Experimental Study of Ternary Pd-Si-C Phase Equilibria and Pd/SiC Interface Reactions

The phase diagram of Pd-Si-C was investigated by experimental methods (XRD, SEM/EDX) and approximate thermodynamic calculations. Based on these results several isothermal sections between 700 and 1000°C are developed. Bulk diffusion couples between Pd and monocrystalline SiC were studied in the same temperature range, 700 to 900°C. A comparison of reaction behaviour between monocrystalline 6H-SiC and ceramic HIP-SiC with Pd is given. The formation of periodic bands consisting of Pd 2 Si + C and Pd 2 Si is clearly observed in the Pd/6H-SiC diffusion zone. These periodic bands are obscured in the Pd/HIP-SiC diffusion couples. In addition, a fine periodic substructure in the two-phase layer (Pd 2 Si + C) is detected. Furthermore, at least a modest joining pressure may be required to produce the reaction zone and the periodic bands. The sequence of reaction layers as observed in the diffusion couples, SiC/C+Pd 2 Si/Pd 2 Si/-/C+Pd 2 Si/Pd 2 Si/Pd 3 Si/Pd, could be related to the isothermal section at 800°C. At 850 °C a liquid phase is formed in the diffusion zone. Interpretations pertaining to the observed diffusion paths are discussed based on the ternary solid state equilibria.