Growth structure and growth defects in pulsed laser deposited Cr–CrN x–CrC xN 1− x multilayer coatings

Abstract

Chromium carbonitride (CrC x N 1− x ) coatings are becoming more and more interesting for wear protection applications due to their increased hardness and improved wear performance compared to chromium nitride (CrN x ) hard coatings. Further improvements seem to be possible by using multilayer coatings of these two materials. In the current work such multilayer structures were deposited by the Pulsed Laser Deposition (PLD) technique at room temperature using an industrially designed 4-beam multi-spot PLD evaporator. The coatings were investigated by means of transmission electron microscopy (TEM) in order to solve their growth mechanisms and microstructure development. Due to the very high hardness and brittleness of the coatings, the TEM sample preparation has to be based on gallium focused ion beam cutting. Although the chemical analyses revealed a significant Ga atom contamination of the samples originating from the sample preparation, the face-centered cubic CrN-based phases and their textures, found in electron micro-diffraction analyses as well as in X-ray diffraction measurements, were scarcely influenced by the incorporated atoms. Great influences on the phase formation result from oxygen atom trapping from the rest gas atmosphere prior deposition. A very fine grained (2–5 nm) structure was found for the pure chromium adhesive interface layers, which are necessary for high adhesion of the hard coating layers. These hard ceramic layers–CrN x and CrC x N 1− x –possess much coarser (8–15-nm grain size), micro-columnar structures. Furthermore, influences on the film growth are caused by defects on the substrate surface like cracks and contaminating dust particles.