Preparation and Properties of Boron Carbide Continuous Filaments

Abstract

Boron carbide filaments are promising reinforcements for use in both resin and metal composites because of their potentially high strength, high elastic modulus, and low density. This paper discusses the preparation and properties of such filaments from the viewpoint of their ultimate usefulness in such applications. Continuous boron carbide filaments were vapor deposited on tungsten substrates having a boron precoat from mixtures of boron trichloride, methane, and hydrogen at 1 atm and temperatures between 1100° and 1200°C. Deposition rates were considerably less than for boron alone; a close relationship was seen between the stoichiometry of the feed gas, filament composition, and mechanical properties. In extended runs, average strengths of 390,000 psi were achieved, with individual values as high as 474,000 psi (1‐in. gauge). Elastic modulus values up to psi were also characteristic of the product. In prototype epoxy resin composites of less than optimum uniformity and homogeneity, bend strengths up to 244,000 psi and moduli up to psi were measured at 85 v/o filaments, indicating that efficient transfer of stress to the filaments occurred.