Evaluation of the optimum solute concentration for good glass forming ability in multicomponent metallic glasses

Previous work suggests that the size factor may be the most crucial one on the glass forming ability (GFA). But the alloys in a system have significant deference for GFA. A criterion λn is defined in the present work to comprehensively evaluate concentration dependence of GFA of alloys in a system. It is found that the values of λn of bulk glass formers with greatest GFA in Zr-, Pd-, Mg-, Nd- and Fe-based systems are nearly constant of 0.18. Based on the mathematical description of regular polytopes and the dense random packing of hard sphere (DRPHS) model, a cluster model is suggested. This model provides the physical meaningful origin of the λn from the view of free volume. The glass structure of bulk glass formers with λn≈0.18 has optimum defect concentration within the framework of the cluster model. In the term of λn criterion, an alloy with λn of about 0.18 will be one of bulk glass former candidates, which is verified by the experimental result of ZrAlNi system.