No description available.

No description available.

Manufacturing titanium alloys with simultaneous improvement in strength and ductility poses a challenge which exceeds that of purely cubic metals. Various thermal and thermomechanical strategies have been proposed to regulate the geometrical arrangement of alpha + beta phases and texture of the alpha phase in an effort to impart the microstructure with concurrent strengthening and toughening. This study explores two potential methods of achieving mechanical enhancement. The first involves the substitution of molybdenum for a portion of vanadium in Ti-64 (alpha + beta, 6.0 Al, 4.0 V weight %, balance Ti), thereby creating a new alloy, termed Ti-639 (alpha + beta, 6.5 Al, 1.7 Mo, 1.7 V, 0.3C, 0.19O, 0.3 Si weight %, balance Ti). Electron backscatter diffraction(EBSD)and transmission electron microscopy are used to study the preservation of the as-received microstructure of TIMETAL 639, owing to the low diffusivity of molybdenum. EBSD texture analysis of solution heat treated TIMETAL 639 shows a marked effect of beta phase on the recrystallization of new globular alpha grains within preexistent colonies, leading to the generation of a distinct depleted bimodal microstructure. Quasi-static compression mechanical testing indicates a measurable increase in mechanical response of the depleted bimodal microstructure,about 90MPa higheryield, with a 6% higher strain at failure, when compared to identically heat treated Ti-64 samples. This alloy design strategy enhances the performance of alpha + beta titanium alloys while foregoing additional prolonged aging heat treatments associated with Ti-64.The second method involves a processing strategy to impart near-net shape structureswith ultraine grain microstructures without resorting to severe mechanical deformation. The proposed strategy relies on utilizing a cyclic rapid heat treatment (CRHT) process to generate refined martensitic microstructures in aerospace grade Ti-64. Analysis of resultant microstructures using EBSDreveals trends in microstructure refinement during successive CRHT iterations. For the given heat treatment parameters, three CRHT cycles yielded an optimum microstructure refinement, by effectively harnessing discontinuous dynamic recrystallization,while diminishing the occurrence of dynamic recovery and continuous dynamic recrystallization.

Typescript. / Digitized by Kansas Correctional Industries

Combustive Synthesis or Self-Propagating High-Temperature Synthesis (SHS), is an energy-efficient combustion method of producing metallic, ceramic and composite materials from their constituent powders. This thesis presents the results of an experimental and numerical evaluation of the propagation velocity for the SHS solid-solid reaction of titanium and carbon, as well as a study of the ignition process for the reaction. The experimental results show the dependency trend of the wave propagation speed on various parameters: diameter of the reactant compact, density of the compact, reactant mixture composition, and dilution of the reactant mixture with the inert product TiC. Conditions at which the reaction ceases to propagate in a self-supporting manner are also identified. This thesis attempts to generalize the existing experimental observations of the gasless SHS process by means of a dimensional analysis, thus offering a mechanistic framework within which future developments can be correlated. The implementation of the new reaction kinetics model of Kanury and some suitable dimensionless variables permit the main factors affecting the process to be embedded in a single key parameter, the Da number. This parameter includes the overall effects of thermal properties, stoichiometry of the reaction, carbon particle size, a process constant, a compression effect and the diffusion of one reactant through an intermediate complex. The study of propagation covers a broad range of possible Da numbers that could arise for different conditions found in experiments. A section in numerical calculations of the preheated length is included as well. Comparison of the numerical and experimental results for propagation are found to be in reasonable agreement, thus validating the suitability of the analytical model. The numerical study includes an examination of the ignition problem for a stoichiometric mixture, using a prescribed surface temperature boundary condition. For this condition, an ignition threshold curve is determined above which ignition will always occur and below which no ignition is possible. / Graduation date: 1992

No description available.

No description available.

Thesis (Ph. D.)--Columbia University, 1936. / Vita. Bibliography: p. 39.

Thesis--University of Florida. / Description based on print version record. Typescript. Vita. Includes bibliographical references (leaves 235-244).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1984. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 304-319).