Electrochemical Behaviour of PACVD TiN-Coated CoCrMo Medical Alloy
Abstract
:1. Introduction
2. Materials and Methods
3. Results and Discussion
3.1. SEM and EDS Results
3.2. Electrochemical DC Results
3.3. Electrochemical AC Results
- Rs—electrolyte solution resistance between the working electrode and the reference electrode in a three-electrode cell;
- Rox—the resistance of the oxide layer;
- Rct—polarization resistance or resistance to charge transfer on the electrode/electrolyte interface;
- Cdl—double layer capacity at the electrode/electrolyte interface;
- Cox—capacity of the oxide layer;
- CPEdl or Constant Phase Element—modified phase element introduced to improve the representation of the impedance by the model, and depends on the empirical constant for the determination of n behaviour which represents the capacitive properties of the layers, and is in the range from 0 to 1. If n = 0, CPE will act as a resistor, and if n = 1, CPE will act as a capacitor;
- CPEox—modified phase elements for the impedance of the oxide layer. Determination of CPEox is provided through empirical constants nox.
- Rs—electrolyte solution resistance between the working electrode and the reference electrode in a three-electrode cell;
- Rct—polarization resistance or resistance to charge transfer on the electrode/electrolyte interface;
- Rcoat—the resistance of the coating;
- Cdl—double layer capacity at the electrode/electrolyte interface;
- Ccoat—capacity of the coating;
- CPEdl or Constant Phase Element—modified phase element introduced to improve the representation of the impedance by the model, and depends on the empirical constant for the determination of n behaviour which represents the capacitive properties of the layers, and is in the range from 0 to 1. If n = 0, CPE will act as a resistor, and if n = 1, CPE will act as a capacitor;
- CPEcoat—modified phase elements for the coating impedance. The determination of CPEcoat is provided through the empirical constants ncoat.
4. Conclusions
- SEM analysis of the cross-section proved the uniform thickness and density, and the topography analysis of the surface determined the presence of micrometal TiN drops.
- DC testing proved that the TiN/CoCrMo and CoCrMo samples have more positive values of the corrosion potential at 36 °C in comparison with 25 °C.
- The TiN coating shows better chemical stability at both temperatures in comparison with the CoCrMo alloy in a 0.9% NaCl solution.
- AC electrochemical testing shows higher values of the polarization resistance (Rct) for the CoCrMo alloy in comparison with the TiN coating in a 0.9% NaCl solution at both temperatures, which can be explained by the formation of more stable oxide layers on the CoCrMo alloy.
- SEM/EDS micrographs revealed that the surface morphology of the TiN layers after linear polarization is highly heterogeneous with corrosion products.
- The corrosion rate on the samples with the TiN coating in 0.9% NaCl was 8.3 times lower at 25 °C, and 2.25 times lower at 36 °C than CoCrMo alloy without coating.
- The TiN coating provides 87.96% protection at 25 °C, and 55.62% protection at 36 °C.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Sample | T, °C | Ecorr, mV vs. SCE | vcor, µA/y | jcor, µA/cm2 | Rp, Ω/cm2 | η, % |
---|---|---|---|---|---|---|
CoCrMo | 25 ± 1 | −700 ± 0.065 | 6.59 ± 0.027 | 0.641 ± 0.029 | 6.43 × 103 ± 0.279 | |
36 ± 1 | −240 ± 0.030 | 3.38 ± 0.038 | 0.328 ± 0.036 | 17.98 × 103 ± 0.174 | ||
TiN/CoCrMo | 25 ± 1 | −592 ± 0.072 | 0.793 ± 0.046 | 0.117 ± 0.049 | 375 × 103 ± 0.345 | 87.96 |
36 ± 1 | −190 ± 0.006 | 1.50 ± 0.051 | 0.222 ± 0.053 | 301 × 103 ± 0.231 | 55.62 |
Sample | Rs, Ω·cm2 | CPEox, S·sn·cm2 | nox | Cox, F/cm2 | Rox, Ω·cm2 | CPEdl, S·sn·cm2 | ndl | Cdl, F/cm2 | Rct, Ω·cm2 |
---|---|---|---|---|---|---|---|---|---|
CoCrMo (25 ± 1) °C | 8.25 | 1.10 × 10−4 | 0.91 | - | 4.81 × 103 | 8.79 × 10−4 | 0.56 | - | 2.11 × 105 ± 0.085 |
CoCrMo (36 ± 1) °C | 22.12 | - | - | 2.12 × 10−10 | 3.41 × 105 | - | - | 2.90 × 10−11 | 4.92 × 105 ± 0.048 |
Sample | Rs, Ω·cm2 | CPEcoat, S sn cm2 | ncoat | Ccoat, F/cm2 | Rcoat, Ω·cm2 | CPEdl, S sn cm2 | ndl | Cdl, F/cm2 | Rct, Ω·cm2 |
---|---|---|---|---|---|---|---|---|---|
TiN (25 ± 1) °C | 7.59 | 1.20 × 10−4 | 0.79 | - | 2.17 × 104 | - | - | 8.99 × 10−4 | 2.84 × 104 ± 0.057 |
TiN (36 ± 1) °C | 28.26 | 3.32 × 10−4 | 0.66 | - | 90.78 | - | - | 6.93 × 10−5 | 2.38 × 104 ± 0.045 |
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Jakovljević, S.; Alar, V.; Ivanković, A. Electrochemical Behaviour of PACVD TiN-Coated CoCrMo Medical Alloy. Metals 2017, 7, 231. https://doi.org/10.3390/met7070231
Jakovljević S, Alar V, Ivanković A. Electrochemical Behaviour of PACVD TiN-Coated CoCrMo Medical Alloy. Metals. 2017; 7(7):231. https://doi.org/10.3390/met7070231
Chicago/Turabian StyleJakovljević, Suzana, Vesna Alar, and Antonio Ivanković. 2017. "Electrochemical Behaviour of PACVD TiN-Coated CoCrMo Medical Alloy" Metals 7, no. 7: 231. https://doi.org/10.3390/met7070231