MCBÜ Açıkerişim Sistemi :: Browsing by Author "Irizalp, SG"

Browsing by Author "Irizalp, SG"

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Performance of Fe-based hardfacings on hot forging die: experimental, numerical and industrial studies
Saklakoglu, N; Irizalp, SG; Dogan, S; Ildas, G; Saklakoglu, IE
This paper is an investigation into the use of Fe-based alloys as part of wear resistant hardfacing materials in AISI 1.2714 tool steel. Four different weld hardfacing alloys were deposited on 1.2714 steel substrates using tungsten inert gas welding (TIG) process. Wear tests were carried out using a pin-on-disc wear tester at room temperature. Microhardness and micrographs of the weld overlays were obtained. High-temperature properties were estimated by numerical analysis. The phases of the hardfacings were obtained by XRD and also estimated by numerical analysis. The results from the laboratory tests were then compared with the results obtained from field studies. The results showed that some Fe-based alloys improved dies lifetime; others created poor surfaces. A Fe-based hardfacing alloy D which included high C with Cr, W, Mo had the best wear behavior among the weld overlays.
Characterization of microplastic deformation produced in 6061-T6 by using laser shock processing
Irizalp, SG; Saklakoglu, N; Yilbas, BS
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.
Effects of shot peening and artificial surface defects on fatigue properties of 50CrV4 steel
Saklakoglu, N; Bolouri, A; Irizalp, SG; Baris, F; Elmas, A
Shot peening processes are commonly used for improving the fatigue properties of steels. Shot peening introduces a compressive residual stress field in the near surface of steel, which can reduce or stop the growth of fatigue cracks and improve fatigue properties. This study experimentally investigated the effect of shot peening on the fatigue properties of 50CrV4 steel alloys with different artificial surface defects. Drilling tools were used to introduce different artificial defects with root radii of 0.585 mm and 0.895 mm on the surface of unpeened samples. The shot peening was applied to the drilled and undrilled samples. Scanning electron microscopy (SEM) observations, micro-hardness and X-ray diffraction residual stress measurements were conducted to analyse the characteristics of the shot-peened and unpeened samples. The results show that the shot peening leads to the transformation of the retained austenite to martensite in the near-surface microstructure. The hardness rates of the surface and near surface both increase by 8% after the shot peening. The peened samples exhibit compressive residual stresses with a high degree of isotropy in the near surface. The fatigue properties of samples were experimentally evaluated by conducting 3-point bending tests. The results indicate that the shot peening improves the fatigue life of drilled and undrilled samples. For the defects with the root radius of 0.895 mm, the shot peening leads to a 500% improvement in the fatigue life compared to unpeened samples regardless of defect depth. For the defects with the root radius of 0.585 mm, the improvement in fatigue life is 40% for the defect depth of 0.2 mm compared to unpeened samples. The improvement increases to 60% and 200% by increasing the defect depths to 0.4 mm and 0.6 mm. The fatigue properties are linked to the changes in the features of defects mainly caused by the deformation hardening and compressive residual stress after shot peening.
Investigation of wear behaviour of thixoformed and conventional gravity cast AlSi8Cu3Fe alloys
Saklakoglu, N; Irizalp, SG; Ercayhan, Y; Birol, Y
Purpose - In the present work, thixoformed AlSi8Cu3Fe alloy was investigated for its tribological properties. The tribological analysis reveals good sliding wear behaviour for thixoformed alloy due to thixotropic microstructural character. The results are compared with sliding wear behaviour of conventional gravity cast alloy. This paper aims to discuss these subjects. Design/methodology/approach - In this study, thixoforming and gravity casting methods are used to produce materials. The ball-on-disc CSM tribometer was used to carry out the tribological tests that were performed under dry sliding conditions, under two different loads of 1N and 5N. Wear tests were performed first on the conventional gravity cast samples and then on the thixoformed counterparts in exactly the same fashion to facilitate a comparison. The microstructural characterizations are performed in optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. Findings - Thixoformed samples have better wear resistance than conventional gravity cast samples. The wear performance improves in thixoformed AlSi8Cu3Fe alloy thanks to changing the microstructure. The superiority of the former is attributed to its structural features. Originality/value - In this study, the thixoforming of AlSi8Cu3Fe alloy can provide important wear performance in comparison with conventional casting of AlSi8Cu3Fe alloy. This alloy is known to be used widely in automotive industry. Therefore, the alloy is highly exposed to wear and it is thought that thixoforming method can increase the wear resistant.
Pulsed Nd:YAG laser shock processing effects on mechanical properties of 6061-T6 alloy
Irizalp, SG; 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 sin(2) Psi 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. (C) 2013 Elsevier Ltd. All rights reserved.
Near surface modification of aluminum alloy induced by laser shock processing
Saklakoglu, N; Irizalp, SG; 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. (C) 2014 Elsevier Ltd. All rights reserved.
Influence of Laser Peening With and Without Coating on the Surface Properties and Stress Corrosion Cracking Behavior of Laser-Welded 304 Stainless Steel
Irizalp, SG; Koroglu, BK; 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.
Laser Peening of Metallic Materials
Irizalp, SG; Saklakoglu, N
Study on surface and mechanical properties of stainless steel plates with multiple shot peening and laser peening without coating
Irizalp, SG; Koroglu, BK; Mutlu, O
This article compares the effects of single and multiple SP treatments, as well as LPC and LPWC treatments, on the surface and mechanical properties of 304SS. Experimental data were generated to compare the surface conditions, microhardness, and tensile properties. The surface roughness of multiple SP and LPC treatments was similar and relatively low. The microhardness layer could be obtained 100% deeper in LP-treated samples than in SP-treated samples. The maximum microhardness reached on the surface of SP-treated samples is 30% higher than that of LP-treated samples. Tensile test results showed an almost 50% increase in strength for LPWC and multiple SP treatments. X-ray phase analysis revealed that a more intense alpha'-martensite phase was formed in triple SP treatments compared to single SP treatments. The analysis also revealed the formation of low amounts of alpha'-martensite due to local melting in both LPC and LPWC samples, with a reported broadening of the austenite peaks. Additionally, the work hardening effect likely offsets the detrimental surface conditions after SP and LPWC treatments, showing that multiple SP and LPWC surface treatments have beneficial effects in terms of mechanical and metallurgical properties. It has been revealed that LPWC exhibits better mechanical properties than LPC, and multiple SP treatments have better mechanical properties than single SP treatments.
Stress Corrosion Cracking Behavior of Tungsten Inert Gas Welded Age-Hardenable AA6061 Alloy
Irizalp, SG; Koroglu, BK
The effects of two temper conditions (T4 and T6 heat treatments) upon the stress corrosion cracking (SCC) of AA6061 plates have been investigated in this work. AA6061 alloys were double-side-welded by the tungsten inert gas (TIG) welding method. SCC behavior of both the as-welded and as-received alloys was reported. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to determine the precipitate structure of the thermal-altered zones and the base metal (BM), and also the hardness variations were examined using microhardness testing (Vickers hardness). The small-size precipitate structures in the T6 tempered alloy and the coarser precipitate structures in the T4 tempered alloy were found by microstructural investigations. As a result, T4 temper heat treatment of this alloy considerably reduced its susceptibility to stress corrosion cracks due to relatively coarse and more separate precipitate morphology. In welded specimens, SCC failure occurred in the area between the heat-affected zone (HAZ) and the base metal. Stress corrosion resistance in the fusion zone was strong in both temper conditions. The aim of this work was to obtain the effects of heat treatment and welding on SCC behavior of the age-hardenable aluminum alloy. The authors conclude that a deep insight into the SCC resistance of AA6061 alloy indicates the precipitate particle distributions and they are the key point for AA6061 alloy joints in chloride solution.
Effect of Shot Peening on Residual Stress Distribution and Microstructure Evolution of Artificially Defected 50CrV4 Steel
Irizalp, SG; 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.
WEAR BEHAVIOR OF Al/SiC/GRAPHITE AND Al/FeB/GRAPHITE HYBRID COMPOSITES
Sahin, S; Yüksel, N; Durmus, H; Irizalp, SG
Silicon carbide is often the preferred reinforcement in the production of aluminium-powder composites. In this study, aluminium composites were produced with 10 % and 20 % silicon-carbide and ferroboron reinforcements and (0, 0.5, 1 and 1.5) % graphite additions using powder metallurgy. The effects of the reinforcement type, the amount and the graphite content on the wear resistance were investigated. When compared with the unreinforced aluminium sample, it was clear that the increasing reinforcement increased the wear resistance. It was determined that the increasing graphite content negatively affects the wear resistance. The sample including 20 % ferroboron and 0 % graphite showed the minimum wear rate.
High strength and high ductility behavior of 6061-T6 alloy after laser shock processing
Irizalp, SG; 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 ISP-treated 6061-T6 alloy. This observation was an indication of stacking fault energy (SFE) decrease. Work hardening capability was recovered after LSP impacts. (c) 2015 Elsevier Ltd. All rights reserved.
Optimization of weld bead geometry of laser welded ANSI 304 austenitic stainless steel using grey-based Taguchi methodOptimierung der Schweissraupengeometrie von laserstrahlgeschweisstem austenitischem ANSI 304-Edelstahl unter Verwendung der grau-basierten Taguchi-Methode
Irizalp, SG; Koroglu, BK
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.
Effect of Fe-rich intermetallics on the microstructure and mechanical properties of thixoformed A380 aluminum alloy
Irizalp, SG; Saklakoglu, N
The effect of alpha-Fe and beta-Fe intermetallics concentration and morphology as well as alpha-Al morphology on the microstructure and mechanical properties of thixoformed and gravity cast A380 alloy was reported. The alpha-Al15Si2(Fe,Mn)(3) intermetallic particle was observed polyhedral morphology in thixoforming while it was observed Chinese script morphology in conventional gravity casting. The beta-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 alpha-Al. The mechanical properties of the alloys have been enhanced by thixoforming compared with the conventional cast condition. Copyright (C) 2014, Karabuk University. Production and hosting by Elsevier B.V. All rights reserved.
Laser Shock Processing of 6061-T6 Aluminium Alloy: Thermal Modelling and Analysis
Zafar, H; Saklakoglu, N; Irizalp, SG; Khan, S; Shuja, SZ; Boran, K; Yilbas, BS
Laser shock processing of 6061-T6 aluminium alloy is carried out. Temperature and stress fields are simulated in line with the experimental conditions. Metallurgical changes due to the laser shock and microhardness in the laser treated region are examined using analytical tools that include scanning and transmission electron microscopes and microhardness tester. The depth of shock affected region, plastic strain, and dislocation density are determined numerically and experimentally in the laser treated region. It is found that the temperature attains high values at the centre of the irradiated spot resulting in high rate of evaporation at the surface. The recoil pressure formed, due to high evaporation rate, at the laser treated surface results in plastic deformation of about 500 mm below the surface. A dislocation density of the order 2 x 10(13) to 4 x 10(13) cm(-2) occurs in the surface region. Although high temperature gradients result in high stress levels in the region below the surface vicinity, high recoil pressure results in crack free surface with compressive stress.

Browsing by Author "Irizalp, SG"

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