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.

One of the main objectives during primary processing of titanium alloys is to reduce the prior beta grain size. Producing an ingot with smaller prior beta grain size could potentially eliminate some primary processing steps and thus reduce processing cost. Trace additions of boron have been shown to decrease the as-cast grain size in alpha + beta titanium alloys. The primary focus of this dissertation is to investigate the effect of boron on microstructural stability and thermomechanical processing in beta titanium alloys.Two metastable beta titanium alloys: Ti-15Mo-2.6Nb-3Al-0.2Si (Beta21S) and Ti-5Al-5V-5Mo-3Cr (Ti5553) with 0.1 wt% B and without boron additions were used in this investigation. Significant grain refinement of the as-cast microstructure and precipitation of TiB whiskers along the grain boundaries was observed with boron additions. Beta21S and Beta21S-0.1B alloys were annealed above the beta transus temperature for different times to investigate the effect of boron on grain size stability. The TiB precipitates were very effective in restricting the beta grain boundary mobility by Zener pinning. A model has been developed to predict the maximum grain size as a function of TiB size, orientation, and volume fraction. Good agreement was obtained between model predictions and experimental results. Beta21S alloys were solution treated and aged for different times at several temperatures below the beta transus to study the kinetics of alpha precipitation. Though the TiB phase did not provide any additional nucleation sites for alpha precipitation, the grain refinement obtained by boron additions resulted in accelerated aging. An investigation of the thermomechanical processing behavior showed different deformation mechanisms above the beta transus temperature. The non-boron containing alloys showed a non-uniform and fine recrystallized necklace structure at grain boundaries whereas uniform intragranular recrystallization was observed in boron containing (open full item for complete abstract)

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)

The beneficial influence of boron additions on processing, microstructure, physical and mechanical properties of various titanium alloys has been recognized since 1950's. However, boron additions to titanium alloys to obtain specific microstructures and mechanical properties for several niche applications, including automotive and aerospace, have been actively studied during the past 25 years. The addition of boron concentrations greater than 0.05 wt.% to titanium alloys creates a dispersion of TiB. The presence of TiB enhances the tensile and fatigue strengths as well as the wear resistance as compared to the original titanium alloy. Although these improvements in mechanical properties are attractive, there are still two major obstacles in using these alloys: (1) relationship of microstructure and mechanical properties in Ti-B alloys needs further investigation to optimize the alloys for specific commercial applications; and (2) cost to benefit ratio of producing these alloys is high for a given application(s). The Armstrong process is a novel process that can produce commercially pure (CP) titanium and titanium alloy powder directly from TiCl4 (and other metal halides or as required, to obtain the desired alloy composition). The Armstrong process uses sodium as a reducing agent, with similar reactions as the Hunter process using sodium as a reducing agent and Kroll process using magnesium as a reducing agent. The Armstrong process forms CP-Ti and titanium alloyed powder, which can be directly consolidated or melted into the final product. In comparing the downstream processing steps required by the Kroll and Hunter processes with direct consolidation of Armstrong powder, several processing features or steps are eliminated: (1) restriction of batch processing of material, (2) blending of titanium sponge and master alloy material to create titanium alloys, (3) crushing of the sponge product, (4) melting, and (5) several handling steps. The main objective of this res (open full item for complete abstract)