Effect of Al composition tuning on properties and structure in Zr-Co-Al metallic glass

The variation of glass forming ability, mechanical properties and atomic structure in Zr72−xCo28Alx (x = 14–19 at%) and Zr56Co44−xAlx (x = 13–20 at%) bulk metallic glasses derived from composition tuning has been studied by using copper-mold suction, high-energy X-ray diffraction, extended X-ray absorption fine structure experiments and ab initio molecular dynamics simulations, respectively. Both experimental and theoretical results indicate that glass forming ability was enhanced when composition approached Zr56Co28Al16, attributed to the densification in the first shell around Co atoms with the increase of 11-coordinated polyhedra. In addition, a ductile-to-brittleness transition induced by minor substitution of larger-sized atoms by smaller-sized atoms has been found. As good glass forming ability is usually accompanied by dense atomic arrangement, the increasing larger-sized atoms may tend to offer more free volume which is beneficial to plastic flow. Compositional tuning, along with structural tuning to influence both glass forming ability and plastic flow, offers a reliable method to develop ductile metallic glasses.