Browsing by Author "Celik, Ayhan"

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Biomechanical Analysis of Spinal Implants with Different Rod Diameters Under Static and Fatigue Loads: An Experimental Study
(Walter de Gruyter GmbH, 2019) Kovaci, Halim; Yetim, Ali Fatih; Celik, Ayhan
Spinal implants are commonly used in the treatment of spinal disorders or injuries. However, the biomechanical analyses of them are rarely investigated in terms of both biomechanical and clinical perspectives. Therefore, the main purpose of this study is to investigate the effects of rod diameter on the biomechanical behavior of spinal implants and to make a comparison among them. For this purpose, three spinal implants composed of pedicle screws, setscrews and rods, which were manufactured from Ti6Al4V, with diameters of 5.5 mm, 6 mm and 6.35 mm were used and a bilateral vertebrectomy model was applied to spinal systems. Then, the obtained spinal systems were tested under static tension-compression and fatigue (dynamic compression) conditions. Also, failure analyses were performed to investigate the fatigue behavior of spinal implants. After static tension-compression and fatigue tests, it was found that the yield loads, stiffness values, load carrying capacities and fatigue performances of spinal implants enhanced with increasing spinal rod diameter. In comparison to spinal implants with 5.5 mm rods, the fatigue limits of implants showed 13% and 33% improvements in spinal implants having 6 mm and 6.35 mm rods, respectively. The highest static and fatigue test results were obtained from spinal implants having 6.35 mm rods among the tested implants. Also, it was observed that the increasing yield load and stiffness values caused an increase in the fatigue limits of spinal implants.
Effect of Bilayer Numbers on Structural, Mechanical, Tribological and Corrosion Properties of TiO2-SiO2 Multilayer Film-Coated Β-Type Ti45Nb Alloys
(Elsevier Sci Ltd, 2023) Comakli, Onur; Yazici, Mustafa; Demir, Merve; Yetim, Ali Fatih; Celik, Ayhan
Protective films with excellent tribological performance and good corrosion resistance are needed in general because titanium implants are used in aggressive environments and always suffer from severe wear and corrosion. In this study, TiO2-SiO2 multilayer films were deposited with different numbers of bilayers (2, 4, and 8) on beta-type Ti45Nb alloy substrates by physical vapour deposition. The influence of number of bilayers on microstructure, wettability, mechanical features, tribological performance and electrochemical behaviour of TiO2-SiO2 multilayer films were comparatively observed via XRD, XPS, SEM, AFM, nanoindentation tester, contact angle measurement system, reciprocating tribo-tester, and electrochemical corrosion media. The surface hardness, wear and corrosion resistance values of multilayer film-coated substrates were higher than the untreated substrate values. These properties and adhesion resistance and hydrophobicity of coated samples also increased with increase in number of bilayers due to the smaller grain size, increased layered interfaces and high structural density.
Effect of Boronizing on the Structural, Mechanical and Tribological Properties of CoCrW Dental Alloy Produced by Selective Laser Melting
(Emerald Group Publishing Ltd, 2019) Uzun, Yakup; Kovaci, Halim; Yetim, Ali Fatih; Celik, Ayhan
Purpose This paper aims to investigate the effects of boriding on the structural, mechanical and tribological properties of CoCrW dental alloy manufactured by the method of selective laser melting. Design/methodology/approach In this study, CoCrW alloy samples that are used in dentistry were manufactured by the method of laser melting, and boriding treatment was made on the samples at 900 degrees C and 1,000 degrees C for 1, 4 and 8 h. The structural, mechanical and tribological effects of boriding on the samples were analyzed using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, microhardness and an abrasion test device. Findings According to the results, the best outcomes in terms of abrasion strength and hardness were obtained in the sample that was subjected to boriding at 1,000 degrees C for 4 h. Originality/value This study produced CoCrW alloys, which are fundamental biomaterials that are used in dentistry, by a different production method called selective laser melting and improved their surface characteristics by boriding.
The Effects of Aging Time on the Structural and Electrochemical Properties of Composite Coatings on Cp-Ti Substrate
(Springer Singapore Pte Ltd, 2017) Comakli, Onur; Yazici, Mustafa; Yetim, Tuba; Yetim, Ali Fatih; Celik, Ayhan
TiO2-SiO2 composite films were produced on commercially pure titanium (CP-Ti) substrate by a sol gel method to investigate the behavior of sol aging time and its potential effects on the structural and electrochemical properties of composite coatings. Anatase-TiO2 and quartz-SiO2 peaks were observed on all composite coated samples according to XRD results. It was observed that the average grain size increased with sol aging time. Also, the average smallest grain size was seen at composite coatings prepared from unaged sol according to the width of the peaks. Electrochemical behavior of coated samples was mainly investigated by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) in Simulated Body Fluid (SBF) solution. In corrosion tests, the composite coatings showed better anti-corrosion behavior than that of uncoated samples. In addition, the corrosion properties of the composite films were considerably affected by sol aging time. Corrosion resistance of coatings decreased with increasing aging time and the best result was obtained from composite coatings prepared from unaged sol.
The Effects of Boriding on Metal-Ceramic Bond Strength of Co-Cr Alloy Fabricated by Selective Laser Melting
(Taylor & Francis Ltd, 2021) Uzun, Yakup; Yanikoglu, Nuran; Kovaci, Halim; Yetim, Ali Fatih; Celik, Ayhan
Boriding is a method used to increase the biocompatibility and strength of metallic materials. However, by this time, no study has been encountered in the literature regarding investigation of the effects of boriding on metal-ceramic bond strength of Co-Cr alloy fabricated by selective laser melting. Boriding of metallic surfaces may be an alternative to increase the roughness and adhesion strength of the metal surface. The aim of this study was to analyze the effects of boriding on the metal-ceramic bond strength of a Co-Cr alloy fabricated by selective laser melting. In this study, metal substructures of 0.1 mm, 0.2 mm and 0.3 mm thickness values were produced from CoCrW powders with the method of selective laser melting, borided at 900 degrees C for 1 h and coated with porcelain. After the procedures, the effects of the boriding process on metal-porcelain bonding were determined by in vitro fracture tests. The 0.1 mm 900 degrees C 1 h (521.22 +/- 56.37 N), (p < 0.001), 0.2 mm 900 degrees C 1 h (619.55 +/- 20.94 N), (p = 0.051) and 0.3 mm 900 degrees C 1 h (592.11 +/- 260.58 N) specimens showed the highest bond strength, significantly higher than that of the 0.1 mm Untreated (299.88 +/- 61.56 N), 0.2 mm Untreated (480.55 +/- 11.87 N) and 0.3 mm Untreated (520.00 +/- 165.52 N), (p = 0.29) specimens. According to the results, with the help of the boriding process applied on the surfaces of the metal substructure samples, the bonding resistance of the porcelain applied onto the metal substructures increased by approximately 74, 29 and 14% in comparison to the samples that were not borided respectively for the thicknesses of 0.1, 0.2 and 0.3 mm. Boriding of metallic surfaces increased the bond strength of the metal material with ceramics.
Influence of Plasma Nitriding Treatment on the Adhesion of DLC Films Deposited on AISI 4140 Steel by PVD Magnetron Sputtering
(Taylor & Francis Ltd, 2017) Kovaci, Halim; Baran, Ozlem; Bayrak, Ozgu; Yetim, Ali Fatih; Celik, Ayhan
Duplex surface treatments composed of diamond like carbon (DLC) coating followed by plasma nitriding have drawn attention for a while. In this study, AISI 4140 steel substrates were plasma nitrided at different treatment temperatures and times. Then, DLC films were deposited on both untreated and plasma nitrided samples using PVD magnetron sputtering. The effect of different plasma nitriding temperatures and times on the structural, mechanical and adhesion properties of DLC coatings was investigated by XRD, SEM, microhardness tester and scratch tester, respectively. It was found that surface hardness, intrinsic stresses, layer thickness values and phase distribution in modified layers and DLC coating were the main factors on adhesion properties of duplex coating system. The surface hardness and residual stress values of AISI 4140 steel substrates significantly increased with both DLC coating and duplex surface treatment (plasma nitriding+DLC coating). Increasing plasma nitriding temperature and time also increased the diffusion depth and the thickness of modified layers. Hard surface layers led to a significant improvement on load bearing capacity of the substrate material. However, it was also determined that the process parameters, which provided lower intrinsic stresses, improved the adhesion properties of the duplex coating system.
Investigation of Mechanical, Tribological and Magnetic Properties After Plasma Nitriding of AISI 316L Stainless Steel Produced with Different Orientations Angles by Selective Laser Melting
(Elsevier Science Sa, 2023) Yazici, Mustafa; Comakli, Onur; Yetim, Tuba; Yetim, Ali Fatih; Celik, Ayhan
In this study, AISI 316L stainless steel samples were produced with different orientations (0 & DEG;, 45 & DEG;, and 90 & DEG;) using selective laser melting (SLM). In addition, plasma nitriding of the samples produced with SLM was performed at 400 & DEG;C for 4 h. The effect of different orientation on the structural, mechanical, tribological, and magnetic properties of 316L stainless steel was investigated. The same measurements also were made after the plasma nitriding process. The results showed that the phase composition and microstructure of the non-nitriding and nitridied samples were affected from the built orientation. Especially the XRD peaks shifted to the left with a decrease in the orientation angle. It was obtained that the highest modified layer thickness was measured from the samples produced with an angle of 0 & DEG;. It was observed that the surface hardness, residual stress, wear resistance and antimagnetization tendency values of nitridied samples were higher than the non-nitriding samples. Furthermore, these values tended to increase with the decrease in build orientation angles.
Investigation of the Usage Possibility of CuO and CuS Thin Films Produced by Successive Ionic Layer Adsorption and Reaction (SILAR) as Solid Lubricant
(Elsevier Science Sa, 2018) Kovaci, Halim; Akaltun, Yunus; Yetim, Ali Fatih; Uzun, Yakup; Celik, Ayhan
CuO and CuS films were coated on AISI 4140 steel samples by Successive Ionic Layer Adsorption and Reaction (SILAR) to investigate their usability as solid lubricant. Wear tests were performed using pin-on-disk tribo-tester under dry and lubricated conditions. The structural, morphological and morphological features of untreated, CuO and CuS coated samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and microhardness, scratch analysis. The surface examinations indicated that needle-like structures formed after coating processes and CuO and CuS films exhibited oleophobic behavior. CuO and CuS thin films reduced the coefficient of friction due to the low shear strength of bonding in transfer films. CuO and CuS films decreased the wear rates in comparison to untreated sample for both dry and lubricated conditions. Also, CuO thin films exhibited better wear resistance than CuS films in dry and lubricated wear tests. The overall results revealed that both CuO and CuS films produced by SILAR can be an alternative to conventional solid lubricants.
A Novel Method for Improving Plasma Nitriding Efficiency: Pre-Magnetization by DC Magnetic Field
(World Scientific Publ Co Pte Ltd, 2017) Kovaci, Halim; Yetim, Ali Fatih; Bozkurt, Yusuf Burak; Celik, Ayhan
In this study, a novel pre-magnetization process, which enables easy diffusion of nitrogen, was used to enhance plasma nitriding efficiency. Firstly, magnetic fields with intensities of 1500G and 2500G were applied to the untreated samples before nitriding. After the pre-magnetization, the untreated and pre-magnetized samples were plasma nitrided for 4 h in a gas mixture of 50% N-2-50% H-2 at 500 degrees C and 600 degrees C. The structural, mechanical and morphological properties of samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and surface tension meter. It was observed that pre-magnetization increased the surface energy of the samples. Therefore, both compound and diffusion layer thicknesses increased with pre-magnetization process before nitriding treatment. As modified layer thickness increased, higher surface hardness values were obtained.
Superamphiphobic TiO2 Film by Sol-Gel Dip Coating Method on Commercial Pure Titanium
(Springer, 2024) Aslan Cakir, Mevra; Yetim, Tuba; Yetim, Ali Fatih; Celik, Ayhan
The oxide coatings obtained with both superhydrophobic and superoleophobic properties on CP-Ti samples, which are frequently used as biomaterials, were produced using the solgel dip-coating method. The obtained oxide-coated titanium samples have been performed using XRD, SEM, EDS, 3D optical profilometer, optical tensiometer. After the coating process, electrochemical corrosion experiments were performed to determine the electrochemical properties. As in vitro cytotoxicity test of untreated and coated samples, MTT and LDH release tests were performed and their biocompatibility properties were evaluated. As a result of the experiments, it was observed that the resistance of the surface to corrosion current increased considerably due to the low free surface energy values of the film obtained with the superamphiphobic coating after the solgel dip coating. As a result of the in vitro cytotoxicity test of oxide-coated superamphihobic titanium material surfaces, it was determined that the biocompatibility increased after 24 h. It has been observed that the superhydrophobic and superoleophobic films obtained after coating have self-cleaning, antibacterial, and anticorrosion properties.
Tribocorrosion Behavior of Plasma Nitrided Hardox Steels in NaCl Solution
(Elsevier Sci Ltd, 2018) Hacisalihoglu, Ilyas; Yildiz, Fatih; Celik, Ayhan
In this study, the effect of plasma nitriding treatment on structural, wear, corrosion and tribocorrosion properties of different type Hardox steels (400, 450 and 500 type) was investigated using X-ray diffraction, microhardness tester, scanning electron microscope, 3D profilometer and reciprocating wear tester coupled with electrochemical corrosion cell. The plasma nitriding treatments were performed in 50%N-2-50%H-2 gas mixture at 500 degrees C for 1 and 4 h. The tribological tests were carried out in dry and open circuit potential conditions at 10 N normal force in 3.5% wt. NaCl aqueous solution at room temperature. Nitriding changed the electrochemical degradation mechanism of surface to pitting corrosion. Plasma nitriding time of 1 h significantly improved the corrosion and wear resistance of the Hardox steels.
Tribological and Electrochemical Behavior of Ag2O/ZnO Nanocomposite Coating on Commercial Pure Titanium for Biomedical Applications
(Emerald Group Publishing Ltd, 2019) Comakli, Onur; Yatim, Fatih; Yazici, Mustafa; Yetim, Tuba; Celik, Ayhan
Purpose This paper aims to investigate the structural, tribological and electrochemical properties of Ag2O, ZnO, NiO coatings and Ag2O/ZnO/NiO nanocomposite films deposited on commercially pure titanium. Design/methodology/approach Ceramic thin films (Ag2O, ZnO, NiO coatings and Ag2O/ZnO/NiO nanocomposite film) were deposited on commercially pure titanium (CP-Ti) substrate. Surface characterization of the uncoated and coated samples was made by structural surveys (scanning electron microscopic examinations and X-ray diffraction analyses), hardness measurements, tribological and corrosion experiments. Findings Results were indicated that sol-gel coatings improved the wear and corrosion resistance of CP-Ti, and the best results were seen at the nanocomposite coating. It may be attributed to its small grain size, high surface hardness and high film thickness. Originality/value This study can be a practical reference and offers insight into the influence of nanocomposite ceramic films on the increase of hardness, tribological and corrosion performance. Also, the paper displayed a promising approach to produce Ag2O/ZnO/NiO nanocomposite coating on commercially pure titanium implants for biomedical applications.
Tribological Behavior of DLC Films and Duplex Ceramic Coatings Under Different Sliding Conditions
(Elsevier Sci Ltd, 2018) Kovaci, Halim; Yetim, Ali Fatih; Baran, Ozlem; Celik, Ayhan
Diamond-like carbon (DLC) films are effectively utilized to improve the tribological properties of materials due to their low friction coefficient, good wear resistance and high hardness. In recent years, different pre-treatments such as plasma assisted diffusional processes have been used to increase long-term durability of these coatings. In the present work, DLC films were deposited on untreated and plasma nitrided AISI 4140 low-alloy steel samples using physical vapor deposition method (PVD). The effect of nitride layers on the structural and mechanical properties of DLC films was examined by XRD, SEM, microhardness tester and reciprocating tribotester. The wear tests were performed under dry, saltwater and lubricant environments. The microhardness results indicated that surface hardness considerably increased after duplex treatment and this caused to increase plastic deformation resistance of the material. The reciprocating test results showed that DLC films deposited on untreated and plasma nitrided samples reduced the coefficient of friction because of the formation of transfer film between sliding/mating surfaces. Also, wear rates improved significantly after duplex treatment in consequence of high plastic deformation resistance of duplex treated samples. The highest wear resistance was obtained in lubricated condition while the lowest wear resistance was for the samples tested in dry conditions.
Wear Behavior of Plasma Oxidized CoCrMo Alloy under Dry and Simulated Body Fluid Conditions
(Science Press, 2014) Celik, Ayhan; Aslan, Mevra; Yetim, Ali Fatih; Bayrak, Ozgu
In this study, CoCrMo alloy was oxidized in plasma environment at the temperatures of 600 degrees C to 800 degrees degrees C for 1 h to 5 h with 100% O-2 gas and its tribological behavior was investigated. After the plasma oxidizing process, the compound and diffusion layers were formed on the surface. XRD results show that Cr2O3, alpha-Co and epsilon-Co phases diffracted from the modified layers after plasma oxidizing. The untreated and treated CoCrMo samples were subjected to wear tests both in dry and simulated body fluid conditions, and normal loads of 2 N and 10 N were used. For the sliding wear test, alumina balls were used as counter materials. It was observed that the wear resistance of CoCrMo alloy was increased after the plasma oxidizing process. The lowest wear rate was obtained from the samples that were oxidized at 800 degrees C for 5 h. It was detected that both wear environment and load have significant effects on the wear behavior of this alloy, and the wear resistance of oxidized CoCrMo alloy is higher when oxide-based counterface is used. The wear rates of both untreated and plasma oxidized samples increase under high loads.