Models for continuous casting of metallic glass ribbons I: The applicability of the infinite-viscosity assumption to thermal history calculations

Abstract

In order to establish more reliable thermal history calculations we examined how the melt flow influences the cooling process through convective heat transport. On the basis of the laminar boundary layer theory it was shown that because of the continuous variation in viscosity around the glass transition the thermal history calculated with the assumption of infinite melt viscosity is very similar over a wide temperature region to that computed with the experimental viscosity-temperature relation. It is illustrated that for Fe 40Ni 40P 14B 6 this temperature region includes the range in which time-temperature-transformation diagrams predict significant crystallization rates. However, because of their mathematical simplicity, calculations using infinite viscosity enable important experimental boundary conditions which cannot be properly treated in models which include a more detailed description of melt flow to be taken into account. In this way it is expected that calculations using an infinite melt viscosity can reliably predict thermal history in the temperature region which is most important from the viewpoint of glass formation.