Fabrication And Properties Of Plasma Sprayed Nanometer And Micron Alumina Coatings

Al₂O₃ ceramic coating has the characteristics of high strength,high hardness and good insulation.It has been widely used in the fields of aerospace and electronic appliances.However,due to its brittleness and low toughness,it is limited in many occasions.Therefore,the study of the structure of Al₂O₃ coating to improve the strength and toughness of the coating,making it to adapt to industrial needs has become a major issue.In this experiment,four kinds of powders with different morphology were used to spray,the effect of the morphology on the performance of the coating were studied Then,two kinds of powders with excellent properties were selected,nano-agglomerated aggregates and traditional melt-crushed micro powders,which were sprayed under the power of 14.4,19.2 and 24 kW respectively.The prepared nano-structured coatings and conventional micro-coatings are observed by the scanning electron microscopy and XRD detection,Vickers hardness tester,slow strain stress corrosion tester and LCR digital bridge were used to investigate the mechanical properties and dielectric properties.The influence of spray power on microstructure and phase structure of coatings,the formation mechanism of the structure of nano-structured coating and its toughening and strengthening mechanism is discussed.Finally,the influencing factors of dielectric properties of coatings were studied.The experimental results show that the microstructure of the micro-coating is a lamellar structure,the structure of the coating is dense and the porosity is low.However,The microstructure of the nanostructured coating consists of a fully melted zone and a partially melted zone.In which the semi-melted nanoparticle zone,the diffusely distributed particulate structure and the liquid-like sintered microstructure in the partially melted zone increase the strength of the coating and Toughness,and the area of the partially melted zone can be controlled by the spray power.The microstructure coatings and nanostructured coatings consist of y-Al₂O₃ and a-Al₂O₃,with the increase of spraying power,the content of ?-Al₂O₃ phase increases gradually.The content of y-Al₂O₃ in the coating is the main factor of the dielectric constant.The greater the content of Y-Al₂O₃,the larger the dielectric constant.