Densification Of Ceramic Coating By Mic-arc Oxidation Based On Plasma Micro Discharge

The growth of micro arc oxidation ceramic coating is a process that the energy of plasma micro area discharge gradually increases and the density of ceramic coating gradually decreases.In this paper,the relationship between the micro area discharge energy and the density of ceramic coating during the growth of ceramic coating,the preparation of ceramic coating with the same thickness and different density,and the influence of bipolar negative pulse voltage on the maximum micro area discharge energy during the growth of ceramic coating were studied,It provides a feasible way to solve the contradiction between insulation and heat conduction of ceramic coating.The research results are as follows:In the process of micro-arc oxidation,corresponding to different growth stages,the surface plasma microzone morphology of the sample is as follows:Arc free-glow discharge-silver arc discharge-transition discharge-orange micro-arc discharge-orange large arc discharge.Different arc shapes correspond to different micro discharge energies,and the micro energy gradually increases from 2.19×10-4J to 4.91×10-2J.When the thickness of the ceramic coating increases from 5?m to 40?m,the insulation strength decreases from 79.6MV/m to 19.01MV/m.The density of the ceramic coating decreases with the increase of the thickness.The maximum discharge energy in the microzone during the growth process determines the density of the ceramic coating.When the thickness of the ceramic coating is all 15?m,the morphology of the termination arc on the surface of the sample is different,and the corresponding discharge energy is different.The smaller the energy of the surface plasma microzone is,the better the density is.The breakdown voltage is 725V and 591V,respectively,the difference is 22.7%.Finally,according to the morphology and quantity of arc light on the surface of the sample,the density of ceramic coatings with different thickness can be controlled by controlling the negative pulse voltage to change the discharge energy in the micro area of the ceramic coating during the preparation.When the thickness of the ceramic coating is 40?m,the porosity of the ceramic coating decreases from 27.9%to 45.8%,and the breakdown voltage of the ceramic coating increases from 751V to 1182V.The surface ceramic can improve the thermal resistance of the sample,the thermal resistance of the samples with dense ceramic coating and loose ceramic coating is increased by 53%and 97%respectively compared with the aluminum alloy substrate,and the thermal resistance of the samples with dense ceramic coating is 30%lower than that of the samples with loose ceramic coating.