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The determination of the solidification paths and the liquidus surface in the quasicrystalline region of the Al-Cu-Ru systems

Description: Objective is to determine if conventional slow-growth methods will be successful for growing single quasicrystals in this system. Reaction schemes, isopleths, and a ternary liquidus diagram were constructed using DTA, XRD, microscopy, and energy dispersive spectroscopy. Results suggest a peak in the liquidus near the predicted compositions of Al{sub 65}Cu{sub 23}Ru{sub 12} or Al{sub 65}Cu{sub 20}Ru{sub 15} in the face-centered icosahedral phase field. Further study is needed to verify the existence of a congruently melting phase. There appears to be composition for which slow-growth methods will produce a single-quasicrystal. Directional solidification studies were done on 65Al25Cu10Ru.
Date: December 6, 1995
Creator: Haines, S.
Partner: UNT Libraries Government Documents Department

Model for the Prediction of the Hydriding Thermodynamics of Pd-Rh-Co Ternary Alloys

Description: A dilute solution model (with respect to the substitutional alloying elements) has been developed, which accurately predicts the hydride formation and decomposition thermodynamics and the storage capacities of dilute ternary Pd-Rh-Co alloys. The effect of varying the rhodium and cobalt compositions on the thermodynamics of hydride formation and decomposition and hydrogen capacity of several palladium-rhodium-cobalt ternary alloys has been investigated using pressure-composition (PC) isotherms. Alloying in the dilute regime (<10 at.%) causes the enthalpy for hydride formation to linearly decrease with increasing alloying content. Cobalt has a stronger effect on the reduction in enthalpy than rhodium for equivalent alloying amounts. Also, cobalt reduces the hydrogen storage capacity with increasing alloying content. The plateau thermodynamics are strongly linked to the lattice parameters of the alloys. A near-linear dependence of the enthalpy of hydride formation on the lattice parameter was observed for both the binary Pd-Rh and Pd-Co alloys, as well as for the ternary Pd-Rh-Co alloys. The Pd-5Rh-3Co (at. %) alloy was found to have similar plateau thermodynamics as a Pd-10Rh alloy, however, this ternary alloy had a diminished hydrogen storage capacity relative to Pd-10Rh.
Date: March 1, 1999
Creator: Teter, D.F. & Thoma, D.J.
Partner: UNT Libraries Government Documents Department

Solid-state sintering of tungsten heavy alloys

Description: Solid-state sintering is a technologically important step in the fabrication of tungsten heavy alloys. This work addresses practical variables affecting the sinterability: powder particle size, powder mixing, and sintering temperature and time. Compositions containing 1 to 10 micrometer ({mu}M) tungsten (W) powders can be fully densified at temperatures near the matrix solidus. Blending with an intensifier bar provided good dispersion of elemental powders and good as-sintered mechanical properties under adequate sintering conditions. Additional ball milling increases powder bulk density which primarily benefits mold and die filling. Although fine, 1 {mu}m W powder blends have high sinterability, higher as-sintered ductilities are reached in shorter sintering times with coarser, 5 {mu}m W powder blends; 10{mu}m W powder blends promise the highest as-sintered ductilities due to their coarse microstructural W.
Date: October 1, 1994
Creator: Gurwell, W.E.
Partner: UNT Libraries Government Documents Department

Photovoltaic Devices Employing Ternary PbSxSe1-x Nanocrystals

Description: We report solar cells based on highly confined nanocrystals of the ternary compound PbSxSe1-x. Crystalline, monodisperse alloyed nanocrystals are obtained using a one-pot, hot injection reaction. Rutherford back scattering and energy filtered transmission electron microscopy suggest that the S and Se anions are uniformly distributed in the alloy nanoparticles. Photovoltaic devices made using ternary nanoparticles are more efficient than either pure PbS or pure PbSe based nanocrystal devices.
Date: February 5, 2009
Creator: Ma, Wanli; Luther, Joseph; Zheng, Haimei; Wu, Yue & Alivisatos, A. Paul
Partner: UNT Libraries Government Documents Department

Annealing-induced property improvements in 2-14-1 powders produced by inert gas atomization

Description: The effects of vacuum annealing on the phase constitution and magnetic properties of various size fractions of 3 alloy compositions produced by Inert-gas atomization (IGA) are examined. Annealing results in the oxidation of properitectic {alpha}-Fe formed during cooling of the melt, producing considerable improvement in the hard magnetic properties of the powders largely via the removal of lower-anisotropy magnetic reversal regions.
Date: April 1, 1996
Creator: Lewis, L.H.; Sellers, C.H. & Panchanathan, V.
Partner: UNT Libraries Government Documents Department

Alloy design and phase stability of the ternary alloy titanium-aluminum-niobium

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The authors have used high-precision electronic-structure and cluster-variational method (CVM) techniques to study aspects of alloy design involving the phase stability and ordering tendencies of the ternary system Ti-Al-Nb, and the correlation with these to changes in the electronic structure of these materials. This system is of great interest for aerospace applications due to its desirable mechanical properties and low densities. Total energies were computed for 18 binary and ternary bcc superstructures in order to derive parameters for CVM calculations, which showed important strong ordering tendencies in the alloy phase diagram as a function of temperature and alloy concentration. Structural optimization calculations were used to analyze structural instabilities for bcc, fcc, hcp, O-phase, and {omega}-phase structures. The authors discovered the mechanism for the role of Nb in the structural stability of the O-phase of the ternary intermetallic Ti{sub 2}AlNb. Calculations were also done to investigate the electronic properties associated with the structural stability of a related class of Laves Phase high-temperature structural materials NbCr{sub 2} and HfV{sub 2}.
Date: December 31, 1998
Creator: Albers, R.C.; Chen, Shao-Ping & Wills, J.M.
Partner: UNT Libraries Government Documents Department

Electron concentration and phase stability in NbCr2-based Laves phase alloys

Description: Phase stability in NbCr{sub 2}-based transition-metal Laves phases was studied, based on the data reported for binary X-Cr, Nb-X, and ternary Nb-Cr-X phase diagrams. It was shown that when the atomic size ratios are kept identical, the average electron concentration factor, e/a, is the dominating factor in controlling the phase stability of NbCr{sub 2}-based transition-metal Laves phases. The e/a ratios for different Laves polytypes were determined as followed: with e/a < 5.76, the C15 structure is stabilized; at an e/a range of 5.88--7.53, the C14 structure is stabilized; with e/a > 7.65, the C15 structure is stabilized again. A further increase in the electron concentration factor (e/a > 8) leads to the disordering of the alloy. The electron concentration effect on the phase stability of Mg-based Laves phases and transition-metal A{sub 3}B intermetallic compounds is also reviewed and compared with the present observations in transition-metal Laves phases. In order to verify the e/a/phase stability relationship experimentally, additions of Cu (with e/a = 11) were selected to replace Cr in the NbCr{sub 2} Laves phase. Experimental results for the ternary Nb-Cr-Cu system are reported and discussed in terms of the correlation between the e/a ratio and phase stability in NbCr{sub 2}-based Laves phases. A new phase was found, which has an average composition of Nb-47Cr-3Cu. Within the solubility limit, the electron concentration and phase stability relationship is obeyed in the Nb-Cr-Cu system.
Date: May 12, 1997
Creator: Zhu, J. H.; Liaw, P. K. & Liu, C. T.
Partner: UNT Libraries Government Documents Department

Welding Metallurgy of Alloy HR-160

Description: The solidification behavior and resultant solidification cracking susceptibility of autogenous gas tungsten arc fusion welds in alloy HR-160 was investigated by Varestraint testing, differential thermal analysis, and various microstructural characterization techniques. The alloy exhibited a liquidus temperature of 1387 {deg}C and initiated solidification by a primary L - {gamma} reaction in which Ni, Si, and Ti segregated to the interdendritic liquid and Co segregated to the {gamma} dendrite cores. Chromium exhibited no preference for segregation to the solid or liquid phase during solidification. Solidification terminated at {approx} 1162 {deg}C by a eutectic-type L - [{gamma}+ (Ni,Co){sub 16}(Ti,Cr){sub 6}Si{sub 7}] reaction. The (Ni,Co){sub 16}(Ti,Cr){sub 6}Si{sub 7} phase is found to be analogous to the G phase which forms in the Ni-Ti-Si and Co-Ti-Si ternary systems, and similarities are found to exist between the solidification behavior of this commercial multicomponent alloy and the simple Ni-Si and Ni-Ti binary systems. Reasonable agreement is obtained between the calculated and measured volume percent of the [{gamma} +(Ni,Co){sub l6}(Ti,Cr){sub 6}Si{sub 7}] eutectic-typr constituent with the Scheil equation using experimentally determined k values for Si and Ti from electron microprobe data. The alloy exhibited a very high susceptibility to solidification cracking in the Varestraint test. This is attributed to a large solidification temperature range of 225 {deg}C and the presence of 2 to 5 vol% solute rich interdendritic liquid which preferentially wets the grain boundaries and interdendritic regions.
Date: May 28, 1999
Creator: DuPont, J.N.; Michael, J.R. & Newbury, B.D.
Partner: UNT Libraries Government Documents Department

On the site preferences of ternary additions to triple defect B2 intermetallic compounds

Description: Knowledge of the site preference of ternary solute additions is essential to developing an understanding of how these solutes affect the properties of B2 intermetallic compounds. A quasichemical model will be presented which is able to predict the site preferences of dilute solute additions to triple defect B2 compounds. The only parameters required are enthalpies of formation at the stoichiometric composition. General equations are developed which can be used to determine site occupations and defect concentrations for dilute as well as non-dilute solute additions. These equations use atom pair bond enthalpies as the parameters. It is found that the site preferences of dilute additions are not always in agreement with predictions based on the solubility lobes in ternary Gibbs isotherms, Predictions for dilute additions to NiAl and FeAl are compared to experimental results found in the literature. Satisfactory correlation is found between the model and the experimental results. In addition, the predictions from the model on vacancy concentrations in Fe doped NiAl are compared to recent experimental results by the authors.
Date: December 31, 1995
Creator: Pike, L.M.; Chen, S.L. & Chang, Y.A.
Partner: UNT Libraries Government Documents Department

First-principles study of intermetallic phase stability in the ternary Ti-Al-Nb alloy system

Description: The stability of bcc-based phases in the Ti-Al-Nb alloy system has been studied from first-principles using a combination of ab-initio total energy and cluster variation method (CVM) calculations. Total energies have been computed for 18 binary and ternary bcc superstructures in order to determine low temperature ordering tendencies. From the results of these calculations a set of effective cluster interaction parameters have been derived. These interaction parameters are required input for CVM computations of alloy thermodynamic properties. The CVM has been used to study the effect of composition on finite-temperature ordering tendencies and site preferences for bcc-based phases. Strong ordering tendencies are observed for binary Nb-Al and Ti-Al bcc phases as well as for ternary alloys with compositions near Ti{sub 2}AlNb. For selected superstructures we have also analyzed structural stabilities with respect to tetragonal distortions which transform the bcc into an fcc lattice. Instabilities with respect to such distortions are found to exist for binary but not ternary bcc compounds.
Date: December 31, 1996
Creator: Asta, M.; Ormeci, A.; Wills, J.M. & Albers, R.C.
Partner: UNT Libraries Government Documents Department

High efficiency, radiation-hard solar cells

Description: The direct gap of the In{sub 1-x}Ga{sub x}N alloy system extends continuously from InN (0.7 eV, in the near IR) to GaN (3.4 eV, in the mid-ultraviolet). This opens the intriguing possibility of using this single ternary alloy system in single or multi-junction (MJ) solar cells of the type used for space-based surveillance satellites. To evaluate the suitability of In{sub 1-x}Ga{sub x}N as a material for space applications, high quality thin films were grown with molecular beam epitaxy and extensive damage testing with electron, proton, and alpha particle radiation was performed. Using the room temperature photoluminescence intensity as a indirect measure of minority carrier lifetime, it is shown that In{sub 1-x}Ga{sub x}N retains its optoelectronic properties at radiation damage doses at least 2 orders of magnitude higher than the damage thresholds of the materials (GaAs and GaInP) currently used in high efficiency MJ cells. This indicates that the In{sub 1-x}Ga{sub x}N is well-suited for the future development of ultra radiation-hard optoelectronics. Critical issues affecting development of solar cells using this material system were addressed. The presence of an electron-rich surface layer in InN and In{sub 1-x}Ga{sub x}N (0 &lt; x &lt; 0.63) was investigated; it was shown that this is a less significant effect at large x. Evidence of p-type activity below the surface in Mg-doped InN was obtained; this is a significant step toward achieving photovoltaic action and, ultimately, a solar cell using this material.
Date: October 22, 2004
Creator: Ager, J. W., III & Walukiewicz, W.
Partner: UNT Libraries Government Documents Department

Competing mechanisms for ordering tendencies in BCC CuAuZn{sub 2} and FCC AuFe alloys

Description: We have briefly discussed the ASRO (atomic short-range order) in AuFe and CuAuZn{sub 2}. General points are that (1) we have implemented a first-principles theory of ASRO in N-component alloys which allows determination of the electronic origins of said ASRO; (2) such calculations can provide much information on the high- and (sometimes) low-temperature alloys; and (3) this approach has identified the origin for the novel special-point ASRO in AuFe. Displacement effects, i.e., non-rigid lattice effects, as well as the other contributions beyond band-energy, are being incorporated into the multicomponent alloy calculations. Such improvements will allow us to investigate other alloys, where charge effects may play a role, to ``design`, for example, higher temperature intermetallics through alloying.
Date: July 1, 1995
Creator: Johnson, D.D.; Althoff, J.D.; Staunton, J.B.; Ling, M.F. & Pinski, F.J.
Partner: UNT Libraries Government Documents Department

The Use of Manganese Substituted Ferrotitanium Alloys for Energy Storage

Description: Experimental results are presented on properties of major practical importance in the utilization of manganese-substituted ferrotitanium alloys as hydrogen storage media. Consideration is given to (1) pressure-composition-temperature characteristics, (2) particle attrition properties, (3) effects of long-term cycling on alloy stability, (4) ease of activation and reactivation, and (5) effects of contaminants on alloy activity. The performance of ternary alloys is compared with that of titanium iron as is the development of an optimum ternary alloy for use with a particular peak shaving operation, i.e., the regenerative H2-Cl system.
Date: December 5, 1977
Creator: Johnson, J.R. & Reilly, J.
Partner: UNT Libraries Government Documents Department

Efficiency Improvement of Nitride-Based Solid State Light Emitting Materials -- CRADA Final Report

Description: The development of In{sub x}Ga{sub 1-x} N/GaN thin film growth by Molecular Beam Epitaxy has opened a new route towards energy efficient solid-state lighting. Blue and green LED's became available that can be used to match the whole color spectrum of visible light with the potential to match the eye response curve. Moreover, the efficiency of such devices largely exceeds that of incandescent light sources (tungsten filaments) and even competes favorably with lighting by fluorescent lamps. It is, however, also seen in Figure 1 that it is essential to improve on the luminous performance of green LED's in order to mimic the eye response curve. This lack of sufficiently efficient green LED's relates to particularities of the In{sub x}Ga{sub 1-x}N materials system. This ternary alloy system is polar and large strain is generated during a lattice mismatched thin film growth because of the significantly different lattice parameters between GaN and InN and common substrates such as sapphire. Moreover, it is challenging to incorporate indium into GaN at typical growth temperatures because a miscibility gap exists that can be modified by strain effects. As a result a large parameter space needs exploration to optimize the growth of In{sub x}Ga{sub 1-x}N and to date it is unclear what the detailed physical processes are that affect device efficiencies. In particular, an inhomogeneous distribution indium in GaN modifies the device performance in an unpredictable manner. As a result technology is pushed forward on a trial and error basis in particular in Asian countries such as Japan and Korea, which dominate the market and it is desirable to strengthen the competitiveness of the US industry. This CRADA was initiated to help Lumileds Lighting/USA boosting the performance of their green LED's. The tasks address the distribution of the indium atoms in the active area of their ...
Date: May 13, 2010
Creator: Kisielowski, Christian & Weber, Eicke
Partner: UNT Libraries Government Documents Department

Assessment of the compositional influences on the toughness of TiCr{sub 2}-base laves phase alloys

Description: Systematic studies of alloys based on TiCr{sub 2} have been performed in order to improve the toughness of Laves phase intermetallics. The extent to which alloy compositions and annealing treatments influence the toughness was quantified by Vickers indentation. The single-phase Laves behavior was first established by studying stoichiometric and nonstoichiometric TiCr{sub 2}. Next, alloying effects were investigated with ternary Laves phases based on TiCr{sub 2}. Different microstructures of two-phase alloys consisting of (Ti,Cr)-bcc+TiCr{sub 2} were also examined. Various toughening theories based on vacancies, site-substitutions, crystal structure (C14, C36, or C15) stabilization, and the presence of a second phase were evaluated. The most effective factors improving the toughness of TiCr{sub 2} were determined, and toughening mechanisms are suggested.
Date: March 1, 1997
Creator: Chen, K.C.; Allen, S.M. & Livingston, J.D.
Partner: UNT Libraries Government Documents Department

Correlating radiation exposure with embrittlement: Comparative studies of electron- and neutron-irradiated pressure vessel alloys

Description: Comparative experiments using high energy (10 MeV) electrons and test reactor neutrons have been undertaken to understand the role that primary damage state has on hardening (embrittlement) induced by irradiation at 300 C. Electrons produce displacement damage primarily by low energy atomic recoils, while fast neutrons produce displacements from considerably higher energy recoils. Comparison of changes resulting from neutron irradiation, in which nascent point defect clusters can form in dense cascades, with electron irradiation, where cascade formation is minimized, can provide insight into the role that the in-cascade point defect clusters have on the mechanisms of embrittlement. Tensile property changes induced by 10 MeV electrons or test reactor neutron irradiations of unalloyed iron and an Fe-O.9 wt.% Cu-1.0 wt.% Mn alloy were examined in the damage range of 9.0 x 10{sup {minus}5} dpa to 1.5 x 10{sup {minus}2} dpa. The results show the ternary alloy experienced substantially greater embrittlement in both the electron and neutron irradiate samples relative to unalloyed iron. Despite their disparate nature of defect production similar embrittlement trends with increasing radiation damage were observed for electrons and neutrons in both the ternary and unalloyed iron.
Date: December 22, 1999
Creator: Alexander, D. E.; Rehn, L. E.; Odette, G. R.; Lucas, G. E.; Klingensmith, D. & Gragg, D.
Partner: UNT Libraries Government Documents Department

Pressure dependence of magnetic order in single crystalline CePtGa{sub 1-x}

Description: The authors present measurements of the susceptibility, the specific heat and the resistivity under hydrostatic pressure on a single crystals of an antiferromagnetically ordered Kondo compound CePtGa{sub 1{minus}x} (T{sub N} = 4.2K). They observe a positive temperature response of T{sub N} on application of hydrostatic pressure up to 1.7 GPa.
Date: October 1, 1997
Creator: Modler, R.; Moshopoulou, E.G. & Hundley, M.F.
Partner: UNT Libraries Government Documents Department

Modeling phase transformations in ternary systems: Ferrite dissolution during continuous cooling

Description: The diffusion-controlled phase dissolution (or growth) in a ternary system of finite length has been modeled numerically using an implicit finite-difference method. The analysis has been applied to study the ferrite to austenite transformation in austenitic stainless steel weldments. The iron-chromium-nickel ternary system was taken as representative of this class of materials. The effect of system geometry was evaluated by considering planar, cylindrical, and spherical geometries. The numerical analysis was extended to the case of continuous cooling, for a range of cooling rates from 0.1 to 100 K/s. The results provide information on how quickly the system deviates from equilibrium during cooling, and what the final compositions and phase fractions are as a function of cooling rate. In most cases, the deviation from equilibrium, in terms of residual ferrite content and composition, increased as the cooling rate increased, as expected. However, under some conditions, it was found that the lowest cooling rates actually deviated further from equilibrium than intermediate cooling rates. This curious phenomenon was investigated in detail and was explained in terms of the indirect path toward final. Such indirect equilibration is often found during and typical of diffusion-controlled transformation behavior in multi-component systems.
Date: July 1, 1995
Creator: Vitek, J.M. & Vitek, S.A.
Partner: UNT Libraries Government Documents Department

Phase stability in Be-Nb and Be-Nb-Zr intermetallics

Description: Sputter deposition of Be-Nb alloys at low temperature (30{degrees}C) produces an amorphous phase for compositions >5 at.% Nb. A metastable crystalline phase which can be considered a highly faulted form of the Be{sub 12}Nb occurs at higher deposition temperatures or by low-temperature annealing of the amorphous phase. Because of structural similarities, this metastable phase is a precursor to the formation of either Be{sub 12}Nb or Be{sub 17}Nb{sub 2} upon high temperature annealing. There was no evidence of the Be{sub 5}Nb phase which has been postulated on some phase diagrams. The Be{sub 12}Nb phase can accomodate considerable Zr in the structure and the Be{sub 13}Zr can accomodate Nb into its structure. The Be{sub 13}Zr becomes the predominant phase when the Zr/Nb composition ratio > 1. High temperature annealing of the ternary results in dual-phase regions of Be{sub 12}(Nb,Zr) + Be{sub 17}(NbZr){sub 2} or Be{sub 13}(Zr,Nb) + Be{sub 17}(Zr,Nb){sub 2}, but the coexistence of Be{sub 12}(Nb,Zr) + Be{sub 13}(Zr,Nb) has not been observed. 10 refs., 5 figs.
Date: September 1, 1991
Creator: Brimhall, J.L.; Charlot, L.A. & Bruemmer, S.M.
Partner: UNT Libraries Government Documents Department