Intragranular Tungsten-Titanium Carbide Composite Ceramics via Gas-Solid Displacement Reactions

<p>"Research presented herein details the synthesis and characterization of nanocomposite ceramics featuring novel heterogeneous microstructures of potential interest in a variety of electrical and structural applications. Specifically, W-TiCy composite ceramics featuring tungsten nanoprecipitates located primarily within TiCy grains have been produced via sintering of intragranular nanocomposite powders produced via reaction processing-based techniques. This dissertation details the thermodynamic basis and applied kinetics of a processing scheme for fabricating nanocomposite ceramics whose morphological heterogeneity reflects that originally developed in the powder state. The first study in this series overviews the motivation for applying metallothermic displacement reactions, conducted through gaseous intermediates, to solid solution systems and serves as proof of concept for the demonstrated reaction process. Application of the studied reaction process to commercial (Ti_0.77W_0.23)C powder resulted in the formation of a 27 wt. % W-TiCy composite powder that exhibited significant grain-to-grain microstructural variation caused by polycrystallinity and internal compositional variation in the precursor powder. The second study details the use of a liquid aluminum flux method to improve precursor quality by enabling synthesis of (Ti1_-xW_x)C powders with enhanced homogeneity and Mono crystallinity. The final report details the application of the previously reported gas-solid reaction process to flux-synthesized powders, to produce intragranular nanocomposite powders with up to 28 wt. % W. Subsequent spark plasma sintering resulted in the retention of the fine nanostructures produced in the powder state, as established by SEM and XRD characterization. The two scientific contributions of the present research are 1) the development of a novel processing scheme for producing bulk nanostructured composite ceramics, which has potentially broad applicability in the field of ceramics, and 2) the development of a method for controlling dispersant location in nanocomposite ceramics, specifically in a system with a non-oxide chemistry"--Abstract, p. iv</p>

Name thesis:degree_name

Ph. D. in Ceramic Engineering

Grantor

Missouri University of Science and Technology

Author dc:creator

• Dempsey, Ryan Daniel

• composite
• nanocomposite
• reaction processing
• Ceramic Materials
• Engineering

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/3253

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-4258