Crystallization kinetics of amorphous magnesium-rich magnesium-copper and magnesium-nickel alloys

Abstract

Amorphous magnesium-rich alloys Mg _y X_1-y (X=Ni or Cu and 0.82<y<0.89) have been produced by melt spinning. The crystallization kinetics of these alloys have been determined by in situ X-ray diffraction (XRD) and isothermal and isochronal differential scanning calorimetry (DSC) combined with ex situ XRD. Microstructure analysis has been performed by means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Crystallization of the Mg-Cu alloys at high temperature takes place in two steps: primary crystallization of Mg, followed by simultaneous crystallization of the remaining amorphous phase to Mg and Mg₂Cu. Crystallization of the Mg-Cu alloys at low temperatures takes place in one step: eutectic crystallization of Mg and Mg₂Cu. Crystallization of the Mg-Ni alloys for a Mg content, y>0.85, takes place in two steps: primary crystallization of Mg and of a metastable phase (Mg_∼5.5Ni, with Mg content y=0.85), followed by the decomposition of Mg_∼5.5Ni. Crystallization of the Mg-Ni alloys for a Mg content y<0.85 predominantly takes place in one step: eutectic crystallization of Mg and Mg₂Ni. Within the experimental window applied (i.e., 356 K<T<520 K and 0.82<y<0.89), composition dependence of the crystallization sequence in the Mg-Cu alloys and temperature dependence of the crystallization sequence in the Mg-Ni alloys has not been observed.