Date

2019

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Materials Science and Engineering

First Adviser

Chan, Helen M.

Abstract

Producing the next generation of engineering materials requires new approaches to materials processing. Metal-ceramic composites, especially those with nanoscale features, offer promising combinations of properties, but are underutilized due to complex processing requirements. Two keys to maximizing their impact are tailoring the composite microstructures for particular applications and producing them in a versatile form for simplified processing. Exploiting phase transformations such as eutectoid decomposition and partial reduction of mixed oxides presents a straightforward means of producing composites with tunable microstructures. By fabricating composites in powder form, versatility is maximized for subsequent processing. These approaches were explored in the Co-Ti-O and Cu-Al-O systems and the resulting composites were characterized through XRD, SEM, EBSD, TEM, nanoindentation, and microcantilever beam bending. In-situ partial reduction was utilized to generate novel Co-TixOy composites, including nanocomposites, through the reduction of CoTiO3. The effect of processing variables on the properties of the composites was evaluated through nanoindentation of the embedded cobalt particles. CoTiO3-TiO2 composites were also generated through a eutectoid transformation from the CoTi2O5 phase. Subsequently applying partial reduction to this composite produced a unique Co-TiO2 composite with a layered microstructure. During this investigation, a novel single crystal growth mechanism was observed in the CoTi2O5 phase, which could be utilized to produced CoTiO3-TiO2 and Co-TiO2 composites with controllable microstructures and crystal orientations. In the Cu-Al-O system, a scalable processing approach was demonstrated utilizing partial reduction yielding metal-ceramic nanocomposite powders. Partial reduction of the mixed oxide CuAlO2 resulted in a Cu-Al2O3 composite with a nanoscale layered structure. Consolidation of the composite powder through low temperature techniques offers a scalable approach for producing dense metal-ceramic composites with a layered nanoscale microstructure. The many useful properties of the constituent phases in conjunction with the range of controllable microstructures demonstrates that the in-situ partial reduction technique has excellent potential for metal-ceramic composite production.

Available for download on Wednesday, February 05, 2020

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