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

Abstract

Short-range order domains of face central cubic Zr 2 Ni (F-Zr 2 Ni) and tetragonal Zr 2 Ni (T-Zr 2 Ni) type structure with a size about 1—3 nanometers were observed in bulk amorphous Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 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 Δ G 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, Δ T 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.