Microstructural evolution and characterization of interfacial phases in diffusion-bonded SiC/Ta-5W/SiC joints

The evolution of reaction phases formed in diffusion-bonded SiC/Ta-5W/SiC joints was investigated at a joining temperature of 1500-1700 degrees C for 10-90 min. The effects of bonding temperature and holding time on the phase evolution were found to be directly correlated with the thickness of the interfacial reaction layer when a 100-pmthick Ta-5W interlayer was used for joining. In the case of a similar to 7-mu m-thick reaction layer, the interfacial phase constitution consisted of a layered SiC/(Ta,W)/(Ta,W)(5)Si-3/(Ta,W)(2)Si/(Ta,W)(x)Si-y/Ta-5W structure. In the reaction layer with a thickness of similar to 11-26 mu m, the interfacial structure evolved into SiC/(Ta,W)C/(Ta,W)(5)Si-3/(Ta,W)C/(Ta,W)(x)Si-y/(Ta,W)(2)Si/(Ta,W)(x)Si-y/Ta-5W, in which an additional (Ta,W)C/(Ta,W)(x)Si-y layer was inserted between (Ta,W)(5)Si-3 and (Ta,W)(x)Si-y owing to the precipitation of carbon from the (Ta,W)(5)Si-3 layer. When the Ta-5W interlayer was fully consumed to form a stable reaction product, namely the equilibrium state, (Ta,W)(x)Si-y and (Ta,W)(2)Si were eventually transformed into (Ta,W)(5)Si-3, and the final interface structure that was obtained was SiC/(Ta,W)C/(Ta,W)(5)Si-3/(Ta,W)C/(Ta,W)(5)Si-3/(Ta,W)C. This achievement will benefit the design, control, and characterization of SiC/metal interfaces.