Chemical short-range order domain in bulk amorphous alloy and the prediction of glass forming ability

Short-range order domains of face central cubic Zr₂Ni (F-Zr ₂Ni) and tetragonal Zr₂Ni (T-Zr₂Ni) type structure with a size about 1-3 nanometers were observed in bulk amorphous Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti ₅ alloy by using HREM and nano-beam electron diffraction technique. A new thermodynamic model was formulated based on the concept of chemical short-range order (SCRO). The molar fractions of CSRO and thermodynamic properties in Ni-Zr, Cu-Zr, Al-Zr, Al-Ni, Zr-Ni-Al and Zr-Ni-Cu were calculated. According to the principle of maximum ΔG_CSRO, the optimum glass forming ability (GFA) compositions were predicted in binary and ternary alloys. These results were proved to be valid by the experimental data of crystallizing activation energy, ΔT_x and XRD patterns. The TTT curves of Zr-Ni-Cu alloys calculated based on CSRO model shows that the lowest critical cooling rate GFA is in the order of 100 K/s, which is close to the practical cooling rate for the preparation of Zr-based BMG alloys.