Spinning phenomena, 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 of less than abou t 90 mu m diameter, and showing a large Barkhausen effect, were obtained by using a laboratory scale, in-rotating-liquid-spinning process (INROLISP). The spinning conditions, jet stability, morphology of dendritic growth and magnetic properties are discussed for fibers of about 70 mu m diameter with regard to manufacturing. For spinning speeds of less than about 10 m/s, th e jet bounced on the surface of the rotating liquid, such as water, water w ith chemicals lowering the surface tension, and some oils. For speeds >10 m /s, the jet subsequently penetrated under the liquid surface after an inter val of around 100 ms from the start of ejection. The centrifugal force effe ct was considerable in this setup. When the jet bounced, in some part of th e fiber structure primary dendrite arms growing uniformly along the fiber d irection were observed. In another part, however, the direction of the prim ary arm changed gradually far from the fiber axis and a secondary arm becam e the primary arm without observing a clear grain boundary. It is conceivab le that the curvature of the bouncing jet at the ejection point obstructs t he primary arms from growing in a straight line. When the jet penetrated, a "bamboo structure" was observed in the fiber. The penetrating jet formed a cavity of coolant downstream from the jet. This indicates that the penetra ting jet firstly goes through an area of non-contact with the coolant on th e cavity side while making contact with the coolant on the opposite side. T herefore, primary arms tend to grow from the contact to the cavity sides. U sing the zone-annealing process, it was difficult to make a fairly long sin gle crystal from any fiber. In order to control the continuous growth of pr imary arms along the fiber direction, it is suggested that a process able t o cool the jet uniformly around its circumference is required so that the p rimary arms can grow in a straight direction. The necessary conditions to p roduce a fiber having a large Barkhausen effect an a nearly unidimensional shape and a [100] crystal direction of the alpha-phase parallel to the long axis. Furthermore, to obtain an ideal rectangular hysteresis loop, the req uirements of a round shape in the cross section, no residual stress and no precipitation are suggested. (C) 1999 Elsevier Science S.A. All rights rese rved.