Phase equilibria of the Co–Ni–Zn system at 450 °C and 600 °C

The isothermal sections of the Co–Ni–Zn ternary system at 450 °C and 600 °C have been determined experimentally using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray diffraction. Three tri-phase regions have been confirmed at 450 °C and 600 °C, respectively. Three continuous solid solutions regions, i.e. α-Co/α-Ni, γ-Co5Zn21/γ-Ni4Zn22 and γ2-CoZn13/δ-NiZn8, exist in the sections. The solubility of Co in β1-NiZn is up to 15.0 at.% at 600 °C, and 16.5 at.% at 450 °C. The maximum solubility of Ni in β1-CoZn and γ1-CoZn7.8 is 10.5 at.% and 8.1 at.% at 600 °C, and 11.8 at.% and 5.5 at.% at 450 °C, respectively. No true ternary compound was found. The X-ray powder diffraction patterns of the Co–Zn intermediate phases β1 and γ have been obtained experimentally. The results obtained by cell refinement revealed that both Co–Zn compounds β1 and γ belong to the cell type of cubic, and their lattice parameters are 0.63360 and 0.89412 nm, respectively.

► Three tri-phase regions have been identified at 450 °C and 600 °C.
► Three continuous solid solutions regions exist in the Co–Ni–Zn system.
► The β1-CoZn and γ1-CoZn7.8 phases have a high Ni solubility.
► β1-NiZn has a high Co solubility.
► The crystal structures of compounds β1-CoZn and γ-Co5Zn21 have been determined.