Microstructures and mechanical properties of duplex-treated composite ceramic coatings with and without compound layer

Abstract

Duplex-treated composite ceramic coatings with and without compound layer were produced by the combination of plasma nitrocarburizing and follow-up multi-arc ion plating. The microstructures and mechanical properties of the ceramic coatings were investigated by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy, in association with property characterization. The results show that the composite ceramic coatings are composed of an inner nitrocarburized layer, a CrN interlayer and an outmost AlCrTiSiN layer. The AlCrTiSiN layer consists mainly of alternately nanoscaled (Cr,Al)N sublayer and amorphous sublayer with a few (Ti,Al)N phases embedded in a matrix of amorphous Si3N4 and Si. The compound layer has transformed to the γ′-phase sublayer, which enhances considerably the adhesion strength of the CrN interlayer to compound layer. The improved adhesion strength is attributed to the γ′-phase acting as nucleation sites of epitaxial growth for the CrN phase. The composite ceramic coating with compound layer reveals much higher hardness, bearing capacity and wear resistance when compared with the composite ceramic coating without compound layer. The improvement of mechanical and tribological properties is associated with presence of the γ′-phase sublayer, which provides a smooth transition, gradient in hardness and stress between the substrate and the CrN/AlCrTiSiN coating. In addition, the hard γ′-phase sublayer provides a strong supporting effect for CrN/AlCrTiSiN layer under loading.