Journal Information


Scarf Joining of Carbon/Carbon Composites Utilizing Noble Metal Wetting on Tungsten Carbide and Tungsten Trioxide

Masafumi Fukuda and Takahisa Yamazaki

School of Engineering, Tokyo Institute of Technology, Tokyo 152-8552, Japan

Abstract: Brazing is a suitable method for repairing carbon/carbon composites. We attempted high temperature scarf joining of carbon/carbon composites by wetting noble metals on carbon fibers coated with tungsten carbide. Silicon carbide fiber was coated with tungsten trioxide films and carbon films to research the spreading of molten gold on the nonreactive fiber. Tungsten trioxide was formed by heating the tungsten filament in a vacuum chamber and oxidation. Wetting tests of the gold drop were performed on the coated fiber. When the amount of deposited tungsten was increased and the surface temperature of the fiber raised, solidified gold adhered to the coated fiber. This result suggested that tungsten carbide was formed between carbon and tungsten trioxide. Molten gold can wet on tungsten carbide more easily than on tungsten trioxide. Carbon/carbon composites was coated with tungsten carbide and tungsten trioxide under the same conditions as the wetting test. The X-ray diffraction patterns and electron probe micro analyzer (EPMA) results showed that the wettability of molten gold on carbon/carbon composites was improved by tungsten trioxide and tungsten carbide. Gold did not infiltrate the carbon/carbon composites because of the barrier effect of tungsten film and poor wettability of gold on carbon/carbon composites. Carbon/carbon composites were joined in a scarf joint using gold. Joint surfaces of carbon/carbon composites were coated with tungsten carbide and tungsten trioxide. A tensile share test of the scarf joint was conducted, and the ultimate share strength of the scarf joint was 51.2 MPa.

Key words: Carbon/carbon composites, scarf joining, brazing, wettability, gold, tungsten carbide, tungsten trioxide.
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