Tensile Strength of Boron Filament coated with Silicon Carbide and of Uncoated Boron Filament at Elevated Temperatures

Abstract

THE increasing use of boron filaments coated with boron and silicon carbide in composites has resulted in greater interest in the properties of these fibres at ambient and elevated temperatures. At present, commercial boron filaments coated in this way (produced and marketed by United Aircraft Corporation under the trade name ‘Borsic_TM’) are available with ultimate tensile strengths of greater than 400,000 pounds/inch² and moduli above 55 × 10⁶ pounds/inch². This room temperature strength of filament coated with boron is seriously reduced by exposure to air at elevated temperature, while that of the filament coated with silicon carbide is not affected by exposure to air for up to 1,000 h at 600° C (refs. 1 and 2). The study described here was undertaken to further characterize these filaments by determining their elevated temperature strengths after exposure to air at the test temperatures for various times.