Search

Abstract: The phase formation and crystallization kinetics during the thermal treatment of amorphous Zr60Al15Ni25 alloy were investigated by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). By lowering the isothermal annealing temperatures, it is revealed that the crystallization of the amorphous Zr60Al15Ni25 alloy consists of a primary transformation followed by a polymorphic transformation, corresponding to the precipitations of hexagonal Zr6Al2Ni and the Zr5AlNi4 with a U3Si2-typed superstructure. The primary phase being Zr6Al2Ni rather than Zr5AlNi4 in the crystallization is because the latter has a complex structure and its formation requires the diffusion of Al and Zr atoms on a large scale. [Copyright &y& Elsevier]

Abstract: Ni80.3B19.7 alloy was undercooled using glass-fluxing and cyclic superheating method. The solidification process was observed by a high-speed video system. On this basis, the nucleation mechanisms involving in rapid solidification of undercooled Ni80.3B19.7 melts were investigated. The calculation based on the classical nucleation theory demonstrated that in the achieved range of undercooling (ΔT) due to Ni3B phase possesses a higher nucleation rate than that of α-Ni phase, Ni3B phase can always solidify as the primary phase, which is in accordance with the experimental observations. Further, the analyses of experimental results and the calculation in terms of the transient nucleation theory indicated that the time required to form the critical nucleus is much shorter than the time required for solid/liquid (S/L) interface to touch the nucleus, and this will lead to the occurrence of the copious nucleation in the undercooled Ni80.3B19.7 melt. [ABSTRACT FROM AUTHOR]