Surface Properties of Graphene Functionalized TiO2/nHA Hybrid Coatings Made on Ti6Al7Nb Alloys via Plasma Electrolytic Oxidation (PEO)
Abstract
:1. Introduction
2. Results and Discussion
3. Materials and Methods
3.1. Materials
3.2. PEO Treatment
3.3. In-Vitro Corrosion Tests
3.4. Wettability Tests
3.5. Hardness Measurements
3.6. Characterization
4. Conclusions
- The coatings had a porous structure due to the nature of the PEO process. The EDS and XRD results showed that the surfaces of the samples are covered with an oxide layer reinforced with Ca-/P-based and GNS containing hybrid structures.
- Anatase and rutile oxides, hydroxyapatite with very low intensities, and calcium pyrophosphate were mainly found in the coating layers. Besides, an nHA/GNS hybrid structure was confirmed by ATR-IR characterizations.
- The formation rate of the rutile TiO2 phase in the coating layer was increased with the increasing GNS addition. In parallel, the highest surface hardness was obtained in the coating reinforced with 1.5 wt% GNS as about 862 HV. In other words, 1.5 wt% GNS addition to the coating provided an increase of about 48% and 177% in the coating hardness compared to free–GNS coating and uncoated structures, respectively.
- It was observed that the pore diameters are significantly reduced in the coating reinforced with 0.5 wt% GNS additive. However, a small increase in the pore size was determined in the coating reinforced with 1.0 wt% GNS. Nevertheless, the pore diameters again decreased significantly with the addition of 1.5 wt% GNS. By the way, the number of pores increased with an increasing GNS addition, not due to their sizes.
- The results showed that the GNS additive plays an active role in the elemental response of the coating, and its effect is mainly on the change of porosity content and the structure of the HA-based layer deposited on the surface. In particular, 1.0 wt% GNS doped HA coating has a high rate of Ca, P, and O elements, and the Ca/P ratio of the coating is closer to the stoichiometric ratio of the HA. The lowest Ca/P ratio was seen in HA composite coating with a 0.5 wt% GNS additive. This is due to the higher amount of GNS in the coating and lower pore size.
- The lowest surface roughness values were obtained in 0.5 and 1.5 wt% GNS containing coatings. Similarly, the roughness values of the 1.0 wt% GNS and free–GNS coatings were very close to each other. The results were very much in agreement with the pore size and numbers obtained from SEM observations.
- The best hydrophilic property was obtained in the coating reinforced with 1.5 wt% GNS as 88°.
- The corrosion susceptibilities of the free–GNS and 1.0 GNS containing coatings were very similar to each other. On the other hand, the most resistant coating to corrosion was 1.5 wt% GNS containing coating. The Rp value of the sample was nine times higher compared to the one without a GNS sample. As a result, the reduced pore sizes and increasing coating thickness are important factors affecting corrosion resistance of the PEO treated coatings positively, if the GNS acts as a barrier to the closing of pores.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Sample Availability
References
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Coating | Pore Number | Surf. Area (µm2) | Avg. Pore Dia. (µm) | Por. Ratio (%) | Coat. Thickness (µm) |
---|---|---|---|---|---|
only nHA | 1804 | 2480 | 1.375 | 8.600 | 8.789 |
nHA/0.5GNS | 3051 | 2102 | 0.689 | 3.862 | 7.617 |
nHA/1.0GNS | 2560 | 4689 | 1.832 | 8.590 | 10.40 |
nHA/1.5GNS | 2880 | 1955 | 0.679 | 3.592 | 4.164 |
Coating | Ti | Al | Nb | O | Ca | P | C |
---|---|---|---|---|---|---|---|
only HA | 27.36 | 1.00 | 0.65 | 56.99 | 9.11 | 4.88 | - |
nHA/0.5 GNS | 33.11 | 1.98 | 0.54 | 56.87 | 0.96 | 1.99 | 4.49 |
nHA/1.0 GNS | 27.57 | 0.67 | 0.50 | 57.58 | 6.28 | 3.58 | 3.83 |
nHA/1.5 GNS | 30.76 | 1.58 | 0.74 | 56.41 | 2.91 | 3.15 | 4.46 |
Measurement Value | Only nHA (Free–GNS) | nHA/0.5 GNS | nHA/1.0 GNS | nHA/1.5 GNS |
---|---|---|---|---|
Min (μm) | −4.758 | −4.758 | −4.758 | −1.280 |
Max (μm) | 2.913 | 1.317 | 2.404 | 2.070 |
Mid (μm) | −0.923 | −1.721 | −1.177 | 0.395 |
Mean (μm) | 0.495 | −0.801 | −0.312 | −0.082 |
Rpv (μm) | 7.671 | 6.076 | 7.162 | 3.350 |
Rq (μm) | 1.130 | 0.588 | 0.974 | 0.566 |
Ra (μm) | 0.946 | 0.461 | 0.769 | 0.442 |
Rz (μm) | 7.612 | 5.931 | 6.961 | 3.165 |
Rsk | 0.322 | −0.753 | 0.428 | −0.703 |
Rku | 2.571 | 3.851 | 3.930 | 3.175 |
Sa (µm) | 1.032 | 0.8885 | 0.7894 | 0.4587 |
Sq (µm) | 1.237 | 0.9942 | 1.022 | 0.572 |
Area (µm2) | 2141 | 1815 | 2378 | 1714 |
Coating | Ecorr (mV) | Icor (×10−6, A·cm−2) | Icc (×10−6, A∙cm−2) | Corr. Rate (×10−6, mm·yr−1) | Rp (ohms·cm2) |
---|---|---|---|---|---|
only nHA (free–GNS) | −229 | 60 | 115 | 0.944 | 450,006 |
nHA/0.5GNS | −165 | 47 | 83 | 0.739 | 608,018 |
nHA/1.0GNS | −253 | 75 | 178 | 1.180 | 218,178 |
nHA/1.5GNS | −81 | 7 | 15 | 0.110 | 2,724,289 |
Composition | Al | Nb | Fe | N | O | C | Ti |
---|---|---|---|---|---|---|---|
Ti6Al7Nb | 6.12 | 7.07 | 0.12 | 0.01 | 0.18 | 0.02 | Bal. |
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Yigit, O.; Ozdemir, N.; Dikici, B.; Kaseem, M. Surface Properties of Graphene Functionalized TiO2/nHA Hybrid Coatings Made on Ti6Al7Nb Alloys via Plasma Electrolytic Oxidation (PEO). Molecules 2021, 26, 3903. https://doi.org/10.3390/molecules26133903
Yigit O, Ozdemir N, Dikici B, Kaseem M. Surface Properties of Graphene Functionalized TiO2/nHA Hybrid Coatings Made on Ti6Al7Nb Alloys via Plasma Electrolytic Oxidation (PEO). Molecules. 2021; 26(13):3903. https://doi.org/10.3390/molecules26133903
Chicago/Turabian StyleYigit, Oktay, Niyazi Ozdemir, Burak Dikici, and Mosab Kaseem. 2021. "Surface Properties of Graphene Functionalized TiO2/nHA Hybrid Coatings Made on Ti6Al7Nb Alloys via Plasma Electrolytic Oxidation (PEO)" Molecules 26, no. 13: 3903. https://doi.org/10.3390/molecules26133903