Laser Shock Peening Process Research Articles

Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

Effect of Protective Coating Layer and Overlapping Factor on the Microstructure and Mechanical Properties of Rene-80 Ni-Based Superalloy in Laser Shock Peening Process

Tribological behavior and surface characteristics of severe surface plastic deformed as-cast and 3D-printed SS316L using LSP

The effect of laser shock peening (LSP) on as-cast and three-dimensional (3D)-printed SS316L alloys was studied. The LSP process was found more dominant than the 3D-printing technique over as-cast alloy steel for enhancing the properties. The process of laser shock peening results in microlevel changes in the structure of the material. This, in turn, leads to grain refinement and the increase of compressive residual stresses. After LSP treatment, the surface microhardness value increased by 33% in both as-cast and 3D-printed SS316L alloys with the hardness gradient from surface to subsurfaces. The wear rate of as-cast specimens and 3D-printed specimens were reduced to 1.28 10−6 and 1.14 10−6 g/m, respectively, and tensile value increased up to 22% after LSP treatment. The scanning electron microscopy images on the wear track confirm the vulnerability of the untreated SS316L alloys with adhesion wear and surface delamination. This difference was because the wear rate of the 3D-printed specimens was lesser than the as-cast SS316L alloys due to their layer-by-layer high-temperature finishing. The samples were characterized by optical microstructure to identify the surface refinement, and confirmed by the transmission electron microscope images along with specified area electron diffraction pattern for the accumulation of dislocation and grain refinement after LSP treatment. The accumulated residual stress was measured by X-ray diffraction technique and it found the highest compressive residual stress after LSP treatment was accrued by 3D-printed SS316L alloy with 310 MPa.

Quantitative analysis of deformation characteristics and corrosion properties of high energy laser shock peened Ni-based superalloy

This study examines the influence of high-energy laser shock peening (LSP) using 7 J and 10 J pulse energies on the sub-surface deformation characteristics of Inconel 718 superalloy. High-magnitude compressive residual stresses were induced into the samples after LSP with large residual stress depths of the order of 2 mm – the experimental observations were in good agreement with finite element analyses of the LSP process. The propagation of intense shock waves led to an increased strain hardening and dislocation densities that were experimentally quantified by synchrotron diffraction and transmission electron microscopy. Microscopic analyses revealed highly refined grain structure only at the surface without much refinement observed in the residual depth region. Alongside high degree of strain hardening, a profuse amount of adiabatic shear bands was observed in the hardened depth, indicative of simultaneous strain localisation under such high laser pulse energy. These bands occurred along common slip planes in the Ni γ-matrix and could be potential areas of instability leading to failure. The LSP-treated samples exhibited improved corrosion resistance, with higher laser pulse energy peened samples performing better.

Optimization of multi-axis laser shock peening process for nickel alloy components based on workpiece curvature and equipment dynamic performance

Optimization of multi-axis laser shock peening process for nickel alloy components based on workpiece curvature and equipment dynamic performance

Investigation into the cavitation erosion of rolled Ti6Al4V titanium alloy strengthened by the ultrasonic-assisted laser shock peening process

The novel process known as ultrasonic-assisted laser shock peening (ULSP) is conducted on hot rolled Ti6Al4V titanium alloy with polished surface to improve its cavitation erosion (CE) resistance. The microstructure and phase structure were investigated by transmission electron microscope and X-Ray diffractometer. The microhardness and residual stress were measured by microhardness tester and X-Ray residual stress analyzer. After that, the CE mass loss and morphology were analyzed through high-precision analytical balance and scanning electron microscope to reveal the CE resistance mechanism of ULSP. The results show that ULSP treatment causes plastic deformation at the surface layer, resulting in refined grains and complex dislocation structures. The aforementioned process produces a hardened layer and compressive residual stress (CRS) layer with notable amplitude and deep influence. The surface microhardness of the ULSP-9J specimen is 410 ± 4 HV, which is a 14.8 % increase compared to the LSP-9J specimen. The CRS of the ULSP-9J specimen is −329 ± 6 MPa. As a result, it is vital in preventing the formation and propagation of CE cracks, strengthening the material's resistance to CE damage, reducing mass loss, and enhancing the overall morphology of CE.

A Comprehensive Review on Finite Element Analysis of Laser Shock Peening.

Laser shock peening (LSP) is a formidable cold working surface treatment that provides high-energy precision to enhance the mechanical properties of materials. This paper delves into the intricacies of the LSP process, offering insights into its methodology and the simulation thereof through the finite element method. This review critically examines various points, such as laser energy, overlapping of shots, effect of LSP on residual stress, effect of LSP on grain refinement, and algorithms for simulation extrapolated from finite element analyses conducted by researchers, shedding light on the nuanced considerations integral to this technique. As the significance of LSP continues to grow, the collective findings underscore its potential as a transformative technology for fortifying materials against mechanical stress and improving their overall performance and longevity. The discourse encapsulates the evolving landscape of the LSP, emphasizing the pivotal role played by finite element analysis in advancing our understanding and application of this innovative surface treatment.

Effect of scanning strategy and laser peening on microstructure and fatigue properties of laser-directed energy deposition-built 15-5 PH stainless steel

PurposeThe aim of this paper is to study the effect of laser shock peening (LSP) on mechanical behaviour of the laser-directed energy deposition (LDED)-based printed 15-5 PH stainless steel with U and V notches. The study specifically concentrates on the evaluation of effect of scan strategy, machining and LSP processing on microstructural, texture evolution and fatigue behaviour of LDED-printed 15-5 PH steel.Design/methodology/approachFor LSP treatment, 15-5 PH steel was printed using LDED process with bidirectional scanning strategy (XX [θ = 0°) and XY [θ = 90°]) at optimised laser power of 600 W with a scanning speed of 300 mm/min and a powder feed rate of 3 g/min. Furthermore, LSP treatment was conducted on the V- and U-notched fatigue specimens extracted from LDED-built samples at laser energy of 3.5 J with a pulse width of 10 ns using laser spot diameter of 3 mm. Post to the LSP treatment, the surface roughness, fatigue life assessment and microstructural evolution analysis is performed. For this, different advanced characterisation techniques are used, such as scanning electron microscopy attached with electron backscatter diffraction for microstructure and texture, X-ray diffraction for residual stress (RS) and structure information, Vicker’s hardness tester for microhardness and universal testing machine for low-cycle fatigue.FindingsIt is observed that both scanning strategies during the LDED printing of 15-5 PH steel and laser peening have played significant role in fatigue life. Specimens with the XY printing strategy shows higher fatigue life as compared to XX with both U- and V-notched conditions. Furthermore, machining and LSP treatment led to a significant improvement of fatigue life for both scanning strategies with U and V notches. The extent of increase in fatigue life for both XX and XY scanning strategy with V notch is found to be higher than U notch after LSP treatment, though without LSP samples with U notch have a higher fatigue life. As fabricated sample is found to have the lowest fatigue life as compared to machines and laser peened with both scan strategies.Originality/valueThis study presents an innovative method to improve the fatigue life of 15-5 PH stainless steel by changing the microstructure, texture and RS with the adoption of a suitable scanning strategy, machining and LSP treatment as post-processing. The combination of preferred microstructure and compressive RS in LDED-printed 15-5 PH stainless steel achieved with a synergy between microstructure and RS, which is responsible to improve the fatigue life. This can be adopted for the futuristic application of LDED-printed 15-5 PH stainless steel for different applications in aerospace and other industries.Graphical abstract

Fatigue prediction and optimization of laser peened turbine blade using artificial neural networks and ANFIS

AbstractThis paper investigates the fatigue behavior prediction of Ti‐6Al‐4V thin‐leading‐edge turbine blade specimens treated with laser shock peening (LSP) using two advanced artificial intelligence (AI) methods: artificial neural networks (ANNs) and adaptive network‐based fuzzy inference system (ANFIS). The study aims to estimate the endurance under high cycle loading conditions. First, using ABAQUS and MATLAB software, the modified Crossland criterion for uniaxial loading is applied to recalibrate endurance limit values based on modifications induced by the LSP process. Then, these techniques are employed to predict the modified Crossland criterion profile and endurance limit values influenced by the LSP treatment. Specifically, numerical values are used as training and testing data for these AI models. As a result, these AI methods provide highly accurate prediction and optimization of the modified Crossland criterion and endurance limits, demonstrating their reliability and effectiveness.

Microstructure evolution and surface strengthening behavior of 300 M ultrahigh strength steel under engineered surface treatments

In this work, the most efficient and common engineered surface treatments identified as shot peening (SP), laser shock peening (LSP) and ultrasonic surface rolling process (USRP) were utilized to impact the 300 M ultrahigh strength steel. The microstructure evolution and surface strengthening behavior were carefully characterized and compared for the 300 M steel with various treatments. Besides, the underlying mechanisms for difference in grain refinement and surface mechanical properties by the arranged surface modification are revealed. The results indicate that a gradient structure with nano-grains at the top surface appears on the SP, LSP and USRP treated samples. The process of repeated impacts of SP in different directions leads to activation of multiple slip systems, which thus causes severe refined grains and dense dislocation activities associated with dislocation tangles, dislocation walls and blocking. A great variety of strikes per unit area by USRP results in higher plastic deformation compared to SP where numerous dislocation cells and deformation bands were generated. In contrast to SP and USRP, fewer slip systems are activated in LSP due to the short duration time which thus leads to the thinnest refined grain layer and more planar dislocation structures. The combination of low plastic work and lack of refined grains leads to lowest full width at half maximum (FWHM) in case of LSP samples whereas high FWHM comes from both fine grain size and dislocations in SP. The grain refinement and plastic work contributes to an increase of microhardness and compressive residual stress for the SP, LSP and USRP samples. To be clear, SP leads to a higher magnitude of hardness and compressive residual stress on the topmost surface while LSP causes a larger depth due to that shock wave in LSP influences material to much greater depth. Besides, the decomposition and redistribution of carbides are also noticed on the surface layer after the surface treatments with very high strain rate where numerous dislocations accumulate at the border of the carbides and slip trace is also observed within the carbides.

Effect of power density on microstructure characterization and fatigue behavior of laser shock peened Rene-80 Ni-based superalloy

The microstructure plays a crucial role in determining the mechanical properties and performance of materials, particularly in high-strength alloys such as Rene-80. This study focuses on the microstructure characterization of Rene-80 nickel-based superalloy after undergoing Laser Shock Peening (LSP), an advanced surface treatment technique imparting beneficial residual stresses and improving fatigue life. The primary objective of this research is to investigate how varying power densities during the LSP process affect the microstructure of the Rene-80 superalloy. The power density in LSP is a critical parameter that influences the intensity of shock waves imparted onto the material’s surface, consequently impacting the microstructure. Through advanced microscopy techniques and analysis, the study explores the resulting microstructural changes, including surface roughness, dislocation density, and the presence of defects like dislocations and dislocation cells. These alterations are vital indicators of the material’s mechanical properties, such as tensile and fatigue strength. LSP samples were characterized using various techniques, including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. Additionally, the mechanical performance of the samples was assessed through low-cycle fatigue tests and tensile tests, both conducted before and after LSP treatment. The optimal power density for Laser Shock Peening is determined to be 2.5 HEL. At this power density, the shock wave generated does not create a molten layer on the surface but accumulates defects, resulting in maximum compressive residual stress at the surface. LSP induces intense plastic deformation in the sample, distorting γ’ precipitates. Higher power densities lead to the formation of cross-linked sets of slip bands, highlighting defect slip as the main mechanism of plastic deformation in the LSP process. Understanding these effects is essential for optimizing the LSP process parameters to achieve desired mechanical properties and enhance the performance and longevity of components made from Rene-80 nickel-based superalloy in high-stress applications. It was found that the fatigue life of the samples increased by 500% and optimizing the effect of power density on the LSP process led to an improvement in the fatigue life of the Rene 80 samples.

Corrosion evolution of 316L stainless steel after ultrasonic severe surface rolling and laser shock peening processing

Laser shock peening induced smaller grain size than ultrasonic severe surface rolling for 316L stainless steel. Furthermore, laser shock peening processing facilitated to induce more strain induced α′-martensites. Therefore, the refined grains and α′-martensite enhanced significantly the hardness of 316L stainless steel. Moreover, laser shock peened sample exhibited better corrosion resistance than ultrasonic severe surface rolled one in a medium containing chloride ions. Although α′-martensite would decrease passivation and anti-corrosion ability of 316L stainless steel, the grain refinement promoted the diffusion activity of chromium element, which accelerated surface passivation process.

Microstructure, microhardness, tensile and fatigue investigation on laser shock peened Ti6Al4V manufactured by high layer thickness directed energy deposition additive manufacturing

Thin layer thickness in additive manufacturing (AM) has always been a hindering factor leading to long completion times. Increasing layer thickness is accompanied by a higher tendency of surface cracks and inferior mechanical properties. These can be improved with laser shock peening (LSP). Emphasizing on the high layer thickness, this paper elucidates the high-layer thickness laser directed energy deposition (LDED) AM and the effects of LSP on the fabricated parts. Primary focus was given to the investigation of surface microcracks, microstructures, tensile and fatigue properties. Ti6Al4V bulk sample was prepared using the LDED process. Tensile, fatigue, and other samples were extracted to investigate the above-mentioned properties using different characterization tools such as optical microscope, scanning electron microscope, Vickers microhardness tester, and universal testing machine. Results showed proper depositions without major defects despite the high-layer thickness. Micro-cracks were limited to the surface only, and typical Widmanstätten patterns with parallel α lath and mixed α+β microstructures are observed. Yield strength (YS) varied from 730 MPa to 940 MPa, while ultimate tensile strength (UTS) ranged from 799.5 MPa to 953.75 MPa. Even though laser peening significantly improved micro-hardness by 49.81 % on average, not all fatigue samples observed enhanced fatigue life. A maximum improvement of 40.34 % in fatigue performance was observed in the LDED+LSPed samples. The strain hardening, plastic deformation, and grain refinement during the LSP process contributed to the enhanced mechanical properties. Some samples’ reduced fatigue life may be due to the anisotropic nature of additively manufactured parts, internal defects, and surface cracks on the specific samples. Considering high layer thickness, vertical orientation of samples, and as-prepared samples, our research shows a promising high layer thickness additive manufacturing process. The current research can be used as a base for further study on other properties and characteristics.

Measurement of laser shock peening induced residual stress by nanoindentation and comparison with XRD technique

Laser shock peening (LSP) is an innovative surface treatment technique successfully used to improve fatigue performance of metallic components. It is based on the application of high intensity laser and suitable overlays with the aim to generate high pressure shock waves on the surface of the mechanical part to be treated. Shock waves generate severe plastic deformations and, consequently, compressive residual stresses (RS). An accurate measurement of these latter is crucial for predicting the resistance of treated parts under service loads and to assess the effectiveness of LSP process.In this paper, a non-destructive method, based on the nanoindentation technique and finite element analysis (FEA), was developed to measure the RS generated by LSP process on AA-7050-T451 samples. In particular, the methodology is based on the analysis of the nanoindentation peak load variation generated by the presence of residual stresses on a component. Obtained results were compared, for validation, with the measurements carried out by the most consolidated X-ray diffractometer (XRD) technique. The results showed a satisfactory agreement between the two techniques, revealing nanoindentation as a promising and reliable method for characterizing RS induced by LSP.

Effects of sacrificial coating material in laser shock peening of L-PBF printed AlSi10Mg

ABSTRACT The objective of this work is to study the effects of different coating materials (black paint, thermoplastic elastomers, black vinyl tape and uncoated surfaces) in Laser Shock Peening (LSP) processing of laser powder bed fusion (L-PBF) printed thin AlSi10Mg tubes. The investigations were carried out with pre-identified optimal LSP parameters for the AlSi10Mg material. The study was performed using an analysis of surface residual stresses, where a maximum compressive stress of −85 MPa has been reached, while the depth of the compressive regime stays till 2 mm. The microstructural study reveals the multifold dislocation of the grains and formation of new sub-grains, thus changing the grain boundaries in all experiments due to lattice strain development by LSP. Microhardness has also shown alteration after LSP and accounted for a 5–15% increase in it after LSP. Surface properties, such as roughness and volumetric parameters, have also shown changes after LSP processing.

Artificial neural network and ANFIS approaches for mechanical properties prediction and optimization of a turbine blade treated by laser shock peening

This research article covers a comprehensive investigation on the prediction and optimization of residual stresses, plastic deformations and damage induced by laser shock peening (LSP) on a thin Ti-6Al-4 V leading edge sample of a turbine blade. The study is based on a two-part approach: the first part involves a numerical simulation of the LSP process and the characterization of its effects on the material. The finite element analysis (FEA) is used to simulate the complex interactions between laser parameters, material properties and mechanical response. This numerical analysis generates valuable insights into the residual stress distribution, the plastic deformation and the potential damage within the sample being treated. Based on the numerical results, the second part highlights the novel application of the artificial neural network (ANN) and the adaptive neuro-fuzzy inference system (ANFIS) methods. By taking advantage of the strength of ANN and ANFIS, the models are able to learn accurately from all the data generated by numerical simulations, allowing them to precisely predict and optimize the effects induced by LSP: residual stresses, plastic strains and damage. This paper provides a significant contribution to the field of materials science and engineering, by offering an in-depth comprehension of the LSP process impact on Ti-6Al-4 V leading-edge turbine blade specimens. The combined utilization of numerical analysis and artificial intelligence AI-driven techniques offers a comprehensive approach to optimize the LSP process, leading to the fatigue resistance improvement and service life extension of turbine blades and other critical aerospace components. The proven capability of ANN and ANFIS enables innovative solutions in aerospace engineering and surface treatment technologies, promoting the AI implementation in materials processing and design.

Microstructural evolution and mechanical properties of 7050 aluminum alloy modified via laser shock peening at different heat-treated states

In this study, a combination of laser shock peening (LSP) and solid solution treatment (ST) was employed to modulate the microstructures of 7050 aluminum alloy, aiming to optimize mechanical properties and fatigue life. Microstructure observations showed that after LSP, the material experienced significant plastic deformation, introducing numerous dislocations, thereby enhancing the mechanical and fatigue properties of 7050Al. In comparison to a single LSP process, the process of ST prior to LSP is more advantageous for promoting the accumulation of dislocations and the transmission of shock waves, leading to the successful introduction of a deeper hardened layer exceeding 1 mm in depth. The migration and movement of dislocations result in the formation of subgrains, consequently initiating a mechanism for fine-grain strengthening. The surface hardness demonstrates a 30% increase, accompanied by a rise in residual compressive stress by 167 MPa. The yield strength and ultimate tensile strength exhibit notable increments of 23% and 17%, respectively, which attributed to the synergistic interplay of grain boundary strengthening, precipitation strengthening, and dislocation strengthening. Moreover, the fatigue life shows a substantial enhancement of 5.3 times.

Microstructure and high-temperature tribological properties of Ti–6Al–4V alloy treated by laser shock peening

The high-temperature wear resistance plays an important role for Ti–6Al–4V alloy components working in extreme environments, especially vital for avoiding unexpected failure. However, the reasonable method of surface modification should meet the requirement of improving in wear resistance and less decreasing in mechanical properties simultaneously, which brings a great challenge. In the present research, the laser shock peening (LSP) technique was applied to optimize the superficial layer of Ti–6Al–4V alloy by different processing. The microstructure, elastic modulus, nano-hardness and high-temperature tribology properties of the LSP processed Ti–6Al–4V were investigated to reveal the improving effect. The results demonstrate the LSP processing transforms the dual-size grain structure to relative homogeneous grain structure and forms the gradient nano-structure in superficial layer. With the increasing of LSP processing numbers, the density of geometrically necessary dislocation (GND) decreases obviously, but the density of statistically stored dislocation (SSD) rises significantly, which promotes the increase of total dislocation density compared with the as-received (AR) alloy. Due to the crystal evolution, the Ti–6Al–4V alloy with three-times LSP processing has the lowest wear rate which is less than half of the as-received state. The observations on worn surface and adjacent cross-sectional microstructure reveal the severe scratching and many inner microcracks in the AR sample but the slight scraping and few inner microcracks in the three-times LSP processed sample. Considering the elevated nano-hardness and elastic modulus, the improved tribological properties should be mainly attributed to the optimized microstructure and dislocation state by LSP processing. The present research provides a more reasonable method to improve the high-temperature wear properties of Ti–6Al–4V alloy.

Research on FSW Welds of Al-Alloy Modified by Laser Shock Peening Process

Research on FSW Welds of Al-Alloy Modified by Laser Shock Peening Process

The Effect of Laser Shock Peening (LSP) on the Surface Roughness and Fatigue Behavior of Additively Manufactured Ti-6Al-4V Alloy

Laser shock peening (LSP) uses plasma shock waves to induce compressive residual stress at the surface of a component which has the potential to improve its fatigue properties. For AM parts, the existence of internal defects, surface roughness, and tensile residual stresses leads to noticeably lower fatigue strength compared to materials produced through conventional processes. Furthermore, there is a tendency for greater scatter in the fatigue behavior of these parts when compared to traditionally manufactured components. In this study, the effect of LSP on the roughness and fatigue behavior of Ti-6Al-4V alloy constructed through Laser Powder Bed Fusion (L-PBF) technique was investigated. Two types of samples were designed and tested: as-built surface air foil samples for four-point bending tests and machined surface straight gage samples for uniaxial fatigue testing. Two sets of process parameters, optimized and non-optimized, were also used for the fabrication of each sample type. It was found that LSP had negative effects on the smooth (i.e., machined) surface samples, whereas for as-built surfaces the roughness was enhanced by decreasing the sharpness of the deep valleys and partially remelting the loosely bonded particles on the peaks. It was found that the scatter of the fatigue data decreased for optimized machined samples, while no clear improvement was observed in their lives. However, all non-optimized samples showed improvements in fatigue lives after the LSP process.

Surface modification of fully austenitic stainless steel SMO 254 by laser shock peening to induce compressive residual stress

ABSTRACT The laser shock peening process was conducted with varying pulse densities on the SMO 254 material. The formation of an α martensitic layer from the austenitic structure was witnessed after conducting the laser shock peening process, with the migration of elements across the grains. The increase in the surface roughness value, measured by the Atomic force microscope and Mahr surface profilometer, is directly proportional to the rise in pulse density. An elevated value of compressive residual stress of −786 MPa and a higher Vickers micro hardness value of 365 HV were obtained in the specimen where a pulse density of 6000 pulse/cm2 was applied.