Study of Amorphous-Crystalline Phase Transformations by DSC and Dilatometer in the Case of Al-Based Amorphous Alloys

The amorphous-crystalline transformation is studied by DSC and dilatometer. From the DSC signal the characteristic temperatures and the heat evolved during each transformation step can be determined. The dilatometer depicts the thermal contractions accompanying the changes in topological short range order. Although the characteristics temperatures determined by DSC and dilatometer, two methods are slightly different their dependences on the heating rate are very similar, where from the activation energies of each transformation steps can be determined using the Kissinger plots. As an example, two aluminum-based amorphous ribbon samples (Al88Mm5Ni5Co2 and Al85Y8Ni5Co2) will be measured and compared. 1. Introduction 20 years have been passed since the discovery of the first ductile Al-based amorphous alloy ribbons with superior mechanical properties compared to the conventional aluminum alloys [1, 2]. These ribbons have been obtained by melt spinning technique starting from a multicomponent ingot contained as a rule rare earth (RE) metal and one or two late transition metals (TMs) [3]. It has been found that alloys with high glass forming ability (low critical cooling rate for glass formation or large critical thickness) are the so-called strong metallic glasses in the Angell plot [4]. Unfortunately, the Al-based glasses belong to the fragile glasses with low glass forming ability and consequently no bulk metallic glass (BMG) exits on Al-base. The bulk amorphous samples can be obtained only by hot consolidation of the amorphous ribbon flakes, which should be performed below the transformation temperature. Therefore, the thermal stability of these ribbons (in amorphous or nanocrystalline state) marks a limit of their applicability, and the study of the kinetics of crystallization of Al-based alloys is an important task to which several studies have been devoted so far (for a review, see [5]). In order to reduce the price of the alloy in this paper we have studied a composition containing Mischmetal instead of pure RE element. Mischmetal (Mm) is a natural mixture of rare earth metals; typical composition contains 48% cerium, 25% lanthanum, 17% neodymium, and 5% praseodymium, with the balance being the other lanthanides. Many studies were devoted to compare the behavior of Mm-substituted alloys with those with pure rare earth elements [5–7]. In the present paper the kinetics of crystallization are studied for two alloys of nominal compositions Al85Y8Ni5Co2 and Al88Mm5Ni5Co2 by DSC and dilatometer. We have chosen these two compositions because they show big