General route to fabricate ultrafine metallic glass powders directly from their own crystalline states by localized pulsed electrical discharge atomization

Localized pulsed electrical discharge (PED) atomization is developed as a general route to fabricate ultrafine metallic glass powders with high purity and sphericity, which cannot be achieved by conventional techniques, like mechanical alloying, chemical reduction and water/gas atomization. The new atomization process starts with a localized melting on crystalline alloy surface by PED. During the melting process, multiple crystalline phases in the starting alloy are melted and then homogenized to form a uniform melted zone. Finally, the melted zone is atomized to produce ultrafine powders under the explosive force. The obtained particle size is mainly in the range of 1–10 μm. The results also show that it is easier to vitrify the produced powders for alloys with higher glass-forming ability (GFA). However, considering that the cooling rates achieved by PED atomization and melt-spinning technique are comparable, the GFA of the starting alloy will not play a determining role in the formation of glassy powders as long as it can guarantee the formation of glassy ribbons by melt-spinning technique. In this case, the ratio of melted zone size to crystalline phase size become the determining factor. The amorphization degree and compositional homogeneity can be improved by refining the starting alloy with low GFA. Besides, the experimental and simulation results both eliminate the possible Mo pollution from the tool electrode. This work will hopefully expand the applications of metallic glasses.