Production of flaky amorphous alloy powders in Co-Si-B system by a two-stage quenching technique of gas atomization and centrifugal spinning

Co _72.5 Si _12.5 B ₁₅ powder produced by a new combined technique consisting of high-pressure gas atomization followed by centrifugal spinning was found to be amorphized in the entire powder particle size range from minus 25μm to plus 88μm. The powder particle morphology is mainly spherical for particles below 25μm in diameter and flaky with a thickness of about 5μm for particles of size above 37μm. Although the crystallization temperature T _x of the powder particles remains constant over the entire size range, heat of crystallization ΔH _x increases with increasing powder particle size. This unexpected change in ΔH _x has been attributed to the two-stage process in which flaky powder was produced by spinning of supercooled liquid droplets obtained by gas atomization. Additionally, it was found that a blend of flaky and spherical morphologies is very effective for the production of fully dense amorphous bulk material having high saturation magnetization by uniaxial pressing at temperatures below T _x . It is therefore expected that this two-stage quenching technique leading to rapid solidification of supercooled liquid will find application for the production of alloy powders to be used for the formation of amorphous alloy bulk material exhibiting good soft ferromagnetism.