Joining silicon nitride ceramic using a composite powder as active brazing alloy

The aim of this study was to join silicon nitride ceramic using a Cu-Ti bi-metallic composite powder. The microstructure and mechanical properties obtained were similar to results obtained with conventional active brazing alloys but with different kinetics. The experimental results obtained show the potential in using the composite powder as a brazing alloy. The reaction layer produced at the ceramic/filler metal interface was composed mainly of TiN and Ti5Si3. Similar to many active ceramic brazing processes, the reaction layer was formed in two stages, where the initial step was controlled by a liquid/solid reaction, followed by diffusion controlled growth. Depending on the brazing parameter, the reaction layer thickness ranged between 4 and 12 mum. Reaction layer growth was modeled and the effective activation energy was found to be 64 kJ/mole. The four-point bending strength varied between 250 and 400 MPa, depending on joining conditions. The crack propagation mode was through the interface for low strength joints and through the ceramic for high strength joints. (C) 2004 Elsevier B.V. All rights reserved.