Laser Shock Processing Treatment Research Articles

The Effect of Viscous Drag on the Maximum Residual Stresses Achievable in High-Yield-Strength Materials in Laser Shock Processing.

In this paper, the experimentally observed significant increase in yield stress for strain rates beyond 104 s-1 (viscous regime) is explicitly considered in laser shock processing (LSP) simulations. First, a detailed review of the most common high-strain-rate deformation models is presented, highlighting the expected strain rates in materials subject to LSP for a wide range of treatment conditions. Second, the abrupt yield stress increase presented beyond 104 s-1 is explicitly considered in the material model of a titanium alloy subject to LSP. A combined numerical-analytical approach is used to predict the time evolution of the plastic strain. Finally, extended areas are irradiated covering a squared area of 25 × 25 mm2 for numerical-experimental validation. The in-depth experimental residual stress profiles are obtained by means of the hole drilling method. Near-surface-temperature gradients are explicitly considered in simulations. In summary, the conventionally accepted strain rate range in LSP (106-107 s-1) is challenged in this paper. Results show that the conventional high-strain-rate hardening models widely used in LSP simulations (i.e., Johnson Cook model) clearly overestimate the induced compressive residual stresses. Additionally, pressure decay, whose importance is usually neglected, has been found to play a significant role in the total plastic strain achieved by LSP treatments.

High strain rate plastic deformation driven microstructure evolution in AlCoCrFeNi dual-phase high entropy alloy

High strain rate plastic deformation under laser shock processing (LSP) has been applied to the AlCoCrFeNi dual-phase high entropy alloy (HEA) for optimizing the microstructure and properties. Phase constituents, microstructure evolution of the HEA before and after LSP were investigated. Microstructures of the HEA samples were examined using scanning electron microscopy and transmission electron microscopy. Results showed that the microstructure in the LSPed region was obviously refined. High density dislocations were produced in the alloy and dislocation slip was the main plastic deformation mode during LSP treatment. When the laser energy increased to 5 J and 7 J, nano-precipitates, twins and stacking faults appeared, and the plastic deformation mode was a mixture of deformation twinning and dislocation slip. The refined grains, dislocation structures, deformation-induced twins and stacking faults were analyzed and associated with the microhardness. The microhardness of the HEA was significantly improved after LSP, which can be attributed to the synergistic strengthening of grain refining strengthening, precipitation strengthening and dislocation strengthening.

Improving the Wear and Corrosion Resistance of Aeronautical Component Material by Laser Shock Processing: A Review.

Since the extreme service conditions, the serious failure problems caused by wear and corrosion are often encountered in the service process for aeronautical components. Laser shock processing (LSP) is a novel surface-strengthening technology to modify microstructures and induce beneficial compressive residual stress on the near-surface layer of metallic materials, thereby enhancing mechanical performances. In this work, the fundamental mechanism of LSP was summarized in detail. Several typical cases of applying LSP treatment to improve aeronautical components' wear and corrosion resistance were introduced. Since the stress effect generated by laser-induced plasma shock waves will lead to the gradient distribution of compressive residual stress, microhardness, and microstruture evolution. Due to the enhancement of microhardness and the introduction of beneficial compressive residual stress by LSP treatment, the wear resistance of aeronautical component materials is evidently improved. In addition, LSP can lead to grain refinement and crystal defect formation, which can increase the hot corrosion resistance of aeronautical component materials. This work will provide significant reference value and guiding significance for researchers to further explore the fundamental mechanism of LSP and the aspects of the aeronautical components' wear and corrosion resistance extension.

The Effect of Laser Shock Processing on the Anti-Corrosion Performance of LENS-Fabricated Ti-6Al-4V Alloy

Titanium alloys are prone to increased oxidation rates when exposed to higher temperatures during application. As a result, the components suffer mechanical failure due to the formation of the alpha-case layer at 500 °C. To improve its corrosion and oxidation properties, and ultimately its mechanical performance, it is necessary to modify its surface properties. In this study, a LENS 3D-printing system was used to fabricate titanium alloy sample coupons, while surface treatment was performed using laser shock processing (LSP) to improve the surface properties. The characterisation of the samples was performed to establish a basis for the corrosion behaviour of the 3D-printed material and the effect of LSP treatment on the rate of corrosion. The samples fabricated at the moderate laser energy density of 249 J/mm3 showed the best-performing properties as the microstructures that evolved showed elevated hardness profiles, which were associated with material property improvements such as high strength and corrosion resistance. After subjecting the samples to LSP treatment, the properties of the LENS samples showed a further improvement in corrosion resistance.

Laser shock processing on selective laser melted 15-5PH stainless steel: Improving mechanical properties and wear resistance

Laser shock processing (LSP) is an effective mechanical surface hardening technology to refine the microstructure on the near-surface layer of material, thereby improving the mechanical properties, service lives, wear resistance, corrosion resistance and so on. In this work, the 15-5PH stainless steel experimental samples were fabricated by selective laser melting (SLM). Subsequently, a SIA-LSP-23 series LSP system with laser energy of 6 J, pulse width of 15 ns and spot diameter of 3 mm was applied to treat the surface of SLMed 15-5PH stainless steel experimental samples. Meanwhile, the mechanical properties, surface topography, microstructural evolution and wear behaviour of SLM 15-5PH stainless steel experimental samples prior and after LSP treatment were investigated. After the LSP treatment, the XRD diffraction peaks were shifted without any new phase formation. Since the severe plastic deformation, the surface roughness was increased. The tensile residual stress in near-surface layer was transformed to beneficial compressive residual stress. At the same time, the microhardness and the wear resistance of SLMed 15-5PH stainless steel were improved due to the refine effect of the microstructures induced by LSP.

Microstructural Evolution and Surface Mechanical Properties of the Titanium Alloy Ti-13Nb-13Zr Subjected to Laser Shock Processing.

As a progressive surface-hardening technology, laser shock processing (LSP) can enhance the mechanical properties and extend fatigue life for metallic components through laser-generated high-pressure plasma shock waves. In this work, LSP was used to treat titanium alloy Ti-13Nb-13Zr experimental coupons, and the microstructural response and surface mechanical properties of the Ti-13Nb-13Zr experimental coupons were investigated. After the LSP treatment, the X-ray diffraction (XRD) peaks were shifted without any new phase formation. The surface roughness of the experimental coupons increased, which can be explained by the LSP-induced severe plastic deformation. The LSP treatment effectively enhanced the surface compressive residual stress of Ti-13Nb-13Zr. Meanwhile, the microhardness of the Ti-13Nb-13Zr was also obviously increased after the LSP treatment. The experimental results also showed that the number of shocks times is an important factor in the improvement of surface mechanical properties. LSP treatment with multiple shocks can lead to more severe plastic deformation. The surface roughness, surface compressive residual stress and microhardness of the Ti-13Nb-13Zr experimental coupons shocked three times are higher than those after one shock. What is more, grain refinement accounts for the mechanical properties' enhancements after the LSP treatment.

Analysis of the thermal stability of residual stresses induced in Ti-6Al-4 V by high density LSP treatments

Laser Shock Processing (LSP) is increasingly applied as an effective technology for the improvement mechanical and surface properties of metallic materials for different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields allowing an improved mechanical behavior. In this paper, the special case of Ti-6Al-4 V alloy is considered with specific consideration of the microstructural changes and residual stresses fields justifying those macroscopic effects. In particular, the effect of the application of different typical LSP intensities on the microstructure and residual stresses fields introduced in this material and their possible correlation to the associated surface effects are analyzed. Emphasis is placed on the study of the thermal stability of these fields after an aging heat treatment at typical high temperature working conditions. The results show that, according to expectations, a certain level of residual stresses and dislocation density remains after in-work thermal aging. The combination of different material characterization techniques has made possible to obtain a correlated set of results highlighting the complementarity of different scale approaches from surface (X-ray) to bulk (neutrons) methods. A model based on the evolution of immobile dislocation density is proposed to rationalize the distribution of dislocation densities, pointing out that plastic deformation is retained. The results clearly show such material improvement stability under typical heavy-duty conditions, thus endorsing the use of the LSP for Ti-6Al-4 V as a suitable technology for industrial applications in relatively high temperature conditions.

Effects of laser shock processing on θ-Al2O3 to α-Al2O3 transformation and oxide scale morphology evolution in (γ’+β) two-phase Ni-34Al-0.1Dy alloys

• The oxidation resistance of (γ’+β) two-phase NiAlDy alloy is optimized by LSP. • LSP reduces scale growth rate due to its impact on initial oxidation behavior. • LSP promotes θ-α transition by increasing dislocation density and surface roughness. • LSP leads to distinction in oxide scale morphology on both the γ’ and β phase. • LSP facilitates the formation of large Al 2 O 3 particles (2–3 μm) on the β phase. (γ’+β) two-phase Ni-Al is a promising high-temperature protective coating material used on Ni-base superalloys since it has good interfacial compatibility with superalloys due to the low Al content compared to single-phase β-NiAl. In this paper, we aim to improve the oxidation resistance, whereby Ni-34Al-0.1Dy, a (γ’+β) two-phase Ni-Al alloy, was treated by laser shock processing (LSP) and the oxidation behavior at 1150 °C was investigated. The results showed that after oxidation, Al 2 O 3 scale formed on the original β phase of the untreated alloy with a small grain size (200–800 nm), while for the LSP-treated samples, the scale grown on the original β phase was dominantly composed of larger Al 2 O 3 grains with a size of 2–3 μm. The distinction was attributed to the promotion of θ-Al 2 O 3 to α-Al 2 O 3 transformation induced by the LSP, because the dislocation density, as well as surface roughness, were increased during LSP treatment which can provide heterogeneous nucleation sites for α-Al 2 O 3 . In addition, the larger-size Al 2 O 3 particles, derived from the direct conversion of needle-like θ-Al 2 O 3 in the initial oxidation stage, could rapidly overspread the whole β phase surface thus reducing the scale growth rate.

Microstructure Evolution and Properties of Gradient Nanostructures Subjected to Laser Shock Processing in 300M Ultrahigh‐Strength Steel

Herein, gradient nanostructures (GNs) are created in 300M ultrahigh‐strength (UHS) steel by laser shock processing (LSP). Microstructure evolution and properties of GNs subjected to LSP with different pulse energies are thoroughly characterized on 3D profiler, scanning electron microscope (SEM), transmission electron microscope (TEM), X‐ray diffractometer (XRD), X‐ray stress analyzer, nanoindenter, and tensile tester. Results show successful creations of GNs in 300M steel after LSP treatments. With the increase in pulse energy, the size of the surface layer is refined from 15 nm (3 J) to 10 nm (7 J), and the corresponding grains are amorphized to some extent. Meanwhile, many substructure defects such as dislocation tangles and deformation twins (DTs) are noted in the subsurface. The dislocation density and the number of DTs increase with the pulse energy. Further, the high compressive residual stress is introduced to the 300M steel surface after LSP, and the corresponding hardness is improved substantially. The compressive residual stress, depth of the affected layer, and the hardness rise significantly with the pulse energy. Apart from improvements in strength and plasticity, the fracture morphology is changed from a typical ductile fracture to quasicleavage and ductile mixed fracture.

A method for obtaining the fraction of absorbed energy of material based on laser shock processing experiment and simulation

Fraction of absorbed energy (FAE) is an important parameter to determine the plasma shock wave pressure. With the purpose of obtaining the FAE of material and accurately calculating the plasma shock wave pressure, a method based on laser shock processing (LSP) experiment and finite element simulation was proposed in this work. The Ni-based superalloy GH4169 was selected as experimental material, and the experimental sample was treated by single-point LSP. The residual stress of experimental sample after LSP treatment was determined using sin2ψ method by X-ray residual stress device. In finite element simulation, the initial value of FAE was assumed as 0.1, and then, the LSP finite element simulation was performed with the change of FAE until the results obtained by LSP experiment and simulation were fell into an allowable range. Based on this method, the FAE with 0.13 for Ni-based superalloy GH4169 was obtained. This work can enrich the theory of LSP and provide theoretical guidance for researchers to obtain the accurate FAE of materials.

The effect of laser shock processing on mechanical properties of an advanced powder material depending on different ablative coatings and confinement medias

Based on the effect of confinement media and ablative coating, laser shock processing (LSP) is a surface modification processing with properties of high efficiency, cleaning, and non-pollution. At room temperature, water is used as the common confinement media and black tape is used as ablative coating in LSP. However, due to the instability of water and black tape at high temperature, warm laser shock processing (WLSP) favors silicone oil as confinement media and aluminum foil as ablative coating, where aluminum foil is pasted on specimen surface by thin vacuum grease. Due to the differences in confinement media and ablative coating, this work focuses on the effect of confinement media and ablative coating on surface quality and mechanical property of FGH98 powder material treated by LSP. FGH98 specimens were strengthened by LSP at room temperature with different confinement medias and ablative coatings. Three groups were divided based on confinement media and ablative coating: water+black tape, water+aluminum foil, and silicone oil+aluminum foil. The group of black tape and silicone oil was removed for the absence of practical significance in engineering. 2D and 3D surface topography was observed by white-light interference surface profilometer (WLI). In addition, surface microhardness and compressive residual stress were determined. The results show that a circular pit is induced by LSP, and its shape is similar to the shape of the Gaussian curve. Compared with the other groups, the 2D surface topography of the circular pit section in the silicone oil+aluminum foil group is smoother, which would delay crack initiation. After LSP treatment, surface microhardness is improved by 7.8-10.6%, and compressive residual stress raises from 355MPa to 896MPa in the first group. According to the comparison of residual stress and surface quality, the effect of confinement media and ablative coating groups on laser shock pressure is ranked in order: water+black tape > water+aluminum foil > silicone oil+aluminum foil. The main reasons for that group order are that shock pressure may be consumed by grease cream and the reduced acoustic impedance of silicone oil is lower than that of water.

Using an artificial neural network to predict the residual stress induced by laser shock processing.

With the purpose of using the artificial neural network (ANN) method to predict the residual stresses induced by laser shock processing (LSP), the Ni-Cr-Fe-based precipitation-hardening superalloy GH4169 was selected as the experimental material in this work, and the experimental samples were treated by LSP with laser power densities of 4.24GW/cm2, 7.07GW/cm2, and 9.90GW/cm2 and overlap rates of 10%, 30%, and 50%. The depth-wise residual stresses of experimental samples prior to and after LSP were taken according to the x-ray diffraction sin2ψ method and electrolytic-polished layer by layer. The ANN model for residual stress prediction was established, and the laser power density, overlap rate, and depth were set as input parameters, while residual stress was set as the output parameter. The residual stresses of untreated samples and those treated with laser power densities of 4.24GW/cm2 and 9.90GW/cm2 were selected as the training sets, and the data of experimental samples treated with a laser power density of 7.07GW/cm2 were reserved as testing sets for validating the trained network. After LSP, beneficial stable compressive residual stresses were introduced in the material's near surface, and the overall maximum compressive residual stresses were formed on the top surface (surface residual stress). Depending on the LSP process parameters, the surface residual stresses ranged from -236MPa to -799MPa, and the compressive residual stress depths of all treated samples were over 0.50 mm. According to the results obtained by ANN, the coefficient of determination R2 of the training sets is 0.9948, which shows a good fitness for the training network. The R2 of the testing sets is 0.9931, which is less than that of the training sets but still shows high accuracy. This work proves that the ANN method can be applied to predict the residual stress of metallic materials by LSP treatment with high accuracy and provides a guiding value for the optimization of the LSP process.

The Role of Laser Shock Processing Treatment in the Growth Dynamics of Fatigue Cracks in Specimens of Ti-6Al−4V Titanium Alloys Damaged by Foreign Objects

Foreign object damage (FOD) is one of the main factors reducing the service life of wings, engine blades, aircraft compressors, and highly loaded machine components. This article presents a detailed study of the peculiarities of the growth rates of fatigue cracks upon FOD in the vicinity of the leading edge of a Ti-6Al−4V titanium alloy blade exposed to preliminary laser shock processing treatment. The FOD and the laser shock processing treatment were modeled using 3D numerical analysis by the finite-element method. The resulting range of changes in the effective stress intensity ratios takes into account both the fields of residual stresses caused by FOD and the crack closure effect due to residual compression stresses. The derived effective stress intensity ratios are used to analyze the growth rates of fatigue cracks in complex residual stress fields. Such actual operational loading modes are considered as low-cycle and multicycle fatigue, separately and in combination.

Effect of laser shock processing on mechanical properties of Ti-45.5Al-2Cr-2Nb-0.15B alloy

In order to study the effect of laser shock processing (LSP) on mechanical properties of Ti-45.5Al-2Cr-2Nb-0.15B alloy. The Ti-45.5Al-2Cr-2Nb-0.15B alloy samples, after the treatment of vibration stress relief, were LSP treated by a high energy nanosecond Nd:YAG laser. The surface micro-hardness, surface residual stress and surface roughness of samples prior & after the LSP treatment were tested by the micro-hardness tester, hole-drilling strain method and the roughness tester, respectively. The experiment results show that after the treatment of LSP, resulting in a certain residual compressive stress on the surface of the sample. When the laser energy is increased to 7 J, the surface residual stress is increased from 0 MPa to −311 MPa, the surface micro-hardness is increased from 311 HV to 366 HV, and the surface roughness is increased from 43 μm to 72 μm. With the treatment of LSP, the mechanical properties of Ti-45.5Al-2Cr-2Nb-0.15B alloy is improved greatly.

The New Technologies Developed from Laser Shock Processing.

Laser shock processing (LSP) is an advanced material surface hardening technology that can significantly improve mechanical properties and extend service life by using the stress effect generated by laser-induced plasma shock waves, which has been increasingly applied in the processing fields of metallic materials and alloys. With the rapidly development of modern industry, many new technologies developed from LSP have emerged, which broadens the application of LSP and enriches its technical theory. In this work, the technical theory of LSP was summarized, which consists of the fundamental principle of LSP and the laser-induced plasma shock wave. The new technologies, developed from LSP, are introduced in detail from the aspect of laser shock forming (LSF), warm laser shock processing (WLSP), laser shock marking (LSM) and laser shock imprinting (LSI). The common feature of LSP and these new technologies developed from LSP is the utilization of the laser-generated stress effects rather than the laser thermal effect. LSF is utilized to modify the curvature of metal sheet through the laser-induced high dynamic loading. The material strength and the stability of residual stress and micro-structures by WLSP treatment are higher than that by LSP treatment, due to WLSP combining the advantages of LSP, dynamic strain aging (DSA) and dynamic precipitation (DP). LSM is an effective method to obtain the visualized marks on the surface of metallic materials or alloys, and its critical aspect is the preparation of the absorbing layer with a designed shape and suitable thickness. At the high strain rates induced by LSP, LSI has the ability to complete the direct imprinting over the large-scale ultrasmooth complex 3D nanostructures arrays on the surface of crystalline metals. This work has important reference value and guiding significance for researchers to further understand the LSP theory and the new technologies developed from LSP.

Numerical simulation of the surface morphology and residual stress field of IN718 alloy by Gaussian mode laser shock

Laser shock processing (LSP) is a new surface modification technology that can improve mechanical properties and extending fatigue life. The numerical simulation was utilized in this work, the IN718 alloy was treated by Gaussian mode laser with the laser pulse energy of 3−7 J, laser pulse width of 12 ns and laser spot in diameter of 3 mm. And the effects of laser pulse energy on the surface morphology and residual stress field of material was investigated. The numerical simulation results showed that after the treatment of LSP, the plastic deformation and compressive residual stress layer with a certain depth is formed on the near surface of material. The amount of the plasticity deformation of material was increased with the laser pulse energy. And the compressive residual stress in surface and the direction of depth are increased with the laser pulse energy too. With the laser pulse energy from 3−7 J, the maximum compressive residual stresses are appeared at the center of the surface corresponding to the laser spot. When the laser pulse energy is increased from 3 J–7 J, the plastic deformation in depth is increases from 0.50 μm–1.86 μm, and the maximum compressive residual stress is increased fromt 362 MPa–742 MPa. In conclusion, LSP can improve mechanical properties of IN718 significantly, and the laser pulse energy is the most important factor to affect the LSP effect. This work can provide a certain theoretical guidance for researchers to study the IN718 alloy treated by LSP.

Efficacy of laser shock processing of biodegradable Mg and Mg-1Zn alloy on their in vitro corrosion and bacterial response

Laser shock processing (LSP) is increasingly applied as an effective technology for improving the properties of different metallic components. This is done principally to enhance their corrosion and fatigue life behaviour, stress corrosion cracking resistance, etc. In this paper, LSP has been applied to a commercially pure Mg and a Mg-1Zn alloy (wt%) which is aimed to be used as a biodegradable material for biomedical applications. The rational for microalloying with Zn is not only influencing the bacterial response, but also enhancing corrosion resistance and mechanical strength of Mg without causing any toxic effect. The present work is focussed on the examination of the effects of the LSP treatment on the relevant surface related properties of the samples and their correlation with the surface and subsurface induced modifications such as residual stress state, microstructural, roughness, hardness, etc. Central to this investigation is the study of the corrosion response and antibacterial properties against Staphylococcus epidermidis of the different samples as a function of material and LSP parameters. The results show that the application of LSP introduces compressive residual stresses up to 1 mm deep. This occurs together with a significant improvement in corrosion resistance, and less bacterial colonization.

Q-switched Nd:YAG laser shock processing effects on mechanical properties of C86400 Cu-Zn alloy

The aim of this paper is to investigate the effects of Nd:YAG laser shock processing (LSP) on micro-hardness and surface roughness of 86400Cu-Zn alloy. X-ray fluorescence technique was used to analyze the chemical composition of this alloy. LSP treatment was performed with a Q-switched Nd: YAG laser with a wavelength of 1064 nm. The results show that laser shock processing can significantly increase. The micro-hardness and surface roughness of the LSP-treated sample. Vickers diamond indenter was used to measure the micro-hardness of all samples with different laser pulse energy and the different number of laser pulses. It is found that the metal hardness can be significantly increased to more than 80% by increasing the laser energy and the number of laser pulse irradiated per unit area. The relationship between laser pulse energy and the value of surface roughness is a proportionality due to the increase in ablation processes which are associated with LSP at sample surface caused by the increasing of laser pulse energy.

The real-time acquisition and analysis software system for laser-induced plasma acoustic wave signal

In order to realize the online detection of laser shock processing and aim at the phenomenon of laser-induced plasma acoustic wave, the SIA-AEDAC-01 acoustic emission acquisition card is used to collect acoustic wave signals. The real-time acquisition and analysis software system for laser-induced plasma acoustic wave signal is studied and designed. The test experiment for feasibility and accuracy of the system is designed. Firstly, the laser-induced plasma acoustic wave signal propagating in air is collected by the online detection laser shock processing system, and then the system gets the laser-induced plasma acoustic wave signal energy. The residual stress of the test pieces after the treatment of laser shock processing was measured by an X-ray stress analyzer to verify the reliability. The experimental results show that the laser-induced plasma acoustic wave signal can be collected and analyzed in real-time by the real-time acquisition and analysis software system, which is designed and developed in this work, and the software system can accurately get the acoustic signal energy. At the same time, both the acoustic wave signal energy and the surface residual stress of the test pieces are increased with the laser energy, and their change curve is consistent. In conclusion, the real-time acquisition and analysis software system for laser-induced plasma acoustic wave signal can satisfy the requirements of online detection of laser shock processing with accurate and reliable performance, and meet the online monitoring requirements of laser shock processing.

The effect of material cyclic deformation properties on residual stress generation by laser shock processing

Laser shock processing (LSP) is a mechanical surface treatment to induce a compressive residual stress state into the near surface region of a metallic component. The effect of the cyclic deformation properties of ductile materials on the final residual stress fields obtained by LSP is analysed. Conventional modelling approaches either use simple tensile yield criteria, or isotropic hardening models if cyclic straining response is considered for the material during the peen processing. In LSP, the material is likely to be subject to cyclic loading because of reverse yielding after the initial plastic deformation. The combination of experiment and modelling shows that the incorporation of experimentally-determined cyclic stress-strain data, including mechanical hysteresis, into material deformation models is required to correctly reflect the cyclic deformation processes during LSP treatment and obtain accurate predictions of the induced residual stresses.