1. Sezgin Cengiz1, Mehmet Yazici1,2, Y. Gencer1,*, M. Tarakci1,
Characterization of The Coating Formed by MAO on Pure Zirconium in Yttrium Acetate Tetrahydrate Containing Electrolyte
Sezgin Cengiz1, Mehmet Yazici1,2, Y. Gencer1,*, M. Tarakci1,
1Gebze Institute of Technology, Department of Materials Science and Engineering, Gebze, Kocaeli, Turkey
2Ondokuz Mayis University, Department of Materials Science and Engineering, Kurupelit, Samsun, Turkey
Abstract:
In this study, oxide coatings were produced on pure zirconium by micro arc oxidation (MAO) method in the electrolytes containing sodium silicate and different amounts of yttrium acetate tetrahydrate (YAT) (1-4 g/l) for the same coating duration of 60 minutes. The surface roughness, microstructure, phase content and chemical composition of the coatings were characterized using scanning electron microscopy, profilometry and X-ray diffractometry. It was found that the surfaces of coatings on zirconium consist of monoclinic-ZrO2, tetragonal-ZrO2 phases. The coating thickness slightly decreases with the presence of YAT in electrolyte and YAT has not considerable effect on surface roughness. As amount of yttrium acetate tetrahydrate (YAT) in the electrolytic solution increased, coating/substrate interface smoothened.
Aim:
In this work, MAO coatings formed on pure zirconium were studied using different electrolytic solutions of sodium silicate, yttrium acetate tetrahydrate and their combination systems. Microstructure and phase compositions of coatings formed on pure zirconium in yttrium containing electrolytes were studied as an enlightening preliminary research of stabilization effect of yttrium on zirconium oxide layers for future studies .
Experimental:
The pure zirconium sheet was sliced to provide specimens with working area 25 mm x 50 mm x 1 mm. The samples were ground and the polished by conventional metallographic techniques. The electrolytes with four different compositions were prepared with a certain amount sodium silicate and YAT by dissolving in distilled water as shown in the Table 1. The MAO coating was carried out by an home-made asymmetric AC power supply. The coated samples were washed in distilled water and then cleaned using ethanol. The surface roughness of the bare substrates and MAO coated samples was determined using the same parameters by means of the same Profilometer. Rigaku D-MAX 2200 X-ray diffractometer (40 kW, 40 mA), with a Cu K radiation over a 2 = 20 to 100, was employed for the characterization of MAO coated substrates. The surfaces and cross section of the MAO coated samples were examined using XL30 FEG ESEM.
Results:
Conclusion:
The coatings are mainly composed of t-ZrO2 and m-ZrO2 phases.
Surface features of equiaxed dendritic cluster were observed on the surface coating of Zr.
The equiaxed dendritic clusters consist of Zr, O rich and which of surroundings have Si and Y rich.
Coating/substrate interface became smoother as amount of YAT in electrolytic solution increased.
Coating thickness decreased with YAT in the electrolyte.
YAT has no considerable effect on surface roughness (Ra).
References
Cengiz, S., Gencer, Y. The characterization of the oxide based coating synthesized on pure zirconium by plasma electrolytic oxidation. Surface & Coating Tecnology, : p
Cheng, Y.L., et al., Characterization of plasma electrolytic oxidation coatings on Zircaloy-4 formed in different electrolytes with AC current regime. Electrochimica Acta, (24): p
Gencer, Y., et al., The Effect of Sodium Silicate Concentration on The Properties of the Coating Formed on Pure Zirconium by Microarc Oxidation Coating Technique. Materials and Manufacturing Technologies Xiv, : p
Gencer, Y., M. Tarakci, and S. Cengiz, Oxide Based Ceramic Coating on Pure Zirconium by Microarc Oxidation Method. Journal of the Faculty of Engineering and Architecture of Gazi University, (4): p
Yerokhin, A.L., et al., Plasma electrolysis for surface engineering. Surface & Coatings Technology, (2-3): p
Fig. 4. The cross section SEM micrographs of MAO coated Zr with different electrolytes; a) A1, b)A2, c) A3, d) A4 (Table 1).
Table 1. The chemical compositions the electrolytic solution
Fig. 5. Surface SEM micrograph and SEM-EDS spectra of MAO coating for A4 electrolytic a) surface SEM image, b) SEM-EDS spectrum from “A”, c) “B” and d) “C”.
Fig. 6. Cross sectional SEM micrograph and SEM-EDS spectra of MAO coating for A4 electrolytic a) cross section SEM image, b) SEM-EDS spectrum from “A”, c) “B” and d) “C”.
Fig. 1. The surface XRD patterns of MAO coating of zirconium substrates with different electrolyte of A1, A2, A3, and A4 (Table 1).
Fig. 2. The change in coating thickness and surface roughness with different electrolyte of A1, A2, A3, and A4 (Table 1).
Fig. 3. The surface SEM micrographs result of MAO coated Zr with different electrolyte a) A1, b) A2, c) A3, d) A4 (Table 1).