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Electrodeposited Cobalt-Tungsten as a High-Temperature Diffusion Barrier for Graphite-Fiber/Nickel Composites

Published online by Cambridge University Press:  21 February 2011

N. S. Wheeler and
D. S. Lashmore
N. S. Wheeler
Affiliation:
University of Virginia, Dept.of Materials Science and Engineering, Charlottesville, VA 22906
D. S. Lashmore
Affiliation:
National Institute of Standards and Technology, 224/B166, Gaithersburg, MD 20899
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Abstract

There is a growing demand for advanced composites which can maintain their structural strength in high-temperature environments, particularly for aerospace applications. The use of graphite fiber/nickel metal matrix composites would be desirable if the deterioration of mechanical properties resulting from interdiffusion of carbon and nickel at temperatures in excess of 600°C could be avoided. The present research concerns an electrodeposited cobalt alloy coating containing 5-10.5 at-% tungsten, which was designed to serve as a diffusion barrier between graphite fibers and a nickel matrix. The resulting graphite/Co-W/Ni composite was tested under various time/temperature conditions, and the coating was shown to inhibit diffusion for up to 24 hr at 800°C. Annealed and unannealed coated fibers were analyzed by x-ray diffraction and by transmission electron microscopy The as-deposited coating was found to contain both h.c.p. and f.c.c. cobalt, whereas only f.c.c. was observed after annealing at 1100°C for 1.5 hours. WC was found at the coating/fiber interface.

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References

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