Reversible short-range ordering due to the structural relaxation in amorphous Ni-Cr-B alloys

Abstract

Reversible short-range ordering due to the structural relaxation in two amorphous alloys, Ni68Cr14B18 (Allied Chemical MBF-80) and melt-spun Ni55Cr25B20, was investigated. Excess endothermic peaks were observed in differential scanning calorimetry (DSC) thermograms taken for Ni68Cr14B18 alloy annealed for both 5 and 20 h at 493 K, and this phenomenon can be explained as the decomposition process of short range order formed during annealing. Reversible changes in electrical resistance with isochronal annealing temperature were found in both alloys, which may be caused by the reversible formation and the decomposition processes of short range order. Kinetics of reversible relaxation in Ni55Cr25B20 alloy was also examined under the assumption that the relaxation process exhibits a Gaussian distribution in the logarithm of the relaxation time, that is, a log normal distribution. The mean relaxation time Τm is obtained as an Arrhenius type, Τm=Νo−1exp(Em/kBTa), where kB and Ta are Boltzmann constant and annealing temperature, respectively. As the mean activation energy, Em, and the attempt frequency Νo, values of 2.20 eV and 1.6×1016 sec−1 were obtained.