Helical glassy alloy ribbons: Fabrication and Magnetic properties

Abstract

Metallic glasses may be produced in continuous ribbon or tape form by flowing molten alloy onto a rapidly moving substrate surface. In the present investigation a variation of conventional chill block melt spinning is described. The process is used to fabricate samples with a helical appearance (constant in-plane curvature). Helical ribbon samples were cast using a wide range of process conditions and the dependence of sample cross section on process parameters was found to be well described by empirical equations already established for the fabrication of straight ribbons. Magnetic coercivity measurements of helical ribbons and of straight ribbons wound into toroids revealed a greater as-cast sample coercivity for the helical sample, while retesting after magnetic annealing showed that the helical sample had lower coercivity than toroids assembled using straight ribbon samples. This has been attributed to the increased quenched-in stress level resulting from the greater ribbon-substrate sticking distance to define the in-plane curvature of the helical ribbon. The coercivity of the straight ribbon tested in the form of toroids was found to be highly dependent on stresses induced during the preparation of the sample assembly for magnetic testing.