Cluster formulae for metallic glasses derived from devitrification phases

Abstract

Bulk metallic glasses are known to have a composition formula [cluster](glue atom)_1,3 within the framework of the cluster-plus-glue-atom model. The key issue in applying the cluster formula is the determination of the right clusters and glue atoms. As examples, alloy phases in the glass-forming systems Al–Ni–Zr and B–Co–Si are analysed from the viewpoint of nearest coordination polyhedral clusters. These alloy phases are described by [effective cluster](glue atom) _x , where the effective cluster refers to true cluster composition after taking account of cluster-sharing in the phase structure. For each alloy phase, a principal cluster can be identified that features the local short-range order of that phase. It is pointed out that the principal clusters can express compositions with high glass-forming abilities, as verified by our experiments in Al–Ni–Zr and B–Co–Si–Ta.

Keywords:

• clusters
• cluster formula
• alloy phases
• structure
• amorphous alloys

Acknowledgements

The authors acknowledge financial supports from the National Science Foundation of China (Grant Nos. 51041011 and 51131002).