Papers by Keyword: Laser Shock Processing (LSP)

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Authors: Wei Feng He, Yu Qin Li, Xiang Fan Nie, Rui Jun Liu, Qi Peng Li
Abstract: In this paper, the microstructure and hardness of Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy with and without laser shock peening (LSP) were examined and compared. The titanium alloy samples were laser shock peened with different layers at the same power density. The microscopic structure after LSP are tested and analyzed by SEM and TEM. The results indicated that LSP changed the microstructure evidently. After 3 layers laser shock peening, there are nanocrystallization in the LSP zone. The shock wave provided high strain rate deformation and generated high-density dislocations in the material. Multiple severe plastic deformation caused by 3 to 5 LSP layers helped to rearrange the resultant dislocation, to form dislocation networks, leading to the formation of nanocrystallites. On the other hand, the microhardness across the polished surfaces of the titanium materials with and without LSP was measured. It is obvious that the laser shock peening improved the microhardness of the Ti-5Al-2Sn-2Zr-4Mo-4Cr for about 16% at the surface, and the affected depth is about 300 microns from the surface.
471
Authors: Xu Dong Ren, T. Zhang, Yong Kang Zhang, Da Wei Jiang, Kang Min Chen
Abstract: Cracks were prefabricated on compact tension specimen of 7050 Aluminum alloy, which was laser shock processing(LSP) once and three times. The whole crack initiation process, distribution and size evolution on aluminum alloy was studied with replica technique and through optical microscope. It was found that without LSP, small cracks initiated at the grain boundary and grew quickly. The cracks continued growing in depth. The growth of short cracks had the trend of stop-and-go oscillation, the crack data were relatively scattered, and short cracks had short average length and grew earlier. After LSP, surface residual compressive stress restrained to the trend of crack origins where crack origins would form most easily; after origination, cracks initiated towards the processed region, but stop temporarily if encountering great resistance, and might generate additional crack origins; Moreover, the higher the level of stress created by LSP was, the fewer cracks initiated.
3852
Authors: Guo Min Lin, Li Xia Peng, Yu Feng Zhao
Abstract: The application of two representative laser surface treatments technologies which are laser shock processing technology and laser coating treatment technology are described. The application of laser shock processing in the fields of aero engine disc, wing panel formation, structural welding and strengthening, nuclear power station pressure container strengthening etc and also evaluates the effects are analyzed. The applications of laser coating treatment in the field of aeronautic manufacturing are analyzed in detail. The development direction of laser shock processing and laser coating treatment are indicated finally.
2199
Authors: Ai Xin Feng, Gui Feng Nie, Fen Shi, Chuan Chao Xu, Huai Yang Sun, Peng Cheng Zhou, Jun Wei Wang
Abstract: In order to study the dynamic response of metal of laser shock processing, dynamic strain curves of AM60 Magnesium alloy during laser shock processing were measured by resistance strain gauges. Dynamic strain curves of three equiangular rosette near the shock spot and three strain gauges of different distances from the spot center were studied. The results indicated that the strain rate of AM60 Magnesium alloy decreased and plastic deformation increased with increasing impact times. And one dimensional strain hypothesis of laser shock processing was reasonable.
1876
Authors: Qi Peng Li, Ying Hong Li, Wei Feng He, Wei Li, Yu Qin Li
Abstract: The vibration strength under allowable value leads to the failure of compressor blade of certain aeroengine. In order to solve the problem, laser shock processing on blade was studied. First, the processed part of blade as well as the laser shock processing (LSP) parameters was established. Second, the influence of LSP and tumbling to the vibrate fatigue capability of blades were researched according to the application of the project. Third, the strengthening mechanism of LSP on improving the fatigue performance of the blade was studied. The results show that, LSP is consistently dependable and can prolong the vibration fatigue life of the blade efficiently. LSP can be placed after tumbling or directly replace it during the manufacturing of blade. The grain refinement, higher hardness and compressive residual stress are the three main reasons that enhance the fatigue capability of blade.
184
Authors: Yong Kang Zhang, Xu Dong Ren, Jian Zhong Zhou, Ai Xin Feng
Abstract: Laser shock processing (LSP) employs high-energy laser pulses from a solid-state laser to create intense shock waves into a material, which can induce compressive residual stresses in the target surface and improve its mechanical property efficiency. Three different ablative, sacrificial coating were chosen to protect the 6061-T651 alloys from surface melting by laser pulse. This paper analyzes the effect of the paint and foil coatings on the shock wave propagation into the 6061-T651 alloys and the resulting change in mechanical properties. The depths of hardening by laser processing of 6061-T651 alloys up to 1 mm, and the surface hardness reach to 138HV. When the laser pulse energy density increase from 2.8 GW/cm2 to 3.6 GW/cm2, the surface hardness of the black paint, aluminum foil and silica acid black paint samples increase to 19, 27, 36 respectively.
681
Authors: Y.Y. Xu, Xu Dong Ren, Yong Kang Zhang, Jian Zhong Zhou, Xing Quan Zhang
Abstract: Laser shock processing is an important surface treatment that induces compressive residual stress to components, where the coating plays an important role. This paper deduce a general formula of the optimum thickness of coating according to the law of energy conservation and analysis the influence of coating on residual stress of the titanium alloy in laser shock processing. Titanium alloy with black paint, silica acid black paint and without coating were shocked by laser system respectively. It was found that coating could increase shock pressure amplitude and laser density absorption. Compressive residual stresses at the surface of the sample with the black paint and silica acid black paint are about -212.2MPa and -264.2MPa respectively, while the surface stress on the uncoated specimen is very high tensile stress. The bare surface due to melting and vaporization, leads to a very rough surface. The depth of induced compressive stress could reduce stress corrosion cracking in titanium alloy and improve fatigue lifetime.
1753
Authors: M.L. Zhang, J.M. Wang, Y.F. Jiang, Q.L. Zhang, Q.L. Zhou
Abstract: The solution treatment and solution and aging treatment (T6) were disposed on 7050 aluminium alloy, then local processed by laser shock processing (LSP) with high-rate neodymium glass laser. The microhardness and residual stress on the surface of 7050 aluminium alloy were tested, then how the microstructure influences the residual stress on the surface of 7050 aluminium alloy by laser shock processing was analysed. The results show that the microhardness and residual compressive stress on the surface of 7050 aluminium alloy treated by solution and aging treatment was higher, and decreased obviously treated by solution treatment; the microhardness and residual compressive stress on the surface of 7050 aluminium alloy increased obviously by solution treatment and solution and aging treatment after laser shock processing; treated by solution treatment and solution and aging treatment, the microhardness and residual compressive stress of the material with uniform original structure was higher than the material with nonuniform original structure.
1363
Authors: Rui Fang Chen, Hui Jiang, Yin Qun Hua, Yu Xiao Chen, Zhen Grong Cai
Abstract: The effect of laser shock processing (LSP) on bending fatigue performance of 7075-T651 aluminum alloy was studied. LSP was performed on fatigue testing specimens with optimized parameters. Stress-life fatigue data were generated for both shocked and as-machined conditions. The fatigue improvements of LSP were discussed accounting for the effect of residual stress. The results show that shocked specimens exhibited significantly improved fatigue performance, with as-machined specimens having a factor of 1.6-4.4 improvement in fatigue life (depending on fatigue stress level). The stability of the residual stress induced by LSP under cyclic load was particularly investigated by means of X-ray diffraction measurements. Residual stress relaxation was observed. And the higher the cyclic load, the higher the relaxation rate. Due to the cyclic creep effect, the residual stress decreases linearly with the logarithm of the number of cycles.
430
Authors: Jun Feng Pei, Jun Ning Liu, Wei Ying He
Abstract: Laser shock processing (LSP) is a new technique for metal surface strengthening by which residual compressive stress in the superficial layer can be induced to greatly improve the stress corrosion resistance property. The effect of LSP on sulfide stress corrosion cracking (SSCC) of X70 pipeline steel welded joint has been studied in this paper. A convergent lens is used to deliver 20 J, 20 ns laser pulses by a Q switch Nd:YAG laser, operating at 10 Hz. The pulses are focused to a diameter of 3 mm onto samples. The power density of laser at the surface of the sample was about 5 GW/cm2. The surface residual stress level after LSP is much higher than before. SSCC behavior of X70 pipeline steel welded joint was investigated using slow strain rate testing (SSRT) in H2S solution. Morphology of X70 pipeline steel fracture surface was observed by scanning electron microscope (SEM). It has been demonstrated that LSP is an effective surface treatment technique to improve the stress corrosion cracking (SCC) resistance properties of X70 pipeline steel welded joints.
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