Surface prestressing to improve fatigue strength of components by laser shot peening

The influence of nanosecond laser pulses applied by laser shock peening without absorbent coating (LSPwC) with a Q-switched Nd:YAG laser operating at a wavelength of \ = 1064 nm on 6082-T651 Al alloy has been investigated. The first portion of the present study assesses laser shock peening effect at two pulse densities on three-dimensional (3D) surface topography characteristics. In the second part of the study, the peening effect on surface texture orientation and micro-structure modification, i.e. the effect of surface craters due to plasma and shock waves, were investigated in both longitudinal (L) and transverse (T) directions of the laser-beam movement. In the final portion of the study, the changes of mechanical properties were evaluated with a residual stress profile and Vickers micro-hardness through depth variation in the near surface layer, whereas factorial design with a response surface methodology (RSM) was applied. The surface topographic and micro-structural effect of laser shock peening were characterised with optical microscopy, InfiniteFocus® microscopy and scanning electron microscopy (SEM). Residual stress evaluation based on a hole-drilling integral method confirmed higher compression at the near surface layer (33 um) in the transverse direction (Omin) of laser-beam movement, i.e. -407 ±81 MPa and -346 ± 124 MPa, after 900 and 2500 pulses/cm 2 , respectively. Moreover, RSM analysis of micro-hardness through depth distribution confirmed an increase at both pulse densities, whereas LSPwC-generated shock waves showed the impact effect of up to 800 um below the surface. Furthermore, ANOVA results confirmed the insignificant influence of LSPwC treatment direction on micro-hardness distribution indicating essentially homogeneous conditions, in both I and T directions.

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“…Initially, LSP was developed for the aeronautic industry as the method for the improvement of resistance to fatigue cracking [3][4][5],…”

Section: Introductionmentioning

confidence: 99%

Laser shock peening without absorbent coating (LSPwC) effect on 3D surface topography and mechanical properties of 6082-T651 Al alloy

Trdan

Porro

Ocaña

et al. 2012

Surface and Coatings Technology

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“…The Laser Shock Peening (LSP) process introduces surface compressive residual stresses which improve material properties of various metals [1][2][3]. Its main advantages over conventional treatments is deeper shock wave penetration, as well as process flexibility which allows treatment of parts with complicated geometries.…”

Section: Intensity Contrast Methodsmentioning

confidence: 99%

Characterization of Heterogeneous Response of Al Bicrystal Subject to Micro Scale Laser Shock Peening

et al. 2010

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This letter shows the ability to perform characterization of the strain field in an aluminium bicrystal subject to plane strain condition induced by micro scale laser shock peening. Intensity contrast method, previously used in topographic measurements of strain fields in thin films is employed here. Our results show that this method is applicable for measurements of the plastically deformed bulk materials. Moreover, heterogeneous response of the grain boundary is observed as periodic nature of deformation.Keywords Laser . Bicrystal . Plasticity . X-ray diffraction . Intensity contrast methodThe Laser Shock Peening (LSP) process introduces surface compressive residual stresses which improve material properties of various metals 1-3]. Its main advantages over conventional treatments is deeper shock wave penetration, as well as process flexibility which allows treatment of parts with complicated geometries. The high cost of high power lasers required for LSP led to the development of micro scale laser shock peening [4] (μLSP). This process can be used to improve fatigue life and wear resistance of miniature devices such as micro switches, MEMS, etc. Since the diameter of the laser spot used during μLSP is of the same order of magnitude as the grain size of most materials undergoing the process, the effects of sample anisotropy [5][6][7] and heterogeneity [8] have to be explicitly taken into account in the analysis of the residual field formation.X-ray topography is an excellent non-destructive method for characterization of defects and strain fields in thin films. With this technique the intensity contrast produced by local strain gradients or lattice rotations is used to characterize elastic and plastic deformation fields. The Intensity contrast method has been used for the characterization of metallic thin films processed with μLSP [9,10].The goal of the current study is to employ the intensity contrast method to characterize plastic deformation induced in bicrystal aluminium samples subjected to μLSP. We have been able to observe the effects of heterogeneity as a consequence of shock wave interaction with the grain boundary, and the distribution of plastic deformation throughout the material.An aluminum bicrystal grown from the melt with the modified Bridgman technique was used. The grain boundary between the crystals was a CSL Σ43 symmetric tilt-type with the [110] direction parallel to the tilt axis of the adjoining grains. The surfaces of the individual crystals deviated about 9.5°and 2.5°f rom the ideal (110) and (001) surfaces, respectively. These orientations were chosen because, if the loading line is placed along <110> direction, an approximate plane strain deformation will be induced [11,12]. A frequency tripled Q-switched Nd:YAG laser with wavelength λ = 355°nm in TEM 00 mode was used for the

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“…LSP offers advantages such as a higher depth of plastic deformation (than conventional shot peening) and a minimum effect on surface roughness of the substrate. [70][71][72] LSP has also been used to enhance the surface properties like wear and corrosion resistance of Mg alloys.…”

Section: Laser Shock Peening (Lsp)mentioning

confidence: 99%

Laser Surface Engineering of Magnesium Alloys: A Review

Singh

Harimkar

2012

JOM

121

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Magnesium (Mg) and its alloys are well known for their high specific strength and low density. However, widespread applications of Mg alloys in structural components are impeded by their insufficient wear and corrosion resistance. Various surface engineering approaches, including electrochemical processes (plating, conversion coatings, hydriding, and anodizing), gas-phase deposition (thermal spray, chemical vapor deposition, physical vapor deposition, diamond-like coatings, diffusion coatings, and ion implantation), and organic polymer coatings (painting and powder coating), have been used to improve the surface properties of Mg and its alloys. Recently, laser surface engineering approaches are attracting significant attention because of the wide range of possibilities in achieving the desired microstructural and compositional modifications through a range of laser-material interactions (surface melting, shock peening, and ablation). This article presents a review of various laser surface engineering approaches such as laser surface melting, laser surface alloying, laser surface cladding, laser composite surfacing, and laser shock peening used for surface modification of Mg alloys. The laser-material interactions, microstructural/compositional changes, and properties development (mostly corrosion and wear resistance) accompanied with each of these approaches are reviewed.

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Surface prestressing to improve fatigue strength of components by laser shot peening

Cited by 144 publications

References 3 publications

Laser shock peening without absorbent coating (LSPwC) effect on 3D surface topography and mechanical properties of 6082-T651 Al alloy

Laser shock peening without absorbent coating (LSPwC) effect on 3D surface topography and mechanical properties of 6082-T651 Al alloy

Characterization of Heterogeneous Response of Al Bicrystal Subject to Micro Scale Laser Shock Peening

Laser Surface Engineering of Magnesium Alloys: A Review

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