Laser shock processing of aluminium alloys. Application to high cycle fatigue behaviour
15 Jun 1996-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing (Elsevier)-Vol. 210, pp 102-113
TL;DR: In this article, the role of laser shock processing (LSP) on the cyclic properties of A356, Al12Si and 7075 aluminium alloys was evaluated, and major contributors to the fatigue performance improvements were investigated in order to determine the optimum shock conditions.
Abstract: Subjecting target metallic samples to a very short pulse (about 20 ns) of intense (GW cm−2) laser light generates, through a surface plasma, a high-pressure stress wave propagating to the first millimetre in depth, which is commonly called laser shock processing (LSP). The purpose of this work was to evaluate the role of this novel process on the cyclic properties of A356, Al12Si and 7075 aluminium alloys. Major contributors to the fatigue performance improvements were investigated in order to determine the optimum shock conditions. These were mainly compressive residual stress (RS) levels for which a large range of incident shock conditions was performed. We showed that stress levels were very sensitive to the laser fluence and the number of local impacts, and experimental RS measurements were found to be in good agreement with analytical modelling results. In comparison, a conventional shot peening (SP) treatment was found to lead to higher surface hardening and RS levels, but with a very detrimental roughening not observed after LSP. High cycle (107) fatigue tests carried out on laser- processed, shot-peened and untreated notched samples illustrated the efficiency of LSP as a new, promising method to improve the fatigue limits σD of structures, especially in comparison with enhancements displayed by SP (+22% vs. +10%). According to crack detection electric measurements, fatigue performance improvements with LSP mainly occurred during the crack initiation stage.
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TL;DR: In this paper, the current status of research and development on laser shock processing of metals, also known as laser peening, using Q-switched high power lasers is reviewed and the influence of processing parameters on the laser-induced shock waves in metal components are discussed and analyzed.
933 citations
TL;DR: In this article, the plastic deformation behavior and the effects of the impact time on the LY2 aluminum (Al) alloy during multiple laser shock processing (LSP) impacts were investigated.
316 citations
TL;DR: In this paper, a review of the main process parameters controlling pressure generation in a confined mode is presented, including laser intensity, target material, laser pulse duration, and laser wavelength.
Abstract: The first part of this article presents a review of the main process parameters controlling pressure generation in a confined mode The effect of laser intensity, target material, laser pulse duration, and laser wavelength are, therefore, discussed An optimized process can then be defined The second part of this article deals with the surface modifications induced by laser-shock processing The generation of residual compressive stresses is then highlighted Finally, in the third part, the interest of laser-shock processing is discussed for several typical applications A conclusion will present the future trends of this technique
315 citations
31 Mar 2000-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: The influence of laser peening on the electrochemical behavior of 316L stainless steel in a saline environment was evaluated in this paper, where surface modifications were investigated as they might have beneficial effects on the corrosion behavior.
Abstract: The influence of laser peening (LP) on the electrochemical behavior of AISI type 316L stainless steel in a saline environment was evaluated. Surface modifications were investigated as they might have beneficial effects on the corrosion behaviour. Low residual stress and work hardening levels were found, when compared with a conventional shot-peening (SP) treatment, mainly because of the absence of martensite transformation in the case of LP. Surface changes were accompanied by small roughening effects and a global preservation of the surface chemistry after treatment. Therefore, electrochemical tests performed on samples after LP and SP treatments showed increases in rest potentials, reductions of passive current densities and anodic shifts of the pitting potentials evidenced by a stochastic approach of pitting. The better pitting resistance was observed after LP treatment, which seems to reflect a reduction or an elimination of active sites for pitting at lower potentials. Even though the deleterious surface state of shot peened surfaces possibly counterbalances the beneficial influence of residual stresses, a beneficial influence of mechanical surface treatments has been demonstrated regarding the localized corrosion properties.
308 citations
15 Feb 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, laser peening without protective coating (LPPC) has been applied to water-immersed SUS304 (Type 304) and SUS316L (Type 316L) austenitic stainless steels.
Abstract: Laser peening without protective coating (LPPC) has been applied to water-immersed SUS304 (Type 304) and SUS316L (Type 316L) austenitic stainless steels. The surface residual stress of both materials was converted from tensile to compressive of several hundreds of megapascals by LPPC with a Q-switched and frequency-doubled Nd:YAG laser. The depth of the compressive residual stresses after LPPC exceeded 1 mm from the surface. Accelerating stress corrosion cracking (SCC) tests in a high-temperature and corrosive-water environment showed that LPPC completely prevented the SCC initiation of sensitized SUS304. SCC tests of pre-cracked samples were also performed for SUS304, which indicated that LPPC inhibits the propagation of the small pre-cracks. Rotating bending tests demonstrated that the fatigue strength of SUS316L with LPPC is enhanced by 1.4–1.7 times compared to that of the reference material at 108 cycles.
281 citations
References
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TL;DR: In this article, the authors studied the physical processes involved in laser-produced plasma in confined geometry, and showed that a large fraction of the absorbed laser energy (80% to 90%) is used for the ionization of the medium in these conditions of irradiation.
Abstract: We study in this paper the different physical processes involved in laser‐produced plasma in confined geometry. With this technique, a laser irradiates a target at an intensity of a few GW/cm2, and the produced plasma is confined by a transparent overlay to the laser which covers this target. This configuration has appeared necessary for example for metallurgical applications where, for a given laser energy, enhanced pressures must be realized in order to achieve high shock pressures. Therefore, a physical study of this method is useful in order to optimize this technique. We have first developed an analytical model which describes the different steps involved in this process, points out the interest of this technique, and compares it to the direct ablation regime. In the first stage, during the laser heating, the generated pressure is typically 4–10 times greater than the corresponding one obtained in direct ablation. The second step begins after the switch‐off of the laser and is characterized by an adiabatic cooling of the plasma which maintains the applied pressure over a period which is about 2 times the laser‐pulse duration. Finally, the third stage concerns also the adiabatic cooling of the recombined plasma, but during this period the exerted pressure is too small to realize a plastic deformation of the material. We show that the impulse momentum given to the target is mainly generated during this step. This model allows us to also determine the velocities of thin foils accelerated with confined plasmas, and we show that very high hydrodynamic efficiencies can be achieved by this technique. Experimentally, we measured with quartz gauges, the pressures obtained in confined geometry, for 30‐, 3‐, and 0.6‐ns laser‐pulse duration. This study shows that short pulse durations are sensitive to the initial roughness of the interface, and such an effect should be suppressed by using a liquid confinement. Then, we conclude that a large fraction of the absorbed laser energy (80%–90%) is used for the ionization of the medium in these conditions of irradiation. Finally, we experimentally point out that the laser‐induced breakdown of the confining medium is the main mechanism which limits the generated pressure and show the influence of the laser‐pulse duration on this effect.
1,188 citations
TL;DR: In this article, the dielectric breakdown of a neodynium glass laser at 1.06 μm and pulse width of 3 and 30 ns was studied. And the authors showed that the use of a short rise-time laser pulse is the only way to reduce the effects of the breakdown and to obtain much higher pressure shock waves.
Abstract: Confined plasmas induced by neodynium glass laser at 1.06 μm and pulse width of 3 and 30 ns are studied. The metallic target is covered with a dielectric layer, glass or water, transparent to the laser radiation. Experimental measurements of the pressure induced by the plasma have been performed. For a certain range of laser power density these measurements agree particularly well with an analytical model. At high power densities (10 GW/cm2), the dielectric breakdown appears to be the main limiting process of the confining method. It is observed that this breakdown induces a saturation of the pressure. It is shown that the use of a short‐rise‐time laser pulse is the only way to reduce the effects of the breakdown and to obtain much higher‐pressure shock waves. This is due to the dependence of the dielectric breakdown threshold on the laser pulse rise time.
227 citations
TL;DR: In this article, it is proposed that the incoming beam of electrons or radiant energy produces surface heating with consequent thermal expansion at the surface and propagation of the elastic disturbance, and several experiments supporting this hypothesis are presented.
Abstract: High-frequency elastic waves produced by electron bombardment or electromagnetic wave absorption are investigated. It is proposed that the incoming beam of electrons or radiant energy produces surface heating with consequent thermal expansion at the surface and propagation of the elastic disturbance. Several experiments supporting this hypothesis are presented. Stainless steel, copper, molybdenum, and Invar were used as the target materials.
185 citations
TL;DR: The hole-drilling method is widely used to measure residual stresses in mechanical components and has been shown that strains measured on the surface during an incremental drilling can be related to residual-stress distribution as discussed by the authors.
73 citations
01 Jan 1993
4 citations