Solidification is a common process used in the manufacture of bulk metals, and is fundamentally a phase transformation from liquid to solid that has been studied for many years. A lot of fundamental theories of solidification under near equilibrium conditions have been developed and are widely accepted. In the case of rapid solidification, which is characterized by rapid heat loss and a high interface velocity, non-equilibrium conditions prevail and are not yet understood very well. Due to the promising properties of new alloys and microstructures produced by rapid solidification, industrial interest in this process remains strong. As the present theories of solidification are mainly based on equilibrium conditions, there is strong motivation for developing new theories that explain the solidification behavior under non-equilibrium conditions. In this research, we present experimental results of rapid lateral solidification under the newly geometric heat flow and growth direction, and address critical questions associated with the current theories. This includes identification and quantification of mechanisms governing defect generation and texture formation.
In this research, a pulsed excimer laser was applied as an energy source to melt thin film metallic multilayers of Cu, Cu-Nb, Ag and Au. This leaded to rapid resolidification upon cooling, and unique solidification microstructures. Using this technique, we were able to successfully prepare RLS (rapid lateral solidification) microstructures that were reproduceable and controllable through the laser process parameters. Much of the work presented here was an investigation of the rapid solidification process indirectly by examination of the post-solidified microstructure using electron microscopy. In this thesis we have quantitatively studied several aspects of the microstructure, including: (1) Microstructure of four zones formed during rapid solidification; (2) Mechanism of texture selection; (3) Stacking fault density versus solidification velocity.
It is believed that the microstructure and defects formed in rapid solidification are affected by the thermal gradient and by the high solidification velocity. Based on these experimental results, we are now able to address a number of open questions relating to orientation selection, kinetics of defect formation, S-L interfacial stability, and heat flow in RLS.
|Advisor:||Leonard, John P.|
|School:||University of Pittsburgh|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 71/09, Dissertation Abstracts International|
|Subjects:||Condensed matter physics, Materials science|
|Keywords:||Laser melting, Lateral solidification, Metal thin films|
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