EVALUATION OF THE CONTACT-ANGLE IN RAPID SOLIDIFICATION BY MELT-SPINNING

This paper presents an experimental method for the estimation of the c ontact angle in processing metallic glasses, based on a modeling schem e of the viscosity temperature dependence of liquid alloys and a heter ogeneous nucleation regime during melt-spinning process, when rapid qu enching from the liquid state may result in the formation of either a crystalline or a glassy structure. Melt-spun Mg0.6Cu0.4 ribbons have b een obtained using two different quenching rim velocities of 7.5 and 3 0.0 m s(-1), and were shown to be respectively fully crystalline and f ully amorphous. Numerical simulation has been performed, with assumed values of 45 degrees, 50 degrees and 55 degrees for the wetting angle, all other physical and processing parameters kept identical. If 50 de grees is assumed to be the contact angle for the considered system, th e ribbons processed at a substrate rim velocity of 7.5 m s(-1) are pre dicted to be crystalline, while those processed at 30.0 m s(-1) are pr edicted to be amorphous. This points to the conclusion that, in this s pecific case (Mg0.6Cu0.4 solidifying on a CuBe substrate), the contact angle is close (+/-4 degrees) to 50 degrees. The knowledge of the cri tical contact angle necessary for suppression of nucleation and domina nce of amorphization enables the correct choice of substrate and addit ional processing parameters for the production of glassy metallic mate rial.