Cooling Rate Modeling and Evaluation during Centrifugal Atomization Process

Abstract

Centrifugal atomization is a rapid solidification technique involving fast cooling rates to produce high-quality powders. The final microstructure of the atomized particles is closely linked with the thermal history and cooling rates experienced during the atomization process. However, there is insufficient research on the temperature evolution of metal particles produced by this technique, and most works evaluate the thermal history of the droplet through semi-empirical correlations that lie outside the conditions where they were derived. In this work, the cooling rate of centrifugally atomized Al-4%Cu was studied via mathematical modelling and experimental validation. A heat transfer model was implemented, and the value of the convective heat transfer coefficient was obtained from the Whitaker semi-empirical correlation considering three cases of study for the thermophysical properties of the gas. The validity of the Whitaker correlation was experimentally evaluated by means of cooling rates based on the Secondary Dendrite Arm Spacing (SDAS) technique. The Whitaker correlation with the Reynolds and Prandtl numbers evaluated at the ambient temperature and the gas conductivity evaluated at the film temperature gave the best agreement with the experimental results, with cooling rates in the order of 105 Ks−1 for <32.5 µm powders atomized in He atmosphere.