Nanocrystallization of a CoNbBC metallic glass

We have applied field ion microscopy (FIM), atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM) to study the micro-structural and nano-compositional changes of a rapidly quenched, metallic glass due to annealing. Ribbons of a CoNbBC metallic glass were prepared by the melt-spinning technique. Subsequent annealing at 973 K for one hour produced a fully crystalline, four phase material. The phases consist of a nanocrystalline boride phase, a nanocrystalline Co 3Nb phase, both with average grain sizes of 20–50 nm, a nanocrystalline NbC phase with an average grain size of 10–30 nm, and a relatively pure cobalt matrix. The various phases exhibited significantly different field evaporation and imaging behavior. In the fully crystallized material, which was brittle, initial field evaporation was done at elevated temperatures to maximize specimen life.