Processing of Superconducting Metal/MgB2 Composites

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In this work, the processing of the superconductor MgB<sub>2</sub> was studied to create a fundamental scientific background for the production of superconducting composite wires. The synthesis of MgB<sub>2</sub> from Mg and B powders was investigated in situ to determine reaction rates and kinetic parameters for the application of powder-in-tube technology where powders are combined within a metal tube and drawn into a wire. A technique was developed using synchrotron x-rays to study the reaction within a tube at high temperature. To enhance powder-in-tube technology, the high temperature compressive properties of MgB<sub>2</sub> were measured and large ductile strains were achieved suggesting that MgB<sub>2</sub>, despite being brittle at ambient temp can be deformed plastically at high temperature to create dense core, powder-in-tube wires. An additional process was developed where commercial boron fibers were reacted in situ within liquid Mg, which was subsequently solidified to create a Mg matrix composite with superconducting MgB<sub>2</sub> fibers aligned continuously though the length. The synthesis was also studied in situ using the synchrotron technique as well as ex situ with interrupted reactions and metallography to determine diffusion coefficients and activation energies for the formation of MgB<sub>2</sub>. To determine reaction mechanisms, a numerical model was developed that incorporated microstructural observations of cracking to enhance reaction rate and the model was applied successfully to the reaction of fibers. Additional processing variables were investigated with respect to these fundamental kinetics studies including the effect of fiber diameter, surface treatment, dopant, and reaction under thermal cycling conditions. Based on these observations, future research is described where enhanced superplastic deformation of MgB<sub>2</sub> may be achieved along with enhanced superconducting properties, reaction mechanisms can be determined for carbon doped fibers, reaction kinetics can be determined for solid state reactions, as well as other possible developments for MgB<sub>2</sub> wire technology.

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  • 08/02/2018
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