Effect Of Laser Shock Processing Research Articles

Effects of laser shock processing on the microstructure evolution and the oxidation behavior of TP347H austenitic steel in supercritical water environment

The effects of laser shock processing (LSP) treatment on TP347H austenitic steel were investigated through exploring the residual stress distribution, the evolutions of microstructure and the oxidation behavior in supercritical water (SCW, 640 °C/27 MPa). Results show that the plastic deformation layer (PDL) and the compressive residual stress (about −550 MPa maximum value) were detected on TP347H after LSP, and the fine grain layer existed in PDL. Due to the compressive residual stress in PDL, TP347H after LSP presented an excellent oxidation resistance in SCW, presenting oxidation rate of 0.5–0.8 times compared with TP347H. This was mainly attributed to the increased molar volume of Cr in PDL, leading to the existence of the stress-dependent chemical potential (μs) of Cr. μs promoted the formation of Cr2O3 and FeCr2O4, and improved the diffusion flux of Cr during oxidation.

Influencing effects of variant laser pulse energy on fatigue behavior induced by LSP

The set objective in this study is to understand the effects of laser shock processing of variant laser pulse energies on residual compressive stress, microhardness, fatigue fracture and fatigue life in the application of aircraft lug material. The effects of three variant laser pulse energies of 3.0, 4.0 and 5.7 J were examined along with laser processing parameters. A Q-switch (neodymium (Nd)-doped yttrium aluminum garnet) laser system was used in this experiment with a wavelength, a pulse width, a spot diameter and an overlapping ratio of 1046 nm, 10 nm, 3 mm and 50%, respectively. After laser shock peening (LSP), the superficial layer stress state showed varied results from tensile to residual stress of 50 to −225, −260 and −301 MPa after 3.0, 4.0 and 5.7 J, respectively. The microhardness of the as-received specimen was 137 HV. However, after LSP, it increased to 198, 210 and 223 HV, respectively. The fatigue life performance also significantly increased up to 53 371 (2 × 105) cycles.

Enhancement of surface characteristics of additively manufactured γ-TiAl and IN939 alloys after laser shock processing

The enhancement in laser technology opened up new methods such as additive manufacturing (AM) of metals. While AM offers high design flexibility and reduced material usage, it can also produce problematic parts due to poor surface quality. A variety of post-processing techniques are available to address the drawbacks associated with the surface properties of AM. Laser Shock Processing (LSP) is one of the unique methods that induces compressive residual stress (CRS) on the surface and subsurface by creating severe plastic deformation. In this study, two critical aerospace alloys (γ-TiAl and IN939) were manufactured through two different methods called Powder Bed Fusion with Electron Beam (PBF-EB) and Powder Bed Fusion with Laser Beam (PBF-LB). Subsequently, AM samples were investigated to observe single layer LSP effects on the surface. The results of the laser peening process were determined by residual stress, microhardness and surface roughness measurements. The residual stress profiles showed that LSP significantly induces CRS on the surfaces of AM alloys. For the γ-TiAl and IN939 samples, the maximum values of CRS and depth of CRS were −460 MPa/1000 µm and −516 MPa/700 µm, respectively. Similarly, the microhardness of the materials was increased by 44.4 % for γ-TiAl and 18.2 % for IN939 by laser post-processing. In addition, a comparison of the roughness of the unground and ground AM samples was carried out. Depending on the surface condition of the AM samples, LSP had different outcomes. For example, the extreme roughness of the AM samples was partially reduced by the thermal effects of the high-energy laser shots. When comparing the roughness values in terms of Ra and Rz, there were decreases in the range of 14.7–21.3 % and 3.34–39.3 % for unground IN939 samples. However, for unground γ-TiAl samples, depending on the direction of measurement, roughness variations were observed as a 0.99 % decrease − 5.3 % increase for Ra and a 2.2 % decrease − 14.2 % increase for Rz. The roughness values for ground samples of both alloys were drastically increased, varying between 42.1 % and 7x increase. Sa values were recorded on unground AM samples. For IN939 and γ-TiAl samples these values decreased by 8.41 % and 15.8 % respectively.

Effect of Laser Shock Processing on Microstructure and Mechanical Properties of M50 Bearing Steel

Effect of Laser Shock Processing on Microstructure and Mechanical Properties of M50 Bearing Steel

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.

Effect of laser shock processing on residual stress evolution in martensitic stainless steel multi-pass butt-welded joints

Laser shock processing (LSP) is an innovative approach, which effectively improves the mechanical behavior of metallic structures by introducing compressive residual stress. To evaluate the residual stress evolution in low-carbon 13Cr4Ni martensitic stainless steel multi-pass butt-welded joints induced by LSP, a two-step numerical simulation including welding analysis, at first, followed by LSP calculation with the simulated welding stress results being taken into account, was performed based on ABAQUS software. Effects of LSP parameters such as power density, spot size, overlapping rate and numbers of laser shock on the residual stress variations, were systematically investigated. To validate the reliability and accuracy of the numerical simulation, experiments of welding and LSP were conducted in sequence. The residual stress after welding and LSP were investigated by x-ray diffraction method. Results demonstrate that the simulated results show a good agreement with the experimental datas. The welding residual stress distribution is uneven. Larger tensile stresses appear on the weld surface and its adjacent heat-affected zone, which could be converted into high-level compressive stress after LSP. Furthermore, an ideal residual stress field can be obtained after two successive laser shocks with an overlap rate of 75% when the power density, spot diameter, and pulse width are 7.6 GW cm−2, 4 mm, and 25 ns, respectively.

High temperature oxidation resistance of laser shock modified NiAlHf metallic bond layer

The growth state of the thermally grown oxide (TGO) in thermal barrier coatings (TBC) has a crucial influence on the lifetime of TBC. Laser shock processing (LSP) is a new method for modifying the metallic bond layer. In this paper, NiAlHf coatings were modified through LSP. The effect of LSP on TGO formation in the early oxidation phase, the growth state of TGO at the long oxidation stage and the distribution of Hf element within the NiAlHf coatings after LSP were investigated. The results show that LSP successfully induce two effects on NiAlHf coatings. (1) The original oxide particles on the coatings surface are smaller and distribute more densely after LSP. In the oxidation process, these smaller and denser particles act as nucleation points, which make it easier for them to grow rapidly into a continuous oxide film. (2) LSP introduces high density dislocation lines, dislocation cells, sub-grain boundaries and other crystal defects, which provides more short diffusion channels for the selective oxidation of Al element and promotes the growth of oxide films. Both of these effects promote the rapid formation of a dense, continuous and homogeneous oxide film during the early oxidation stages. In addition, Hf element in the No-LSP samples mainly precipitate along the NiAl grain boundaries during the long-time oxidation process. This tends to cause the accumulation of Hf-rich oxides and accelerates the cracking of the oxide film. In contrast, LSP-induced crystal defects allow Hf-rich oxides uniformly distribute within the coatings. The uniform distribution of Hf-rich oxides is beneficial for improving the oxidation resistance of TGO films.

Thermal fatigue crack growth behavior of Ni60 coating and bonding area on 20CrNiMo alloy strengthened by laser shock processing

After the laser cladding repair of the brake disc surface in high-speed trains, thermal fatigue cracks in the cladding layer and bonding area are easily observed during the service process. With the aim of solving this problem and decreasing hidden risks, effects of laser shock processing (LSP) on the thermal fatigue life and crack growth behavior of the coating and bonding area of the brake disc were investigated. The results indicate that LSP can refine the columnar grain structures of the cladding layer and bonding area while simultaneously converting residual tensile stress into compressive stress; as a result, the thermal fatigue performance of the brake disc repaired by laser cladding is enhanced. After strengthening by LSP, on the one hand, grain refinement made the structure more uniform and generated more grain boundaries; on the other hand, a pre-set compressive stress field in the cladding layer and bonding area existed. Both aspects were beneficial to dissipate the alternating stress generated by the thermal fatigue process, dissipating the driving force of crack extension and promoting the transformation of thermal fatigue cracks from lateral growth along the interface between the cladding layer and bonding area to the growth into the substrate.

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.

The effect of laser shock processing on the microstructures and properties of 2060 Al[sbnd]Li alloys

The microstructures, mechanical properties and corrosion resistance of 2060 AL-Li alloy subjected to laser shock peening (LSP) with power densities of 3, 4 and 5 GW·cm−2 were investigated comprehensively. Microhardness, residual stress, wear resistance and fatigue life were tested on LSP alloys to analyze the mechanical properties and the corrosion behavior was investigated by electrochemical test. X-ray diffraction (XRD) and field emission transmission electron microscopy (FE-TEM) were used to investigate the surface microstructure evolution. The results show that LSP leads to a high magnitude of surface compressive residual stress and a significant increase of dislocation density near the surface in the plastic deformation layer. Additionally, with the increase of laser power density, the microhardness, compressive residual stress and surface roughness increase, while the friction coefficient and wear rate decrease compared to pristine alloy. The fatigue life of the sample with a laser power density of 4 GW·cm−2 reaches the highest value of 6.00 × 104 times, approximately twice that of the pristine sample (2.98 × 104 times), which is mainly attributed to the surface residual compressive stress, high density dislocations and surface hardening owing to the LSP. The corrosion resistance of the LSP alloys modestly decreases in a 3.5% NaCl solution compared with pristine alloy, which mainly ascribes to the increase of surface roughness.

Effect of laser shock processing on water adsorption of electron-beam deposited multilayer coatings

A novel laser shock post-processing (LSPP) technique for reducing the water absorption of porous coatings deposited by electron-beam evaporation was proposed and investigated for first time. It's found the processing parameters of LSPP evidently affected the water absorption through the synergy and competition between the packing density and surface roughness. With optimal processing parameters, LSPP verified an effective and positive effect on reducing water absorption by enhancing the packing density of coatings, without weakening its' original optical performance. It's believed LSPP will provide a promising and optional post-processing method to well ensure the long-term operation stability of the porous coatings and the high-power laser facilities.

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.

Thermal fatigue crack growth behavior of ZCuAl10Fe3Mn2 alloy strengthened by laser shock processing

Abstract The effect of laser shock processing (LSP) on the hardness, surface morphology, residual stress, and thermal fatigue properties of a ZCuAl10Fe3Mn2 alloy was investigated to improve the thermal fatigue performance and decrease the surface crack of high-temperature components. The microstructure and crack morphology were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that laser shock could significantly improve the thermal fatigue performance of the alloy at a pulse energy of 4 J. Under the effect of thermal stress and alternating stress, microstructure around the specimen notch was oxidized and became porous, leading to the formation of multiple micro-cracks. The micro-cracks in the vertical direction became the main cracks, which mainly expanded with the conjoining of contiguous voids at the crack tip front. Micro-cracks in other directions grew along the grain boundaries and led to material shedding.

Effects of laser shock processing, solid solution and aging, and cryogenic treatments on microstructure and thermal fatigue performance of ZCuAl10Fe3Mn2 alloy

The materials used in variable temperature conditions are required to have excellent thermal fatigue performance. The effects of laser shock processing (LSP), solid solution and aging treatment (T6), and cryogenic treatment (CT) on both microstructure and thermal fatigue performance of ZCuAl10Fe3Mn2 alloys were studied. Microstructure and crack morphology were then examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The result showed that, after being subjected to the combination treatment of T6+CT+LSP, the optimal mechanical properties and thermal fatigue performance were obtained for the ZCuAl10Fe3Mn2 alloy with the tensile strength, hardness, and elongation of 720 MPa, 300.16 HB, and 16%, respectively, and the thermal fatigue life could reach 7,100 cycles when the crack length was 0.1 mm. Moreover, the ZCuAl10Fe3Mn2 after combination treatment shows high resistance to oxidation, good adhesion between the matrix and grain boundaries, and dramatically reduced growth rate of crack. During thermal fatigue testing, under the combined action of thermal and alternating stresses, the microstructure around the sample notch oxidized and became loose and porous, which then converted to micro-cracks. Fatigue crack expanded along the grain boundary in the early stage. In the later stage, under the cyclic stress accumulation, the oxidized microstructure separated from the matrix, and the fatigue crack expanded in both intergranular and transgranular ways. The main crack was thick, and the path was meandering.

Effect of Laser-Shock Processing on Generation of Contamination Induced by Nanosecond Laser Irradiation of Aluminum Alloy

Effect of Laser-Shock Processing on Generation of Contamination Induced by Nanosecond Laser Irradiation of Aluminum Alloy

Enhancement of Material Crack Resistance Using Laser Shock Processing

In this paper, we develop a numerical model that allows predicting the effect of laser shock processing of materials on the occurrence of new cracks, as well as on the propagation pattern of existing cracks. Linear cracks and so-called V-shaped cracks are studied. The fields of residual stresses arising during laser shock processing are determined. The optimal modes of laser shock processing in terms of the maximal deceleration of the propagation velocity of the cracks are revealed. The results obtained are in good agreement with the experimental data.

Effect of laser shock processing on oxidation resistance of laser additive manufactured Ti6Al4V titanium alloy

The high-temperature oxidation resistance of laser additive manufactured (LAM) Ti6Al4V before and after laser shock processing (LSP) was investigated. The samples were oxidized at 400−800 °C for 1−50 h in air. The results revealed that the rate of weight gain of the Ti6Al4V fabricated through LAM decreased, and LSP had a positive effect on increasing the oxidation resistance. At an oxidation temperature of 700 °C, an aluminum-rich layer was observed in the cross-section before LSP. After LSP, the aluminum-rich layer changed to three layers. The aluminum-rich layer prevented the diffusion of oxygen, which improved the oxidation resistance of the Ti6Al4V.

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.

Effect of Laser Shock Processing and Aluminizing on Microstructure and High-Temperature Creep Properties of 321 Stainless Steel for Solar Thermal Power Generation

The aluminized layer of 321 stainless steel was treated by laser shock processing (LSP). The effects of constituent distribution and microstructure change of the aluminized layer in 321 stainless steel on creep performance at high temperature were investigated. SEM and EDS results reveal that aluminized coating is mainly composed of an Al2O3 outer layer, the transition layer of the Fe-Al phase, and the diffusion layer. Additionally, LSP conducted on coating surface not only improves the density of the layer structure, resulting in an increment on the bonding strength of both infiltration layer and substrate, but also leaves higher residual compressive stress in the aluminized layer which improves its creep life effectively. Experimental results indicate that the microhardness of the laser-shocked region is improved strongly by the refined grains and the reconstruction of microstructures. Meanwhile, the roughness and microhardness of aluminized steel are found to increase with the laser impact times. On the other hand, the intermetallic layers, whose microstructure is stable enough to inhibit crack initiation, reinforce strength greatly. The anticreep life of aluminized sample with three times LSP was increased by 232.1% as compared to aluminized steel, which could attribute to the increased dislocation density in the peened sample as well as the decrease of creep voids in size and density.

Effects of laser shock processing and shot peening on 253 MA austenitic stainless steel and their consequences on fatigue properties

A comparative study of the influence of laser shock peening without coating (LSPwC) and shot peening (SP) treatments on the low cycle fatigue life of 253 MA austenitic stainless steel was investigated. LSPwC treatments were performed with 2500 pulse/cm2 and 5000 pulse/cm2. To evaluate the effects of each treatment, residual stress, roughness, hardness, and microstructure were analyzed. It is of particular interest the correlation of the fatigue performance with the dislocation microstructure evolution. The results reveal that all the surface treatments increase the surface hardness, induce compressive residual stresses (CRS) and a high density of mechanical twins and dislocations. The stability of the workhardened near surface microstructure results in the improvement of the fatigue life of peened 253 MA. Moreover, the best improvement of fatigue life reached for SP is mainly due to the highest number of twins and the more superficial CRS.