Browsing by Author "Gencalp Irizalp S."
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Item Characterization of microplastic deformation produced in 6061-T6 by using laser shock processing(2014) Gencalp Irizalp S.; Saklakoglu N.; Yilbas B.S.High dislocation densities are formed in the irradiated region of the workpiece during the laser shock processing; in which case, surface hardening is resulted. The process involves with recoil pressure loading at the workpiece surface with the minimum heating effects in the irradiated region. This favors the process to be a good candidate for the surface treatment of metallic materials. Therefore, in the present study, laser shock processing of 6061-T6 aluminum alloy is carried out and the influence of a number of laser pulses and irradiated spot diameter on the treated layer characteristics, including morphology and hardness, are investigated. It is found that the number of laser pulses has significant influence on the resulting surface characteristics such as surface roughness, crystallite size, micro-strain, and microhardness of the alloy. In this case, surface roughness is deteriorated by increasing number of laser pulses and pulse intensity. In addition, fine crystallite structure takes place in the laser-treated region. © 2013 Springer-Verlag London.Item Effect of Fe-rich intermetallics on the microstructure and mechanical properties of thixoformed A380 aluminum alloy(Elsevier B.V., 2014) Gencalp Irizalp S.; Saklakoglu N.The effect of α-Fe and β-Fe intermetallics concentration and morphology as well as α-Al morphology on the microstructure and mechanical properties of thixoformed and gravity cast A380 alloy was reported. The α-Al15Si2(Fe,Mn)3 intermetallic particle was observed polyhedral morphology in thixoforming while it was observed Chinese script morphology in conventional gravity casting. The β-Al5FeSi particle was solidified in the form of small plate in thixoforming while it was solidified in the form of needle-like in gravity casting at the grain boundaries of α-Al. The mechanical properties of the alloys have been enhanced by thixoforming compared with the conventional cast condition. © 2014 Karabuk UniversityItem Pulsed Nd: YAG laser shock processing effects on mechanical properties of 6061-T6 alloy(2014) Gencalp Irizalp S.; Saklakoglu N.; Akman E.; Demir A.The aim of this paper is to investigate effects of single and double shot Nd:YAG laser shock processing (LSP) on residual stress, micro-hardness and tensile properties of 6061-T6 aluminum alloy. The X-ray diffraction technique was used to measure surface residual stress in LSP-treated 6061-T6 samples. The magnitude and directional dependence of the surface residual stress after single shot and double shot LSP were investigated with the sin2 Ψ method. The results show that laser shock processing can significantly increase surface compressive residual stress. In addition, micro-hardness of the LSP-treated sample was measured using a Vickers diamond indenter depending on the depth. The tensile tests of the single shot and double shot LSP-treated and untreated samples were carried out by the Schimadzu tensile testing machine having a video extensometer. Experimental results show that the values of micro-hardness, tensile strength and uniform elongation increase by LSP. © 2013 Elsevier Ltd. All rights reserved.Item Near surface modification of aluminum alloy induced by laser shock processing(Elsevier Ltd, 2014) Saklakoglu N.; Gencalp Irizalp S.; Akman E.; Demir A.This paper investigates the influences of near surface modification induced in 6061-T6 aluminum alloy by laser shock processing (LSP). The present study evaluates LSP with a Q-switched Nd:YAG low power laser using water confinement medium and absorbent overlay on the workpiece. The near surface microstructural change of 6061-T6 alloy after LSP was studied. The residual stress variation throughout the depth of the workpiece was determined. The results showed an improvement of the material resistance to pit formation. This improvement may be attributed to compressive residual stress and work-hardening. The size and number of pits revealed by immersion in an NaOH-HCl solution decreased in comparison with the untreated material. © 2014 Elsevier Ltd.Item High strength and high ductility behavior of 6061-T6 alloy after laser shock processing(Elsevier Ltd, 2016) Gencalp Irizalp S.; Saklakoglu N.The plastic deformation behavior of 6061-T6 alloy which was subjected to severe plastic deformation (SPD) at high strain rates during laser shock processing (LSP) was researched. In LSP-treated materials, the near surface microstructural change was examined by TEM and fracture surfaces after tensile testing were examined by SEM. An increase in strength of metallic materials brings about the decrease in ductility. In this study, the results showed that LSP-treated 6061-T6 alloy exhibited both high strength and high ductility. TEM observation showed that stacking fault (SF) ribbon enlarged, deformation twins formed and twin boundary increased in LSP-treated 6061-T6 alloy. This observation was an indication of stacking fault energy (SFE) decrease. Work hardening capability was recovered after LSP impacts. © 2015 Elsevier Ltd. All rights reserved.Item Laser peening of metallic materials(Elsevier Inc., 2017) Gencalp Irizalp S.; Saklakoglu N.Laser peening is a good candidate for the surface treatment industry because of its localized operation, very fast processing, and ability to use multiple types of radiation; therefore, it has recently become a process used for industrial production. The mechanical recoil impulse that arises from rapidly expanding vapor generates high pulse pressure, and the structure of the workpiece changes. In the laser peening process, no melting takes place and a shock wave is generated; compressive residual stresses are induced in the material surface. It is used primarily to increase the fatigue life and improve cracking resistance of engineering materials. Compared with the traditional shot peening process, laser peening creates a higher magnitude of deeper compressive residual stresses in component surfaces, therefore creating high fatigue resistance in metallic materials because these compressive residual stresses inhibit fatigue crack initiation and propagation. Laser peening also has a significant role in improving microstructure, surface morphology, hardness, strength, fatigue life, and corrosion resistance. Laser peening can be applied to a finished surface of a part or before the finishing step, and the process is applicable to a wide range of metals and alloys of titanium, aluminum, nickel, and steels. © 2017 Elsevier Inc. All rights reserved.Item Effect of Shot Peening on Residual Stress Distribution and Microstructure Evolution of Artificially Defected 50CrV4 Steel(Springer, 2020) Gencalp Irizalp S.; Saklakoglu N.; Baris F.; Kayral S.The aim of this paper is to clarify the effects of shot peening on fatigue life and strain hardening behavior of spring steel samples containing artificial surface defect. Artificial defect acting as pre-cracks is introduced and the effects of this defect on the material surface and the distribution of residual stress away from the defect are investigated before and after shot peening. Shot peening has provided the following modifications on the surface: (1) homogenous compressive residual stress, (2) high dislocation density, (3) superficial strain hardening, (4) retained austenite reduction. In this paper, shot peening is applied to 50CrV4 steel and its effect on surface roughness, microhardness, surface residual stress, crystallite size and dislocation density calculation is determined and SEM observations are used to reveal the properties severely strain-hardened layer. It can be shown that the shot peening can modify the crystallite size, however, the main effect is achieved by increasing the dislocation density and inducing the highly compressive residual stress. The effect of the surface modification to the 3-point bending fatigue life are analyzed. © 2020, ASM International.Item Optimization of weld bead geometry of laser welded ANSI 304 austenitic stainless steel using grey-based Taguchi method; [Optimierung der Schweißraupengeometrie von laserstrahlgeschweißtem austenitischem ANSI 304-Edelstahl unter Verwendung der grau-basierten Taguchi-Methode](Wiley-VCH Verlag, 2020) Gencalp Irizalp S.; Koroglu B.K.This paper investigates the quality characteristics of the welding geometry of the laser welding process for the ANSI 304 austenitic stainless steel, with the use of a pulsed Nd:YAG laser welding system. Laser welding of 2 mm thick ANSI 304 stainless steel is performed at three different levels of three factors, i. e., peak power, welding speed and pulse duration. In this study, a multi-response optimization problem is developed to achieve weld bead geometry with full penetration as well as a narrow bead width and minimum crater. Grey relational analysis based on Taguchi orthogonal array is used to present an effective approach for the optimization of laser welding process parameters. Regression equations between the welding parameters and the bead dimensions for laser welded austenitic stainless steels are developed, which are used in predicting the penetration, width and crater. Finally, the equations are tested for values different from the levels of the parameters in the orthogonal array. It will be beneficial to engineers for continuous improvement in laser welded product quality. © 2020 Wiley-VCH GmbHItem Influence of Laser Peening With and Without Coating on the Surface Properties and Stress Corrosion Cracking Behavior of Laser-Welded 304 Stainless Steel(Springer, 2021) Gencalp Irizalp S.; Koroglu B.K.; Sokol D.This study aims to investigate the effect of laser peening with (LP) and without coating (LPwC) process on subsurface microstructural evolution, mechanical properties, and stress corrosion cracking (SCC) of laser-welded samples fabricated using 304 stainless steel. SCC behavior of this steel has been studied by the slow strain rate test in air and 3.5wt pct NaCl + 0.5 mol/L H2SO4 solution. Microhardness profiles and metallographic microstructures of the peened and unpeened samples presented and compared. Martensitic transformation is observed by XRD on the surface layer of the peened and unpeened samples. These improvements correlate with the formation of dense deformation bands and work hardening effects resulting from high strain plastic deformation. In unpeened specimens, tensile-type residual stresses arising from the welding process occur. In addition, the LPwC process also induces tensile-type residual stress on the surface. The tensile-type residual stresses on the weld metal and base metal surface as a result of thermal effect are not disruptive for SCC performance because the mechanical effect of LPwC produces an extremely strong work hardening layer just below the surface. As a result, although LPwC offers a combined effect of thermal and mechanical effects on the material, it is an effective and useful method in terms of both mechanical performance and corrosive behavior. © 2021, The Minerals, Metals & Materials Society and ASM International.