Microstructure and Magnetic Properties of Undercooled Fe-80at%Ni Alloys

Abstract

Bulk Fe-80at%Ni melts were undercooled by using cyclic superheating and glass slag purification technique, and the maximum undercooling 340 K could be achieved. The microstructures of Fe-80at%Ni alloys were observed by means of optical microscope (OM). The phase composition was identified by X-ray diffraction (XRD) analysis. The magnetic properties of Fe-80at%Ni alloys were measured by vibrating sample magnetometer (VSM) with a DC M-H analyzer. The results showed that there was only single γ-(Fe, Ni) phase existing in undercooled Fe-80at%Ni alloys. Two grain refinements and one grain coarsening were observed in the undercooling range from 28 K to 340 K. The first grain refinement could be ascribed to dendrite-remelting, and the second to recrystallization induced by the stress originating from rapid solidification. The grain coarsening could be considered as a result of solid-state grain coalescence. The measurement of soft magnetic properties showed that the grain size D decreases with an increase of undercooling, the maximum Ms is 109.98emu/g, corresponding to minimum grain size 42.9μm or undercooling 210 K, and the coercive force Hc is in proportion to the reciprocal of grain size D-1.

Research on Undercooling Grain Refinement Technology

“…Fe-80%Ni alloy, based on binary phase diagram of Fe-Ni, is a typical uniform crystallization alloy. From experiments [12], it shows that γ(Ni, Fe), a single-phase and unlimited solid solution could be formed in the rapid solidification process of Fe-80%Ni alloy. Fe-80%Ni alloys have been treated at different degree of supercooling using glass fluxing and cyclic superheating methods by Xie et al [12] The microstructures of the alloys are shown in Fig.…”

“…From the previous study [11][12][13][14][15][16], it was found that the solidification organizations of eutectic alloy, peritectic alloys, partial crystalline alloys, hypo-eutectic alloy, single phase solid solution alloy and dual-phase solid solution alloy etc. have occurred twice grain refinement under undercooling and rapid solidification conditions of thermodynamics.…”

“…The newborn solid phases could be broken due to large internal stress. The destroyed newborn solid phase contains high distortion energy which is the driving force of recrystallization of solidification structures after recalescence [12]. It is so-called dendrite broken off mechanism and recrystallized grain refinement mechanism.…”