Kovacı, H.; Şenel, K.; Acar, M.T.; Bozkurt, Y.B.; Çelik, A.

This study focuses on the comparison of structural, morphological, mechanical, tribological and electrochemical properties of TiO2 films fabricated on Cp-Ti, Ti6Al4V and Ti45Nb alloys, which are widely used in different industries. For this purpose, TiO2 films were grown on Cp-Ti, Ti6Al4V and Ti45Nb materials by anodization method. Structural, morphological and mechanical properties of the samples were determined using XRD, SEM, Micro Raman, contact angle, surface roughness and micro hardness devices. Afterwards, the samples were subjected to wear and corrosion tests using a pin-on-disc wear device and a corrosion device, respectively. Wear tests were carried out in both dry and liquid environments. In electrochemical corrosion tests, Ringer's solution was used and open circuit potential (OCP) and electrochemical polarization analyzes were performed. According to the results of XRD and Raman analyses, it was determined that TiO2 films were successfully grown on the surface of the samples. Additionally, it was observed that these films were in Rutile and Anatase phases and their peak intensities increased with increasing anodization time. While the thickest films were obtained from Ti45Nb samples, the thinnest films were obtained from Cp-Ti samples. As a result of the increase in surface roughness with anodization, surface wettability increased in all samples. It was seen that electrical resistance of the materials was highly effective on the film thickness, surface roughness and surface structures. Wear coefficients decreased in all samples for both dry and liquid wear conditions due to the increased surface hardness and anodic film thickness and the lowest wear coefficients were obtained from the Ti45Nb sample. Corrosion performance of the samples increased with anodization because TiO2 films acted as protective layers on surface of materials.

Bozkurt, Y.B.; Kovacı, H.; Yetim, A.F.; Çelik, 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.

Kovacı, H.; Bozkurt, Y.B.; Yetim, A.F.; Aslan, M.; Çelik, 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.

Kovacı, H.; Baran, Ö.; Yetim, A.F.; Bozkurt, Y.B.; Kara, L.; Çelik, 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 °C, 500 °C and 600 °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 °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.

Çomaklı, O.; Yazıcı, M.; Kovacı, H.; Yetim, T.; Yetim, A.F.; Çelik, A.

Commercially pure titanium (Cp-Ti) is commonly used in different applications due to its good structural properties but its low mechanical and tribological properties restrict its usage areas. Therefore, different surface modifications based on TiO2 formation on material surfaces are applied to enhance surface features of materials. In this study, TiO2 films were produced on Cp-Ti by sol-gel and successive ionic layer adsorption and reaction (SILAR) methods to compare the effectiveness of these methods. The structural, morphological and mechanical features of TiO2 films were investigated by XRD, SEM and nano-indentation tester. The tribological features of coatings were characterized by using a pin-on-disk tribotester. The electrochemical behavior of TiO2 coatings was determined by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analyses. The structural and mechanical analyses showed that sol-gel method caused the formation of more stable and hard film structures with good adhesion in comparison to SILAR method. For that reason, TiO2 films produced by sol–gel process exhibited better wear and corrosion resistance than the films produced by SILAR.

Kovacı, Halim; Akaltun, Yunus; Yetim, Ali Fatih; Uzun, Yakup; Çelik, 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.

Baran, Özlem; Keleş, Ayşenur; Çiçek, Hikmet; Totik, Yaşar; Efeoğlu, İhsan

Al and Al alloys exhibit low wear resistance although they are used in a wide range of automobile and aerospace industries. Therefore, in this study, transition metal nitride films were deposited using Closed Field Unbalanced Magnetron Sputtering (CFUBMS) system on this metal alloy in order to improve the wear resistance. The structural properties of the films were analyzed by XRD, SEM, EDS and AFM. The hardness values of the films were determined with a nanohardness test. A pin-on-disc tribometer was used to determine the friction and wear behavior of the films under different conditions: 50% RH in air and argon gas. Ti [Nb, V] N films on the Al-2024 alloys exhibited very dense and columnar microstructure. The lowest surface roughness, the highest film thickness and hardness values were obtained as 49 nm, 440 nm and 12 GPa from TiNbVN film, respectively. Also, TiNbVN film exhibited the lowest friction coefficient values under different tribo-test conditions. The thickness and hardness values of TiNbN film were 400 nm and 9.6 GPa, respectively. TiVN film with the lowest thickness (360 nm) and hardness (6 GPa) showed the highest friction coefficients under both conditions. The indenter penetration values were 18.75%, 26.4% and 15.23% for TiNbN, TiVN and TiNbVN films, respectively. Wear behavior of the films was significantly affected from the film thickness, hardness, surface roughness and friction coefficient values.

Keleş, Ayşenur; Çiçek, Hikmet; Baran, Özlem; Totik, Yaşar; Efeoğlu, İhsan

Transition metal nitride coatings are very attractive materials due to their hardness and toughness. On the other hand, adhesion properties of these coatings are generally low because of their brittleness. To overcome this disadvantage, these coatings are produced with different deposition techniques. In this work, V and Nb doped ternary TiN-based coatings were deposited on M2 and H13 steel substrates with closed field unbalanced magnetron sputtering (CFUBMS) system. The microstructure and thickness properties were determined using Scanning Electron Microscope (SEM). The chemical composition of the coatings was examined by Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD). The mechanical properties of the coatings were carried out by nanohardness test. The critical load values (Lc) of the coatings were pointed out using a scratch tester. The thickness values of the coatings were 400 nm and 360 nm for TiNbN and TiVN, respectively. The highest thickness, nanohardness and Lc values were obtained from TiNbN coating. The maximum nanohardness and Lc values were measured as 35 ± 1.8 GPa and 63 N from TiNbN coating on M2 steel, respectively. On the other hand, TiVN coating on both steels showed lower nanohardness and adhesion behavior. It was clearly seen that different substrates had an important effect on microstructure and mechanical properties of coatings.

Cicek, Hikmet; Baran, Ozlem; Keles, Aysenur; Totik, Yasar; Efeoglu, Ihsan

Transition metal nitrides, especially ternary phase films attract attention due to their high mechanical and tribological features. Besides these, fatigue properties play a very important role on the performance in service life of these types of films. TiVN and TiNbN films were deposited on M2 and H13 steel substrates by reactive magnetron sputtering system. Fatigue properties of the films were characterized via multipass scratch tests. 100, 250 and 500 cycles with bidirectional multipass scratch tests were conducted at room temperature by applying 20 N constant load. Structural properties were determined with X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Mechanical features of the films were observed with nano hardness tests. Fatigue behaviors, deformation types, coefficient of frictions of the films and effect of different substrates were discussed comparatively. According to the results, the TiVN films showed better fatigue resistance than the TiNbN films although critical adhesion load value of the TiNbN films was higher than the TiVN films. The TiVN films generally showed ductile type cracks at the edge of the tracks and the TiNbN films showed more brittle type cracks. Additionally, the films deposited on M2 substrates exhibited better strength than those of H13 substrates.

Akaltun, Y.; Aslan, M.; T.Yetim; T.Çayir; Çelik, A.

The CuO, MgO and Al2O3 films were deposited on Cu, Mg and Al substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) method. While the MgO thin film showed hydrophilic behavior with contact angle of 75°, the Al2O3 film was hydrophobic with the contact angle of 117°. The best enhancement in terms of the wetting behavior was obtained from the copper oxide films. For these films, maximum static water contact angle was 164°. Results showed super-hydrophobic property and unique shape of form. Moreover, the superhydrophobic surface of CuO film exhibited higher corrosion resistance than MgO and Al2O3 films.