PhD, University of Cincinnati, 2000, Engineering : Materials Science

The overall objectives of this dissertation are fabrication of titanium diboride-colloidal alumina composite coating on carbon substrate, and study of the concerned properties of being used as a protective coating in Hall-Heroult cell. A unique aqueous suspension spraying coating procedure has been developed to apply thick (>1 mm) and crack-free TiB 2 coating on carbon substrate, in which colloidal alumina is initially used as the inorganic binder to avoid the drawbacks of carbonaceous additives. The processing parameters in coating application and densification such as composition of the suspension, coating thickness, sintering temperature and time are optimized to produce thick and crack-free TiB 2 coating with high electrical conductivity and high mechanical strength. General physical and mechanical properties of the coating material, such as density, porosity, electrical conductivity, micro-hardness and flexural strength are determined; Microstructure and morphology of this unique TiB 2 -colloidal alumina composite are characterized; Properties of interest for specific utilization as a protective coating in aluminum producing cell such as wetting behavior with molten aluminum are examined. Features associated with aqueous spraying coating process, such as viscosity of the suspension, drying behavior, critical cracking thickness, interfacial bonding strength and thickness of interfacial bonding region are determined. This dissertation also represents an extensive investigation on TiB 2 -colloidal alumina composite coating. The function of the nano-sized colloidal alumina is understood in terms of forming aid and sintering aid. Based on the intensive analysis of the experimental data, a pattern in which TiB 2 particles are coated by nano-sized colloidal alumina in the suspension is successfully postulated to explain the property dependence on colloidal alumina addition. The sintering process of TiB 2 -colloidal alumina composite coating is an energy activate proce (open full item for complete abstract)

Committee: J. Sekhar (Advisor) Subjects: Engineering, Materials Science

Doctor of Philosophy, The Ohio State University, 2006, Physics

Microstructure features in TiB-reinforced titanium alloys are correlated with mechanical properties. Both laser deposition and arc melting are used to fabricate test alloys where microstructure evolution with heat treatment is examined. SEM and TEM investigations of microstructure are coupled with 3D reconstruction to provide an adequate picture of phases in these alloys. Mechanical properties are then studied. Wear testing of several test alloys is presented, followed by hardness and modulus measurements of individual phases via micro- and nano-indentation as well as a novel micro-compression technique. Bulk mechanical properties are then tested in Ti-6Al-4V and Ti-555 (Ti-5Al-5V-5Mo-3Cr-1Fe) with varying amounts of boron. Image processing methods are then applied to high resolution back-scattered scanning electron microscope images to quantify microstructure features in the tensile test specimens, and these values are then correlated with mechanical properties.

Committee: John Wilkins (Advisor) Subjects: