Wetting pattern characterization of rapidly solidified centrifuge melt-spun metallic ribbons

Abstract

The wetting pattern characterization of rapidly solidified centrifuge melt-spun metallic Al-Ge ribbons has been enabled by measuring the roughness of the rim-contact side of the ribbons. Roughness parameter values were obtained using the SEM ability of amplitude modulation and line scanning of the smooth ribbon surfaces, and micro-computerized digitizing of the line profiles. In such a manner, quantification of the wetting patterns is possible. As a result, the respective contribution of the ejection pressure and the extraction velocity on the wetting patterns of the solidifying ribbons is evaluated. In centrifuge melt spinning, the roughness of the rim-contact surface of the ribbons increases when extraction velocities are increased. Despite the additional roughness and the “bad” thermal contact conditions for effective heat transfer, higher cooling rates (as measured by secondary dendritic arm spacings), are achieved. It appears that a kind of dragging occurs, reducing the ribbon thickness by a shear drawing mechanism. This behaviour is characteristic of centrifuge melt spinning because of the specific hydraulic and heat transfer features involved with the counter-rotating of the crucible and the substrate.