Three samples of Ti(C,N) were fabricated with 40 vol.% Ni3Al: Ti(C0.3N07), Ti(C0.5N0.5) and Ti(C0.7N0.3), as well as TiC with 10, 20, 30 and 40 vol.% Ni3Al binder addition by means of melt infiltration and sintering. Each sample was evaluated for density and microstructure before being placed in a flat cell for electrochemical testing. Open circuit potential was evaluated, followed by the application of a cathodic potential, whereby the response was tracked using Corrware corrosion software throughout the duration of potentiodynamic testing. Following corrosion testing, each sample was reevaluated for changes in microstructure and chemical composition. Ti(C,N) samples were found to have adequate resistance to corrosion, with increased resistance with increasing carbon content, however these samples demonstrated a greater frequency of breakdown and repassivation, suggesting a greater susceptibility to corrosion, despite the initial improved resistance. SEM imaging demonstrated significant crevice corrosion throughout. TiC-cermets demonstrated similar results in terms of SEM evaluation of microstructure. TiC-cermets with the lowest binder content (10 vol.% Ni3Al) demonstrated greater initial resistance to corrosion but also had the greatest potential for breakdown.

Thesis, (M.S.)--Oregon Graduate Institute of Science and Technology, 1998.

Thesis (Ph. D.)--Ohio State University, 1998. / Advisor: William A. Brantley, Oral Biology Program. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 1998. / Advisor: William A. Brantley, Oral Biology Program. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 120-124).

This dissertation discusses the synthesis, processing, and characterization of titanium carbide (TiC) and titanium diboride (TiB2) based materials for structural and electronic application. A series of TiB2 and TiC-TiB2 powders was prepared through a novel carbon coated precursors method. Reaction process, phase evolution, and microstructures were analyzed and characterized. The synthesized powders have the advantages of fine particle size (nano to submicron grade, 100nm to 800nm), high purity (low levels of contaminations such as free carbon and oxygen), loose agglomeration, and high surface area (~2.5 m2/g to 7.2 m2/g). Using the synthesized powders, three categories of composites were prepared: (1) TiB2-TiC-Ni composites with improved mechanical properties for structural applications; (2) TiB2-TiNiFeCrCoAl high-entropy alloy (HEA) composites with enhanced hardness and toughness for structural application; (3) TiC-Ti3Al based composites with good electrical and oxidation properties as the interconnect in solid oxide fuel cell. The author focuses on the sintering mechanism, microstructure and interface, reactions, and properties characterizations of above three types of composites. Correlations of processing-microstructures-properties are discussed and established based on scientific observation.

Over the last two decades there has been an increased interest in understanding the influence of trace boron additions in Ti alloys. These additions refine the prior β grain size in as-cast Ti alloys along with increasing their modulus and yield strength due to the precipitation of TiB. TiB also acts as a heterogeneous nucleation site for α precipitation and has been shown to influence the α phase morphology. B is completely soluble in liquid Ti but has a negligible solubility in both body centered cubic β and hexagonal close packed α phases of Ti. Thus, during solidification of hypoeutectic B containing alloys, B is rejected from β into the liquid where it reacts with Ti to form pristine single crystal whiskers of TiB. Despite a substantial amount of reported experimental work on the characterization of TiB precipitates, its formation mechanism and influence on α phase precipitation are still not clear. The current work is divided into two parts – (i) understanding the mechanism of TiB formation using first principles based density functional theory (DFT) calculations and (ii) elucidating how TiB influences the α phase morphology and crystallography in titanium alloys using electron microscopy techniques. TiB exhibits anisotropic growth morphology with [010] direction as its predominant growth direction and displays a hexagonal cross section with (100), (101), and (10) as the bounding planes. A high density of stacking faults has been experimentally observed on the (100) plane. The present study, by using DFT based nudged elastic band (NEB) calculations, elucidates for the first time that the diffusion of B through TiB is via an interstitial-assisted mechanism as opposed to vacancy-assisted mechanism hypothesized in literature. This one dimensional interstitial-assisted diffusion results in the anisotropic growth of TiB. In addition, the energetics of TiB- α interfaces was calculated to understand the hexagonal cross-section of TiB. The intimate mixing of B27 and Bf structures and their co-existence with stacking faults has been explained by calculating the interfacial energy of B27/Bf interfaces along with stacking fault formation energy. The boride precipitates have also been shown to modify the morphology of α phase from lath like to more equiaxed like. However, the influence of TiB on the crystallography of α precipitation has not been explored in great detail. The present study will clearly demonstrate, for the first time, the influence of various alloying elements present in the titanium alloy, on the resulting effect of B addition on α morphology and its crystallography in Ti alloys. Thus, the influence of B addition on α precipitation in two classes of commercial Ti alloys, i.e. β alloys and α + β alloys have been explored. It has been found that TiB nucleated α can either become equiaxed by a loss of Burgers orientation relationship (OR) with β or can retain the lath morphology in case of alloys containing a combination of Ti, Al and Mo.

No / Despite the extensive utilization of biomolecule-titania interfaces, biomolecular recognition and interactions at the aqueous titania interface remain far from being fully understood. Here, atomistic molecular dynamics simulations, in partnership with metadynamics, are used to calculate the free energy of adsorption of different amino acid side chain analogues at the negatively-charged aqueous rutile TiO2 (110) interface, under conditions corresponding with neutral pH. Our calculations predict that charged amino acid analogues have a relatively high affinity to the titania surface, with the arginine analogue predicted to be the strongest binder. Interactions between uncharged amino acid analogues and titania are found to be repulsive or weak at best. All of the residues that bound to the negatively-charged interface show a relatively stronger adsorption compared with the charge-neutral interface, including the negatively-charged analogue. Of the analogues that are found to bind to the titania surface, the rank ordering of the binding affinities is predicted to be "arginine" > "lysine" ≈ aspartic acid > "serine". This is the same ordering as was found previously for the charge-neutral aqueous titania interface. Our results show very good agreement with available experimental data and can provide a baseline for the interpretation of peptide-TiO2 adsorption data. / Veski

Call number: LD2668 .T4 1961 L39

No description available.