Laser Shock Peening Research Articles

Determination of optimal laser hardening mode of hard alloy pins for mining tools

Determination of optimal laser hardening mode of hard alloy pins for mining tools

Laser hardening of steel with a 120 kW laser at high throughput

Lasers can be used as a possible method for steel surface hardening. This process involves a laser acting as a heat source and the sample itself as a heat sink for the required rapid cooling. Typically, spot sizes are in the millimeter range and laser powers are in the kilowatt range. The emergence of commercial fiber lasers in the 100-kW class enables higher throughput levels. We demonstrate an increase in hardness from 160 HV100 to 600 HV100 of 1.7225 / 42CrMo4 / AISI 4140 steel with 10 ms pulses at 120-kW peak power (spot diameter = 38 mm) and a feed rate of 95 mm/s. A width of increased hardness of over 26 mm was achieved, along with a 10 mm wide stripe of uniform hardness. The hardness was increased within a depth of 0.9 mm being homogeneous down to 0.6 mm. Further improvements may be achieved through advanced beam shaping and enhanced scanning parameters.

Effect of laser shock peening as a pretreatment on ion nitriding of precipitation hardened stainless steel

Laser shock peening (LSP) is emerging as an advanced technology to improve the fatigue life of engineering products. Also, this can improve wear and corrosion resistance as add-on benefits to the properties of the materials. In the present investigation, a systematic understanding of the hybrid surface treatment that combines LSP with ion nitriding, also known as plasma nitriding (PN) of precipitated hardened (PH) stainless steel was conducted to improve the effective case hardening layer. The effect of input parameters such as laser spot diameter, the number of superimposed layers, and overlap rate was investigated on the performance characteristics, which include surface morphology, microhardness, and the change in microstructure after the proposed treatment. The surface characterization results reveal that an 80% laser overlap rate modified the surface roughness of PN samples owing to higher surface roughness values induced by ablation during the LSP treatment. The microhardness and optical microscopy (OM) results revealed an increase in the effective hardening layer thickness of about 115% for a 40% overlap rate owing to the absence of blind spots. In addition, XRD analysis revealed the presence of Fe4N and CrN compounds on the surface of the PN samples. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) elemental mapping reveals the presence of a nitrogen-rich phase in the effective hardened layer and increased effective hardened layer thickness owing to grain refinement of LSP pre-processing.

Tribological Behavior of Duplex Stainless Steel with Laser Peening Treatments Without Coating

Tribological Behavior of Duplex Stainless Steel with Laser Peening Treatments Without Coating

Revealing the fretting corrosion mechanisms of laser shock peened cold spray 316 L stainless steel

The influence of laser shock peening (LSP) on the fretting corrosion (FC) resistance of cold spray (CS) 316 L stainless steel (SS) was investigated. Results reveal that LSP allowed for less surface fracturing to occur during FC. The influence of FC also promoted the formation of Ni within the wear scar. Due to the accumulation of debris, galvanic corrosion occurred, increasing the wear-corrosion synergism. Despite this, the surface-strengthening effect of LSP had a dominant effect on FC degradation resistance, ultimately reducing material loss. Based on these findings, LSP is a viable treatment to control the FC resistance of CS 316 L SS.

Effect of laser shock peening on the dissolution of precipitates and pitting corrosion of AA6061-T6 with different original surface roughness

The effect of laser shock peening (LSP) on the electrochemical corrosion behavior of AA6061-T6 with different original surface roughness in the 3.5 wt% NaCl solution was investigated by surface morphology measurement, microstructural characterization, and electrochemical corrosion testing. The results show that LSP improves passivation current density by 76.6%− 78.2% and polarization resistance by 287.2%− 288.9%, but does not change the influence law of the surface roughness on the corrosion behavior of aluminum alloy. LSP promoted the complete dissolution of nano-sized Al8Fe2Si particles, generation of ultrafine grains, and local dissolution of micron-sized Al8Fe2Si particles, contributing to the improved corrosion resistance.

Improving fatigue initiation life of open-hole fibre metal laminates by laser shock peening

Although drilling open holes in fibre metal laminates reduces weight, it brings potential crack initiation sites. This paper investigates the effect of laser shock peening (LSP) on fatigue performance of open-hole titanium-based carbon-fibre/epoxy laminates (Ti-CF FMLs). A method based on multi-step simulation was proposed for the reconstruction of LSP induced residual stress field in open-hole Ti-CF FMLs. The results show that the fatigue initiation life of open-hole Ti-CF FMLs is improved by 22.1 %–81.0 % after LSP, depending on the structure of FMLs and the applied fatigue load. The improved fatigue crack initiation life attributes to compressive residual stress generated throughout the entire depth of the hole wall in outer titanium layer in Ti-CF FMLs after LSP. However, LSP leads to the formation of tensile residual stress far from the hole edge, resulting in accelerated propagation of fatigue crack. The fatigue initiation lives of open-hole Ti-CF FMLs before and after LSP were calculated by finite element simulation and theoretical method, showing good consistency.

Effect of Carburizing Composite Laser-Shock Processing on Properties and Microstructure of 20CrNiMo Steel

In the service process of gears, premature fatigue failure or fracture of gears is often caused by poor surface performance. 20CrNiMo steel is a commonly used material for gears. Laser-shock peening (LSP), carburizing treatment (CT), and hybrid modification of carburizing treatment and laser-shock peening (LSP + CT) were carried out to improve the performance of 20CrNiMo steel. The hardness, residual stress, microstructure, subgrain size, and toughness of the samples were analyzed following various modification methods. It was observed that the properties of the composite-modified gradient structure materials achieved through carburizing and laser-shock peening were superior to those modified using single methods. After the composite treatment of carburizing and laser shocking, the samples exhibited the most significant increase in hardness, up to 916HV0.1, with a surface layer experiencing residual compressive stress as low as −635 MPa. Simultaneously, a gradient microstructure was formed on the surface layer, with 80% of the crystallites being in the nanoscale range. Furthermore, the toughness was notably enhanced. Experimental results confirm the improvement in the properties of 20CrNiMo samples, resulting in the creation of a functionally graded material through the composite treatment of carburizing and laser shocking.

Enhancing elevated-temperature fretting wear performance of GH4169 by tuning wear mechanism through laser shock peening

Turbine disks and blades made of GH4169 for turbine engines are highly prone to fretting wear damage. In this work, we used laser shock peening (LSP) to improve the elevated-temperature fretting wear performance of GH4169, and the corresponding underlying mechanisms are also systematically investigated. Fretting wear experiments conducted on specimens following LSP treatment reveal that the wear resistance of GH4169 was significantly improved, namely a 12.7% reduction in average friction coefficient and a 67.0% decrease in wear rate. Multiscale electron microscopy characterizations reveal that the gradient microstructures induced by LSP serve as the main contributor, which promotes the transition of mechanisms from adhesive wear to abrasive wear, then leading to an exceptional fretting wear performance.

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.

An adaptive cepstrum feature representation method with variable frame length and variable filter banks for acoustic emission signals

Acoustic emission technology is widely employed in defect detection, structural health monitoring, fault diagnosis, and other applications due to its benefits of non-contact, real-time, sensitivity, and flexibility. To implement efficient and timely intelligent monitoring, it is crucial to promptly and precisely gather the time-varying properties in the non-stationary acoustic emission signals. The current work proposes an adaptive cepstrum feature representation method that combines variable frame length and variable filter bank. The variable frame length is implemented based on the spectral distribution correlation, and the optimal frame length and frame rate are selected by iterative operations. The variable filter bank, on the other hand, characterizes the local measure features of variable frame length signals by setting dynamic weight distributions. The proposed adaptive cepstrum algorithm can be used as an auxiliary tool to initially analyze complex non-stationary signals, and thus effectively identify the time-varying and frequency components in acoustic emission signals. The superiority of the proposed method has been confirmed on simulation data. Furthermore, the practical performance of the proposed method is evaluated and illustrated based on the burst signal from laser shock peening processing and the mixed signal from pipeline leakage. The proposed method can be extended to other broadband signals and can be used for feature pre-processing before deep learning network modeling to improve recognition accuracy due to its high time–frequency resolution.

Finite-element simulation of residual stresses induced by laser shock peening in TC4 samples structurally similar to a turbine blade

This study is devoted to the investigation of residual stresses distribution (RSD) in a TC4 sample treated with laser shock peening. The study placed special emphasis on analyzing the RSD at the part of the samples structurally similar to a turbine blade, which is more frequently subjected to damage during service according to the aircraft statistics. Results of simulation showed that low power density of 1.11 GWt/cm2 could not induce compressive residual stress on the surface of a treated object. Furthermore, increasing the overlapping of laser spots does not improve the situation and still fail to induce surface compressive residual stress at a laser intensity of 1.11 GWt/cm2. The compressive stresses occur only with the rise in power density. Reducing the spot size from 3 mm to 1 mm for the power density of 10 GWt/cm2 results in a 20% increase in the magnitude of compressive residual stress in the area of interest. Moreover, applying 35% overlapping further enhances this value. In addition to increasing the magnitude of residual stress, this approach also leads to a more homogeneous RSD of the treated material.

A novel physically interpretable end-to-end network for stress monitoring in laser shock peening

The data-driven method based on acoustic emission signals is gradually becoming a hot topic in the field of laser shock peening quality monitoring. Although some existing deep learning methods do provide excellent monitoring accuracy and speed, they lack physical interpretability in nature, and the opacity of these decisions poses a great challenge to their credibility. The weak interpretability of deep learning models has become the biggest obstacle to the landing of artificial intelligence projects. To overcome this drawback, this paper proposes a monitoring strategy that can achieve physical interpretability in feature extraction, selection and classification, namely, jointly generating monitoring results and explanations. Specifically, it is an end-to-end model that combines convolutional neural units, gated recurrent units, and attention mechanisms. Firstly, a wavelet analysis with physical meaning that can be autonomously learned is performed on the acoustic emission. Then, the contribution of features is distinguished based on the correlation of information in different frequency bands, and redundant and noisy features are removed. Finally, the interpretability evaluation of processing quality is realized by using gated recurrent units with attention mechanisms. The effectiveness and reliability of the proposed method are confirmed by the experimental data of both laser shock peening at small and large gradient energies compared to state-of-the-art feature methods, CNN- and LSTM-based models. Most importantly, the physical interpretation of acoustic emission signals during the processing can increase the credibility of decisions and provide a basic logic for on-site judgments by professionals.

Effect of laser shock peening on fretting corrosion behaviors of aluminum alloy in different aqueous environments

Effect of laser shock peening on fretting corrosion behaviors of aluminum alloy in different aqueous environments

The effect of laser hardening on the operation resistance of rolls of multi-roll mills and the quality of the rolling strip

The effect of laser hardening on the operation resistance of rolls of multi-roll mills and the quality of the rolling strip

Microstructure and wear behaviors of 17-4 PH stainless steel fabricated by laser cladding with post laser shock peening treatment

Laser cladding (LC) technology provides an attractive and cost-effective way to prepare wear-resistant coating on high-value engineering components. However, the thermal effect of coating will lead to a large amount of residual tensile stress in the coating, which seriously affects the wear performance. This paper investigated the influence of laser shock peening (LSP) on the microstructure and wear behaviors of wire-based LC 17-4 PH coating. Results showed that there was no laser remelting phenomenon during LSP process, and all residual austenite in cladding layer transformed into martensite after LSP treatment, accompanied by a more compact and uniform microstructure. LSP can introduce severe plastic deformation to form dislocation structures on the top surface of the coating, which lead to grain refinement through dynamic recrystallization (DRX), and the average grain size decreased from 4.15 μm to 1.81 μm when the laser energy is 9J. Meanwhile, the high strain rate plastic deformation induced by LSP generated high residual compressive stress on the material surface, with a maximum value of 500 MPa. The surface microhardness of the cladding layer increased by 100HV after LSP treatment, reaching to a peak of 458HV at a laser power of 9J, and gradually decreased along the depth direction, presenting a gradient distribution. After LSP treatment, GCr15 steel counter ball was used to simulate the sliding friction of solid particles under real working conditions. Results showed that the friction coefficient (COF) and wear rate of 17-4 PH coating were significantly reduced. Furthermore, the wear type changed from dominative adhesive to slight abrasive wear. The improvement of microhardness and wear properties were attributed to the combined effects of Hall-Petch and Taylor hardening strengthening.

Non-Fourier heat conduction in 2D thermal metamaterials

The challenge of achieving precise control over heat conduction has persisted for years. Recent advancements in thermal metamaterials have offered a promising avenue for addressing this challenge. Yet, predicting the behaviors of non-Fourier heat conduction within these metamaterials remains elusive. In this study, we leveraged the extended plane wave expansion method (EPWEM) to decipher the complex band structures inherent to two-dimensional (2D) thermal metamaterials. To ascertain the reliability of our approach, wave transmission in the time-domain and band structures derived from the finite element method (FEM) were juxtaposed against EPWEM results. Our findings revealed the presence of both directional and complete band-gaps in the complex band structures. Then a thermal bridge is predicted via the proposed complex band structure strategy and demonstrated numerically. By shedding light on non-Fourier heat conduction within thermal metamaterials, our analysis paves the way for groundbreaking applications in domains like laser hardening, laser cladding, metal additive manufacturing, and so on.

The Role of Carbides in Forming the Steels Structure and Properties under Pulsed Laser Irradiation

Introduction. At present, in scientific publications, there is no unambiguous understanding and reasoned metal physical justification of the role of the carbide phase of irradiated materials in forming the required structure and achieving a given degree of hardening of surface layers of steels during pulsed laser treatment, especially in the zone of laser hardening from a solid (austenitic) state. The solution to this issue is of great importance, since it allows us to reasonably and purposefully design the required structure of surface layers of products of various functional purposes with high performance properties. The complexity and insufficiently detailed study of the process of structure formation in the surface layers of steels under extreme thermal effects of pulsed laser radiation required a series of metal physical experiments to study the fine structure of steels after high-speed high-temperature hardening. The aim of this article was to obtain, quantify and critically analyze the array of results of metal physical studies and to assess the degree of influence of the carbide phase on the formation of structure and properties of surface layers of steels in the process of pulsed laser hardening in different modes, that is, with and without melting the surface of the samples. Materials and Methods. In the work, carbon and alloyed tool steels were subjected to surface laser irradiation at a Kvant 16 installation. The radiation power density was 70–200 MW/m2. Optical, scanning probe and electron microscopy were used in conducting metal physical studies, as well as methods of diffractometric, spectral and durometric analysis of steels before and after laser treatment. Results. It was shown that laser treatment of steels with a radiation power density of 130–200 MW/m2 led to a local change in the chemical composition in the laser-fused areas of the spot, partial or complete dissolution of carbides present in the irradiated metal and an increase in the amount of residual austenite in the fused areas up to 40–60 %. It was found that on P6M5 steel, the maximum possible hardness of the irradiated zones was achieved by dissolving 30 % of carbides, on 9XC, HVG steels — 60–70 %. It was shown that under pulsed laser irradiation with q=70–125 MW/m2, that is, without melting the steel surface, "white zones" formed around carbide inclusions under the influence of thermo-deformation stresses at the boundaries of the "carbide – steel matrix" composition. They had irretrievability, dispersion of the structure and increased hardness (10–12 GPa). It was determined that the maximum hardness of laser-hardened metal in the zones of laser hardening from a solid state was achieved if the "white zones" occupied 40 % of the irradiated area of steel. It was found that the dispersion of carbides in this case was 0.5–1.5 microns. Discussion and Conclusion. The results of the conducted studies indicate that in order to obtain the best combination of hardness and viscosity of the irradiated zones during laser treatment with melting of the surface of steels of different chemical composition, it is necessary to dissolve different amounts of carbides. The dispersed structure of laser-fused steel zones, along with a sufficiently high content of residual austenite, predetermine the possibility of improving the operational characteristics of irradiated materials, especially under conditions of external shock loads. The analysis of the conducted metal physical studies irradiated without melting the surface of steels allows us to conclude that in order to obtain a high degree of hardening, it is necessary and expedient to ensure the presence of a certain volume of dispersed carbides in the structure of the irradiated steel. The structural composition of "white zones" formed during laser treatment without melting the steel surface contributes to obtaining a unique level of operational properties. The results of the performed studies contribute to the theory of steel structure formation under conditions of extreme heat exposure and allow for a rational choice of modes of surface laser processing of products and their operability.

Deformation by design: data-driven approach to predict and modify deformation in thin Ti-6Al-4V sheets using laser peen forming

Abstract The precise bending of sheet metal structures is crucial in various industrial and scientific applications, whether to modify deformation in an existing component or to achieve specific shapes. Laser peen forming (LPF) is proven as an innovative forming process for sheet metal applications. LPF involves inducing mechanical shock waves into a specimen that deforms the affected region to a certain desired curvature. The degree of deformation induced after LPF depends on numerous experimental factors such as laser energy, the number of peening sequences, and the thickness of the specimen. Consequently, comprehending the complex dependencies and selecting the appropriate set of LPF process parameters for application as a forming or correction process is crucial. The main objective of the present work is the development of a data-driven approach to predict the deformation obtained from LPF for various process parameters. Artificial neural network (ANN) was trained, validated, and tested based on experimental data. The deformation obtained from LPF is successfully predicted by the trained ANN. A novel process planning approach is developed to demonstrate the usability of ANN predictions to obtain the desired deformation in a treated region. The successful application of this approach is demonstrated on three benchmark cases for thin Ti-6Al-4V sheets, such as deformation in one direction, bi-directional deformation, and modification of an existing deformation in pre-bent specimens via LPF. Graphical abstract

Identification of Johnson-Cook material model parameters for laser shock peening process simulation for AA2024, Ti–6Al–4V and Inconel 718

This paper addresses the identification of Johnson-Cook material model parameters for the simulation of high strain rate processes such as laser shock peening. A combined numerical and experimental approach is described for the identification of the material parameters for AA2024-T3, Ti–6Al–4V, and Inconel 718 alloys. Validation of the parameters was performed based on depth-resolved residual stress profile evaluation after both experimental and numerical laser shock peening application. However, it has been observed that the strain rate-dependent coefficient identified at low strain rates is insufficient for accurately representing the behavior of the Ti–6Al–4V alloy. Consequently, there is a need to identify and determine the appropriate parameter specifically tailored to the strain rates that are relevant to the intended application of the material. The outcomes of this study provide significant insights into the accurate identification of Johnson-Cook material model parameters for laser shock peening simulations. The findings emphasize the critical importance of considering the strain rate-dependent coefficient C in the Johnson-Cook material model to enhance the accuracy and precision of representing material behavior in simulation efforts.