NANOCRYSTALLIZATION OF A CO-NB-B-C METALLIC-GLASS

We have applied field ion microscopy (FIM), atom probe field ion micro scopy (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 glas s were prepared by the melt-spinning technique. Subsequent annealing a t 973 K for one hour produced a fully crystalline, four phase material . The phases consist of a nanocrystalline boride phase, a nanocrystall ine Co3Nb phase, both with average grain sizes of 20-50 nm, a nanocrys talline NbC phase with an average grain size of 10-30 nm, and a relati vely pure cobalt matrix. The Various phases exhibited significantly di fferent field evaporation and imaging behavior. In the fully crystalli zed material, which was brittle, initial field evaporation was done at elevated temperatures to maximize specimen life.