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The Uranium-Titanium Alloy System

Description: Abstract: "A uranium-titanium constitution diagram is presented. There is complete solid solubility between titanium and gamma uranium above about 2100 F. Only one compound exists in the system. It has a hexagonal structure based on U2Ti. It has a fairly wide range of stability, particularly on the titanium side. Beta-titanium solid solution decomposes eutectoidally into alpha titanium and compound at 1150 F. Eutectoid composition is about 72 atomic per cent titanium. Gamma-uranium solid solution decomposes eutectoidally at 1325 F into beta uranium and compound. Eutectoid composition is about 6 atomic per cent titanium. Beta uranium and compound react peritectoidally at 1233 F to give alpha uranium. Solubility of titanium in alpha and beta uranium is low as is the solubility or uranium in alpha titanium."
Date: November 5, 1952
Creator: Udy, Murray C. & Boulger, Francis W.
Partner: UNT Libraries Government Documents Department

Preparation, Cladding, and Evaluation of Titanium-boron Dispersions

Description: This report discusses tests on the preparation and cladding of hot-pressed and pressure-bonded titanium-boron. It explores the properties of titanium-boron as a control material in reactors.
Date: June 9, 1957
Creator: Paprocki, Stan J.; Keller, Donald L.; Hodge, Edwin S.; Cunningham, George W.; Gedwill, Michael A. & Lozier, Donald E.
Partner: UNT Libraries Government Documents Department

Elevated-Temperature Fatigue Properties of Two Titanium Alloys

Description: Report presenting an investigation to evaluate the unnotched fatigue properties of two titanium alloys at elevated temperatures. A variety of temperatures were tested and the results are provided in tabular form and as curves of stress versus cycles to failure for each test temperature. Both alloys were found to have potential use at the temperature ranges investigated.
Date: April 24, 1956
Creator: Rey, William K.
Partner: UNT Libraries Government Documents Department

Phase Separation and Second Phase Precipitation in Beta Titanium Alloys

Description: The current understanding of the atomic scale phenomenon associated with the influence of beta phase instabilities on the evolution of microstructure in titanium alloys is limited due to their complex nature. Such beta phase instabilities include phase separation and precipitation of nano-scale omega and alpha phases in the beta matrix. The initial part of the present study focuses on omega precipitation within the beta matrix of model binary titanium molybdenum (Ti-Mo) alloys. Direct atomic scale observation of pre-transition omega-like embryos in quenched alloys, using aberration-corrected high resolution scanning transmission electron microscopy and atom probe tomography (APT) was compared and contrasted with the results of first principles computations performed using the Vienna ab initio simulation package (VASP) to present a novel mechanism of these special class of phase transformation. Thereafter the beta phase separation and subsequent alpha phase nucleation in a Ti-Mo-Al ternary alloy was investigated by coupling in-situ high energy synchrotron x-ray diffraction with ex-situ characterization studies performed using aberration corrected transmission electron microscopy and APT to develop a deeper understanding of the mechanism of transformation. Subsequently the formation of the omega phase in the presence of simultaneous development of compositional phase separation within the beta matrix phase of a Ti-10V-6Cu (wt%) alloy during continuous cooling has been investigated using a combination of transmission electron microscopy and atom probe tomography. The results of these investigations provided novel insights into the mechanisms of solid-state transformations in metallic systems by capturing the earliest stages of nucleation at atomic to near atomic spatial and compositional resolution.
Date: May 2011
Creator: Devaraj, Arun
Partner: UNT Libraries

Creep of Nearly Lamellar TiAl Alloy Containing W

Description: Effects of W on the creep resistance of two nearly fully lamellar TiAl alloys with 1.0 and 2.0 at.%W have been investigated. In the low stress regime (LS) a nearly quadratic (1.5<n<2) creep behavior was observed. It is found that the addition of W can improve the creep resistance; however, the addition of excess W can result in the formation of {beta} phase, which produces an adverse effect on the creep strength.
Date: April 8, 2004
Creator: Hodge, A M; Hsiung, L M & Nieh, T
Partner: UNT Libraries Government Documents Department

High temperature properties of alloys being considered for design of a concentric canister launcher

Description: This report describes a study to determine the high temperature mechanical properties of several titanium alloys and to compare them with properties of AISI 316L stainless steel and ASTM A 387 structural steel. The steel materials are less costly to procure but exhibit good resistance to corrosion in seawater environments. Six titanium alloys were evaluated as candidate materials for use in a c Concentric Canister Launcher (CCL). Each titanium alloy was tested at three temperatures (68°, 2000°F, and 2400°F). Strain-rate changes tests were used to determine the strain rate sensitivity of the alloys at each test temperature. Optical metallography was performed on two of the alloys to determine the relationship between test temperature and microstructure (presence of second phase precipitates, grain size). Complete test results are includes, a long with figures and tables of test data.
Date: June 1, 1998
Creator: Kassner, M E; Lowry, R W & Rosen, R S
Partner: UNT Libraries Government Documents Department

Mechanical response and microcrack formation in a fine-grained duplex TiAl at different strain rates and temperatures

Description: Compressive behavior of this alloy was studied at strain rates of 0. 001 and 2000 sec{sup -1} and temperatures from -196 C to 1200 C. Temperature dependence of yield stress was found to depend on strain rate: At the quasi-static strain rate, 0.001 sec{sup -1}, the yield stress decreases with temperature with a plateau between 200 and 800 C. At the high strain rate, 2000 sec{sup -1}, the yield stress exhibits a positive temperature dependence above 600 C. Strain hardening rate decreases dramatically with temperature in the very low and high temperature regions with a plateau at intermediate temperatures for both strain rates. As the strain rate increases, the strain hardening rate plateaus extended to higher temperatures. The strain rate sensitivity increases slightly with temperature (but less than 0.1) for strain rates above 0.001 sec{sup -1}. However, at a strain rate of 0.001 sec{sup -1}, there is a dramatic increase in the strain rate sensitivity with temperature; above 1100 C, the rate sensitivity becomes much larger. Microcracks occurring in grain interiors and at grain boundaries were observed at all strain rates and temperatures. Formation and distribution of microcracks were found to vary depending on strain rate and deformation temperature.
Date: October 1996
Creator: Jin, Z.; Cady, C.; Gray, G. T., III & Kim, Y.-W.
Partner: UNT Libraries Government Documents Department

Passive films and blistering of titanium

Description: Coupons of titanium alloys under consideration as components of the Engineered Barrier System in the proposed repository at Yucca Mountain have been evaluated for their passive film composition and stability. Oxide depths and compositions on specimens exposed in long-term corrosion testing for one year were determined with x-ray photoemission spectroscopy. The specimens removed from long-term testing, as well as separate coupons polarized cathodically in an electrochemical cell, exhibited blistering associated with hydride formation in both scanning electron microscopy and atomic force microscopy.
Date: December 1, 1998
Creator: Bedrossian, P J; Estill, J C; Farmer, J C; McCright, R D & Phinney, D L
Partner: UNT Libraries Government Documents Department

Task 6.7.3 - Interfacial Mass Transport Effects in Composite Materials

Description: Advanced metal-matrix composites (MMCS) consisting of titanium-based alloys possess some unique mechanical, physical, and chemical characteristics that make them highly desirable for aircraft and gas turbine engines. Tailoring MMC properties is essential for advanced product design in materials processing. The main factors that affect materials processing and, further, the nature of a metal-ceramic interface, its structure, and morphological stability is liquid surface mass transport related to adhesional wetting (physical effect) and reactive wetting (chemical effect).' Surfaces and interfaces dominate many of the technologically important processes in composite materials such as liquid-solid sintering and joining. The objective of this work is threefold: 1) to get insight into the role of the nonstoichiometry of chemical composition in ceramic materials used as reinforcement components in MMC processing, 2) to extend previous energetic analysis of mass transport phenomena to wetting behavior between liquid metal and the quasi-solidlike skin resulting from the presolidification of liquid on nonstoichiometric solids on a scale of interatomic distance, and 3) to provide experimental verification of our concept.
Date: February 1, 1998
Creator: Nowok, Jan W.
Partner: UNT Libraries Government Documents Department

Strengthening strategy for a ductile metastable β-titanium alloy using low-temperature aging

Description: This article demonstrates that low-temperature aging (LTA) treatments for short time periods can in fact enhance the yield strength while preserving substantial elongation-to-failure in ω containing β titanium alloys.
Date: May 10, 2017
Creator: Sun, F.; Zhang, J.Y.; Vermaut, P.; Choudhuri, Deep; Alam, Talukder; Mantri, Srinivas Aditya et al.
Partner: UNT College of Engineering

Microstructure and Creep Properties of TiAl-Ti3Al In-Situ Composites

Description: Objectives: {lg_bullet} Exploit thermomechanical-processing techniques to fabricate TiAl/Ti3Al in-situ laminate composites with the size of lamella width down to submicron or nanometer length-scales. {lg_bullet} Characterize microstructure and elevated-temperature creep resistance of the in-situ composites. {lg_bullet} Investigate the fundamental interrelationships among microstructures, alloying additions, and mechanical properties of the in-situ composites so as to achieve the desired properties of the in-situ composites for high-temperature structural applications.
Date: February 18, 2004
Creator: Hodge, A M & Hsiung, L L
Partner: UNT Libraries Government Documents Department

Exceptional Properties in Friction Stir Processed Beta Titanium Alloys and an Ultra High Strength Steel

Description: The penchant towards development of high performance materials for light weighting engineering systems through various thermomechanical processing routes has been soaring vigorously. Friction stir processing (FSP) - a relatively new thermomechanical processing route had shown an excellent promise towards microstructural modification in many Al and Mg alloy systems. Nevertheless, the expansion of this process to high temperature materials like titanium alloys and steels is restricted by the limited availability of tool materials. Despite it challenges, the current thesis sets a tone for the usage of FSP to tailor the mechanical properties in titanium alloys and steels. FSP was carried out on three near beta titanium alloys, namely Ti6246, Ti185 and Tiβc with increasing β stability index, using various tool rotation rates and at a constant tool traverse speed. Microstructure and mechanical property relationship was studied using experimental techniques such as SEM, TEM, mini tensile testing and synchrotron x-ray diffraction. Two step aging on Ti6246 had resulted in an UTS of 2.2GPa and a specific strength around 500 MPa m3/mg, which is about 40% greater than any commercially available metallic material. Similarly, FSP on an ultra-high strength steel―Eglin steel had resulted in a strength greater than 2GPa with a ductility close to 10% at around 4mm from the top surface of stir zone (SZ). Experimental techniques such as microhardness, mini-tensile testing and SEM were used to correlate the microstructure and properties observed inside SZ and HAZ's of the processed region. A 3D temperature modeling was used to predict the peak temperature and cooling rates during FSP. The exceptional strength ductility combinations inside the SZ is believed to be because of mixed microstructure comprised of various volume fractions of phases such as martensite, bainite and retained austenite.
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Date: May 2017
Creator: Tungala, Vedavyas
Partner: UNT Libraries

Combinatorial Assessment of the Influence of Composition and Exposure Time on the Oxidation Behavior and Concurrent Oxygen-induced Phase Transformations of Binary Ti-x Systems

Description: The relatively low oxidation resistance and subsequent surface embrittlement have often limited the use of titanium alloys in elevated temperature structural applications. Although extensive effort is spent to investigate the high temperature oxidation performance of titanium alloys, the studies are often constrained to complex technical titanium alloys and neither the mechanisms associated with evolution of the oxide scale nor the effect of oxygen ingress on the microstructure of the base metal are well-understood. In addition lack of systematic oxidation studies across a wider domain of the alloy composition has complicated the determination of composition-mechanism-property relationships. Clearly, it would be ideal to assess the influence of composition and exposure time on the oxidation resistance, independent of experimental variabilities regarding time, temperature and atmosphere as the potential source of error. Such studies might also provide a series of metrics (e.g., hardness, scale, etc) that could be interpreted together and related to the alloy composition. In this thesis a novel combinatorial approach was adopted whereby a series of compositionally graded specimens, (Ti-xMo, Ti-xCr, Ti-xAl and Ti-xW) were prepared using Laser Engineered Net Shaping (LENS™) technology and exposed to still-air at 650 °C. A suite of the state-of-the-art characterization techniques were employed to assess several aspects of the oxidation reaction as a function of local average composition including: the operating oxidation mechanisms; the structure and composition of the oxides; the oxide adherence and porosity; the thickness of the oxide layers; the depth of oxygen ingress; and microstructural evolution of the base material just below the surface but within the oxygen-enriched region. The results showed that for the Ti-Mo, Ti-Al and Ti-W systems a parabolic oxidation rate law is obeyed in the studied composition-time domain while Ti-Cr system experiences a rapid breakaway oxidation regime at low solute concentrations. The only titanium oxide phase present in ...
Date: May 2015
Creator: Samimi, Peyman
Partner: UNT Libraries

First Principles Study of Metastable Beta Titanium Alloys

Description: The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple hexagonal w phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the b phase, thwarts its transformation to w, and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other w forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether w can transform to a -phase in the crystal bulk or if it occurs only at high-energy regions such as grain boundaries. Furthermore, what is the nature of the a phase embryo? (iv) Although previous computational results discovered a new wa transformation mechanism in pure Ti with activation energy lower than the classical Silcock pathway, it is at odds with the a / b / w orientation relationship seen in experiments. First principles calculations based on density functional theory provide an accurate approach to study such nanoscale behavior with full atomistic resolution, allowing investigation of the complex structural and chemical effects inherent in the alloyed state. In the present work, a model Ti-Mo ...
Date: August 2015
Creator: Gupta, Niraj
Partner: UNT Libraries

Models for predicting damage evolution in metal matrix composites subjected to cyclic loading

Description: A thermomechanical analysis of a continuous fiber metal matrix composite (MMC) subjected to cyclic loading is performed herein. The analysis includes the effects of processing induced residual thermal stresses, matrix inelasticity, and interface cracking. Due to these complexities, the analysis is performed computationally using the finite element method. Matrix inelasticity is modelled with a rate dependent viscoplasticity model. Interface fracture is modelled by the use of a nonlinear interface constitutive model. The problem formulation is summarized, and results are given for a four-ply unidirectional SCS-6/{beta}21S titanium composite under high temperature isothermal mechanical fatigue. Results indicate rate dependent viscoplasticity can be a significant mechanism for dissipating the energy available for damage propagation, thus contributing to improved ductility of the composite. Results also indicate that the model may be useful for inclusion in life prediction methodologies for MMC`s.
Date: March 1, 1995
Creator: Allen, D.H.; Hurtado, L.D. & Helms, K.L.E.
Partner: UNT Libraries Government Documents Department

Structure factor measurement in TiAl and silicon

Description: It proved impossible to obtain results with sufficient precision for TiAl reproducibly (<0.1%) from samples of different thicknesses. In order to ascertain the origin of this inconsistency, this study concentrates on the development of the experimental and theoretical tools required for such refinement and measurements for Si have been performed.
Date: March 1, 1996
Creator: Swaminathan, S.; Wiezorek, J.M.; Jones, I.P.; Zaluzec, N.J.; Fraser & Maher, D.M.
Partner: UNT Libraries Government Documents Department

Galvanic corrosion study of container materials using zero resistance ammeter

Description: Galvanic corrosion behavior of A 516 steel separately coupled to six different corrosion-resistant alloys was investigated in an acidic brine (pHa2.70) at 30{degree}C 60{degree}C and 80{degree}C using zero resistance ammeter technique. The corrosion-resistant alloys include Alloys 825, G-3, G-30, C-4 and C-22; and Ti Grade-12, which were coupled to A 516 steel at an anode-to- cathode area ratio of one. The galvanic current and galvanic potential were measured as a function of time at all three temperatures. Optical microscopic examination was also performed on all tested specimens to evaluate the extent of surface degradation due to galvanic coupling. The overall results are presented in this paper.
Date: November 1, 1997
Creator: Roy, A. K., LLNL
Partner: UNT Libraries Government Documents Department

Micromechanisms of Twin Nucleation in TiAl: Effects of Neutron Irradiation

Description: The so-called radiation-induced ductility (RID) reported in neutron-irradiated 47at%Al alloys is attributed to the formation of effective twin embryos in the presence of interstitial-type Frank loops in {gamma}-TiAl and the subsequent nucleation and growth of microtwins during post-irradiation tensile deformation. The stability of large faulted Frank loops is explained in terms of the repulsive interaction between Shockley and Frank partials. Interaction of only six ordinary slip dislocations with a Frank loop can facilitate a pole mechanism for twin formation to work. The relative ease of heterogeneous twin nucleation is the reason for the RID and the lack of changes in yield strength and work hardening.
Date: January 28, 1999
Creator: Hishinuma, A. & Yoo, M.H.
Partner: UNT Libraries Government Documents Department