Designing (Hf,Ta)Fe2-Based Zero-Thermal-Expansion Composites Consisting of Multiple Laves Phases

MgZn2-type (Hf,Ta)Fe2 with negative thermal expansion during magnetic transition is a good ingredient to prepare zero-thermal-expansion composites. In this paper, we provide a basic strategy to design such composites through introducing another Laves phase by atomic substitution. Co, Ni, Al and V are selected to replace Fe in the (Hf,Ta)Fe2, respectively. The former two elements cause additional MgCu2 (C15) phase in the MgZn2 (C14) matrix. The induced C15 phase shows positive thermal expansion, which can compensate the negative thermal expansion of the C14 matrix. With a suitable Co or Ni-content, zero thermal expansion can be realized in a given temperature region. Unlike Co or Ni substitution, replacing Fe by Al or V causes another C14 phase with a higher doping element content relative to the C14 matrix. The two C14 phases have different magnetic transition temperatures as well as negative-thermal-expansion temperature regions. In this case, zero thermal expansion is also realized due to the thermal expansion compensation between the two C14 phases. We further analyze the relationship between the phase constitution and character of doping element, which can provide promising ways to design (Hf,Ta)Fe2-based zero-thermal-expansion composites.