Experimental technique for studying high-temperature phase equilibria in reactive molten metal based systems
Department of Mechanical Engineering
Doctor of Philosophy
Dreizin, Edward L.
Sacksteder, Kurt R.
High temperature phases
The general objective of this work is to develop an experimental technique for studying the high-temperature phase compositions and phase equilibria in molten metal-based binary and ternary systems, such as Zr-O-N, B-N-O, Al-O, and others. A specific material system of Zr-O-N was selected for studying and testing this technique.
The information about the high-temperature phase equilibria in reactive metal-based systems is scarce and their studying is difficult because of chemical reactions occurring between samples and essentially any container materials, and causing contamination of the system.
Containerless microgravity experiments for studying equilibria in molten metal-gas systems were designed to be conducted onboard of a NASA KC-135 aircraft flying parabolic trajectories. A uniaxial apparatus suitable for acoustic levitation, laser heating, and splat quenching of small samples was developed and equipped with computer-based controller and optical diagnostics. Normal-gravity tests were conducted to determine the most suitable operating parameters of the levitator by direct observations of the levitated samples, as opposed to more traditional pressure mapping of the acoustic field. The size range of samples that could be reliably heated and quenched in this setup was determined to be on the order of 1-3 mm. In microgravity experiments, small spherical specimens (1-2 mm diameter), prepared as pressed, premixed solid components, ZrO2, ZrN, and Zr powders, were acoustically levitated inside an argon-filled chamber at one atmosphere and heated by a CO2 laser. The levitating samples could be continuously laser heated for about 1 sec, resulting in local sample melting. The sample stability in the vertical direction was undisturbed by simultaneous laser heating. Oscillations of the levitating sample in the horizontal direction increased while it was heated, which eventually resulted in the movement of the sample away from its stable levitation position and the laser beam.
The follow-up on-ground experiments were conducted to study phase relations in the Zr-O-N system at high-temperatures. Samples with specific compositions were laser-heated above the melt formation and naturally cooled. Recovered samples were characterized using electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. Results of these analyses combined with the interpretations of the binary ZrO and Zr-N phase diagrams enabled us to outline the liquidus and the subsolidus equilibria for the ternary Zr-ZrO2-ZrN phase diagrams.
Further research is suggested to develop the microgravity techniques for detailed characterization of high-temperature relations in the reactive, metal based systems.
njit-etd2005-023 (187 pages ~ 9,730 KB pdf)
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Created April 7, 2005