Papers by Keyword: Laser Shock Processing (LSP)

Abstract: The effect of the Laser Shock Processing (LSP) on the microstructure of the surface layer of a commercially pure alluminum was studied. LSP process was performed with a high-power Q-switched Nd:YAG ReNOVALaser, operating in a pulse mode (18 ns), with a power density of 0,43 GW/cm2. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and a Scanning Transmision Electron Microscopy (STEM) have been used to study the microstructure of the surface layer of the investigated material after laser treatment. SEM investigation showed that after LSP process surface melting occurs but is restricted to a thin layer. However, both TEM and STEM images indicate that under the thin melting layer a high density of dislocations were visible. It has been found that the laser beam with employing parameters caused plastic deformation of the surface layer of the investigated aluminum.

Abstract: The distribution of the compressive residual stresses which caused by laser shock processing is a new surface strengthening technology to improve the quality of material surface. ABAQUS is used to simulate the distribution of residual stress field impacted by the laser power densities and the spot shapes. The consequences indicate that: following the laser power intensities increasing, the reflection waves coming from the spot edges should loaded reversely, inducing the opposite deformation, leading to the “residual stress drops” phenomenon; the spot shapes also influent the converging of the reflection waves toward the center, and the residual stress drops at the center are different. This research provides a basis for a better effect of LSP with the optimization of the technological parameters and the decrease of the residual stress drops at the center of the shocked zones.

Abstract: Based on the FEM code ABAQUS and MSC.Fatigue, the process of LSP before hole-drilling was adopted to study the residual stress field of aluminum alloy7050T7451 with Fastener Holes after Laser shock processing (LSP), and the fatigue life of the specimens by LSP was analyzed in this paper. The results indicate that multiple laser shock processing can improve the residual compressive stress and fatigue life to a certain degree, and with the increasing number of shot, the strengthening effect gradually decreases. The ratio of the fatigue life of specimens treated by LSP to the fatigue life of untreated specimens is gradually decreased as the mean stress σm increases, and when the σm is 67.3MPa, the fatigue life of specimens treated by LSP advances 719%, compared with that of untreated specimens.

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.

Abstract: Laser shock processing (LSP) is being increasingly applied as an effective technology for the improvement of metallic materials surface properties in different types of components as a means of enhancement of their corrosion and fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses field into metallic alloy pieces allowing an improved mechanical behaviour, explicitly the life improvement of the treated specimens against wear, crack growth and stress corrosion cracking. Additional results accomplished by the authors in the line of practical development of the LSP technique at an experimental level (aiming its integral assessment from an interrelated theoretical and experimental point of view) are presented in this paper. Concretely, follow-on experimental results on the residual stress profiles and associated surface properties modification successfully reached in typical materials (especially Al and Ti alloys) under different LSP irradiation conditions are presented along with a practical correlated analysis on the protective character of the residual stress profiles obtained under different irradiation strategies and the evaluation of the corresponding induced properties as material specific volume reduction at the surface, microhardness and wear resistance. Additional remarks on the improved character of the LSP technique over the traditional “shot peening” technique in what concerns depth of induced compressive residual stresses fields are also made through the paper.

Abstract: In order to study the effect of laser shock processing (LSP) on titanium alloy, a TC4 alloy sample was processed by Nd:YAG laser with the wavelength of 1.06μm and pulse width of 12ns, and its micro-hardness and residual stress were examined and analyzed. The experimental results show that an evident strengthening layer of sample forms in the laser shock processing area. Laser shock processing improves micro-hardness and residual compressive stress of the sample significantly such as surface micro-hardness increases by up to 28.4%, the tensile stress changed into compressive stress, the layer of compressive stress distributes more than 1mm in depth and the compressive stress in the surface reaches up to -304MPa with 5J pulse energy. The effect of laser shock evidently strengthens the TC4 alloy, which improves the fatigue life of the aviation material and the performance of resist stress and rust by a large margin.

Abstract: The liquid confinement medium (LCM) and the free confinement medium (FCM) made by ourselves were used as confinement overlays of laser shock processing (LSP) respectively, stainless steel 304 was shocked by Nd:Glass laser. The parameters of LSP are the wavelength of 1.06μm, the pulse duration of 20ns, and output energy of 35~40J. The laser was focused on a spot of Ф5mm. Firstly, the profiles of shocked regions of samples were measured by Taylor Hobson admeasuring apparatus, in which two different confinement mediums are used by LSP. Secondly, the ruinous behavior of the free confinement overlays induced by laser shock wave is observed and analyzed. Analyzed and compared with the experiments results, it is discovered that the effects of LSP are different with using different confinement mediums.

Abstract: This paper explores the properties of Fe40NiCrSiAl alloy treated by different methods. The hardness, elastic modulus and resistivity are tested. The results indicate that: after LSP to rolled Fe40NiCrSiAl alloy, the hardness increased 25.22%, the elastic modulus increased 7.17% and the resistivity decreased 39%. TEM photographs demonstrated that there appeared dislocations, martensite transformation and twin crystals inside the material after being treated by LSP. Twin crystals are the main reason attributing to the improvement of material electrical properties.

Abstract: Laser Shot Peening without protective Coating (LPPC) was performed on SS304 austenitic stainless steel using a 300 mJ, 10 ns pulse, 1064 nm wavelength Nd:YAG laser with three different pulse densities. A thin layer of water was used as a confinement layer. The peened specimen was characterised with XRD, AFM and a Profilometer. The stress evaluated at the surface of the laser peened sample shows a maximum compressive stress of 1.6 GPa. The surface roughness and depth profile of microhardness before and after LPPC were investigated.The LPPC region indicate substantial improvement in microhardness and compressive residual stress, with marginal increase of surface roughness.

Abstract: In this paper, the microstructure and microhardness of laser shock processed (LSP) Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si titanium alloy with and without annealing were examined and compared. The titanium alloy samples were LSP processed with 3 layers at 4.24GW/cm². Some of the samples were vacuum annealed at 623K for 10 hours. The microscopic structure with and without annealing were tested and analyzed by SEM, TEM. The results indicated that after LSP, the shock wave provided high strain rate deformation and led to the formation of ultra-fine grain. Comparing with the samples without annealing, the dislocation density was lower and the grain-boundary was more distinct in the annealed samples, but the sizes of the ultra-fine grain didn’t grow bigger after annealing. On the other hand, the microhardness measurement was made on the cross-section. It is obviously that the laser shock processing improved the microhardness of the Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si for about 12.2% at the surface, and the hardness affected depth is about 500 microns. The microhardness after annealing is 10 HV_0.5 lower, but the affected depth is not changed. The titanium alloy after LSP is thermostable at 623K; thus break the USA standard AMS2546, in which titanium parts after LSP are subjected in subsequent processing should not exceed 589K.