TRANSIENT FGM JOINING OF SILICON-CARBIDE CERAMICS - A FEASIBILITY STUDY

The feasibility of joining SiC and SiC/SiC composites using Ge-based t ransient liquid phases was examined by measuring the contact angles of Ge and Ge-rich Ge-Si alloys on both SiC and reaction bonded SiC (RB-S iC). The contact angle decreased with increasing anneal time and with increasing anneal temperature. The contact angle of molten Ge on SiC a t 1150 degrees C after 180 min was approximate to 80 degrees; contact angles on RB-SiC under the same conditions were greater than those on SiC. The addition of small amounts of Si to the Ge resulted in a signi ficant decrease in the contact angle. This beneficial change was obser ved when experiments were conducted using SiC, RB-SiC, and even C. A p owder of Ge or of a mechanical mixture of Ge and Si powders was applie d to the interface between polished SIC blocks and the assembly was he ated to 1150 degrees C to form a bond via a Ge-based interlayer. While the blocks were joined and exhibited some strength, the resulting str engths were low, and further research is required to produce the level and reproducibility of strength required for practical applications. (C) 1997 Elsevier Science Limited.