Production of Fe–C Amorphous Powders by a Two-Stage Quenching Technique

In order to clarify the cooling capacity of the two-stage quenching technique by a combination of high-pressure argon gas atomization and centrifugal spinning, the morphology and structure of Fe_85.6C_14.4 and Fe_82.6C_17.4 powedrs produced by the technique were examined as a function of particle size fraction. The powder particle morphology is mainly spherical for small particles below 25 μm in diameter and flaky (with a thickness of about 1 to 4 μm) for particles with sizes above about 44 μm. The as-quenched structure consists of α′+Fe₃C+γ phases for the spherical powders and an amorphous phase for the flaky powders. The formation of the amorphous phase is different from the result of the melt-spun ribbons in which α′+Fe₃C+γ phases are formed. It is therefore concluded that the two-stage quenching technique leading to the formation of flaky powders has an enhanced cooling rate because of a reduced thickness and a large contact surface of the flaky powders obtained by the spinning of super-cooled liquid droplets formed during gas atomization.