Cailiao Baohu (Sep 2023)
Effect of Concentration of Lithium Tetraborate Electrolyte on the Micro-Arc Oxidation Ceramic Layer on Zr-4 Alloy
Abstract
In order to improve the service performance of Zr-4 alloy in nuclear industry and avoid introducing impurity elements， the micro-arc oxidation ceramic layer was prepared on the surface of Zr-4 alloy with Li2B4O7 as electrolyte.The effects of lithium tetraborate concentration on phase composition， microstructure， film thickness， hardness， roughness， wear resistance and corrosion resistance of micro-arc oxidation ceramic layer were investigated.Results showed that as the concentration of Li2B4O7 increased in the range of ρ(Li2B4O7)＝3～15 g/L， the conductivity of the electrolyte continued to increase， and the roughness of the ceramic layer continued to increase overall， which only slightly decreased when the electrolyte concentration changed from 6 g/L to 9 g/L.The thickness of micro-arc oxidation ceramic layer first continuously decreased in the range of ρ(Li2B4O7)＝3～9 g/L and then increased in the range of ρ(Li2B4O7)＝9～15 g/L.The hardness of the ceramic layer first decreased in the range of ρ(Li2B4O7)＝3 ～6 g/L， and then increased in the range of ρ(Li2B4O7)＝6 ～15 g/L.In addition， the ceramic layers were all composed of monoclinic zirconia (m-ZrO2).As the concentration of Li2B4O7 in the electrolyte increased， the porosity of the ceramic layer decreased and the micropore size changed little.The friction coefficient of the ceramic layer increased continuously in the range of ρ(Li2B4O7)＝3～12 g/L， and decreased when ρ(Li2B4O7)＝15 g/L.By comprehensive comparison， the ceramic layer with moderate thickness， good hardness， smooth and continuous surface， small porosity and pore size， good wear resistance and corrosion resistance could be obtained in the electrolyte with ρ(Li2B4O7) ＝ 15 g/L.
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