bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fabrication and Properties of Granular Fe-Ni Alloys
Authors: Gavrin A. , Chien C. L. 
Published: March 2011

ABSTRACTGranular alloys of the form (Fe50Ni50)x(Al2O3)1−x, where x is the volume percent, have been produced by sputtering from a single composite target. The microstructure has been verified by X-ray diffraction and by transmission electron microscopy (TEM). The grains are single phase FeNi alloys with the fcc structure and range in size from 15 Å to 50 Å. Superparamagnetism has been observed, and the coercivity has been found to decrease with increasing grain size. The results are compared to previous work on granular Fex(SiO2)1−x.
Study of the Lattice Dynamics of Iron Nanocrystals by Mossbauer Spectroscopy
Authors: Childress J. , Levy A. , Chien C. L. 
Published: March 2011

ABSTRACTThe vibrational properties of iron particles with nanometer sizes in Fe-SiO2 and Fe-A12O3 granular materials are studied by Mössbauer spectroscopy. The spectra include contributions from metallic Fe atoms at the core of the particles and apparently from surface and oxidized Fe atoms, which are analyzed separately. The temperature dependences of the recoilless fractions are analyzed using the Debye model. The Mossbauer Debye temperature ΘM for metallic Fe is found to decrease dramatically with smaller grain sizes, indicative of a “softening” of the phonon spectrum.
Coercivity in Granular Fe - Al2O3
Authors: Streitz F. H. , Chien C. L. 
Published: March 2011

ABSTRACTWe present the results of a comparison between the magnetic properties of granular Fe–Al2O3 and Fe–SiO2. Granular Fe-SiO2 was found earlier to display an anomalous increase in coercivity which appears to scale with the Fe grain size. The Fe-Al2O3 samples were prepared under similar conditions and their magnetic properties determined. The coercivity in granular Fe-Al2O3 is also seen to increase with increasing grain size, showing that the effect is not unique to the Fe-SiO2 system. A major difference between granular Fe–Al2O3 and Fe–SiO2 is the size of the Fe grains, which are smaller in Al2O3.
Microstructure and Magnetic Behavior of Fe/Ti Multilayered Films
Authors: Ono Satoshi , Nitta Michio , Naoe Masahiko 
Published: March 2011

ABSTRACTFe/Ti multilayered films composed of Fe and Ti layers with various thickness ( dFe of 10 ∼ 1000 A and dTi of 10 ∼ 200 A ) have been prepared at Ar gas pressure of 2 mTorr by two pairs of Facing Targets Sputtering apparatus which can deposit very thin and continuous films on plasma-free substrates. The total thickness of Fe layers was 1000 A in all of the specimen films.The periodic microstructure due to compositional modulation was clearly observed not only in the low angle region of X-ray diffraction diagrams but also in the Auger electron spectroscopic depth profile.With decreasing dFe from 1000 to 20 A, the diffraction intensity of (110) plane in the Fe bcc phase lowered for dTi of 10∼200 A and its interplanar spacing ( d-spacing ) increased for dTi above 50A. This diffraction peak disappeared with further decreasing d below 15 A. At dFe around 25 A, a different peak appeared at the angle slightly lower than that of Fe(110) peak. The diffraction intensity of (002) plane in the Ti hcp phase increased with decreasing dFe. However, its d-spacing depended little on the dFe and took the same value as that of bulk Ti except for very small dTi.The net saturation magnetization of Fe layers in all of the specimen films decreased gradually with decreasing dFe from 1000 to 50 A, decreased abruptly with further decreasing dFe and became nearly zero at dFe below 15A.The films annealed at 200 and 400 °C showed obscure periodic microstructure and had larger d-spacing of ∝ −Fe(110) and smaller saturation magnetization than those of the as-deposited ones.
X-Ray Diffraction analysis of Au/Ni Multilayers
Authors: Chaudhuri J. , Shah S. , Jankowski A. F. 
Published: March 2011

ABSTRACTX-ray diffraction is a useful method to measure the microscopic strain profile in multilayered materials. Depth profiles of strain in the modulation direction are obtained by an iterative fitting of the experimental diffraction pattern with a kinematic model. This approach was used to characterize the coherency strain profile in Au/Ni superlattices.The accommodation of coherency strain through the superlattice is dependent upon the atomic misfit between the component materials and the thickness of each layer. The depth profile of strain was determined for multilayers with repeat periodicities of 2.92 nm and 4.26 nm. A significant volume fraction of interfaces is present in these nanometric dimensioned laminates.
Microstructure of Nanocrystalline Ceramics
Authors: Hahn H. , Logas J. , Höfler H. J. , Bier Th. , Averback R. S. 
Published: March 2011

ABSTRACTThe microstructure of nanocrystalline (n-) TiO2 was studied as a function of sintering temperature up to 1273 K. Grain growth was monitored using x-ray diffraction and scanning electron microscopy. Measurements of density and permeability of He and Ar were also conducted. The specific surface area and the total pore volume were determined quantitatively using the nitrogen adsorption method. These measurements revealed that highly compacted n-TiO2 had green body densities as high as 75 % of bulk density and that sintering occurred at much lower temperatures than in conventional powder. Densification proceeded by loss of the small pores first. The possibilities of achieving high densities with limited grain growth will be discussed.
Chemical Vapor Deposition of Ultrafine Ceramic Structures
Authors: Gallois B. M. , Mathur R. , Lee S. R. , Yoo J. Y. 
Published: March 2011

ABSTRACTUltrafine ceramic structures based on the nitrides and carbides of titanium and silicon have been synthesized in a computer-controlled hot-wall CVD reactor. Layered deposits have been produced by pulsing the reactant gases judiciously under software control. The development of a columnar structure which is endemic to most CVD materials has been suppressed. Skeletal structures of filaments have also been grown with appropriate catalysts by the vapor-liquid-solid mechanism and immediately infiltrated in situ with different materials to produce filament-reinforced composite coatings.Ultrafine-grained carbon films and filaments have been grown from methane-hydrogen mixtures by RF plasma-assisted CVD. The microstructural features of these materials are of the order of 20 to 100 nm. The subgrain structure determined by Raman spectroscopy varies from 2 to 3 nm.
Cryomilling of Nano-Phase Dispersion Strengthened Aluminum
Authors: Luton M. J. , Jayanth C. S. , Disko M. M. , Matras S. , Vallone J. 
Published: March 2011

ABSTRACTIn recent years considerable effort has been expended on the development of dispersion strengthened alloys by mechanical alloying. Our research has shown that considerable improvement in microstructure control and properties can be gained by carrying out milling at cryogenic temperatures. We have found that aluminum and dilute aluminum alloys can be dispersion strengthened with aluminum oxy-nitride particles by the use of a slurry milling technique where the fluid medium is liquid nitrogen. The alloyed powders produced by this technique are strengthened by aluminum oxy-nitride particles which are typically 2–10 nm in diameter and with a mean spacing of 50–100 nm. The dispersoids are generated during the milling process by adsorption and reaction with components of the liquid nitrogen bath. On thermal treatment prior to consolidation, the alloyed powders recrystallize to a grain size which is typically in the range 0.05 to 0.3 μm. The alloys exhibit a yield stress in excess of 325 MPa at room temperature and a virtually temperature independent yield stress of about 130 MPa at temperatures greater than 375° C. The paper describes the preparation of dispersion strengthened aluminum by cryomilling, the characteristics of the microstructure and discusses some aspects of the mechanical properties.
Statics and Dynamics of Grain Boundaries in Ni3Al
Authors: Farkas Diana 
Published: March 2011

ABSTRACTVarious modeling techniques have been used to study the structure of grain boundaries in ordered compounds, particularly Ni3Al. The techniques include computer simulation, group theoretical analysis and the cluster variation method for high temperature effects. A multiplicity of possible grain boundary structures was analyzed for different misorientations and grain boundary plane location. 1The influence of several alloy properties like atomic size differences and deviation from stochiometry on the occurrence of these different structures is analyzed. The implications of these results for grain boundary misorientation distribution, grain boundary plane location and faceting behavior are discussed and compared to experimental findings. The possibility of orderdisorder transitions in the grain boundary region is also discussed.
The Microchemistry of Grain Boundaries in Ni3Al
Authors: Sieloff D. N. , Brenner S. S. , Ming-Jian Hua 
Published: March 2011

ABSTRACTGrain boundary regions in B-doped as well as B-free Ni3AI were studied by field-ion microscopy and atom probe microanalysis. In the ductile, recrystallized, Ni-rich alloys the segregation of boron was often accompanied by an enrichment of nickel. Such an enrichment was not observed at boundaries in B-free alloys. Boron was also observed to segregate to the boundaries in a 25.2A1 - IB alloy which was reported to contain boron clusters. Such clusters were not observed, instead a high concentration of boron pairs were found.
On Microstrucitural Evolution in Gas Atomized Ti-50 at.% Al-2 at.% Nb Powder
Authors: Shih Donald S. , Scarr Gary K. , Chesnutt James C. 
Published: March 2011

ABSTRACTMicrostructural development in helium gas atomized Ti-50A1-2Nb (at.%) powder has been characterized using x-ray diffractometry and transmission electron microscopy. The structure of the as-atomized powder was a mixture of two phases: an ordered fct (L10)γ TiAl phase and an hcp α Ti phase containing fine (≈ 10–20 nm) D019 α2 domains. Large powder (≈ 250 μm) contained ≈ 14 volume % hcp phase, while fine powder (≈37 μm) contained ≈ 72 volume % hcp phase. However, this α+α2 constituent was metastable and transformed to the γ phase during annealing.
Slip System Modification in NiAl
Authors: Miracle D. B. , Russell S. , Law C. C. 
Published: March 2011

ABSTRACTAn effort to modify the slip vector in the B2 compound NiAl was undertaken to overcome the brittle failure associated with the <100> slip vector which typically operates in this compound. Alloying additions were made to reduce the ordering energy of NiAl, and hence to promote <111> slip. Preliminary indications showed that Cr and Mn were effective in producing <111> slip in polycrystalline NiAl tested at room temperature. Two-surface slip trace analyses and TEM g·b analyses performed on aligned crystals of NiAl showed that <111> dislocations operate on either { 110} or {112} slip planes. However, the slip vector at 660°C was seen to revert to <100>, which operates on both {100} and {110} planes.
Stacking Sequence Changes in A3B-Type Close-Packed Structures: a One-Dimensional Stacking Model
Authors: Pei Shiyou , Massalski T. B. 
Published: March 2011

ABSTRACTStructural modifications resulting from changes in the sequence of stacking of close-packed layers are very common in A3B-type transition-metal alloys. In the present work, a one-dimensional model of stacking has been explored. We found that the stacking changes observed in these alloys can be interpreted in terms of interactions between a few adjacent layers.
Deformation and Defects in Laves Phases
Authors: Livingston J. D. , Hall E. L. , Koch E. F. 
Published: March 2011

ABSTRACTPrototype Laves Phases MgCu2 and MgZn2 have been deformed in compression at various temperatures and strain rates, and dislocations produced by deformation have been characterized by TEM. Ternary cubic Laves phases Mg(Cu,M)2, where M-Al, Ni, Si, and Zn, have also been deformed, and substantial solution hardening was observed
Ab Initio Calculations of Ordered Intermetallic Phase Equilibria
Authors: Sluiter M. , Fontaine D. De , Guo X. Q. , Podloucky R. , Freeman A. J. 
Published: March 2011

ABSTRACTGeneral procedures for computing alloy phase equilibria from ab initio electronic structure calculations are reviewed and applied to the Al-Li phase diagram. Free energies were calculated by the cluster variationm.method (CVM) in the tetrahedron approximation for the fcc and bcc lattices and ordered superstructures. Input was provided by first principles FLAPW calculations. The computed phase diagram for both stable and metastable structures agrees remarkably well with the experimental one.
Microstructure and Elevated Temperature Flow Properties of Rapidly Solidified TiAl-Base Alloys
Authors: Graves J. A. , Ghosh A. K. 
Published: March 2011

ABSTRACTRapid solidification processing (RSP) of TiAl-base alloys often results in the formation of metastable crystalline products (e.g., Ti3Al) A key parameter controlling both the solidification pathway and the stability of the metastable structure is alloy chemistry. This study focuses upon the influence of minor alloy additions on the microstructure and properties of Ti52Al48 alloys produced by RSP. While alloys having minor Ta addi ions (<1 at.%) maintain near-equilibrium solidification structures similar to the binary alloy, the addition of Cr at a level of 5 at.% results in a nearly 100 vol.% metastable Ti3Al structure containing a fine dispersion of TiCr2 grain boundary precipitates. These precipitates limit grain growth during elevated temperature exposure, maintaining the fine (TiAl) grain size created during decomposition of the metastable product structure. Mechanical property evaluation of the consolidated RSP material indicates a greatly reduced flow stress for the fine grained Cr modified alloys. A preliminary analysis attributes this to the reduction in grain size and enhanced elevated temperature diffusion rates for the Cr containing TiAl-base alloys.
On the Macroscopic Flow Behavior of the Phases Present in Ti-24Al-llNb
Authors: Giths S. J. , Koss D. A. 
Published: March 2011

ABSTRACTThe deformation behavior of two alloys whose compositions (Ti-25Al-9Nb and Ti-11Al-23Nb in at.%) correspond to alpha-two and beta phases in the Ti-24Al-11Nb alloy has been investigated. Results from both compression and tensile tests over a range of temperatures from 27° to 650°C indicate that the yield stress as well as the strain and strain-rate hardening characteristics of the Ti-24-11 alloy are controlled by the Ti3Al-base alpha-two phase. In contrast to the Alpha-two alloy, the Beta alloy has a flow stress which is very sensitive to temperature and strain rate at 650°C, suggesting the onset of high temperature creep processes.
Mechanical Alloying Behavior in the Nb-Si, Ta-Si, and Nb-Ta-Si Systems
Authors: Kumar K. S. , Mannan S. K. 
Published: March 2011

ABSTRACTThe mechanical alloying behavior of elemental powders in the Nb-Si, Ta-Si, and Nb-Ta-Si systems was examined via X-ray diffraction. The line compounds NbSi2 and TaSi2 form as crystalline compounds rather than amorphous products, but Nb5Si3 and Ta5Si3, although chemically analogous, respond very differently to mechanical milling. The Ta5Si3 composition goes directly from elemental powders to an amorphous product, whereas Nb5Si3 forms as a crystalline compound. The Nb5Si3 compound consists of both the tetragonal room-temperature α phase (c/a = 1.8) and the tetragonal high-temperature β phase (c/a = 0.5). Substituting increasing amounts of Ta for Nb in Nb5Si3 initially stabilizes the α-Nb5Si3 structure preferentially, and subsequently inhibits the formation of a crystalline compound.
Pressure Casting of Ni3Al/Al2O3 Composites
Authors: Nourbakhsh Said , Liang Fei-Lin , Margolin Harold 
Published: March 2011

ABSTRACTA series of Du Pont PRD-166 and FP fiber reinforced Ni and nickel aluminide matrix composites, containing Ti or Y as a wetting agent, were produced by pressure casting. Modulus values determined under compression varied from 273 to 287 GPa in a direction parallel to the fibers and ranged from 148 to 159 in a direction normal to the fibers. Modulus values parallel to the fiber direction were approximately 5% lower than that predicted by the rule-of-mixtures. The much lower values of modulus normal to the fibers has been attributed to a number of sources which include fiber/matrix and fiber/fiber debonding and stress concentration resulting from voids existing at fiber/fiber bonds. It was observed, qualitatively, that good bonding between matrix and fiber occurred when Ti diffused from the matrix into fibers. The presence of Al in the matrix tended to inhibit Ti diffusion, increasingly as Al content increased. Thus fiber/matrix bond strength was poorer in the aluminides than in an alloy containing no Al. Y was not found to improve bonding, and an interface reaction zone was obserced in some areas where liquid metal initially entered the fiber preform.
Deformation Behavior of NiAl-Based Alloys Containing Iron, Cobalt, and Hafnium
Authors: Pank D. R. , Nathal M. V. , Koss D. A. 
Published: March 2011

ABSTRACTThe effects of alloying additions on the mechanical properties of the B2 intermetallic NiAl have been investigated in both the melt-spun ribbon and consolidated, bulk form. The study is based on a matrix of NiAl-based alloys with up to 20 a/o Co and Fe additions and with reduced Al levels in the range of 30 – 40 a/o. Characterization of the melt-spun ribbon by optical and scanning electron microscopy indicates a range of microstructures: single phase β γ, necklace phase surrounding either martensitic or β grains, and a mixture of equiaxed martensitic and γ grains. Bend ductility is present in melt-spun and annealed ribbons exhibiting the γ necklace structure and in a single phase β material containing 20 a/o Fe.The analysis of compressive flow behavior on consolidated, bulk specimens indicates that the single phase γ alloys exhibit a continuous decrease in yield stress with increasing temperature and profuse microcracking at grain boundaries. In contrast, multiphase (γ + either martensite or β) alloys tend to display a peak in flow stress between 600 and 800K with little or no signs of microcracking. In general, heat treatments which convert the martensitic grains to β + γ result in improved strength at temperatures above 600K and better resistance to crack initiation. These results are discussed in terms of the effects of β, martensite and γ on the yield stress and flow behavior of NiAl-based alloys.
Fabrication and Mechanical Properties of Ni3Al-Al2O3 Composites
Authors: McKamey C. G. , Povirk G. L. , Horton J. A. , Tiegs T. N. , Ohriner E. K. 
Published: March 2011

ABSTRACTThe objective of this study is to develop a metal-matrix composite based on the intermetallic alloy Ni3Al reinforced with Al2O3 fibers, with improved high-temperature strength and lower density compared to the matrix material. This paper summarizes results of initial fabrication and mechanical tests on specimens produced using IC-15 [Ni-24% Al-0.24% B (at.%)] and IC-218 [Ni-16.5% Al-8% Cr-0.4% Zr-0.1% B (at.%)], with 20 vol. % Al2O3 fibers. Fabrication methods include both hot-pressing and hot-extrusion. Mechanical tests include four-point bending and tensile tests. The integrity of the fiber-matrix interface was studied and correlated with mechanical properties. Tensile ductilities of approximately 10% at room temperature were achieved for Ni3Al/Al2O3 composites with controlled material processing and interfacial structure. Fabrication of composites by hot-extrusion produced better tensile properties at room temperature, but superplastic behavior (i.e., low strengths, high ductilities) at 1000°C.
1200 to 1400 K Slow Strain Rate Compressive Properties of NiAl/Ni2AlTi-Base Materials
Authors: Whittenberger J. Daniel , Viswanadham R. K. , Mannan S. K. , Kumar K. S. 
Published: March 2011

ABSTRACTOwing to their superior strength in comparison to other single phase intermetallics, NiAl-Ni2AlTi alloys have potential for the matrix material in high temperature composites. An investigation of two compositions, Ni-40Al-10Ti and Ni-45Al-5Ti with and without 20 vol. pct. TiB2 in the form of −1μm diameter particles, was initiated with materials produced by the Martin Marietta XDTM process and compacted by hot pressing. The as fabricated materials were fully dense and polycrystalline where the grain sizes measured −8μm for Ti-poor and about 15μm for the Ti-rich unreinforced materials but could not be determined for ei her TiB2-containing composite. Elevated temperature compression testing was conducted to approximately 8 percent deformation between 1200 and 1400 K with strain rates varying from −10−4 to −10−7 s−1. While the majority of the tests exhibited diffuse yielding over approximately one percent strain followed by negative strain hardening, a few experiments resulted in steady state behavior where deformation continued under a constant stress. The flow strengths on yielding of both forms of Ni-40Al-1OTi were higher than those for the Ni-45Al-5Ti versions. Although for each matrix composition the addition of 20 vol. pct. TiB2 decreased the strength at the higher strain rates in comparison to the TiB2-free forms, the particles do provide reinforcement during slow deformation conditions. Optical microscopy of tested specimens revealed that these materials are generally quite brittle as numerous longitudinal and transverse cracks were found irrespective of the type of stress-strain behavior.
Continuous Ordering Reactions in NiAl/Ni2, AlTi Dual Phase Alloys
Authors: Tso N. C. , Sanchez J. M. 
Published: March 2011

ABSTRACTThe Cluster Variation Method is used to study metastable phase equilibrium and possible ordering reactions in the Ni2AlTi⇆;NiAl dual phase alloy system. The Cluster Variation Method was also used to model the corresponding binary alloys and the results were extrapolated to the ternary system. The occurrence of a continuous ordering reaction in the Ni-Al-Ti system is proposed and possible decomposition reactions are discussed.
The Effect of Boron on the Microstructure of Ni2 AITi.
Authors: Schuon S. R. , Rehzets V. 
Published: March 2011

ABSTRACTIngots with a nominal composition of Ni–34a/o Al–15a/o Ti + O.Ow/o B, 0.05w/o B, 0.1w/o B or 0.3w/o B were prepared and compression tested at a strain rate of 1.7 x 10–7/s at room temperature, 650°C, 870°C, and 1000°C in air. Alloys were single-phase Ni2 AITi and borides were contained in all compositions containing boron. The compressive yield strength and the ultimate compressive strength of NA2AITi containing boron is strongly affected by the type and distribution of borides. The formation of TiB2 at 0.3w/o B increased the strength at room teperature, 650°C, 870°C, ang 1000°C, while formation of a TiB-Ni2 AITi eutectic at 0.05w/o and 0.lw/o B decreased strength at all temperatures. Crack deflection by TiB2 is an important strengthening mechanism at room temperature and 650°C. However, at 1000°C, dispersion strengthening may be an important strengthening factor.
The Alloying of Titanium Aluminides with Carbon
Authors: Cam G. , Flower H. M. , West D. R. F. 
Published: March 2011

ABSTRACTAn investigation has been made on the constitution of the Ti-Al-C system in the range of 15–55 at% Al and of 0.1–1.0 at% C and the temperature range of 1250–450 °C. Equilibria including three compounds TiC, Ti3AlC, and Ti2AlC have been studied and transmission electron microscopy (t.e.m.) observations of ordering reactions in az have been made.
The Effect of Microalloying B on the High Temperature Mechanical Properties of Ti3Al
Authors: Newkirk Joseph W. , Feldewerth Gerald B. 
Published: March 2011

ABSTRACTThe effect of adding boron to Ti3Al on the microstructure and high temperature tensile properties has been studied. Boron caused a large grain refinement that dominated the tensile properties at all temperatures. Particles of Ti2B were found in all of the boron containing alloys. TiB was found only at concentrations of 0.1% B or more.