Microstructural Studies of Vapor-Deposited Nickel/Ceramic Composites
by
Mihir Mahendra Shah
J. M. Rigsbee
Department of Materials Science and Engineering
Abstract
This research program examines fundamental aspects of metal/ceramic interactions through the analysis of model composites produced by plasma-assisted physical vapor deposition (ion plating) and consisting of thin (< 1µm) metallic films on ceramic substrates. The two major aspects of this research are: 1) the investigation of the effects of ion bombardment on the nucleation behavior and growth morphologies of the films, as well as the development of any film/substrate orientation relationships; and 2) the study of the interactions between metals and ceramics in a thin-film geometry, with emphasis on interface compound formation, comparing ion-assisted and high temperature processing.
The primary microanalytical technique employed was cross-section transmission electron microscopy, with scanning electron microscopy and Auger electron spectroscopy utilized as well. In addition, a tensile adhesion test and microhardness indentations were used to evaluate mechanical strength.
An optimal processing window was defined for DC ion plating in nickel/cordierite system in order to obtain maximum film/substrate adhesion. For the case of RF ion plating of nickel films on basal orientation sapphire substrates, ion bombardment during deposition was shown to have significant effects on the nucleation and growth behavior of the films. Bombardment enhanced adatom mobility was sufficient to result in a crystallographic orientation relationship between the film and the substrate, with close packed planes and directions being parallel. Ion bombardment was not sufficient, however, to produce any interfacial reaction phases in the as-deposited condition. A nickel aluminate spinel did form at the interface upon heat treatment (1000°C, 2 hrs.) and was always crystallographically related to the substrate, independent of the as-deposited crystallography. Metallic films were more resistant to disbonding than oxide films, with a strong interface being achieved via ion-assisted deposition.
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