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Evaluation of The Physical Properties of Hazelnut Shell Dust-Added Brake Pad Samples Treated With Cryogenic Process
(Gazi Univ, 2019) Akıncıoğlu, Gülşah; Akıncıoğlu, Sıtkı; Öktem, Hasan; Uygur, İlyas
After understanding that asbestos fibers are harmful to human health; researchers have investigated for alternative and eco-friendly materials. Agricultural products can be an example of these alternative and environmentally friendly materials because they are easily supplied. Thus, in this study, asbestos-free automotive brake pads produced from %7 hazelnut dusts with other seventeen additives. Hazelnut shell is preferred because it is widespread in our country. Cryogenic process applied at -80 degrees C to the brake pads. Before and after cryogenic treatment, the produced brake pads properties such as water absorption, hardness test, porosity and microstructural examinations were investigated. The hardness values of brake pads increases after cryogenic and cyclic-cryogenic process. The highest values obtained for the B-CYC sample.
Gas tungsten arc welding of 7075 aluminum alloy: microstructure properties, impact strength, and weld defects
(Iop Publishing Ltd, 2018) Çevik, Bekir
Precipitation-hardened 7075 (Al-Zn-Mg-Cu) aluminum alloys have low specific density and high strength. Because of these advantages, they are commonly used as construction materials in the aerospace industries. Even though they have such important and common areas of usage, their weldability is quite difficult. It is important to weld this alloy used in these industrial areas. In this study, 3 mm-thick 7075-T651 aluminum alloy materials were joined using different welding currents via gas tungsten arc welding (GTAW) method. The metallographic examinations were carried out to determine macrostructural and microstructural properties of the weld zones. Also, notch impact and hardness tests were performed to determine the mechanical properties of the welded samples. The results obtained as a result of the tests were evaluated and interpreted. The grain size of the weld center increased due to heat input occurring with increase of the welding current. Micro cracks (hot cracking) occurred in the roots of welding seams. The increase in the welding current affected the hardness distribution of the weld zone. The impact strength of the welded sample was negatively affected by the grain coarsening and micro cracks in the welding seam.
Friction Stir Welding of 7075-T651 Aluminium Alloy
(Carl Hanser Verlag, 2016) Çevik, Bekir; Özçatalbaş, Yusuf; Gülenç, Behçet
The microstructural changes, mechanical properties and residual stress distribution of 7075-T651 Al alloy joined using friction stir welding were investigated in this study. Welding was performed at 900, 1 250, and 1 600 rev/min and 20, 40, and 60 mm/min welding speeds. Mechanical tests were carried out on the welded joints in addition to microstructural examinations performed using a scanning electron microscope. Furthermore, residual stress distribution of the joints was determined by the hole drilling method. Generally, higher tensile strength was obtained at medium rotational and welding speeds. Tunnel defects were formed in the root of the weld seam. At high welding speeds, insufficient filling in the joints led to microvoids and large grain bands on the retreating side of the weld seam. The tensile strength of the welded specimens decreased at the rate of 26-45 % compared to the reference material. Lower residual stresses were determined in the specimens joined at a high rotational speed.
Experimental optimization of dry sliding wear behavior of in situ AlB2/Al composite based on Taguchi's method
(Elsevier Sci Ltd, 2012) Köksal, Sakıp; Fıçıcı, Ferit; Kayıkçı, Ramazan; Savaş, Ömer
A wear rate prediction model for aluminum based composites reinforced with 10 and 30 wt.% in situ aluminum diboride (AlB2) flakes was developed using Taguchi's method by considering the parameters of sliding velocity, normal load, sliding distance and reinforcement ratio. Having produced the in situ reinforced bulk of composite, the final shape of the test samples was given through squeeze casting method. The wear behavior of the specimen was investigated using pin-on-disk rig where the samples sliding against a steel disk under different conditions. The orthogonal array, signal-to-noise ratio (S/N) and analysis of variance (ANOVA) were employed to study the optimal testing parameters on composite samples. The experimental results demonstrate that the normal load and reinforcement ratio were the major parameters influencing the specific wear rate for all samples, followed by sliding velocity. The sliding distance, however, was found to have a negligible effect on the specific wear rate. Moreover, the optimal combination of the testing parameters has been predicted. The predicted specific wear rates for all the test samples were found to lie close to that of the experimentally observed ones. (c) 2012 Elsevier Ltd. All rights reserved.
Effect of welding speed on the mechanical properties and weld defects of 7075 Al alloy joined by FSW
(Redakcia Kovove Materialy, 2016) Çevik, Bekir; Özçatalbaş, Yusuf; Gülenç, Behçet
In this study, 7075-T651 Al alloys were joined by friction stir welding (FSW) at a fixed rotational speed and different welding speeds. The stirring tool used in the welding processes was comprised of a shoulder of 20 mm in diameter and modified M6 x 1 HSS hand taps used as pins. The FSW was performed at a rotational speed of 1600 rpm and at welding speeds of 20, 40, and 60 mm min(-1). Mechanical and metallographic tests were carried out on the welded joints and the effects of the welding speed on the mechanical and metallurgical properties of the welded specimens were investigated. Welding speed significantly affected the microstructure and mechanical properties of the joining. Results showed that the average grain size of the weld nugget was reduced as welding speed was increased. In addition, it was found that high welding speed negatively affected the mechanical properties of the weld nugget.
Effect of tool material on microstructure and mechanical properties in friction stir welding
(Carl Hanser Verlag, 2016) Çevik, Bekir; Özçatalbaş, Yusuf; Gülenç, Behçet
Although the number of experimental studies investigating the effect of friction stir welding (FSW) parameters on joining properties have increased recently, there are not sufficient numbers of studies on the effect of the stirring tool material in friction stir welding. This study investigated the effect of stirring tool materials on microstructure, mechanical properties and residual stress of joints. Samples of 7075-T651 Al alloys were joined by FSW using uncoated and TiN-coated X210Cr12 alloy steel stirring tools. The welding processes were performed at rotational speeds of 900, 1250 and 1600 rpm and at a welding speed of 60 mm x min(-1). Mechanical and metallographic tests were applied to the welded joints and residual stress analysis was performed using the hole drilling method. The best mechanical properties were determined in the welded samples joined by the uncoated tool at a rotational speed of 900 rpm. It was also determined that the TiN-coated tool negatively affected the mechanical and metallurgical properties of the weldements. Moreover, the highest longitudinal residual stresses were specified in the joining performed by the uncoated tool.
Effect of welding processes on mechanical and microstructural properties of S275 structural steel joints
(Carl Hanser Verlag, 2018) Çevik, Bekir
S275 structural steel is a popular low carbon steel type that can be used in many different general engineering and structural applications. These steels are widely used in steel construction, maintenance, machinery and manufacturing industries. Welded joints of this steel used in the mentioned industrial areas are important. In this study, 10-mm thick S275 structural steel sheets were joined by using gas metal arc welding (GMAW) and flux cored arc welding (FCAW) methods. Tensile, bending, and hardness tests were performed to determine the mechanical properties of the welded samples. In addition, metallographic investigations were carried out to determine the microstructural properties of the weld zones. As a result of the microstructural studies, it was found that different structures such as grain boundary ferrites, polygonal ferrites, Widmanstatten ferrites and acicular ferrites are formed in the weld metal and coarse-grained region. It was determined that the hardness of the weld metal was higher than HAZ and base metal in all welding parameters. The highest tensile and bending strengths were obtained from those samples joined by using the FCAW method. As a result of the tensile test, separation occurred in the transition region between the weld metal coarse-grained regions.
Effect of surfactant concentration in the electrolyte on the tribological properties of nickel-tungsten carbide composite coatings produced by pulse electro co-deposition
(Elsevier Science Bv, 2015) Kartal, Muhammet; Uysal, Mehmet; Gül, Harun; Alp, Ahmet; Akbulut, Hatem
A nickel plating bath containing WC particles was used to obtain hard and wear-resistant particle reinforced Ni/WC MMCs on steel surfaces for anti-wear applications. Copper substrates were used for electro co-deposition of Ni matrix/WC with the particle size of <1 mu m tungsten carbide reinforcements. The influence of surfactant (sodium dodecyl sulfate, SDS) concentration on particle distribution, microhardness and wear resistance of composite coatings has been studied. The nickel films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effects of the surfactant on the zeta potential, co-deposition and distribution of WC particles in the nickel matrix, as well as the tribological properties of composite coatings were also investigated. The tribological behaviors of the electrodeposited WC composite coatings sliding against M50 steel ball (empty set 10 mm) were examined on a CSM Instrument. All friction and wear tests were performed without lubrication at room temperature and in the ambient air (relative humidity 55-65%). (C) 2015 Elsevier B.V. All rights reserved.
Effect of particle concentration on the structure and tribological properties of submicron particle SiC reinforced Ni metal matrix composite (MMC) coatings produced by electrodeposition
(Elsevier Science Bv, 2012) Gül, Harun; Kılıç, Fatih; Uysal, Mehmet; Aslan, Serdar; Alp, A.; Akbulut, Hatem
In the present work, a nickel sulfate bath containing SiC submicron particles between 100 and 1000 nm was used as the plating electrolyte. The aim of this work is to obtain Ni-SiC metal matrix composites (MMCs) reinforced with submicron particles on steel surfaces with high hardness and wear resistance for using in anti-wear applications such as dies, tools and working parts for automobiles and vehicles. The influence of the SiC content in the electrolyte on particle distribution, microhardness and wear resistance of nano-composite coatings was studied. During the electroplating process, the proper stirring speed was also determined for sub-micron SiC deposition with Ni matrix. The Ni films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The depositions were controlled to obtain a specific thickness (between 50 and 200 mu m) and volume fraction of the particles in the matrix (between 0.02 and 0.10). The hardness of the coatings was measured to be 280-571 HV depending on the particle volume in the Ni matrix. The tribological behaviors of the electrodeposited SiC nanocomposite coatings sliding against an M50 steel ball (empty set 10 mm) were examined on a tribometer. All the friction and wear tests were performed without lubrication at room temperature and in the ambient air (with a relative humidity of 55-65%). The results showed that the wear resistance of the nanocomposites was approximately 2-2.2 times more than those of unreinforced Ni. (C) 2011 Elsevier B.V. All rights reserved.
Effect of PC electrodeposition on the structure and tribological behavior of Ni-Al2O3 nanocomposite coatings
(Elsevier Science Sa, 2014) Gül, Harun; Uysal, Mehmet; Akbulut, Hatem; Alp, Ahmet
In this study, Ni-Al2O3 metal matrix composite (MMC) coatings were prepared from a modified Watt's type electrolyte by pulse current (PC) plating under current densities varying between 1 and 9 A/dm(2). The tribological tests were performed with a reciprocating ball-on-disk apparatus sliding against a M50 steel ball (empty set 10 mm). The wear tests were carried out at sliding velocities of 50, 100 and 150 mm/s under a constant load. The results compared with our previously published work of DC electrodeposited coatings. The results showed that the electrodeposition method can significantly affect the microstructure and tribological behavior of Ni-Al2O3 nanocomposite coatings. For the same current density, PC electrodeposition creates coatings with higher co-deposited particle content more homogenous particle distribution, higher wear resistance at high sliding distance and improved friction coefficients. The superior dispersion of Al2O3 nanoparticles in PC-coated materials contributed to its increased load bearing capacity. Detailed tribological tests and characterization showed that DC- and PC-coated nanocomposite layers yielded different wear mechanisms depending on the sliding velocity. (C) 2014 Elsevier B.V. All rights reserved.
Effect of Continuous and Pulsed Currents on Microstructural Evolution of Stainless Steel Joined by TIG Welding
(Carl Hanser Verlag, 2015) Durgutlu, Ahmet; Fındık, Tayfun; Gülenç Behçet; Çevik, Bekir; Kaya, Yakup; Kahraman, Nizamettin
In this study, AISI 316L series austenitic stainless steel sheets were joined by tungsten inert gas welding method in continuous and pulsed currents. Regarding microstructural investigation and hardness values of weld metal, samples were welded to investigate the effect of current type on grain structures of weld metal. Results showed that samples welded by using pulsed current had considerable different properties compared to the samples welded by using continuous current. While the weld metals of joinings obtained by using continuous current displayed a coarse-grained and columnar structure, weld metals obtained by using pulsed current had a finer-grained structure. It was also found that hardness values of samples, which were welded with continuous and pulsed current, were quite different.
Effect of CTAB concentration in the electrolyte on the tribological properties of nanoparticle SiC reinforced Ni metal matrix composite (MMC) coatings produced by electrodeposition
(Elsevier, 2013) Kılıç, Fatih; Gül, Harun; Aslan, Serdar; Alp, A.; Akbulut, Hatem
In this study, a nickel sulfate bath containing SiC nanoparticles (between 100 and 1000 nm) was used to obtain hard and wear-resistant nanoparticle reinforced Ni-SiC MMCs on steel surfaces for anti-wear applications, such as dies, tools and working parts. The influence of stirring speed and surfactant concentration on particle distribution, microhardness and wear resistance of nano-composite coatings has been studied. The nickel films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The depositions were controlled to obtain a specific thickness (between 50 and 200 mu m) and particle volume fraction in the matrix (between 0.02 and 0.12). The hardness of the resulting coatings was also measured and found to be 280-571 Hv, depending on the particle volume in the Ni matrix. The effects of the surfactant on the zeta potential, co-deposition and distribution of SiC particles in the nickel matrix, as well as the tribological properties of composite coatings, were investigated. The tribological behaviors of the electrodeposited SiC nano composite coatings sliding against M50 steel ball (empty set 10 mm) were examined on a CSM Instrument. All friction and wear tests were performed without lubrication at room temperature and in the ambient air (relative humidity 55-65 %). The results showed that the wear resistance of the nano composites was approximately 2-2.2 times higher than unreinforced Ni deposited material. (c) 2012 Elsevier B.V. All rights reserved.
Determination of Friction-Wear Performance and Properties of Eco-Friendly Brake Pads Reinforced with Hazelnut Shell and Boron Dusts
(Springer Heidelberg, 2018) Akıncıoğlu, Gülşah; Öktem, Hasan; Uygur, İlyas; Akıncıoğlu, Sıtkı
Brake pads are the most important component of an automobile braking system. In recent studies, brake pads have been produced by varying the constituents of existing compositions and by making new formulations with other friction materials. This study evaluated two sets of asbestos-free automotive brake pads produced from boron oxide (6%) and hazelnut shell (7%) dusts and seventeen other components. All ingredients were mixed and pressed to manufacture the sample eco-friendly brake pads in the same shape as commercial Clio pads. Hardness, porosity, compressibility, shear and wear tests were carried out on the samples, and the test results were compared with those of the commercial pad.
Tribological Properties of TiO2 Reinforced Nickel Based MMCs Produced by Pulse Electrodeposition Technique
(Springer India, 2015) Algül, Hasan; Gül, Harun; Uysal, Mehmet; Alp, A.; Akbulut, Hatem
Nickel-TiO2 composite coatings were prepared under pulse current conditions by co-deposition of TiO2 particles and nickel from a Watts type bath. The effect of TiO2 particle concentration was studied on microhardness, friction coefficient and wear resistance. The morphological features and the structures were studied by scanning electron microscope, X-ray diffraction analysis and 3D profilometry facilities. A wide particle size range (between 95 and 140 nm) was chosen to provide a high dispersion and load bearing ability for the co-deposited layers. It was determined that increasing the particle concentration in the electrolyte dramatically increased the co-deposited TiO2 particles in the coating. The results showed that the high concentration of TiO2 particles in the electrolyte yielded the highest amount of particles co-deposited in the plating layer. The influence of the co-deposited TiO2 volume on microstructure and tribological properties in the coating were investigated. The wear tests were carried out using a constant load by a reciprocating ball-on disk configuration. Wear loss and friction coefficients of Ni/TiO2 composites were decreased by increasing TiO2 content in the electrolyte because of the increasing content of TiO2 in the deposited layer. The change in wear mechanisms by changing TiO2 content was also determined.
The Preparation of Zeolite/Ag Composite Powders by Electroless Deposition Process
(Springer, 2014) Uysal, Mehmet; Karslıoğlu, Ramazan; Gül, Harun; Aslan, Serdar; Keskin, S.Y.; Okumuş, S.C.; Alp, A.
Core-shell Ag-coated zeolite composite powders were synthesized using silver electroless deposition process, which was carried out in an ammonia-based coating solution containing silver nitrate as a precursor material. The influence of the chemical components and powder concentration in the Ag coating was investigated by scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction techniques. The zeolite/Ag composite powders were fabricated in order to find an antibacterial material and a new implant material based on the microstructural change of zeolite/Ag composites powders using different parameters of Ag deposition.
The effects of welding speed on the microstructure and mechanical properties of marine-grade aluminium (AA5754) alloy joined using MIG welding
(Redakcia Kovove Materialy, 2019) Çevik, Bekir; Koç, M.
AA5754 aluminium alloys are commonly used in marine and offshore applications as well as in shipbuilding equipment. It is of great importance to weld this alloy in these industrial areas. This study investigated the penetration, microstructure, and mechanical properties of AA5754 Al alloy sheets that were joined using robotic metal inert gas (MIG) welding at different welding speeds. The joints were welded at three welding speeds by keeping the welding current constant, and then macrostructure and microstructure of the samples taken from these joints were examined Afterward, their hardness, tensile and bending tests were carried out. It was found that the increase in the welding speed decreased the amount of accumulated metal and the penetration rate. Formation of macro- and micro-porosities was observed in the root sections of the weld seams. It appeared that the welding speed increased, the quantity and size of these defects increased, and the mechanical properties were negatively affected by the increase in the welding speed.
The Effects of Critical Welding Parameters on Tensile-Shear Properties of Friction Stir Spot Welded Polyethylene
(Gazi Univ, 2017) Çevik, Bekir; Gülenç, Behçet; Durgutlu, Ahmet
The aim of this study was to investigate the weldability of high density polyethylene via friction stir spot welding method. Polyethylene sheets were joined with dwell times of 60 to 100 s, three different pin profiles (M6x1, M6x1.25, M6x1.5) and pin lengths of 3.75 to 4.75 mm by using rotational speed of 900 rpm and delay time of 45 s. During welding processes, the temperatures were measured under the welding centers. The tensile-shear tests were performed to welded samples. Also, macrostructures of welding nuggets were examined. The small welding nuggets were formed by using the lower dwell time. The melting in welding nugget occurred in the all dwell times during the welding. The dwell time affected on the friction temperature. The key (pin) hole closed when sufficient friction temperature (dwell times of 80 and 100 s). The pin profiles directly affected the welding quality. Large screw pitch range of the pin and the small pin length from 4.5 mm negatively affected the weld fracture load. Pin length of the stirring tool directly affected the quality of welding.
The effects of cryogenic-treated carbide tools on tool wear and surface roughness of turning of Hastelloy C22 based on Taguchi method
(Springer London Ltd, 2016) Akıncıoğlu, Sıtkı; Gökkaya, Hasan; Uygur, İlyas
In this study, Taguchi method has been applied to evaluate the effect of cryogenically treated tools in turning of Hastelloy C22 super alloy on surface roughness. The optimum parameters (cryogenic treatment, cutting speed, and feed rate) of turning were determined by using the Taguchi experimental design method. In Taguchi method, L9 orthogonal array has been used to determine the signal noise (S/N) ratio. Analysis of ANOVA was carried out to identify the significant factors affecting surface roughness. The statistical analysis indicated that feed rate, with a contribution percentage as high as 87.64 %, had the most dominant effect on machining performance, followed by the cryo-treated tools treatment and cutting speed, respectively. The confirmation tests indicated that it is possible to improve surface roughness significantly by using the Taguchi method. Surface roughness was improved by 28.3 and 72.3 % by shallow (CT1) cryogenic treatment and deep cryogenic treatment (CT2) applied on cementite carbide tools (UT). It found that wear resistance of tungsten carbide insert was increased by shallow and deep cryogenic treatments.
The effect of welding speed on mechanical and microstructural properties of 5754 Al (AlMg3) alloy joined by laser welding
(Iop Publishing Ltd, 2018) Çevik, Bekir; Gülenç, Behçet
5754 (AlMg3) alloys have advantages such as good strength, perfect corrosion resistance and cold forming in addition to the low specific density. Because of these advantages, they are commonly used in automotive, chemical and food industries, and especially in the vessel and yacht industry. However, in spite of having such important and common areas of usage, it is very difficult to join Al and its alloys by traditional welding methods. This study focused on joining of 5754 Al alloy materials, which are hard to be joined by the traditional welding methods but have common areas of usage, by using the laser welding method. Laser welding method has many advantages such as the low heat input, deep penetration, low residual stress, and distortion compared to traditional welding methods. For this purpose, 3 mm thick 5754 Al alloy sheets were joined by using the laser welding method. The welding processes was carried out selecting three welding speeds (3, 4.8, and 6 m min(-1)). The macrostructure, microstructure, hardness, tensile, and impact strength properties of the samples taken from the welded joints were examined. It was observed that micro-porosity and micro-void defects formed in the microstructure of the weld metal. The rate and size of these defects increased with increasing welding speed. The increase in the welding speed decreased the amount of the accumulated metal and the penetration rate. The mechanical properties were also negatively affected by the increase in the welding speed.
The effect of pure argon and mixed gases on microstructural and mechanical properties of S275 structural steel joined by flux-cored arc welding
(Redakcia Kovove Materialy, 2018) Çevik, Bekir
Studies on the use of various welding methods and equipment (electrode, welding wire, welding powder, etc.) in welding of steels have intensively continued nowadays. Flux-cored arc welding technology is one of the welding methods which have mostly been investigated and applied to different metals in recent years. In this study, the effect of different shielding gases on microstructural and mechanical properties of S275 structural steel joined by flux-cored arc welding was examined. Pure argon (100% Ar) and a mixed gas (86% Ar, 12% CO2, 2% O-2) were used as shielding gas in welding processes. A double V groove of 50(degrees) was opened on steel sheets. Welding processes were performed horizontally by using a 1.2 mm-diameter rutile flux-cored wire. Tensile, hardness, and bending tests were used to determine mechanical properties of welded samples. In addition, metallographic examinations were performed to determine microstructural properties of weld zones. As a result of the tensile test, the highest mechanical properties were obtained from weld seams by the mixed gas. There were crack and rupture defects in weld zone as a result of bending tests. In all welding parameters, the hardness of weld metal was higher than that of the heat affected zone (HAZ) and base metal. The microstructure studies revealed that grain coarsening occurred in HAZ.

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