Stability of an amorphous alloy of the Mm-Al-Ni-Cu system

Abstract

An investigation was made of the stability of melt-spun ribbons of Mm 55 Al 25 Ni 10 Cu 10 (Mm = Mischmetal) amorphous alloy. The structural transformations that occurred during heating were studied using a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Crystallization took place through a multi-stage process. The first stage of transformation corresponded to the formation of a metastable phase followed by cfc-Al precipitation, while in the second stage, exothermic transformations led to the formation of complex and unidentified Mm(Cu, Ni) and MmAl(Cu, Ni) phases. The transformation curves recorded from isothermal treatments at 226 °C and 232 °C indicated that crystallization occurred through nucleation and growth, with diffusion-controlled growth occurring in the first crystallization stage. The supercooled liquid region, ∆T x , at 40 K/min was ~80 K. This value was obtained by the substitution of Mm (=Ce + La + Nd + Pr) for La or Ce, saving chemical element-related costs.