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Structure and morphology of whitlockite coating electrophoretically deposited on NiTi shape memory alloy

Dudek K., Goryczka T.

Engineering of Biomaterials

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2017

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Vol. 20, no. 140

2--6

EN

In order to improve the biocompatibility of NiTi shape memory alloy, the surface was modified by formation of multifunctional layer consisted of titanium oxides and whitlockite ceramic. Amorphous TiO2 interlayer was produced on NiTi substrate by autoclaving at 134°C for 30 minutes while the following whitlockite coatings were deposited using electrophoresis (EPD). Electrophoresis was performed under different voltage (from 20 to 80 V) at time periods (from 30 to 120 s). Applied deposition parameters 20 V and 60 s resulted in forming homogenous whitlockite coating, consisted of β-Ca3(PO4)2 and β-Ca2P2O7, on passivated NiTi alloy. In the next step, the material was heat-treated in vacuum condition at 1000°C for 2 h. As a result of sintering crystallization of titanium oxides was observed. The obtained layer was cracks-free. Applied deposition process increased the roughness of surface. Deposited whitlockite agglomerates had an average thickness ca. 5.6 μm. The structure of CaP coating material after applied heat-treatment remained unchanged in comparison to initial powder material. However, the partial decomposition of NiTi parent phase to equilibrium ones was observed. The whitlockite coating was also observed to have no impact on the martensitic transformation responsible for shape memory effect. Additionally, applied sintering condition changed the sequence of martensitic transformation from one to two-step.

2

Influence of PAA on the Microstructure and Corrosion Resistance of Electrophoretically Deposited SiO2 and Ni/SiO2 Coatings on X2CrNiMo17-12-2 Steel

Ratajski T., Kalemba-Rec I., Dubiel B.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 4

2073--2079

EN

The effect of anionic surfactant in the form of polyacrylic acid (PAA) on the electrophoretic deposition of the SiO2 and Ni/SiO2 coatings on X2CrNiMo17-12-2 stainless steel was examined. Parameters of the process, such as chemical composition of the suspensions, voltage between the electrodes and the deposition time were experimentally selected. Zeta potential measurements showed a beneficial effect of polyacrylic acid on the SiO2 and Ni particles stability in ethanol. Scanning and transmission electron microscopy studies revealed that the microstructure of the coatings obtained from the suspensions containing polyelectrolyte is more homogenous and has less amount of desiccation cracks on the surface. The results of the polarization tests have shown that addition of anionic surfactant improves also corrosion resistance of the coatings in 3.5% NaCl solution.

3

Influence of polyethylenimine on the electrophoretic deposition of SiO2 and Ni/SiO2 coatings on 316L stainless steel

Ratajski T., Kalemba-Rec I., Dubiel B.

Inżynieria Materiałowa

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2016

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Vol. 37, nr 4

184--189

EN

The aim of the present work was to investigate the influence of polyethylenimine, a cationic polymer surfactant, on the microstructure and corrosion resistance of SiO2 and Ni/SiO2 coatings electrophoretically deposited on 316L stainless steel. The relationship between zeta potential and pH of the ethanol-based suspensions of SiO2 and Ni powder particles with addition of polyethylenimine was determined. The parameters of electrophoretic deposition process (applied voltage, time, distance between electrodes) were developed to prepare good quality coatings. Cathodophoresis from suspensions with polyethylenimine addition was performed with slightly lower applied voltage and time as compared to anodic deposition of coatings without surfactant. The microstructure of the coatings, their surface roughness and adhesion to the substrate were investigated. The protective behaviour of the coatings was studied by potentiodynamic measurements in 3.5% NaCl water solution. The microstructure and properties of the coatings were compared with those obtained without polyethylenimine addition. It was determined that the microstructure of SiO2 and Ni/SiO2 coatings deposited from suspensions containing polyethylenimine was more uniform and contained smaller amount of cracks and voids than the coatings achieved without polyelectrolyte. It was also observed that the quality improvement of the coatings deposited on 316L steel due to addition of polyelectrolyte with binding properties leads to increase of their corrosion resistance.

PL

Celem pracy było zbadanie wpływu polietylenoiminy (PEI) na stabilność zawiesin na bazie etanolu używanych do osadzania elektroforetycznego (EPD) powłok SiO2 i nanokompozytowych powłok Ni/SiO2 na stali 316L. Zbadano mikrostrukturę powłok oraz topografię powierzchni, przyczepność do podłoża i odporność na korozję w 3,5% roztworze NaCl.

4

Manufacturing, Microstructure and Corrosion Resistance of Electrophoretically Deposited SiO2 and Ni/SiO2 Coatings On X2CrNiMo17–12–2 Steel

Ratajski T., Kalemba-Rec I., Dubiel B.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 2B

1221--1227

EN

The SiO2 and Ni/SiO2 coatings were electrophoretically deposited on X2CrNiMo17-12-2 steel using ethanol-based suspensions of the SiO2 and Ni powders. The influence of the zeta potential and concentration of the suspensions, the applied voltage and deposition time on the quality of the coatings was studied. Microstructure of the plan-view and cross sections of the coatings was investigated using scanning electron microscopy. The plan-view images revealed the uniform microstructure of the coatings with sporadically observed cracks, pores as well SiO2 and Ni agglomerates. On the cross-sections, the Cr2O3 layer, resulted from oxidation of the substrate during sintering of the coatings was observed. The polarization tests have shown that SiO2 and Ni/SiO2 coatings improve the corrosion resistance of the X2CrNiMo17-12-2 steel in 3.5% NaCl aqueous solution.