Deposition and properties of novel nitride superlattice coatings. Final report, May 1990--January 1996

The authors have fulfilled the primary objectives of this research program which were to establish the feasibility of depositing polycrystalline nitride superlattices with high hardnesses on steel substrates, to understand the relationship between deposition process parameters, film microstructure, and resulting film properties, and to investigate the theories of superlattice strengthening/hardening. An opposed-cathode unbalanced magnetron sputtering system was modified for the deposition of the superlattices. Thin films of several microns thick, composed of many alternating thin layers of two (or more) different materials with periods between 3 and 150 nm, were deposited at low temperature onto various engineering substrate mate5rials such as steel. They have developed several superlattices with superior properties unattainable from either single-layer or thicker multilayer coatings. The nitride superlattices that they have explored so far include TiN/NbN, TiN/VN, NbN/VN, TiN/CrN, AlN/TiN, TiN/Ni, and TiN/NiCr. The effects of deposition parameters on film structure and properties were systematically studied, and optimized parameters for both monolithic films and superlattices were developed. The results of this research show that polycrystalline nitride superlattices have great promise for replacing commonly used nitride-based wear protective coatings. The existence of metastable crystalline phases has been observed in some of the superlattices explored, which they have named nanolayer-stabilized materials. The theoretical knowledge and experimental methods developed in this work have already been used to design and produce superlattice coatings for industrial work. A parallel industrial group program has been established to transfer the superlattice coating technology to industry. The detailed results achieved in this project have been discussed in over a dozen publications. The most important results from the work are summarized