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Browsing by Author "Saklakoglu, N"

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Mechanical properties and microstructural evaluation of AA5013 aluminum alloy treated in the semi-solid state by SIMA process
Saklakoglu, N; Saklakoglu, IE; Tanoglu, M; Oztas, O; Cubukcuoglu, O
The microstructure and mechanical properties of AA5013 aluminum alloys prepared by strain-induced melt activation (SIMA) process were studied to investigate the effects of cold working and heat treatment conditions. The specimens Subjected to deformation ratios of 30 and 50% and various heat treatment time and temperature regimes were characterized in the present study. The results revealed that for the desired microstructure of the alloy, the optimum heat treatment temperature and time were 650 degreesC and 60 min, respectively, for both deformation ratios. However, the specimens with 50% cold working exhibited more brittle behavior while they contain finer grains with uniform distribution along the cross-sections as compared to 30% cold working. (C) 2004 Elsevier B.V. All rights reserved.
Effect of the surface nanocrystallization on tribological behavior of the Cu based bimetallic materials (CuPbSn)
Gençer, GM; Yolcu, C; Kahraman, F; Saklakoglu, N
In this study, ultrasonic impact treatment was used to improve the tribological behavior of copper-based bimetallic materials that are used in internal combustion engine bearings and bushes. Bimetallic materials were obtained by coating three different CuPbSn alloys by sintering on the material surfaces of carbon steel substrate. After the sintering process, bimetallic materials were treated by ultrasonic impact process. As a result of the metallographic examination, sintered layers have uniform structure along the cross-section of the bimetallic materials. In addition, it was determined that the porosity of sintered materials decreased after the ultrasonic impact treatment. Due to the grain refinement and work hardening, higher hardness was obtained in the fine-grained layer. The hardness of the ultrasonic impact treated samples always higher than the untreated material. Because of the high surface hardness, ultrasonic impact treated samples showed higher wear resistance. The highest wear resistance was detected in the samples with the highest Sn content. Because Sn and Cu combine to form Cu3Sn intermetallic phase in Cu-Pb alloys and Cu3Sn increases the strength of the Cu-Pb alloys. Thus, increasing the Sn content in the Cu-Pb alloy resulted in the wear resistance increase. Furthermore, the formation of the SnO2 intermetallic phase on the sample surface has a significant effect on the wear resistance increase by preventing adhesion.
Characterization of austenitic stainless steel after plasma immersion nitrogen and carbon implantation
Saklakoglu, IE; Saklakoglu, N; Short, KT; Collins, GA
It has been shown in the literature that plasma immersion ion implantation (PIII) can increase the wear resistance of austenitic stainless steel without losing its corrosion resistance. In this work, the effect of PIII treatment with C ions introduced into the chamber during the process on the tribological properties of AISI 316 L stainless steel has been studied and the results compared. (c) 2006 Elsevier Ltd. All rights reserved.
Tribological behavior of PIII treated AISI 316 L austenitic stainless steel against UHMWPE counterface
Saklakoglu, N; Saklakoglu, IE; Short, KT; Collins, GA
The aim of this work was to study the tribological benefits of PIII treated austenitic stainless steel by nitrogen ions and/or C ions in a ringer solution, which simulates the environment of the human body. This was achieved by hardness, wear and friction testing, and atomic force microscopy and XRD studies. The results showed that the samples, both treated and untreated, exhibited virtually no wear from contact with the ultra high molecular weight polyethylene (UHMWPE) pins, however, the pins themselves exhibited wear. The amount of wear of the pins was found to decrease with increasing PIII treatment temperature, but addition of C to the chamber caused some increase the amount of wear on the pins. Although C ions reduced to improve the hardness, friction characteristic was improved by formation of carbon-expanded austenite. (c) 2005 Elsevier B.V. All rights reserved.
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.
Tribological behaviour of plasma immersion ion implanted AISI 304 stainless steel against polymer and ceramic counterfaces
Saklakoglu, N; Saklakoglu, IE; Ceyhun, V; Agaçhan, N; Short, KT; Collins, GA
Type 304 austenitic stainless steel samples were implanted with nitrogen using plasma immersion ion implantation (PIII) at different temperatures between 350 and 500 degrees C. Treated and untreated samples have been studied by wear-friction testing, microhardness measurement and scanning electron microscopy ( SEM). The experimental results indicated that the hardness and wear resistance is improved by increasing the penetration depth of nitrogen, whereas the friction coefficient is significantly increased by PIII.
The life of WC-Co cutting tools treated by plasma immersion ion implantation
Saklakoglu, IE; Saklakoglu, N; Ceyhun, V; Short, KT; Collins, G
In this study, the tool life of plasma immersion nitrogen-implanted cutting inserts while machining AISI 4140 steel has been investigated. The implantation time was 5 h and the temperature was in the range 320-520 degrees C. Implantation dose was similar to 2 x 10(18) ions cm(-2) for all treatments. Surface topography of the implanted surfaces was obtained from atomic force microscopy. Results of the turning tests are discussed in terms of tool life (flank wear) and surface roughness of the workpieces. The results show that plasma immersion nitrogen implantation increased tool life by about 85%. (C) 2006 Elsevier Ltd. All rights reserved.
Microstructural Evolution of ETIAL 160 Aluminium Alloy Feedstock Produced by Cooling Slope Casting
Saklakoglu, N; Birol, Y; Kasman, S
Owing to its superior flow and mould-filling capability, a fully globular structure is essential for semisolid processing technologies. The present work was undertaken to identify the cooling slope casting process parameters that, upon heating to the semisolid state, gives the required globular structure for the ETIAL 160 alloy. Of the two pouring temperatures investigated, 605 degrees C and 615 degrees C. the lower pouring temperature was found to provide more globular grains surrounded by liquid phases.
Formation of Globular Microstructure in A380 Aluminum Alloy by Cooling Slope Casting
Saklakoglu, N; Gencalp, S; Kasman, S; Saklakoglu, IE
Thixoforming and related semi-solid processing (SSP) methods require thixotropic materials. One of the many SSP techniques is the cooling slope (CS) casting process, which is simple and has minimal equipment requirements, and which is able to produce feedstock materials for semisolid processing. When the feedstock is reheated to the semisolid temperature range, non-dendritic, spheroidal solid particles in a liquid matrix suitable for thixoforming are obtained. In this study, equipment for the CS technique was first established, and then the effects of the pouring temperature and inclined slope angle on the microstructures of A380 aluminum alloy (ISOAlSi8Cu3Fe) were studied. Optimum parameters for thixoforming experiments were selected, and it was found that the microstructure produced by the inclined plate depended on its angle and the pouring temperature.
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.
The effect of thermomechanical process on metallurgical and mechanical properties of 38MnVS6 micro alloyed steelEinfluss des thermomechanischen Prozesses auf die metallurgischen und mechanischen Eigenschaften von mikrolegiertem 38MnVS6-Stahl
Erçayhan, Y; Saklakoglu, N
This study aims to have the proper mechanical properties without applying any heat treatment process after hot forging by using 38MnVS6 micro alloyed steel in tow hook manufacturing which is used in automobiles. The effect of forging temperature and cooling rate on metallurgical and mechanical properties of micro alloyed steel is investigated. The samples of micro alloyed steel are forged at 800 degrees C, 850 degrees C, 900 degrees C, 1050 degrees C and cooled down at the rates of 0.75 degrees C/s and 1.5 degrees C/s. The forging temperature and the cooling rate have a significant effect on toughness by the experimental and numerical studies. The amount of ferrite increases with a decreasing forging temperature, and the toughness is improved by increasing the amount of ferrite. Also, by increasing the cooling rate after forging at 1050 degrees C, the acicular ferrite is observed which has a positive effect on both the toughness and strength of the micro alloyed steel.
Characterization of hot forged P285NH steel by metallurgical investigation and reliability analysisCharakterisierung von warmgeschmiedetem P285NH-Stahl durch metallurgische Untersuchungen und Zuverlassigkeitsanalyse
Saklakoglu, N; Çivi, C; Hocalar, Ç; Demirok, S
An extensive study was carried out to investigate the effect of cooling rate after hot forging process and normalization step on the hardness, strength and impact toughness and microstructure of P285NH steel. Understanding of the combined effect of cooling rate and normalization on the mechanical and microstructural properties of the steel would help to select conditions required to achieve optimum mechanical properties. The results indicated that the microstructures of all forging and cooling conditions were dominated by ferrite and pearlite phases with different morphologies and grain sizes according to various cooling rates. Conveyor cooling led to a formation of relatively fine acicular ferrite and pearlite grains in comparison to batch cooling which presented coarse polygonal ferrite with pearlite. Based on the data fluctuation of Charpy tests, the normal distribution provided a statistical analysis method for assessing the reliability. Through the statistical analysis of the distribution function, it can be concluded that normalization step is necessary for higher reliability. Both batch cooling and conveyor cooling did not give the required reliability level for safety components due to heterogeneities in the microstructure.
The Effects of Cooling Slope Casting and Isothermal Treatment on Wear Behavior of A380 Alloy
Saklakoglu, N; Gencalp, S; Kasman, S
In this study, A380 aluminum alloy feedstock produced with cooling slope casting was exposed to isothermal treatment to obtain a globular microstructure which is a key feature for semisolid forming. The dendritic primary phase in the conventionally cast A380 alloy has readily transformed into a non-dendritic one in ingots cast over a cooling plate from pouring temperatures between 615, 630 and 650 degrees C. After the casting process, isothermal treatment was carried out at 565 degrees C in induction unit. Isothermal treatment yields a globular microstructure. To determine the tribological properties of this alloy, a pin-on-disc tribometer was used to carry out tribological tests under dry sliding conditions. The results showed that both cooling slope casting and isothermal treatment has an effect on tribological properties.
Selective laser melting of Ti6Al4V alloy: Effect of post-processing on fatigue life, residual stress, microstructure, microhardness and surface roughness
Önder, S; Saklakoglu, N; Sever, A
In this study; turning, milling, heat treatment and shot peening (SP) post-process operations alone or in different combinations were performed on Ti6Al4V specimens which were produced by selective laser melting (SLM); then the effects of these operations on the fatigue life, residual stress, microstructure, microhardness and surface roughness were investigated. SP processes were carried out in two different types, traditional and multiple, and it was observed that the multiple SP process, which was carried out with the same almen intensity as traditional, with a smaller ball diameter, was effective in reducing the surface roughness. As a result of the heat treatment, alpha + beta transformation was observed in the microstructure. alpha phase was seen in both lamellar and globular forms. Traditional SP and multiple SP processes provided a significant increase in microhardness values in the 0-250 mu m depth range. A significant decrease in the microhardness values of the heat-treated specimens was observed due to the alpha + beta transformation in the microstructure. Traditional SP and multiple SP processes enabled the residual stress type to become compressive type in both the x-axis and the y-axis in the 0-150 mu m depth which is a very critical region for fatigue cracks despite the x-axis direction surface unmachined. Fatigue test were performed on machined, multiple shot-peened and machined after heat-treated specimens. The best results in terms of fatigue strength were obtained in the specimens that were heat-treated. It was observed that the most important cause of fatigue crack initiation in multiple shot-peened specimens was an internal defect located deeper than 250 mu m. Fisheye formation was observed on fracture surfaces of some multiple shot-peened fatigue specimens.
Influence of Ag content on microstructure and intermetallic phases of AlSi12 alloy
Turker, A; Saklakoglu, N
The main objective of this study is to examine the influence of trace additions of silver on the morphology and composition of the complex microstructure of the intermetallic phases in AlSi12 alloy. Intermetallics were found in short or long rod, or 'Chinese Script', forms containing Si, Fe, Mn, Ag and Mg, These compounds became richer towards the grain boundaries. It was observed that the high Ag content intermetallics were created in the form of short rods. In all samples with added Ag, the dendritic structures had transformed into non-dendritic ones. The addition of Ag, in addition to the degeneration of the dendritic structures, enhanced the transformation from rosette form to globular morphologies. The results showed that the amount of eutectic Si increased with small additions of Ag to the AlSi12 alloy. It was established that in general the Ag is distributed within the eutectic structure.
The Effect of Heat Treatment on The Wear and Corrosion Behavior of AISI 440B Martensitic Stainless Steel in Different Environments
Saklakoglu, N; Eyici, G; Aslan, N; Hocalar, C; Çimen, O
This study demonstrates that the austenitization temperature of AISI 440B martensitic stainless steel crucially influences wear and corrosion resistance. As the austenitization temperature increases, Cr23C6 carbides dissolve, leading to increased Cr and C concentrations in the austenite matrix. Higher Cr content enhances corrosion resistance, while increased C content raises hardness. However, excessively high austenitization temperatures result in increased retained austenite due to lowered Mf temperatures and grain coarsening, which significantly reduces hardness. Electrochemical corrosion tests that have been done in wet wipe solution and NaCl solution have shown that a high carbon content can break the martensitic crystal lattice, destabilizing the protective oxide film and reducing corrosion resistance. This study identifies 1110 degrees C as the optimal austenitization temperature for AISI 440B martensitic stainless steel, balancing both wear and corrosion resistance effectively.
Experimental evaluation and FE simulation of phase transformations and tensile stresses in hot forging and controlled cooling
Hocalar, C; Saklakoglu, N; Demirok, S
This paper encompasses the development of a microstructure-based numerical model (FEM) of the conveyor cooling process after the hot forging of industrial steel with accu-rate predictions of the volume fraction of phases as yield and tensile strengths. An experi-mental procedure for validating the FEM was conducted using optical and scanning electron microscopy and tensile tests. Results showed very good agreement between the phase predic-tions of the 3D FEM model and those obtained from direct measurement of forged parts, with an average error of about 3.6 and 6.9 % for ferrite and pearlite phases, respectively. Tensile test results were evaluated at a 90 % reliability level, and very good agreements were obtained with an error of about 3 and 5 % for the yield and tensile strengths. The methodology could predict the phase transformations, and the mechanical properties during cooling after the hot forging of the steel were investigated.

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