Browsing by Author "Tekdir, H."

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Additive Manufacturing of Multiple Layered Materials (Ti6Al4V/316L) and Improving Their Tribological Properties with Glow Discharge Surface Modification
(Pergamon-Elsevier Science Ltd, 2021) Tekdir, H.; Yetim, A. F.
Selective Laser Melting (SLM), which is a kind of laser powder bed fusion additive manufacturing technology, is commonly used in the manufacturing of AISI 316L stainless steel components. This study aims to enhance the mechanical and tribological properties of 316L manufactured by using SLM and plasma oxidation treatment in a glow discharge atmosphere. For that reason, Ti6Al4V layers were formed on 316L stainless steel samples by selective laser melting. Samples with a duplex structure (316L substrate and Ti6Al4V layer) were oxidized at 650 degrees C and 750 degrees C for 1 h and 4 h in the plasma atmosphere. The characterization of the formed Ti6Al4V and oxide layers is determined by the Vickers micro-hardness tester, scanning electric microscope, 3D profilometer, Energy dispersive X-ray spectrometer, and X-ray diffractometer. Wear tests were performed against Al2O3 balls under a load of 10 N, dry sliding ambient air conditions by a pin-on-disk tribometer. It was observed that the hardness and wear resistance of Ti6Al4V layered and plasma-oxidized samples were better than the uncoated 316L samples due to the formation of titanium oxide phases and diffusion zone depth. The best wear resistance is obtained in the sample with the highest hardness value.
A Comprehensive Study on the Fatigue Properties of Duplex Surface Treated Ti6Al4V by Plasma Nitriding and DLC Coating
(Elsevier Science Sa, 2023) Yetim, A. F.; Kovaci, H.; Uzun, Y.; Tekdir, H.; Celik, A.
This study aims to investigate the effects of duplex surface treatment consisting of plasma nitriding and DLC coating on the fatigue properties of Ti6A4V alloy. For this investigation, Ti6Al4V samples were plasma nitrided at 650 degrees C, 700 degrees C and 750 degrees C for 1, 2 and 4 h and then DLC films were produced on the plasma nitrided samples. The structural, mechanical and morphological features of the samples were characterized by XRD, SEM, micro hardness tester and scratch tester. Fatigue tests were performed on the samples by using stress life method. On the surface and sub-surface of the samples, a compound layer and a diffusion zone were formed by plasma nitriding, respectively and XRD results revealed that these layers consisted of Ti2N and TiN phases. The raising process time and temperature caused to increase the thickness of these layers and they also increased the surface hardness of the samples. On the other hand, DLC coated samples exhibited more surface hardness than untreated and all the plasma nitrided samples. Fatigue analyses revealed that plasma nitriding reduced the fatigue strength of the material in all process conditions. Although plasma nitriding formed hard surface and sub-surface layers, the brittle structure of the layers and the great difference of elastic modulus between the substrate and nitride layers caused to decrease the fatigue strength of the material. Although DLC coating increased the fatigue strength of untreated and plasma nitrided samples at 650 degrees C for 1 h, 700 degrees C and 750 degrees C for 4 h), the fatigue strength of duplex treated samples (plasma nitrided at 650 degrees C for 1 h, 700 degrees C and 750 degrees C for 4 h and DLC coated) was lower than the fatigue strength of untreated material, similar to only plasma nitrided materials. This showed that the fatigue strength of duplex treated Ti6Al4V was controlled by plasma nitriding.
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.
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.
Multi-Pass Scratch Properties of Titanium and Vanadium-Doped Diamond-Like Carbon Coatings Applied on Commercially Pure Titanium Under Different Tribological Environments: Dry, Bio-Aqueous, and Lubricated Conditions
(Elsevier, 2025) Tekdir, H.; Yetim, A. F.
This study examined the influence of titanium (Ti) and vanadium (V) doping on the mechanical performance and scratch resistance of diamond-like carbon (DLC) coatings applied to commercially pure titanium (Cp-Ti) substrates. The coatings were produced using physical vapor deposition (PVD), and scratch tests were performed under dry, Ringer's solution, and lubricated conditions. Structural and mechanical characteristics were assessed via X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and microhardness tests. Surface hardness, residual stress, and coating thickness showed notable changes with Ti and V incorporation compared to untreated Cp-Ti. Scratch resistance varied with environment, with lubricated conditions offering the highest resistance and producing narrower scratches than those in Ringer's solution. These outcomes were linked to the uniform carbide distribution and increased compressive residual stresses in the doped coatings.
Synthesis and Characterisation of Single and Duplex ZnO/TiO2 Ceramic Films on Additively Manufactured Bimetallic Material of 316L Stainless Steel and Ti6Al4V
(IOP Publishing Ltd, 2023) Yetim, T.; Tekdir, H.; Taftali, M.; Turalioglu, K.; Yetim, A. F.
Selective laser melting (SLM), one of the Laser Powder Bed Fusion (LPBF) additive manufacturing methods, has enabled the layered production of Ti6Al4V/316L layered samples, thanks to the layer-by-layer construction. Although 316L and Ti6Al4V are used in many engineering applications, their wear performance is limited. This study aims to improve the tribological and electrochemical properties of Ti6Al4V/316L layered samples. Thus, ZnO, TiO2 monolayer, composite, and ZnO/TiO2, TiO2/ZnO multilayer ceramic films on Ti6Al4V/316L layered surface sample, were coated via the sol-gel dip-coating process. The structural, morphological, and tribological properties of ZnO-TiO2 ceramic films were analyzed via x-ray diffractometer, Scanning Electron Microscopy (SEM), and 3D profilometer. The tribological properties of these coatings were examined using a reciprocating tribo-tester, and the electrochemical properties of samples were evaluated through potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Structural and mechanical results indicated that ZnO and TiO2 films (monolayer, composite, and multilayer-coated) have higher surface roughness and hardness values than additively manufactured Ti6Al4V/316L layered models. Both single and multilayer ZnO and TiO2 ceramic-coated films improved the wear resistance of the Ti6Al4V/316L substrate. Also, The best tribological and corrosion resistance was acquired for the multilayer film (ZnO/TiO2) among all the coated models.
The Tribological and Corrosion Properties of Anodized Ti6Al4V/316L Bimetallic Structures Manufactured by Additive Manufacturing
(Elsevier Science Sa, 2021) Turalioglu, K.; Taftali, M.; Tekdir, H.; Comakli, O.; Yazici, M.; Yetim, T.; Yetim, A. F.
In this study, layered Ti6Al4V/316L substrates were formed by Laser Powder Bed Fusion. TiO2 ceramic layers were produced on the Ti6Al4V/316L structures by an anodic oxidation method at different coating times (15, 30, and 60 min) to advance the wear features of layered Ti6Al4V/316L structure. The surface characterizations, wear and electrochemical behaviors of all specimens were examined via scanning electron microscopy, X-ray diffraction, a microhardness device, a reciprocating tribo-tester, and electrochemical corrosion experiments. According to the outcomes, the wear and corrosion resistance of the anodic oxidized specimens were higher compared to untreated 316L and layered Ti6Al4V/316L substrates, and the best results were obtained from the anodized specimen treated for 60 min.
Tribological Behavior of Plasma-Sprayed Yttria-Stabilized Zirconia Thermal Barrier Coatings on 316l Stainless Steel Under High-Temperature Conditions
(Elsevier, 2023) Yetim, A. F.; Tekdir, H.; Turalioglu, K.; Taftali, M.; Yetim, T.
Yttria Stabilized Zirconia (YSZ) coatings by plasma spray coating were performed to investigate the behavior of 316L Stainless Steel (SS) under high temperatures. The structural and mechanical properties of YSZ films were examined by successful scanning electron microscopy and Vickers microhardness. A tribotester determined the friction and wear properties at 500 and 1000 degrees C temperature conditions. The results showed that the surface hardness values of the YSZ-coated samples were significantly improved due to obtained ceramic layer compared with untreated 316L samples. Although the abrasive wear mechanism was observed in both the coated and uncoated samples, it was observed that higher temperatures produced smoother wear tracks. Also, increased wear test temperatures resulted in micro cracks and structural degradations on the surface of untreated stainless steel samples.