Growth of small particles of iron-cobalt alloys prepared by gas-evaporation technique

Abstract

The crystal structure and habit of small particles of iron-cobalt alloys prepared by a gas-evaporation technique have been investigated by means of electron microscopy and X-ray diffraction. Most of the particles consist of the single phase of ferrite or austenite, though the nominal composition of starting materials is around 87 at% Co in which the two phases exist at room temperature. This result suggests that the two-phase region in the phase diagram is narrower for the small particles than for the bulk system. The morphology of the ferrite or the austenite particles is similar to that of the pure-iron or the pure-cobalt ones, respectively, but considerably modified due to the impurity effect. On rare occasions, the particles consisting of the two phases are observed with the crystal relation of (110) fer|(200) aus. They show the external shape in which the two halves of a football are stuck together. It is inferred that they grow through the coalescence process between the ferrite and the austenite particles.