Study of the influence of microstrukture on electric properties of plasma-sprayed aluminia coatings using the scanning electron microscope mirror effect (SEMME) method

摘要

Pure alumina coating obtained by thermal spraying can find applications as electrical insulating layer. Thermally-sprayedceramic coatings exhibit a complex lamellar structure with a network of interconnected pores, interlamellarand intra-lamellar cracks. In this work, the influence of the microstructure on electric properties for plasma-sprayedalumina coatings was investigated. Coatings have been sprayed with different pressures and gases usinga CAPS (‘Controlled Atmosphere Plasma Spraying’) as well as different alumina feedstock powders. Detailedquantitative image analysis of cross-section views allowed to select six microstructures with different porosity levelsand cracks orientation distributions. In order to assess the behaviour of the electrical insulation and the influence oflocal defects on electric properties, the so-called Scanning Electron Microscope Mirror Effect (SEMME) methodhas been applied on outer surfaces and on cross-sections of the different selected alumina coatings. This method,originally developed to study the ability of a bulk insulating material in trapping of charges from an electron beamirradiation in a SEM, revealed to be successfully feasible for porous materials such as thermally-sprayed ceramiccoatings. It has been shown that cracks orientation modified both propagation and trapping of charges andtherefore the electric properties of plasma-sprayed alumina coatings.