The commercially most significant process for the production of amorphous and/or microcrystalline materials in the form of ribbons, wires, or foils is the rapid solidification of melted metal via melt-spinning processes. In this production process, a melted metal is sprayed through a nozzle onto a casting roller, casting rim, or casting drum which is rotating at speeds of up to 30 m/s. In so doing, the melt cools at a rate of cooling between 104-106 K/s, solidifies on the casting surface to form a continuous ribbon, and is separated from the casting roller. In U.S. Pat. No. 4,142,571, an apparatus of this type for the production of metallic thin ribbons is described.
In the production process described for metal ribbons or foils the following problems or requirements for the casting wheel material arise:
a) The casting wheel material must have a sufficiently high thermal conductivity in order to discharge the heat being released during the solidification of the melt or during the further cooling of the solidified ribbon, wire, or foil. If this is not the case then, for example, the following problems can arise: sparking, no formation of ribbons, the strived-for microstructure of the metal foil to be produced, and thus its strived-for properties, not being achieved (for example, poor magnetic properties of amorphous foils due to partial crystallization), and/or the ribbon produced being brittle and thus mechanically not further processible.
b) The casting wheel material must be highly resistant to thermal as well as mechanical stress since the surface of the casting wheel is exposed to significant wear through its interaction with the melt or with the solidified ribbon. The occurrence of wear is expressed in a poor quality of the ribbon produced, such as, for example, holes, rough surfaces, and so on. These mechanical defects affect the mechanical and magnetic properties of the produced ribbon sensitively. The wear of the casting wheel furthermore leads to a poor thermal contact between casting wheel and ribbon or to a poor spreading of the melted metal on the casting wheel. Thus the rate of cooling of the ribbon is reduced which brings on the problems already cited under a). The constellation of problems of casting wheel wear just described occurs in particular with longer casting times and worsens with increasing casting time until finally proper ribbon formation is no longer possible.
It is thus one objective of the invention to find a material whose use as casting wheel material makes possible the problem-free production of amorphous or microcrystalline, qualitatively high-value metal alloys, in particular in large commercial amounts and which minimizes the problems described above.