Glass formability of ferrous- and aluminum-based structural metallic alloys

Synthesis of ferrous- and aluminum-based amorphous metals as prospective structural materials is presented and discussed in light of atomic size–composition interaction effects. The search of prospective bulk metallic glasses (BMGs) may benefit from noting that current BMG alloys can be broadly categorized into two atom size-composition classes, distinctly different from ordinary metallic glasses which can exist over a much wider atom size-composition range. The high formability of one class of BMGs is suggested to be due to the presence of a structure-reinforced network or backbone formed by tightly bound components in the undercooled liquid. For the ferrous-based BMG alloys investigated, it is proposed that zirconium-boron and molybdenum–carbon atom pairs constitute the strong backbone structures. Although aluminum-based BMG has not been reported, the good formability of some current aluminum-glasses is suggested to be due to the presence of backbone structures formed by transition metal–lanthanide and magnesium–copper pairs. The ferrous-based bulk metallic glasses obtained have a high reduced glass transition temperature reaching 0.63 and large supercooled liquid region up to 100 K. These bulk metallic glasses are found to be non-ferromagnetic above 160 K as well as having Vickers hardness and specific tensile strengths that far exceed those reported for steel alloys. Magnetization and susceptibility results are presented and compared with ab initio magnetic-structure calculations [D.M. Nicholson, M. Widom, Y. Wang, unpublished results]. Relevant factors on forming bulk metallic glasses are discussed.