Relationship between the precipitation of face-centered cubic Zr₂Ni phase and the stability of supercooled liquid state in Zr-Cu-Ni-Al metallic glasses

The crystallization processes of (Zr_0.64Ni_0.36)_100-xAl_x (x = 5, 7.5 and 10) and (Zr_0.64Ni_0.36-0.0xCu_0.0x)₉₅Al₅ (x = 0, 6, 10, 13 and 16) metallic glasses were studied by using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and transmission electron microscopy (TEM). For the (Zr_0.64Ni_0.36)_100-xAl_x (x = 5 and 7.5) and (Zr_0.64Ni_0.36-0.0xCu_0.0x)₉₅Al₅ (x = 0, 6, 10 and 13) alloys, crystallization proceeds through double-stage exothermic reactions. The first exothermic reaction corresponds to the precipitation of a metastable face-centered cubic Zr₂Ni (F-Zr₂Ni). For the (Zr_0.64Ni_0.36)_100-xAl_x (x = 10) and (Zr_0.64Ni_0.36-0.0xCu_0.0x)₉₅Al₅ (x = 16) alloys, crystallization proceeds through a single-stage exothermic reaction, corresponding to the precipitation of stable crystalline phases. Accompanying the above changes in crystallization mode, the supercooled liquid region ΔT_x, defined as the temperature interval between the glass transition temperature T_g and the and the crystallization temperature T_x, increases from 39 K for (Zr_0.64Ni_0.36)₉₅Al₅ to 64 K for the (Zr_0.64Ni_0.36)₉₀Al₁₀ in (Zr_0.64Ni_0.36)_100-xAl_x (x = 5, 7.5 and 10) alloy series, and from 39 K for (Zr_0.64Ni_0.36)₉₅Al₅ to 70 K for (Zr_0.64Ni_0.20Cu_0.16)₉₅Al₅ in the (Zr_0.64Ni_0.36-0.0xCu_0.0x)₉₅Al₅ (x = 0, 6, 10, 13 and 16) alloy series. The reason for the stabilization of the supercooled liquid state at higher Al concentrations in the (Zr_0.64Ni_0.36)_100-xAl_x (x = 5, 7.5 and 10) alloy series and at higher Cu concentrations in the (Zr_0.64Ni_0.36-0.0xCu_0.0x)₉₅Al₅ (x = 0, 6, 10, 13 and 16) alloy series is discussed.