The role of open spaces to glass-forming ability in bulk metallic glasses

Element-specific positron annihilation spectroscopy for Fe-B-Y-Nb bulk metallic glasses (BMGs) successfully sheds light on the role of interstitial open spaces in the amorphous matrix, as e.g., geometrically ideal open space, referred to as a Bernal hole, and large-scale nanovoids to glass-forming ability (GFA), yielding the following rules. Applying main constituent atoms in smaller sizes such as Fe, the Bernal holes get small without enhancing GFA since other elements cannot diffuse therein. On the contrary, main constituent atoms in larger sizes such as Ce form the large Bernal holes, which are feasible to accept other elements thus being responsible for GFA. The present findings is of pivotal importance in designing excellent BMGs with high GFA from the viewpoint of elemental combination of materials.