Spinning Condition, Structure and Magnetic Properties of Fe-6.5 mass%Si Alloy Fiber Produced by the In-Rotating-Liquid-Spinning Process

Almost zero magnetostrictive Fe-6.5 mass%Si alloy fibers less than about 90 μm in diameter, having a large Barkhausen effect in magnetic properties were obtained by using the laboratory scale, the In-Rotating-Liquid-Spinning Process (INROLISP). The spinning conditions, jet stability, morphology of dendritic growth and magnetic properties were discussed for the fiber about 70 μm in diameter from the manufacturing viewpoint. In the case of spinning speeds of less than about 10 m/s, the jet bounced on the surface of rotating liquid, such as water, water with chemicals lowering surface tension, and some oils. Over 10 m/s, the jet subsequently penetrated under the liquid surface after an interval of around 100 ms from ejecting start. The centrifugal force effect was considered in this phenomenon. When the jet bounced, in some part of the fiber structure, primary dendrite arms growing uniformly along the fiber direction were observed. In another part, however, the direction of the primary arm changing gradually far from the fiber axis and the secondary arm becoming the primary grown to the fiber axis was observed without clear grain boundary. It is considered that the curvature of the bouncing jet at the ejection point obstructs the primary arms growing in a straight line. When jet penetrated, the “bamboo structure” was observed in the fiber structure. The penetrating jet formed the cavity of the coolant at its downstream from the jet. It means that the penetrating jet at first goes through the non-contacting area to the coolant at the cavity side and the contacting area to the coolant at the opposite side. Therefore, the primary arms tend to grow from the contact to the cavity sides. By the zone-annealing process, it was difficult to make any fiber a fairly long single crystal. In order to control the continuous growth of the primary arms toward the fiber direction, it was suggested that the process which is able to cool the jet uniformly around its circumference and make the primary arms grown in a straight jet is needed. The necessary conditions to produce a fiber having the large Barkhausen effect in this alloy, were the nearly unidimensional shape and a [100] crystal direction of arpha-phase parallel to the long axis. Furthermore, to obtain an ideal rectangular hysteresis loop, the cross-sectional round shape, the absence of residual stress and precipitation was suggested.