Investigation on the structures of τ1 and τ2 compounds in the Zr–Fe–Cu system and phase equilibria of the Zr–Nb–Fe–Cu system

Abstract Two intermetallic compounds τ 1 (i.e. Zr(Fe, Cu)) and τ 2 (i.e. Zr 2 (Fe, Cu)) with unconfirmed structures in the Zr–Fe–Cu ternary system have been identified and the equilibrium phase relationship of the quaternary Zr–Nb–Fe–Cu system at 700 °C and 580 °C have been experimentally investigated by using optical microscopy, electron probe micro-analyzer coupled with wavelength-dispersive spectroscopy, transmission electron microscopy and X-ray diffraction on the equilibrated alloys. In the ternary Zr–Fe–Cu system, the results show that τ 1 has the same structure as ZrCu phase with cubic CsCl-type structure, and the structure of τ 2 phase is the same as Zr 2 Fe with tetragonal Al 2 Cu-type structure. The solution mechanism of alloying elements for the τ 1 compound is that the Cu sites are occupied by Fe atoms to stabilize the ZrCu structure, in the meanwhile, the mechanism of τ 2 is that the Fe sites are occupied by Cu atoms. For the quaternary Zr–Nb–Fe–Cu system, there is no new quaternary intermetallic phase detected in the present work. Only three intermetallic compounds, i.e. λ 1 , λ 2 and τ 2 , presented in sub-ternaries were identified in the quaternary system at both 700 °C and 580 °C. It was found that Cu atoms dissolve in λ 1 and λ 2 phases forming cubic (Zr, Nb) 2 (Fe, Cu) and hexagonal (Cu, Fe, Nb) 2 Zr respectively, and Nb atoms dissolve in τ 2 phase forming tetragonal (Zr, Nb) 2 (Fe, Cu).