Y.M. Wang

Cluster formulae for alloy phases

Composition formulae for alloy phases are developed using first-neighbour coordination polyhedra plus their connections. The resultant cluster formulae [cluster](glue atom) x , similar to molecular formulae for chemicals, contain key structural and composition information on the alloy phases. As examples, Al–Ni–Zr alloy phases are analysed with the objective of revealing cluster formula properties such as the principal cluster, the cluster phase and the definition of complex alloy phases.

24 electron cluster formulas as the ‘molecular’ units of ideal metallic glasses

It is known that ideal metallic glasses fully complying with the Hume-Rothery stabilization mechanism can be expressed by a universal cluster formula of the form [cluster](glue atom)1 or 3. In the present work, it is shown, after a re-examination of the cluster-resonance model, that the number of electrons per unit cluster formula, e/u, is universally 24. The cluster formulas are then the atomic as well as the electronic structural units, mimicking the ‘molecular’ formulas for chemical substances. The origin of different electron number per atom ratios e/a is related to the total number of atoms Z in unit cluster formula, e/a = 24/Z. The 24 electron formulas are well confirmed in typical binary and ternary bulk metallic glasses.

A cluster line approach for composition rules of quasicrystals and bulk metallic glasses

This paper analyzes the structure and composition characteristics of ternary quasicrystals and bulk metalic glasses from the viewpoint of atomic clusters. It is pointed out that quasicrystals and bulk metallic glasses satisfy a cluster line rule. The cluster line refers to a straight composition line linking a specific cluster to the third element in a ternary alloy phase diagram. A ternary quasicrystal or bulk metallic glass composition is located at the intersection point of two cluster lines. Ternary quasicrystal and bulk metallic glass compositions can be the expressed with a cluster-plus-glue-atom model which can predict new ternary bulk metallic glasses.

Cluster-based bulk metallic glass formation in Fe-Si-B-Nb alloy systems

Bulk metallic glass formations have been explored in Fe-B-Si-Nb alloy system using the so-called atomic cluster line approach in combination with minor alloying guideline. The atomic cluster line refers to a straight line linking binary cluster to the third element in a ternary system. The basic ternary compositions in Fe-B-Si system are determined by the inetersection points of two cluster lines, namely Fe-B cluster to Si and Fe-Si cluster to B, and then further alloyed with 3-5 at. % Nb for enhancing glass forming abilities. BMG rods with a diameter of 3 mm are formed under the case of minor Nb alloying the basic intersecting compositions of Fe8B3-Si with Fe12Si-B and Fe8B2-Si with Fe9Si-B. The BMGs also exhibit high Vickers hardness (Hv) of 1130-1164 and high Youngs modulous (E) of 170-180 GPa