A combinatorial approach to the optimization of metastable multicomponent hard coatings

Due to the variety of process parameters during the physical vapor deposition of metastable hard coatings, a conventional approach to the development of new coatings is time consuming and expensive. Thus. the ever increasing global market pressures lead to the demand of a cost efficient tool for the development of new products in the advanced materials industry. One possible approach to a fast screening of potential materials for hard coatings could be the adaptation of combinatorial or composition spread technologies to the specific requirements of coatings industry. Combinatorial synthesis and screening is an established technique in pharmaceutical industry and recently combinatorial approaches have been made to the screening of superconductive, magnetoresistant and photoluminescent materials but up to now only very limited work has been done concerning the investigation of hard coatings by combinatorial methods. Despite this, combinatorial approaches can significantly reduce time and costs for the development of multicomponent hard coatings. In this paper, the deposition and characterization of two dimensionally laterally graded hard coatings is presented. The coatings have been deposited by reactive magnetron sputtering, using three metallic targets at a low angle to the substrate surface as well as a system of apertures. To illustrate the advantages of combinatorial approaches for the development of metastable hard coatings, Ti-Al-Hf-N and Ti-Al-Si-N composition spreads will be discussed with special emphasis on the relationship between structure and composition on one hand and oxidation resistance of the quaternary films on the other hand. These two quaternary systems have been chosen because of their technical importance and as model systems with complete solid solution between two of the constituent binaries (TiN and HfN) and with a complete miscibility gap (TiN and Si3N4), respectively. The results illustrate that the combinatorial approach is a powerful and cost efficient tool for the development and optimization of new materials for hard coatings. (C) 2001 Elsevier Science B.V. All rights reserved.