Nanometer scale multilayered hard coatings

Multilayer coatings with layer thicknesses in the nanometer range have been shown to exhibit extremely high hardnesses, making them useful as abrasion -resistant coatings. Hardness values in excess of 5000 kg/mm(2) have been a chieved in multilayers composed of two nitride materials, such as TiN and V N, with bilayer periods of 5-10 nm. This article begins with a review of th e deposition of multilayered coatings by reactive sputtering and the charac terization of these coatings by transmission electron microscopy and X-ray diffraction. The hardness enhancements observed in both isostructural and n on-isostructural nanometer-scale multilayers are then reviewed. Several exp lanations for this enhancement in hardness have been developed in order to understand the hardening process and to develop coatings with even higher h ardness. Models based on dislocation motion within layers and across layer interfaces, as well as Hall-Fetch-type models, have successfully been appli ed to multilayers to explain this hardness enhancement, and they are briefl y outlined. (C) 1999 Elsevier Science Ltd. All rights reserved.