Thermal Expansion and Mechanical Behavior of Graphite-Fiber-Reinforced Tantalum-Carbide Composites

Abstract

Thermal expansion measurements, on a variety of graphite-fiber-reinforced tantalum-carbide composites fabricated at temperatures above 3, 000°C, imply that little bonding exists between fibers and matrix at room temperature. The results of flexure tests tend to confirm this hypothesis. Heating to above 1, 600°C appears to provide significant mechanical interactions between fibers and matrix, presumably caused by differential thermal expansions and interface friction, which lead to highly anisotropic thermal strains at higher temperatures despite isotropic thermal expansion at lower temperatures. One implication is that the thermal expansion behavior of these composites will be similar, in terms of volumetric thermal strain, to that of the carbide matrix, as long as the carbide is the continuous phase of the composite. It was only in those composites which showed evidence of a damaged and/or discontinuous matrix phase that significantly lower volumetric thermal expansions were observed.