Solidification of Highly Undercooled Liquid Metals and Alloys

摘要

The undercooling and solidification of liquid alloys in fine droplet form has been examined by thermal analysis, X-ray diffraction and metallography. New maximum undercooling limits have been established for several metals and hypercooling has been demonstrated for the first time in a metallic system. In alloys some aspects of the phase selection kinetics for formation of metastable phases have been identified in eutectic, peritectic and monotectic reactions. The use of droplet samples allows the measurement of thermodynamic properties of undercooled liquids and the study of microstructure development with changing undercooling. In some alloys, the effective isolation of nucleants that is possible with micron size droplets results in a continuous solidification to the amorphous state. The observations are presented in terms of the potential of undercooling for structure modification and rapid solidification technology. (Author)