Solidification Structure Synthesis in Undercooled Liquids
Abstract
The undercooling of liquid metals is a fairly common observation, but the amount of undercooling is limited usually by the action of heterogeneous catalysts. When a liquid is subdivided into a fine droplet dispersion in order to isolate nucleation catalysis, substantial undercooling may be observed before the onset of solidification, as demonstrated by the increased undercooling limits established in the current work. At high undercooling, the solidification of alloys can result in the suppression of the usual crystallization reactions and in the formation of nonequilibrium phases with distinct and novel microstructures. A number of processing variables have been established to control undercooling including: droplet size. melt superheat, cooling rate and droplet surface chemistry. The application of thermal analysis together with x- ray diffraction and microstructural examination methods has allowed for an evaluation of the kinetic competition during phase selection, for the determination of the decomposition and melting temperatures of metastable phases and for the assessment of metastable phase diagrams. New advances have also been made in the understanding and control of heterogeneous nucleation and in probing the thermal history of rapidly solidifying samples by upquenching studies as well as in the development of new experimental capacity to study composites. The understanding developed from droplet undercooling studies has a direct application to Rapid Solidification Processing (RSP) and allows for an assessment of RSP treatment in terms of the influence of undercooling and metastable phase equilibria on phase selection and novel solidification microstructure development. The basic information that droplet studies yield also has a broad application to many aspects of solidification processing.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 18, 1993
- Accession Number
- ADA276166
Entities
People
- John H. Perepezko
Organizations
- University of Wisconsin–Madison