Browsing by Author "Yildiz, F."

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Dry Sliding Wear Characteristics of Plasma-Nitrocarburized Co-Cr-Mo Alloy
(Springer, 2017) Bayrak, O.; Kovaci, H.; Yildiz, F.; Yetim, A. F.; Celik, A.
Forged low-carbon alloy Co - 27% Cr - 6% Mo - 0.06% C is studied after 2-h plasma nitrocarburizing in a gaseous mixture of 10% CO2 + 20% N-2 + 70% H-2 at 400, 500 and 600A degrees C. The surface layer and the core are studied by diffractometric analysis and scanning electron microscopy. The microhardness and the tribological characteristics of the alloy are determined. The effect of the temperature of nitrocarburizing on the wear resistance, surface roughness and friction coefficient of the alloy is considered.
The Effect of Constant and Variable Temperatures on Fatigue Behavior of Ti6Al4V-Eli Alloy Produced by Laser Powder Bed Fusion Additive Manufacturing
(Wiley, 2025) Tekdir, H.; Yetim, A. F.; Yildiz, F.; Kaymaz, I.; Korkmaz, I. H.
The increasing use of additively manufactured Ti6Al4V components in engineering highlights the necessity of understanding their thermo-mechanical behavior under service conditions. This study systematically investigates the fatigue response of L-PBF-produced Ti6Al4V-ELI alloy under various thermal environments, including constant (25 degrees C, 50 degrees C, 250 degrees C) and cyclic (-50/+50 degrees C) conditions. The influence of heat treatment below the beta-transus temperature and electrochemical polishing on fatigue performance was assessed via stress-life tests. Microstructural and mechanical characterizations were performed through XRD, SEM, EDX, microscopy, and Vickers hardness testing. Results revealed that elevated and cyclic temperatures significantly reduce fatigue life, whereas postprocessing treatments notably enhance fatigue resistance. The lower fatigue limit increased from 260 MPa (as-built) to 500 MPa (heat-treated), and the upper limit from 400-410 MPa to 700-710 MPa. Microstructural analysis identified strain accumulation and microporosity near fracture surfaces, offering insights into the degradation mechanisms under thermal fatigue loading.
The Effect of Post Aging on Wear Properties of a Plasma Nitrided Ferromagnetic Steel Under DC Magnetic Field
(Elsevier Science SA, 2015) Yetim, A. F.; Kovaci, H.; Yildiz, F.; Bayrak, O.; Celik, A.
Plasma nitriding is an effective surface treatment to improve unsatisfactory wear properties of machine elements. Such machine elements may also subject to magnetic fields in many industrial applications. Therefore, AISI 4140 ferromagnetic steel samples were plasma nitrided. Then, the samples were quenched in water and then post-aged at a temperature of 400 degrees C for 30 and 120 min in plasma environment. Reciprocating wear tests were performed under different oriented DC magnetic field to determine wear behavior of the samples. It was obtained that the magnetic field and its orientation during wear test were the most effective parameters on wear behavior. It was observed that post-aged samples showed better wear resistance and lower friction coefficient values than the merely nitrided samples. Hard Fe16N2 precipitations were formed in the nitrided layer after post-aging treatment and their amount increased with magnetic field. This gave rise to improvement the wear resistance. (C) 2015 Elsevier B.V. All rights reserved.
Performance of Plasma Sprayed Al2O3 Coating in Bio-Simulated Environment
(Springer, 2014) Yildiz, F.; Yetim, A. F.; Alsaran, A.; Celik, A.
Alumina coatings deposited on the surface of stainless steel 316L by the method of plasma spraying are studied. Tests for wear and corrosion are preformed in Ringer's solution simulating a human body environment. The structure, microhardness, wear resistance and corrosion resistance of the steel are determined with and without a coating. Deposition of a coating onto the stainless steel is shown to be an effective means for protecting implants from corrosion and wear.
Plain and Fretting Fatigue Behavior of Ti6al4v Alloy Coated with Tialn Thin Film
(Elsevier Sci Ltd, 2013) Yildiz, F.; Yetim, A. F.; Alsaran, A.; Celik, A.; Kaymaz, I.; Efeoglu, I.
In this study, plain and fretting fatigue behaviors of Ti6Al4V alloy coated with TiAlN thin film by using closed field unbalanced magnetron sputtering system (CFUBMS) were investigated. Coating process was carried out in two different power parameters as dc bias and pulse. It was observed that both plain and fretting fatigue resistance of Ti6Al4V alloy improved after TiAlN coating process. Pulsed films were more effective than biased films in terms of fatigue resistance. Also, fretting fatigue behavior of uncoated and coated specimens was examined with finite element analysis. The finite element analysis results were analogous with experimental test results. (C) 2013 Elsevier Ltd. All rights reserved.
Tribocorrosion Properties of Different Type Titanium Alloys in Simulated Body Fluid
(Elsevier Science SA, 2015) Hacisalihoglu, I.; Samancioglu, A.; Yildiz, F.; Purcek, G.; Alsaran, A.
Body fluids and relative motion between implant and bone lead to synergistic degradation reactions, which cause failed implantation or adverse tissue reactions for implant materials used in human body. Because of their good chemical biocompatibility as well as acceptable mechanical properties, titanium (CP Ti) and its alloys are widely used in implant applications. beta-type Ti alloys including alloying elements such as Nb, Zr and Mo have become more popular among the extensively used alpha- and (alpha+beta)-type Ti alloys due to their low elastic modulus, comparable mechanical properties and high biocompatibility. This paper was mainly aimed to investigate the electrochemical and tribological properties of beta-type Ti alloys. Also, traditionally used alpha-type Ti (alpha- CP Ti) and (alpha+beta) type Ti-6A1-4V (alpha/beta- Ti64) alloys were included for comparing the same set of the results. The XRD and SEM investigations and hardness measurements were utilized to analyze the structure, surface morphology and mechanical behavior of the alloys. Simulated body fluid (SBF) was used as corrosive environment. Tribocorrosion tests were carried out at open circuit potential (OCP), cathodic and three different anodic potentials under reciprocating sliding condition. Potentiodynamic scans were obtained with and without wear test. Friction coefficient, current density and volume loss were measured and calculated. The relative motion accelerated the material loss in corrosive environment due to the combined effect of electrochemical reaction and tribological action. All Ti alloys had almost the same sensitivity to the potentiodynamic corrosion. The ratio of depassivation/repassivation affected wear performance of titanium and its alloys during tribocorrosion tests. The rate of chemical reaction was higher in beta-type Ti-15Mo (beta- Ti15) and Ti45Nb (beta- Ti45) alloys as compared to others. The (alpha+beta) type Ti-6A1-4V (alpha/beta-Ti64) and beta type Ti-13Nb13Zr (beta- Ti1313) showed lower volume loss and lower friction coefficient values during tribocorrosion tests than others. The corrosion resistance of the beta- Ti64 alloy exhibited better corrosion resistance than beta- Ti1313 alloy. However, considering the implants applications, the beta- Ti1313 alloy may be a good candidate with relatively low elastic modulus and without toxic alloying elements. (C) 2015 Elsevier B.V. All rights reserved.
Tribological Properties of WC-12Co Coating on AZ91 Magnesium Alloy Fabricated by High Velocity Oxy-Fuel Spray
(Walter de Gruyter GmbH, 2014) Yildiz, F.
In this study, conventional WC-12Co cermet coatings were deposited on AZ91 magnesium alloy using High Velocity Oxy-Fuel spray method. The effects of different coating thicknesses (60 and 120 mu m) and wear loads (20 and 30 N) on tribological properties of AZ91 magnesium alloy coated with WC-12Co were investigated. Structural, mechanical and tribological properties of WC-12Co coatings were analyzed by means of X-ray diffractometer, scanning electron microscope, micro-hardness tester and pin-on-disc tribotester. It was observed that WC-12Co coating is an effective method for improving the wear behavior of AZ91 magnesium alloy.
Wear Behavior of the Plasma and Thermal Oxidized Ti-15Mo and Ti-6Al Alloys
(IOP Publishing Ltd, 2017) Hacisalioglu, I.; Yildiz, F.; Alsaran, A.; Purcek, G.
Titanium and its alloys widely used in load bearing applications. Titanium alloys are capable of providing lower elastic modulus and better corrosion resistance with alloying processes. In spite of the modified mechanical properties, the surface degradation is still the main critical defect. Ti-15Mo alloy is one of the alpa+ beta titanium alloys with acceptable mechanical and chemical superiority. Recent researches in literature show that the wear performance of base Ti-15Mo is relatively low as compared to Ti-6Al-4V, using in high performance applications. Plasma oxidized surfaces increase the tribological and chemical performance of titanium alloys. In this study the Ti-15Mo alloy and Ti-6Al-4V alloys were compared in terms of wear performance. To obtain alloys with similar microstructure they were solution treated at 800 degrees C 1H and then air-cooled. The plasma and thermal oxidations were applied at 650 degrees C for 1 hour. Wear performance of oxidized surfaces investigated in dry conditions. Oxidized surface characterized with XRD, SEM, 3D profilometer and hardness measurements. Wear volume calculated with 3D profilometer. Results show that oxidizing increased the surface roughness and improved the wear performance of Ti15Mo alloy. The plasma and thermal oxidized Ti-15Mo showed a remarkable increase in wear resistance.