Masters Theses
Date of Award
8-1988
Degree Type
Thesis
Degree Name
Master of Science
Major
Metallurgical Engineering
Major Professor
Ben F. Oliver
Committee Members
Charlie Brooks, Duane Bruns
Abstract
TiAl and TiAl + X alloys possess mechanical properties which are beneficial at high temperatures but lessen upon cooling to room temperature. The cause of the change in properties may be the result of the grain boundaries. In an attempt to investigate this phenomenon, single crystals of these alloys were produced.
In order to achieve this end, these ingots were processed in a levitation zone refiner which was computer controlled. The computer control scheme which evolved was one based entirely upon the control of the zone geometry identified by image processing. This type of control allowed an improvement in dimensional control. The processing experience gained from numerous runs yielded a procedure which will improve the efficiency of production of large grains. This procedure consisted of the following:
1. radiograph the ingots before processing in order to prepare for cracks and voids, which may be detrimental to the zone stability:
2. start with a clean processing environment, since oxygen may react with the ingot causing the melting point to rise or changing the electrical and thermal conductivities;
3. align the ingot as well as possible, because misalignment can cause controller difficulty;
4. and maintain continuity of control for it may be the key to successful processing, because drastic changes in control may perturb the growing crystals.
Processing experience also showed the importance of the alloy's phase diagram on the ability to produce large crystals. For ingots with a steep liquidus, a very slight composition variance can produce a wide change in the equilibrium melting temperature, thus making single crystal production a difficult control problem.
The operating experience gained thus far has not been able to conclusively show the importance of diameter control on grain growth, nor has it been able to show the connection between Ingot composition and grain growth. However, large grains of these compound materials were produced despite adverse operating conditions, indicating that the computer controlled levitation zone refiner is a viable alternative processing technique for high temperature materials.
Recommended Citation
Reviere, Robert D., "The computer controlled production of TiAl and TiAl + 1.4 a/o V single crystals via a levitation zone refining technique. " Master's Thesis, University of Tennessee, 1988.
https://trace.tennessee.edu/utk_gradthes/13319
