An evaluation of the partial, transient liquid phase bonding of Si3N4 using Au coated Ni-22Cr foils

The application of the partial transient liquid phase bonding (PTLPB) process for joining silicon nitride ceramics using microdesigned Au/Ni-Cr/Au multilayer interlayers has been investigated. The influence of different bonding parameters, such as time, temperature and interlayer thickness, on the microstructure and chemistry of the ceramic-metal interfaces has been studied. Scanning electron microscopy and electron probe microanalysis investigations revealed that the ceramics were bonded to the Ni-Cr foils by a thin CrN reaction product layer while the Au had alloyed to form a Ni rich solid solution. Joints with room temperature average flexural strength of 272 MPa, were produced under optimized bonding conditions of 4 h at 1000 degrees C. These processing conditions resulted in joints with microstructure and strength equivalent to those obtained by optimized diffusion bonding procedures. The effect of post-bonding annealing in air at 800 degrees C for 60 h on the room temperature joint strength was also assessed.