AGGREGATION OF NB FILAMENTS IN CU-NB SN COMPOSITE DURING LOW-TEMPERATURE INTERMETALLIC GROWTH/

The solid-state diffusion behavior in the layered Cu-Sn/Cu intermetall ic phase system was investigated by using Cu-20 wt.% Nb (filament)/Sn diffusion couple at 400-450 degrees C. Very thin Nb filament is used a s an inert marker for studying the Kirkendall effect-like phenomena. E xperimental results show that the Nb filaments near the interface of C u-Nb/Sn are shifting toward the Cu-Nb side and forming a Nb filament a ggregating zone with the concentration of Nb up to 27-40 wt.% and a wi dth about 10-15 mu m. The study proved that the shift of Nb filament o riginated from volume expansion caused by the formation of epsilon pha se (Cu3Sn). The convoluting or coarsening of ribbon-like Nb filament r esulting from stress relaxation during annealing plays a role of drivi ng force for the aggregation of Nb, making the density of Nb filaments in the aggregating zone dependent on temperature. (C) 1998 Elsevier S cience B.V. All rights reserved.