Manufacture of TE-modules: joining Fe2VAl and Cu through several bonding processes.

Marchal-Marchant, Valentin [UCL] Roy, Geoffrey [UCL] Ryelandt, Laurence [UCL] Poncelet, Olivier [UCL] van der Rest, Camille [UCL] Jacques, Pascal [UCL] et al.

Fe2VAl-based thermoelectric modules are very promising for large scale applications such as industrial energy harvesting since its constituent materials are abundant, non-toxic and low cost. However, the assembly of modules based on Fe2VAl compounds requires to properly bond this thermoelectric material with high electrical conductivity material such as copper. Two types of process have been investigated in the present work: copper metallization directly on Fe2VAl and brazing. Copper metallization has been performed either by diffusion bonding under pressure, physical vapor deposition or electrodeposition. Brazing has been studied by using both low and high temperature (from 300K to 700K) brazing materials in order to enlarge the application field. Very promising results have been obtained for several of those processes in terms of contact resistance measurements (<10μΩ∙cm2), element diffusion (highlighted by SEM and EDX) and mechanical resistance. Moreover, for silver-based brazing, a thin reactive layer has been observed at the surface of Fe2VAl. This layer appears owing to chemical reaction between the brazing material, copper and Fe2VAl. This phenomenon was never observed before and is supposed to have a positive effect on the contact resistance and thus on the module efficiency, as long as it does not involve too large scale elemental diffusion.