Laser peening without coating (LPwC) was done on the titanium TC6 alloy at a wavelength of 532 nm using an Nd:YAG laser. The laser power densities of 3, 6 and 9 GW cm−2 were used to peen the samples. Samples were also peened multiple times (1, 3 and 5 passes) at 6 GW cm−2. Microhardness showed an overall 23% increase from the baseline value. Further, softening of α phase in the bulk was observed above 6 GW cm−2 in the samples peened once and above 1 pass in multiply peened samples. A similar trend was observed from the residual stress analysis of the samples. The maximum compressive residual stress was −1780 MPa at a depth of 50 μm at 9 GW cm−2. The observed softening of α phase was proposed due to adiabatic heating. Microstructural changes due to adiabatic heating resulting in increased β volume fractions were observed and confirmed by synchrotron radiation measurements. © 2017 Elsevier Ltd

Sathya Swaroop N-R

Department of Physics

School of Advanced Sciences

Vellore Campus

Umapathi A

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

Optics & Laser Technology

The titanium alloy Ti-6Al-4V was subjected to laser peening (without coating) at power densities of 3, 6 and 9 GW cm−2. The cross sectional profiles of microhardness and residual stress indicated softening in the bulk (away from the surface) at power density of 9 GW cm−2. This behavior was analyzed using a combination of Zerilli-Armstrong phenomenological model in conjunction with the concept of adiabatic heating. The implications of this analysis was supported by structural changes in terms of α → β transition (analyzed through synchrotron radiation) and microstructural changes in terms of primary α (equiaxed) to secondary α (lamellar) transformation, which is observed for the first time here. Based on this, optimum levels of peening to improve fatigue lives are suggested through relevant experiments. © 2019 Elsevier Ltd

Mechanical properties of a laser peened Ti-6Al-4V

AM80 magnesium alloy was processed with Equal Channel Angular Press (ECAP)for grain refinement. Laser shock peening without coating (LSPwC)were executed on ECAP processed sample at 8 GW cm−2 and further grain refinement were observed at surface. SEM image expose the grain refinement at different stage of processing, and fine grains of sub-micron size were observed at surface level after ECAP + LSPwC. Residual stress were measured using X-ray diffraction, sin2(Ψ)method and compressive residual stress was found after ECAP. LSPwC intensify the compressive residual stress at surface. Increases in magnitude of residual stresses were noticed with 200 and 300% of LSPwC. Increase in surface roughness were noticed from 0.6 to 6.8 μm by increasing the percentage of LSPwC coverage. Fatigue tests were acknowledged the effect of ECAP and ECAP + LSPwC on reliability of grain refinement technique. ECAP sample showed fatigue life of 7539 cycles against as received. Highest fatigue life of 85,268 life cycles was observed with ECAP + LSPwC by 100% of coverage. Further process of LSPwC for 200 and 300%, fatigue life was significantly decreases to 22,987 and 384 cycles respectively. SEM images of fractured surface exhibits effect of ECAP and LSPwC on crack initiation and propagation for failure. © 2019 Elsevier B.V.

Surface and Coatings Technology

Influence of equal channel angular pressing and laser shock peening on fatigue behaviour of AM80 alloy

Laser peening without protective coating (LPwC) is an advanced mechanical surface modification method being used for a wide range of metallic materials for improving their fatigue and corrosion properties. The literature review of LPwC for the last two decades is systematically presented. The mechanism and experimental parameters of LPwC are described comprehensively. The major factors that influence the fatigue or corrosion properties, for example, compressive residual stress (CRS) and surface roughness, are analyzed with great care using the available data from the literature. A list of suggestions for future work in LPwC is given at the end. © 2017 Taylor &amp; Francis.

Materials and Manufacturing Processes

Laser peening without coating—an advanced surface treatment: A review

Influence of deformation induced martensitic (α′) phase transformation and compressive residual stresses on electrochemical properties of austenitic (γ) 321 steel laser peened without protective coating in acidic solution was investigated. Peening induced compressive residual stresses lowered the corrosion rate 19 times compared to untreated condition, subdued the deleterious role of α′ phase. Presence of dual phases (γ and α′) ensued multiple peaks in the active region of the polarization curve and pitting at α′ phase sites. Roughness after peening (≤1 μm) had no effect on corrosion properties. A fivefold increase in charge transfer resistance observed after peening. © 2017 Elsevier B.V.

Materials Chemistry and Physics

Effect of laser peening on electrochemical properties of titanium stabilized 321 steel

Laser peening without coating (LPwC) is an advanced surface modification treatment applied nowadays for many of the industrial alloys, as it tremendously enhance the fatigue and corrosion properties. We report the influence of LPwC on residual stresses, hardness, microstructure, surface roughness and topography of a nickel based superalloy, Inconel 600. LPwC parameter optimization for Inconel 600 that results in larger and deeper compressive residual stresses with relatively smaller surface roughness was carried out. It was noted with optimized LPwC condition that maximum compressive residual stresses was nearly −672 MPa and depth of work-hardening was about 1400 μm, with slight increase in the hardness with a case depth of about 400 μm. The 3D topography indicated roughening at LPwC treated surface and represented the column or steps like feature whilst the average roughness was found to be smaller (≤1 μm). Grain refinement was not observed. The corrosion resistance of LPwC specimen showed tremendous increase with a 106fold decrease in corrosion rate from that of untreated condition. Consequently, larger and deeper pits were observed in the case of untreated specimen while LPwC treated specimen showed no pitting. The chemical composition and chemical state analyzed with XPS indicated a better passivation of the surface film on LPwC specimen. © 2016 Elsevier B.V.

Journal of Alloys and Compounds

Laser shock peening enhanced corrosion properties in a nickel based Inconel 600 superalloy

Laser peening without coating (LPwC) was performed on a Ti-2.5Cu alloy at wavelengths of 1064 and 532 nm and at a constant power density of approximately 7 GW cm−2 with overlap rates of 53%, 63% and 73%. Surface softening due to thermal interaction of laser beam with material was observed till a depth of 500 µm (at 532 nm) and 200 µm (at 1064 nm), based on hardness data. This was corroborated (rather weakly) by residual stress analysis. In addition, softening due to mechanical effects (adiabatic heating) was observed in the bulk. Although there was an increase in mechanical softening with increase in overlap rates at 532 nm, it was observed, upon comparison with peened samples at 1064 nm, that the mechanical softening is a function of wavelength of radiation used for peening. It was observed that the onset of softening was earlier if the wavelength was shorter. Further, evidence of hardening in the form of twinning was found for the 1064 nm case while it was absent for the 532 nm case, for 73% overlap. The workhardened depth was more than 1000 µm, not observed in earlier studies based on residual stress analysis. The direct consequence of softening effect was found in the fatigue results. The fatigue life extended by a factor of 1.4 and 2.3 for the samples peened at 532 nm and 1064 nm respectively, consistent with the observed wavelength dependent onset of softening. © 2016 Elsevier B.V.

Materials Science and Engineering: A

Wavelength dependent deformation in a laser peened Ti-2.5Cu alloy

In this study, Inconel 625 superalloy was laser peened without protective coating to advance its electrochemical characteristics. For this purpose, a water penetrable laser source (wavelength ~ 532 nm) was operated at two power densities (6 and 9 GW cm− 2). Substantial residual compressive stresses developed at 9 GW cm− 2 whilst they were preponderantly tensile and anisotropic at 6 GW cm− 2. Hardness was unchanged after peening due to higher strength of the alloy. Peening increased the roughness but it is merely ≤ 1 μm. Corrosion rate exceedingly lowered about ~ 104 times at 6 GW cm− 2 compared to other conditions with a belittled current density fluctuation over certain applied potential range due to increased roughness. No pitting resulted in untreated and peened specimens. Threefold increase in charge transfer resistance noticed at 6 GW cm− 2 owing to enhanced defect density (measured with X-ray peak broadening). © 2016 Elsevier B.V.

Journal	Data powered by TypesetOptics & Laser Technology
Publisher	Data powered by TypesetElsevier BV
ISSN	0030-3992
Open Access	0