CHARACTERIZATION OF COMPOSITE TRIBOLOGICAL COATINGS - COMPOSITION, MICROSTRUCTURE AND MECHANICAL-PROPERTIES

The present study aims to characterize two kinds of plasma composite c oatings (Cr2O3.CaF2 and Cr2O3.BaF2) with very good tribological proper ties. Chemical and quantitative image analyses show that solid lubrica nt content (CaF2 and BaF2) in the coatings is less than but proportion al to the nominal solid lubricant content in mixed powders for sprayin g. The microstructure of the composite coatings is characteristic of a homogeneous distribution of solid lubricant powders within the Cr2O3 matrix: on a sliding surface, the coating's microstructure consists of the spheroidal solid lubricant particles dispersed in a continuous Cr 2O3 matrix; on cross-section the distinct wavy multilayers (Cr2O3 and solid lubricant) have been compacted to build the composite coating. D uring sliding, the matrix has flowed and the lubricant particles have been removed partially, smashed to very fine fragments and incorporate d with the matrix of which one thin soft film has been made. It is the thin soft film that offers the coatings' very good tribological prope rties. However, the solid lubricant results also in degradation of the mechanical properties. Consequently there is one optimal solid lubric ant content (about 20 vol.%) at which the coating has the best tribolo gical and mechanical properties.