Evaluation of the contact angle in rapid solidification by melt spinning

This paper presents an experimental method for the estimation of the contact angle in processing metallic glasses, based on a modeling scheme of the viscosity temperature dependence of liquid alloys and a heterogeneous nucleation regime during melt-spinning process, when rapid quenching from the liquid state may result in the formation of either a crystalline or a glassy structure. Melt-spun Mg0.6Cu0.4 ribbons have been obtained using two different quenching rim velocities of 7.5 and 30.0 m s−1, and were shown to be respectively fully crystalline and fully amorphous. Numerical simulation has been performed, with assumed values of 45°, 50° and 55° for the wetting angle, all other physical and processing parameters kept identical. If 50° is assumed to be the contact angle for the considered system, the ribbons processed at a substrate rim velocity of 7.5 m s−1 are predicted to be crystalline, while those processed at 30.0 m s−1 are predicted to be amorphous. This points to the conclusion that, in this specific case (Mg0.6Cu0.4 solidifying on a CuBe substrate), the contact angle is close (± 4°) to 50°. owledge of the critical contact angle necessary for suppression of nucleation and dominance of amorphization enables the correct choice of substrate and additional processing parameters for the production of glassy metallic material.