JOINING OF ALUMINUM TO CARBON-CARBON COMPOSITES FOR FUSION REACTOR APPLICATIONS

THE JOINING TECHNOLOGIES CURRENTLY AVAILABLE FOR JOINING METALS TO CARBON-CARBON (C-C) COMPOSITES ARE NOT ENTIRELY SATISFACTORY FOR FUSION REACTOR APPLICATIONS FOR MANY REASONS. ACTIVE BRAZE ALLOYS CONTAINING REACTIVE METALS THAT WET THE CARBON BY FORMING CARBIDES HAVE BEEN THE ACCEPTED METHOD USED COMMONLY TO MAKE BRAZE JOINTS ON C-C AND GRAPHITES. SUCH USE OF ACTIVE BRAZE ALLOYS WHICH CONTAIN STRONG CARBIDE FORMERS OFTEN RESULTS INC THE TENDENCY TO PRODUCE WEAK JOINTS WITH BRAZE METAL FLOWING TO PLACES NOT DESIRED AND YET NOT GOING TO PLACES WHERE IT IS NEEDED. THE PROBLEM OF JOINING C-C TO ALUMINUM (AL) METAL IS ESPECIALLY DIFFICULT BECAUSE OF THE LOW MELTING POINT OF AL, 660 DEGREES CENTIGRADE, AND THE LARGE DIFFERENCE IN COEFFICIENT OF THERMAL EXPANSION BETWEEN AL AND C-C COMPOSITES. A HIGH PURITY VERSION OF THE LOW MELTING EUTECTIC ALLOY OF AL AND ~ 12 WT. % SILICON, MELTING NEAR 600 DEGREES CENTIGRADE CAN BE USED TO JOIN AL, BUT IT IS NOT COMPATIBLE WITH C-C MATERIALS. IN PHASE I THE FEASIBILITY OF SUCCESSFULLY BRAZE JOINING C-C TEST COUPONS TO AL FOR FUSION REACTOR APPLICATIONS WILL BE EVALUATED BY USING A SPECIAL SURFACE PREPARATION AND INFILTRATION TECHNIQUE THAT REPLACES THE C-C SURFACE WITH A COPPER SURFACE WHICH THEN CAN BE BRAZED TO AL.