The liquid-solid transitions of （Co2Si＋CoSi） and （CoSi＋CoSi2） eutectic alloys were realized in drop tube and the rapid eutectic growth mechanism of intermetallic compounds was examined. The experimental and calculated results indicate that with increasing Co content, the intermetallic compound prefers nucleating primarily. The eutectic microstructures experience the transitions of ＇lamellar-anomalous-divorced＇ eutectic with undercooling. In undercooled state, the growth of CoSi intermetallic compound always lags behind others, and no matter how large the undercooling is, this intermetallic compound grows under the solutal diffusion control The calculated coupled zone demonstrates that （Co2Si＋CoSi） eutectic can form within certain undercooling regime, when the composition is in the range from 23.6% to 25.4% Si. And the calculated coupled zone of （CoSi＋CoSi2） covers a composition range from 40.8% to 43.8% Si.
By using the melt spinning techniques, the Fe63Co32Gd5 alloy ribbons with 15-50 m in thickness and 3-7 mm in width were prepared at the wheel speeds of 15, 20, 25 and 35 m/s. The rapid solidification microstructures were characterized by three layers, the middle layer of which reaches 80% thickness and forms the column grain of(Fe,Co) solid with Gd solution. Grain refinement takes place with the increase of the wheel speed. And after 0.5 h heat treatment at 823 K, the ribbon thickness becomes larger and the middle layer of column grain is very orderly perpendicular to the ribbon plane. The coercivity of quenched and annealed Fe63Co32Gd5 ribbons both have the inflection point at the wheel speed of 20 m/s, and the tendency is declining. The heat treatment processing makes the coercivity become lower by improving the order of(Fe,Co)17Gd2 compound. The saturation magnetization of quenched ribbons increases with the enhancement of wheel speed, whereas that of annealed ones decreases firstly and then increases. The minimum coercivity is 5.30×103 A/m and the maximum saturation magnetization is 163.62 A·m2/kg, which is obtained in the conditions of the wheel speed of 35 m/s and 0.5 h heat treatment at the temperature of 823 K.
