The prediction of upper limit of copper content in CoBCu glass-forming alloys

Abstract

The soft magnetic properties of ferromagnetic nanocrystalline alloys can be enhanced considerably by addition of copper until the upper limit of Cu content which is unknown at present. This study explored the upper limit of Cu content in the Co81−XB19CuX (X = 2, 3 and 5) alloy system using ab initio molecular dynamics simulations and experiments. It was found that when the Cu content rose above 2 at%, the first-nearest-neighbor peaks of partial pair distribution function for Cu-Cu pair became stronger steadily with the decreasing temperature, demonstrating that Cu clusters were formed during the quenching processes from initial melt. As to the Cu content was less than or equal to 2 at%, the trace of such clusters was difficult to find. So the maximal Cu content in Co81−XB19CuX alloys in as-quenched amorphous state was predicted to be less than 2 at%. Co81−XB19CuX ribbons were prepared using the melt-spinning technique with as large cooling ability as possible. Structure analysis results from X-ray diffraction patterns of the three as-quenched alloys supported the above theoretical predictions. These results would provide a theoretical reference for the design of ferromagnetic nanocrystalline alloys.