Ayday, Aysun; Duru, Erhan; Kırsever, Derya; Doğan, Fatih

This study investigates the influence of Y2O3 addition on the microstructure, growth kinetics, and mechanical properties of TiO2-based ceramic coatings formed on Ti–6Al–4V alloy through the Micro Arc Oxidation (MAO) process. The experiments were carried out using Ti–6Al–4V plates coated in silicate-based electrolytes, with and without 1 g/L Y2O3, under a constant current density of 5 A/dm2 and a voltage of 360 ± 20 V for different treatment times (1, 3, 7, and 10 min). The coatings were evaluated by weight gain measurements, SEM/EDS analyses, X-ray diffraction (XRD), and constant load scratch testing supported by profilometry. Results revealed that Y2O3 significantly accelerated coating growth during the initial stages, leading to higher weight gains and denser, less porous morphologies compared to Y2O3-free coatings. XRD analysis indicated amorphous TiO2 and anatase phases at short durations, while rutile formation became dominant with longer treatments. Kinetic modeling demonstrated that both coatings initially followed a linear reaction-controlled mechanism (n ≈ 1), with calculated growth constants of 3.44 × 10⁻4 mg/mm2·s for Ti-MAO and 7.45 × 10⁻4 mg/mm2 s for Ti–Y2O3–MAO. However, after approximately 420 s, the Y2O3 coatings exhibited a marked reduction in growth rate due to electrical insulation effects of the thickened ceramic layer, resulting in multi-stage kinetics. Constant load scratch testing showed that Y2O3 incorporation reduced groove depth and width by nearly 45%, improving adhesion strength and mechanical durability. These findings confirm that rare-earth oxide addition is an effective strategy for enhancing the performance of MAO coatings on titanium alloys.

AtıfScopus2·WoS1·OpenAlex2

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Yıldıztaş, Mesut; Ayday, Aysun; Candan, Gökçe; Duru, Erhan; Doğan, Fatih

In this study, micro-arc oxidation (MAO) coatings containing different concentrations of ZrO2 were fabricated on 7075 Al alloy in a silicate-based electrolyte to evaluate their microstructural evolution, surface characteristics, and tribological performance. The coatings were produced at 390 V for 30 min in an electrolyte containing 10 g/L Na2SiO3 with ZrO2 additions of 0, 3, 6, and 9 g/L. Surface and cross-sectional morphologies were examined by SEM/EDS, while surface topography and wear track profiles were characterized by profilometry. Tribological behavior was evaluated under dry sliding conditions using a reciprocating tribometer. The results revealed that ZrO2 incorporation markedly influenced the coating growth behavior and surface morphology. The Zr0-MAO coating exhibited a rough and porous structure with large discharge channels, whereas the addition of ZrO2 led to a more compact and homogeneous morphology with reduced porosity. Among the coated samples, Zr6-MAO exhibited the most refined microstructure and the lowest surface roughness (Ra = 4.24 µm). This sample also showed the best tribological performance, with the lowest coefficient of friction (0.27), wear volume (0.0065 mm3), and wear rate (1.63 × 10−4 mm3/N·m). To provide a comprehensive multi-criteria assessment, grey relational analysis (GRA) was employed by simultaneously considering coating thickness, surface roughness, friction coefficient, wear volume, and wear rate. The GRA results were consistent with the experimental findings and identified Zr6-MAO as the optimum coating condition. These findings demonstrate that a moderate ZrO2 addition is highly effective in improving the compactness and wear resistance of MAO-coated 7075 Al alloy.

İncele

Ayday, Aysun; Durmaz, Mustafa; Duru, Erhan; Kırsever, Derya; Doğan, Fatih

In this study, CeO2-doped ceramic coatings were produced on Al 1050 alloy by micro-arc oxidation (MAO) using a silicate-alkaline electrolyte containing 0, 0.5, 1, and 2% CeO2. The aim was to investigate the effect of CeO2 addition on the microstructure, phase composition, corrosion behavior, and constant-load scratch adhesion performance of the coatings. Surface characterization was carried out by SEM, EDS, XRD, and 3D profilometry, while corrosion performance was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt% NaCl solution. Scratch tests were also performed to assess the mechanical integrity of the coatings. The results showed that increasing CeO2 content improved coating uniformity, reduced surface roughness and porosity, and promoted the formation of a denser oxide structure. XRD analysis confirmed that γ-Al2O3 was the predominant alumina phase in all coatings, while Ce-containing species were incorporated into the oxide layer without forming additional detectable phases. Electrochemical results revealed that CeO2 addition significantly improved corrosion resistance by lowering the corrosion current density and increasing the polarization resistance. Scratch test results further showed improved adhesion-related behavior with reduced crack formation and surface damage. Overall, CeO2 addition effectively enhanced both the corrosion protection and mechanical performance of MAO coatings on Al 1050 alloy.

AtıfScopus1·OpenAlex1

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Doğan, Fatih; Duru, Erhan

Shape memory alloys (SMAs) are known for their exceptional mechanical properties, particularly their superior wear resistance compared to conventional alloys with similar surface hardness. Rare earth oxides are often used as additives to further improve these characteristics. This study investigates the effects of different CeO2 (cerium dioxide) concentrations (0.01 wt.%, 0.1 wt.%, 0.5 wt.%, and 1.0 wt.%) on the properties of CuAlMnFe alloys produced via powder metallurgy (PM). Various analyses were performed, including scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), as well as hardness, wear, and corrosion tests. The increase in wear rate is closely related to the formation of precipitates from CeO2 addition. Improvements in wear resistance and hardness are attributed to the effects of grain refinement and solid solution strengthening due to CeO2. Specifically, the wear rate increased from 1.5 × 10−3 mm3/(Nm) to 3.4 × 10−3 mm3/(Nm) with higher CeO2 content. Additionally, the friction coefficient of the CuAlMnFe alloy was reduced with CeO2 addition, indicating enhanced frictional properties. The optimal CeO2 concentration of 0.5% was found to improve grain uniformity, resulting in better wear resistance. Incorporating CeO2 particles into CuAlMnFe alloy enhances hardness and reduces wear rate when used in appropriate amounts. Additionally, it exhibits superior corrosion resistance, as evidenced by a positive shift in corrosion potential in Tafel measurements in solutions and a decrease in corrosion current density. The C0.5 specimen showed the highest corrosion potential (Ecorr, −588 V) and the lowest corrosion current density (icorr, 6.17 μA/cm2) during electrochemical corrosion in 3.5 wt.% NaCl solution.

AtıfScopus2·WoS2·OpenAlex2

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