Crystallisation behaviour and glass-forming ability in Al–La–Ni system

Abstract

The crystallisation behaviour for alloys in the Al-rich corner in the Al–La–Ni system is reported in this paper. Alloys were selected based on the topological instability criterion ( λ criterion) calculated from the alloy composition and metallic radii of the alloying elements and aluminum. Amorphous ribbons were produced by melt-spinning and the crystallisation reactions were analysed by X-ray diffraction and calorimetry. The results showed that increasing the values of λ from 0.072 to 0.16 resulted in the following changes in the crystallisation behaviour, as predicted by the λ criterion: (a) nanocrystallisation of α-Al for the alloy composition corresponding to λ = 0.072 and (b) detection of the glass transition temperature, T g , for the alloys with composition close to λ ≈ 0.1 line. For compositions corresponding to both ends of the λ ≈ 0.1 line (near the binaries lines) T g could be detected only in the “intermediary” central region, and the alloy we produced in this region was considered the best glass former for the Al-rich corner. Also, except for the alloys with the highest Ni content, crystallisation proceeded by two distinct exothermic peaks which are typical of nanocrystallisation transformation. These behaviours are discussed in terms of compositional ( λ parameter) and topological aspects to account for cluster formation in the amorphous phase.