Rapid solidification and undercooling of Aluminum Germanium alloys: characterization and control of microstructure
In addition to the in-situ solidification and undercooling studies, melt spun ribbons, splat quenched foils and amorphous films of similar compositions have been analyzed. The as-produced microstructures were characterized in the microscope and, subsequently, the amorphous films were heated with the beam to cause crystallization, the products of which were found to vary with composition and heating rate. From these observations, it appears that temperature ranges exist, whether approached by down-quenching from the liquid state or up-quenching from the amorphous state, where the formation of the different phases becomes favorable and that the primary function of cooling rate during rapid solidification is to inhibit nucleation processes so that substantial undercoolings may be achieved. A computer model has been developed in an effort to predict the number of grains which form in highly undercooled Al-30Ge (eutectic) droplets. Specifically, this model utilizes modified nucleation and growth equations for glass forming alloys to predict the number of ..cap alpha..-Al grains which form upon solidification. It is shown that the number of grains increases significantly as the initial undercooling is raised. However, as the undercooling temperatures approach the glass transition temperature, the number of grains is predicted to drop suddenly toward zero resulting in the formation of amorphous (or partially amorphous) microstructures. These predictions are in good agreement with the experimental observations.
- Research Organization:
- Illinois Univ., Urbana (USA)
- DOE Contract Number:
- AC02-76ER01198
- OSTI ID:
- 7120791
- Report Number(s):
- DOE/ER/01198-1409; ON: DE84012395
- Resource Relation:
- Other Information: Portions are illegible in microfiche products. Thesis
- Country of Publication:
- United States
- Language:
- English
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