies of as-machined and LSPed tensile specimens were also characterized and analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cross-sectional optical microscopy (OM). Special attention is paid to the crack initiation location as a function of LSPed coverage area in the gauge part of tensile specimen. Experimental results and analysis indicate that coverage area significantly influenced tensile properties of the tensile specimen. In addition, the grain refinement process in the top surface layer of AM50 magnesium alloy caused by massive LSP impacts is presented. Furthermore, the underlying influence mechanism of LSPed coverage area on tensile properties and crack initiation location of tensile specimen was clearly revealed.

Effects of overlapping rate on the uniformities of surface profile of LY2 Al alloy during massive laser shock peening impacts

Massive laser shock peening (LSP) impacts have been a competitive alternative technology to improve fatigue life, corrosion and wear resistance of metallic component which depend strongly on the generated surface profile and plastic deformation in the surface layer. First, a three-dimensional finite element modeling (FEM) model with different overlapping rates has been developed to predict residual stress distribution and surface profile of LY2 Al alloy. Second, residual stress distribution predicted is validated by experimental data. Next, four kinds of overlapping rates, 30%, 50%, 70%, and 90%, are chosen to investigate the uniformity and affected depth of residual stress. Special emphasis is also placed on the effects of overlapping rate on surface profile and plastic deformation of LY2 AL alloy subjected to massive LSP impacts. Finally, the underlying influence mechanism of overlapping rate on surface profile of LY2 Al alloy is also clearly revealed.

Effects of laser shock peening and groove spacing on the wear behavior of non-smooth surface fabricated by laser surface texturing

Abstract The friction coefficient and wear resistance of non-smooth surface with different conditions are studied in this work. First, the effects of groove spacing on the friction behavior and wear resistance of the non-smooth surface are investigated. Second, the effects of massive laser shock peening (LSP) impact on the dry sliding wear performance of the non-smooth surface manufactured by laser surface texture (LST) are evaluated. In addition, the worn surfaces and typical microstructure in the top surface layer of all samples were characterized by field emission scanning electron microscope (SEM) with an EDS elemental analysis and transmission electron microscopy (TEM). The influence process of groove spacing and LSP on the friction behavior and wear resistance of T9 tool steel are also analyzed and discussed.