STP452: The Importance of Coatings in the Preparation of Al2O3 Filament/Metal-Matrix Composites

    Noone, M J
    Ceramist, physicist, and group leader, respectively, Metallurgy and Ceramics Research, Space Sciences Laboratory, General Electric Co., Philadelphia, Pa.

    Feingold, E
    Ceramist, physicist, and group leader, respectively, Metallurgy and Ceramics Research, Space Sciences Laboratory, General Electric Co., Philadelphia, Pa.

    Sutton, W H
    Ceramist, physicist, and group leader, respectively, Metallurgy and Ceramics Research, Space Sciences Laboratory, General Electric Co., Philadelphia, Pa.

    Pages: 31    Published: Jan 1969


    Abstract

    The strength of composite materials formed by incorporating aligned brittle filamentary reinforcement into a metal matrix is dependent primarily on the strength of the filaments and on how effectively the matrix is able to transfer externally applied loads to the filaments. The interfacial zone between filament and matrix must satisfy several mechanical and chemical requirements if a useful composite is to be obtained: there must be (1) intimate contact between filament and matrix, (2) adequate bonding between filament and matrix, and (3) no chemical attack of the filament by the matrix which would be detrimental to the strength of the filament or to the bonding.

    Al2O3 (sapphire) whiskers offer several advantages for use as reinforcement since they may be grown readily with high aspect ratio (l/d), have high strength and elastic modulus, have relatively low density, and are creep resistant at elevated temperature. However, Al2O3 is not wetted by many metals or alloys, and this causes difficulties in composite fabrication. One of the most practical solutions to this problem has been the application (by sputtering) of thin, metallic coatings to the filaments to enhance wetting and improve bonding to the matrix. In matrices designed for high-temperature applications, corrosive reactions at the filament surface become of critical importance in the development of a serviceable composite. Coatings have been used also to protect the surface of the filaments from degradation by matrix interactions.

    This paper discusses the functions and types of coatings that have been used in the preparation of Al2O3 filament/metal-matrix composites and the importance of the coatings in promoting wetting and bonding and in preventing filament surface degradation during the composite fabrication process.

    Keywords:

    composites, aluminum oxide, whiskers, filament coatings, protection, wetting, bonding, interfaces, evaluation, tests


    Paper ID: STP44700S

    Committee/Subcommittee: D30.07

    DOI: 10.1520/STP44700S


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