COMPATIBILITY EVALUATION BETWEEN COBALT METALLIZED PbTe THERMOELECTRIC LEGS AND AN Ag-Cu-In BRAZING ALLOY BY LONG TERM THERMAL TREATING

Increasing the technology readiness level towards an efficient thermoelectric (TE) device is extremely important. In this research we extend from basic materials research towards improving some of the challenges for practical applications. In TE generators, maximizing the direct heat to electricity conversion efficiency, requires the reduction of any parasitic thermal and electrical contact resistances, between the TE legs and the hot-side metallic contacts. This requirement is especially challenging in the development of intermediate to high temperature TE generators. One reason for that is the insufficient bonding techniques. Due to the fact that in development of TE couples based on both n- and p- type legs, there is no simple way to press together both of the legs into the metallic strap bridging the two, our proposed approach is based on cobalt metallization of the legs prior contacting to a cobalt strap bridging the two legs together. Ag-Cu-In based composition was suggested as a brazing alloy for bonding the cobalt metallization and the cobalt bridge. This study is focused on the interaction between the interfaces following prolong thermal treatment testing. Clear and fine interfaces without any noticeable formation of parasitic interaction layers and with a very low electrical contact resistance were observed, highlighting the potential of such contacts while developing of practical PbTe based TE generators. The final goal of the research is achieving a generator prototype which will work in a lab testing facility.