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| Ceramic coatings were prepared in silicate mixed with different concentrations of phosphate by pulsed bi-polar plasma electrolytic oxidation on Ti-6Al-4V alloy in silicate solution. The phase composition, structure and the elemental distribution of the coatings were studied by XRD, SEM and energy dispersive spectroscopy, respectively. The thermal shock resistance of the coated samples was evaluated by the thermal shock tests. The coating was mainly composed of rutile TiO2 and anatase TiO2, as well as a large amount of amorphous silica oxide. Increasing the concentration of phosphate, the content of TiO2 and the thickness of the coating increased first and then decreased. The micro pores and the micro cracks of the coating increased with the concentration of Na3PO4.The coatings were of double-layer structure, the outer layer was porous and the inner layer was comparatively dense. The distribution of the elements changed greatly within a few micrometers from the interface; otherwise, the coating is basically uniform all throughout the main coating and at the outer part of the coating the distribution of the elements also changed much because of the porosity and the roughness of the coatings. The thermal shock resistance was mainly attributed to the surface state under the similar composition and thickness of the coatings. When the concentration of Na3PO4 was 6g/L, the thermal shock resistance of the coatings was the best in the experimental conditions. |
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| Keywords:plasma electrolytic oxidation; ceramic coatings; phosphate; thermal shock resistance; Ti6Al4V alloy |
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