On the reactive sintering of Heusler Fe2VAl-based thermoelectric compounds

Heusler Fe2VAl-based compounds are promising candidates for thermoelectric conversion of waste heat. In comparison to more conventional thermoelectric materials, the constitutive elements of these alloys are indeed abundant, cheap, and non-toxic. Furthermore, the thermoelectric properties of these compounds can be easily enhanced by either doping or controlled deviation from exact stoichiometry while large power factors compatible with energy harvesting applications can be reached. In the present study, Fe2VAl-based compounds were synthesised by powder metallurgy. Almost fully dense bulk materials were obtained either by field-assisted sintering, also referred to as spark plasma sintering (SPS), of pre-alloyed powders or by spark plasma reactive sintering of mixtures of elemental powders. The influence of the processing route and parameters on the resulting microstructure was assessed. In the specific case of the one-step synthesis and rapid densification of the Fe2VAl compound starting from the elemental powders, a detailed insight in the reaction path was obtained by interrupted sintering cycles followed by careful phase analysis of the partially sintered compacts by X-ray diffraction and elemental analysis. Finally, it is worth emphasising that the thermoelectric properties of the compounds processed by reactive sintering are as good as the ones of samples sintered from pre-alloyed powder or processed by melting and casting.