Production of CrN/NbN superlattice coatings by Cathode Switching Reactive Cathodic Arc Evaporation

Abstract

CrN/NbN superlattice and CrN coatings, approximately 3 pm in thickness, have been deposited on tool steel samples by a modified reactive cathodic arc evaporation technique (CAE) in an industrial-size chamber. Superlattice deposition was achieved by triggering alternatively on Cr and Nb cathodes, obtaining layers of about 4-5 nanometers. X-ray diffraction, scanning and transmission electron microscopy, atomic force microscopy and energy dispersive X-ray analysis were used to determine microstructure and chemical composition of both coatings and coating defects. Diffraction techniques showed for the CrN coating a (220) preferred orientation and a strongly preferred (200) orientation for superlattice samples, with a lattice parameter intermediate between the CrN and the NbN ones. Defect evaluation was focused on shape, dimension, density, clustering and other process-sensitive features. In CrN/NbN superlattice coatings a separation between defects and the surrounding bulk coating was evident, in fact TEM analysis revealed a different microstructure and chemical composition in this area. On the basis of macroparticle formation theory an explanation of the experimental observations is proposed.