INTERFACE STRUCTURE AND REACTION-KINETICS BETWEEN SIC AND THICK COBALT FOILS

Reaction couples of SiC with thick cobalt foils were annealed in an Ar -4 vol % H-2 atmosphere at temperatures between 950 and 1250 degrees C for times between 4 and 100 h. At temperatures above 950 degrees C, s olid-state reactions lead to the formation of various silicides with c arbon precipitates. The typical layer sequence in the reaction tone wa s determined by quantitative microanalysis to be SiC/CoSi + C/Co2Si C/Co2Si/Co2Si+C/... /Co2Si/Co(Si)/Co. The mechanism of the periodic ba nd structure formation with the carbon precipitation behaviour was dis cussed in terms of reaction kinetics and thermodynamic considerations. Two ternary phases, CoSiC2 and Co2SiC3, unstable at room temperature, may exist in the system Co-Si-C. The growth of the reaction zone is d ependent on the square root of time. The reaction kinetics are propose d to estimate the effective reaction constant from the parabolic growt h of the reaction zone. The mechanical properties of the reaction zone s were determined by the microhardness test.