Browsing by Author "Bozkurt, Y. B."

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Corrosion and Tribocorrosion Properties of Duplex Surface Treatments Consisting of Plasma Nitriding and DLC Coating
(Elsevier Sci Ltd, 2021) Kovaci, H.; Bozkurt, Y. B.; Yetim, A. F.; Baran, O.; Celik, A.
In this study, a comprehensive analysis was performed to investigate the corrosion and tribocorrosion behaviour of untreated and duplex ceramic coated AISI 4140 steel. Therefore, samples were plasma nitrided in a glow discharge environment and then, they were coated with diamond-like carbon (DLC) film. Electrochemical impedance spectroscopy, potentiodynamic polarization and tribocorrosion tests were performed in fourteen different parameters. Nitriding treatment increased the surface roughness compared to the base material. The negative effect of roughness on corrosion and tribocorrosion performance has disappeared with the ceramic film thickness increasing with temperature and time. Harder surfaces compared to the base material contributed to the wear resistance. Compound, diffusion layers and DLC film have a barrier effect, delaying the arrival of the corrosive liquid to the base material.
The Effect of Surface Plastic Deformation Produced by Shot Peening on Corrosion Behavior of a Low-Alloy Steel
(Elsevier Science SA, 2019) Kovaci, H.; Bozkurt, Y. B.; Yetim, A. F.; Aslan, M.; Celik, A.
Shot peening treatment is a well-known and practical method to improve surface properties of materials. In this method, surfaces of materials are peened by small steel shots and thus, surface hardening is provided. Although it is used in a wide range of applications, this process could affect the electrochemical behavior of materials because of changing surface properties. Therefore, the effects of shot peening process on the electrochemical properties of a low-alloy steel were examined in the present study. AISI 4140 low-alloy steel samples were shot peened in different intensities of 16 A, 18 A, 20 A and 24 A. Afterwards, corrosion tests were carried out at room temperature in a 3.5% NaCl solution. Open circuit potential (OCP) electrochemical polarization and electrochemical impedance spectroscopy (EIS) analysis were performed in corrosion tests. The microstructural, morphological and surface properties of samples were analyzed by XRD, SEM and 3D surface profilometer. The structural analyses showed that grain structure of the material was affected by shot peening treatment. A plastically deformed zone, which have extended and refined grain structure, formed after shot peening processes. Electrochemical analyses indicated that the corrosion resistance of the material increased with the increasing shot peening intensity owing to grain refinement and formation of sub-grains. Also, examinations on the corroded surfaces showed that crevice corrosion was the main mechanism for shot peened samples.
Enhancing High Cycle Fatigue Performance of Plasma Nitrided AISI 4140 Steel by Post-Aging Treatment and Direct Current Magnetic Field
(Elsevier, 2024) Yetim, A. F.; Kovaci, H.; Tekdir, H.; Kavasoglu, Y. Secer; Bozkurt, Y. B.; Celik, A.
Machine elements become unable to perform their duties as a result of fatigue damage. In addition, machine elements that are subjected to fatigue under cyclic loads are exposed to electric and magnetic fields when they are close to electrical and magnetic field sources such as electric motors. Moreover, plasma nitriding is often used to increase the fatigue strength of materials. Although the fatigue properties of surface-treated materials are frequently studied, the fatigue behavior of these materials under a magnetic field is not fully known. Therefore, this study focuses on examining the effects of magnetic field on the fatigue properties of surface-treated materials. For this purpose, AISI 4140 steel samples were plasma nitrided and subsequently post-aged, and then they were tested using a rotating bending fatigue testing system by exposing them to a magnetic field for 30 % and 100 % of their fatigue life. epsilon-Fe 2 -3 N and gamma'-Fe 4 N phases were seen in surface-treated samples, in addition to these phases, peaks belonging to the alpha"-Fe 16 N 2 phase were observed in post-aged samples. Plasma nitriding raised the hardness of the material because of nitride phases and alpha"-Fe 16 N 2 caused an extra increase. The highest diffusion depth was seen in the post-aged samples because post-aging facilitated the diffusion of nitrogen. Surface treatments increased the fatigue strength of the material. All samples tested under a magnetic field exhibited higher fatigue strength than samples tested without a magnetic field because fatigue crack initiation was prolonged by the magnetic field. Compared to non-magnetic and 30 % magnetic samples, the fatigue strengths of the samples in a 100 % magnetic field were lower. Furthermore, it was observed that applying a magnetic field had no effect on the samples ' fractographic structure.
The Friction and Wear Performance of DLC Coatings Deposited on Plasma Nitrided AISI 4140 Steel by Magnetron Sputtering Under Air and Vacuum Conditions
(Elsevier Science Sa, 2018) Kovaci, H.; Baran, O.; Yetim, A. F.; Bozkurt, Y. B.; Kara, L.; Celik, A.
Diamond-like-carbon (DLC) coatings with high hardness and low friction coefficient exhibit excellent tribological performance under air and vacuum conditions. However, adhesion and cold welding problems in vacuum conditions lead to increase friction coefficient values. These negative effects can be eliminated by different methods such as forming interlayers between coating and substrate or ion treatment of the substrate. In this work, DLC coatings were deposited on untreated and plasma nitrided (at 400 degrees C, 500 degrees C and 600 degrees C for 1 h and 4 h) AISI 4140 steel substrates by magnetron sputtering technique. The effects of plasma nitriding treatment on the friction and wear properties of DLC coatings under air and vacuum conditions were investigated. The structural and mechanical properties of DLC films were examined by XRD, SEM, and microhardness tester, respectively. The friction and wear properties were determined by a tribotester under air and vacuum conditions. The microhardness of samples increased after surface treatments and the highest value was obtained from the sample plasma nitrided at 600 degrees C for 4 h plus DLC coated sample. The wear resistance of samples increased with increasing plasma nitriding time and temperature. Also, it was observed that the samples tested under vacuum condition showed better wear resistance than the samples tested under ambient air. Furthermore, increasing plasma nitriding time and temperature improved the wear performance of the material regardless of the test environment.
Influences of Ti, Al and V Metal Doping on the Structural, Mechanical and Tribological Properties of DLC Films
(Elsevier Science SA, 2021) Yetim, A. F.; Kovaci, H.; Kasapoglu, A. E.; Bozkurt, Y. B.; Celik, A.
DLC films are widely used in different engineering products. However, some problems such as inadequate toughness, insufficient adhesion and internal stresses affect their performance. Therefore, we aimed to enhance the mechanical and tribological features of Cp-Ti by metal-free and metal-doped DLC films in this study. Cp-Ti samples were coated with un-doped and Ti, Al and V metal-doped DLC films by PVD. Their properties were investigated by Raman, XPS, XRD, SEM and wear tester. The results revealed that the incorporation of metal in DLC increased the disorder. Ti, Al and V carbides formed on DLC due to bonding of doping elements with carbon. Metal-doping improved the adhesion and decreased the internal stresses and these improvements caused metaldoped films to exhibit better tribological properties than metal-free film.
Tribocorrosion Properties and Mechanism of a Shot Peened AISI 4140 Low-Alloy Steel
(Elsevier Science SA, 2022) Bozkurt, Y. B.; Kovaci, H.; Yetim, A. F.; celik, A.
Many engineering (biomedical, automotive, aerospace etc.) structures suffer from wear and corrosion damage under service conditions and this situation shortens their useful life. In common cases, these damage mechanisms do not act on materials separately. On the contrary, their combined effect called as tribocorrosion cause more decrease in their lifetime than the individual effects of wear and corrosion. Tribocorrosion damages are directly related to surface properties of materials. In order to improve tribocorrosion performance of materials, different surface modifications were applied to enhance their performance and one of them is shot peening. However, tribocorrosion behavior of shot peened materials have not been clarified so far. Therefore, in this study, the effect of shot peening on the tribocorrosion properties of AISI 4140 low-alloy steel was investigated in detail. AISI 4140 samples were shot peened under different Almen intensities and their tribocorrosion performance were examined. The results revealed that the increasing Almen intensity changed the surface characteristics from hydrophobic to hydrophilic. Also, it was determined that the tribocorrosion performance of the material improved with the increasing shot peening intensity in terms of increased surface hardness.
Wear and Tribocorrosion Behavior of UV Curable Coated CP-Ti
(Elsevier, 2023) Cakir, M. Aslan; Yetim, T.; Bozkurt, Y. B.; Kovaci, H.; Celik, A.
In this study, commercial titanium (Cp-Ti) was coated with a UV-curable film to improve the wearing and tri-bocorrosion performance of Cp-Ti. Wear tests were carried out under dry and simulated body fluid (SBF) test environments, and tribocorrosion tests were also performed in SBF. In tribocorrosion tests, a reciprocating test device coupled with open circuit potential and potentiodynamic polarization test monitoring system was used. SEM investigations showed that a polymeric film with a layer thickness of about 3-4 mu m was deposited on Cp-Ti. It was also found that the Si element in the film considerably increased the hardness and improved the wear performance. According to tribocorrosion test results, the corrosion mechanism has significantly increased the wear rates. The wear resistance of the Cp-Ti surface was markedly enhanced by UV-curable treatment.