Designing (Hf,Ta)Fe2-based zero thermal expansion composites consisting of multiple Laves phases

Abstract

MgZn₂-type (Hf,Ta)Fe₂, known for its negative thermal expansion during magnetic transition, is a key component in the production of zero thermal expansion composites. This paper presents a basic approach for designing such composites by introducing an additional Laves phase through atomic substitution. Specifically, Co, Ni, Al and V were chosen to substitute Fe in (Hf,Ta)Fe₂. The addition of Co or Ni results in the creation of an extra MgCu₂ (C15) phase in the MgZn₂ (C14) matrix. The C15 phase exhibits positive thermal expansion, which effectively compensates for the negative thermal expansion of the C14 matrix. By adjusting the amount of Co or Ni, zero thermal expansion can be achieved in a given temperature range. Meanwhile, the replacement of Fe by Al or V yields another C14 phase with a higher doping element content relative to the C14 matrix. These two C14 phases possess different magnetic transition temperatures and negative thermal expansion temperature regions. The combination of the two C14 phases results in zero thermal expansion due to the effective thermal expansion compensation between them. Our results serve to identify potential approaches for designing (Hf,Ta)Fe₂-based zero thermal expansion composites.

Graphical abstract