A new approach based on a temperature-heating rate-transformation (T-HR-T) curves, useful when heating an amorphous sample under continuous heating conditions, together with the traditional time-temperature-transformation (T-T-T) diagram is presented in the study of the crystallization behaviour of Fe67.5Co15Nb1.5B16 metallic glass, prepared planar flow casting. The study has been carried out by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. The calorimetric results show that there are two separate stages of crystallization. The second stage of crystallization is described correctly by the Johnson-Mehl-Avrami-Erofe'ev equation, with an Arrhenius form of the rate constant, under both isothermal and continuous heating. A more complicated kinetic behaviour is obtained for the first stage of crystallization. Transmission electron microscopy of the specimens after controlled heat treatment shows that the primary crystallization of α-(Fe,Co) dendrites in the amorphous matrix occurs in the first stage of crystallization with, in addition, sporadically secondary precipitation of (Fe,Co)3B crystals. X-ray diffraction experiments confirm these results and show that a progressive enrichment in Fe in the α-(Fe,Co) phase occurs on the first stage of crystallization. From the crystallization kinetic results the low temperature part of the T-T-T and T-HR-T curves of the two exothermic crystalization processes are deduced. © 1992.
|Journal||Acta Metallurgica Et Materialia|
|Publication status||Published - 1 Jan 1992|