bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and Optical Properties of Amorphous Si1-xSnx: H Structures
Authors: Girginoudi D. , Thanailakis A. , Christou A.
Published: March 2011

Amorphous hydrogenated silicon-tin films (α — Six Snx:H) have been prepared by co-electron beam and Knudsen cell deposition. It is shown that the dependence of Eg on x, over the entire range of 0 < x < 0.51 studied, cannot be described by a single linear relationship. The d.c. conductivity measurements indicate two distinct conduction regions as a function of x. The addition of Sn up to x = 0.10 creates a high density of dangling bonds and moves the band edges so a significant conductivity increase is observed. The bonding between Si and H is preferred to Sn and H. Sn-H bonds were observed only for x > 0.40. Photoluminescence measurements show that band edge luminescence dominates at 1.3–1.4 eV.
Structural Characterization of MBE Grown (001) CdTe Films by Means of Transmission Electron Microscopy, Low Temperature Photoluminescence and Double Crystal Rocking Curves.
Authors: Burke M. G. , Choyke W. J. , Doyle N. J. , Feng Z. C. , Hanes M. H. , Mascarenhas A.
Published: March 2011

The effects of chemical etching, mechanical thinning, and ion milling on the low temperature photoluminescence spectra of MBE grown (001) CdTe films are reported. Line defects observed by TEM are correlated with photoluminescence. It is shown that X-ray D.C.R.C, measurements in these films are weighted averages over the whole thickness of the films and therefore weakly reflect the structural perfection of the samples near the surface as deduced by photoluminescence.
Exchange of Bonded Hydrogen in Amorphous Silicon by Deuterium
Authors: Abeles B. , Yang L. , Leta D. P. , Majkrzak C.
Published: March 2011

We show that bonded hydrogen in a-Si:H is readily exchanged by atomic deuterium when exposed to a deuterium plasma discharge. The effective diffusion coefficient for the D.H exchange, 10∼14 cnr/sec at 160°C, is comparable to that of interstitial hydrogen in c-Si.
Structure and Magnetic Properties of Fe/Cu Multilayered Thin Film
Authors: Fukizawa A. , Naoe M.
Published: March 2011

Fe/Cu multilayered films prepared by means of Facing Targets Sputtering have distinct multilayered structure at layer thicknesses above 7Å. The saturation magnetization of Fe in the multilayered film takes almost the bulk thicknesses Fe value above this thickness. However, multilayerd structures did not clearly form at layer thicknesses below 7Å and the saturation magnetization decreased to about half of the bulk value. Considerable variation of confirmed layer thickness, saturation magnetization and coercivity in the multilayerd films were obtained when the total thickness was below 1000Å.
Core and Valence Levels in Hydrogemated Amorphous Silicon
Authors: Burnhara N. A. , Fisher R. F. , Asher S. E. , Kazmerski L. L. , Lucovsky G. , Parsons G. N.
Published: March 2011

Silicon core and valence levels were studied in hydrogenated amorphous silicon (a-Si:H) as a function of hydrogen concentration. The techniques used to establish the core levels were X-ray Photoelectron Spectroscopy and core-level Electron Energy Loss Spectroscopy. Changes in the local densities of states of the silicon 3s and 3p levels were examined with Auger Electron Spectroscopy. The a-Si:H samples were grown by RF sputtering. Their hydrogen concentrations varied from zero to nearly fifteen percent.
Multilayer Fe/Cu Films
Authors: Liou S. H. , Xiao Gang , Chien C. L. , Unruh K. M.
Published: March 2011

Multilayer films consisting of alternating Fe and Cu thin films have been made by a twin-gun sputtering device with a rotating substrate platform. Both proportional modulated films and films with a fixed Cu layer have been fabricated, where the Fe layer has been varied between 10 and 150 Å. These films have been studied by x-ray diffraction, Mö;ssbauer spectroscopy and SQUID magnetometry. Thin Fe layers with thicknesses less than 25 Å, exist only as fee α-Fe. Thicker Fe layers contain both bec and fee Fe. The interface between Fe and Cu appears very sharp with no evidence of Fe-Cu alloys. The α-Fe state orders magnetically below 100 K with a small magnetic moment.
Electron Localization and the Aharonov-Bohm Effect in Two-Dimensional Metal Systems
Authors: Van Haesendonck C. , Bruynseraede Y.
Published: March 2011

During the last few years, it became clear that electron interference phenomena strongly modify the conductance of disordered systems. In thin metal films, this interference produces an anomalous low temperature magneto-resistance which enables to obtain detailed information about the inelastic, spin-orbit and magnetic scattering mechanisms. In a multiply-connected geometry, the interference leads to magnetoresistance oscillations. In long metal cylinders, only the oscillations which are not destroyed by impurity averaging, can be observed (flux period h/2e). In single loops, the original Aharonov-Bohm oscillations with flux period h/e are also present. A review will be presented of recent experimental results obtained for quasi two-dimensional plane films, cylinders, rings and arrays.
Infrared Ellipsometry Study of Oriented Langmuir-Blodgett Monolayers
Authors: Benferhat R. , Drevillon B. , Robin P.
Published: March 2011

The first experimental investigation of the vibrational properties of 1–19 raonolayers of behenic acid deposited on various substrates using a new IR technique : Spectroscopie Phase Modulated Ellipsometry (SPME) is presented. The influence of the cleaning procedure of the substrate is discussed. The preferential tilting direction of the aliphatic chain along the withdrawal direction is confirmed. High sensitivity makes SPME a useful tool to study the structure of more complex organic molecules.
Electrical Transport and In-Situ X-Ray Studies of the Formation of TiSi2 Thin Films on Si
Authors: Hensel J. C. , Vandenberg J. M. , Mattheiss L. F. , Unterwald F. C. , Maury A.
Published: March 2011

The formation of TiSi2 thin films on Si has been investigated by in situ x-ray diffraction and by electrical transport. The x-ray results show unequivocally that the staging proceeds through two orthorhombic polytypes of TiSi2 according to the sequence: sputter-deposited metallic Ti films on Si (001) → TiSi2 (C49 structure) → TiSi2 (C54 structure), with no evidence of lower suicides. Electrical transport shows metallic behavior for all phases and distinctive features in the annealing curves which correlate with the structural transformations. Most importantly, the resistivity, characteristically very high for the C49 phase, undergoes a precipitous drop at the C49 → C54 transition. Total energies for both phases are calculated and, consistent with the occurrence of a structural phase transformation, are found not to differ appreciably.
The Effect of Temperature and Si Concentration on the Mixing of AlAs/GaAs Superlattices
Authors: Mei Ping , Yoon H. W. , Venkatesan T. , Schwarz S. A. , Harbison J. P.
Published: March 2011

The intermixing of AlAs/GaAs superlattices has been investigated as a function of Si concentration following anneals in the range of 500 to 900 C. The superlattice samples were grown by molecular beam epitaxy(MBE) and the near surface layers were doped with silicon at concentrations of 2×10 to 5×1018 cm-3. Si and Al depth profiles were measured with secondary ion mass spectrometry (SIMS).The diffusion length and activation energy of Al as a function of silicon dopant concentration are derived from the SIMS data. In the temperature range studied an activation energy for the Al interdiffusion of -4eV is observed with the diffusion coefficients increasing rapidly with Si concentration.
Comparative Thickness Measurements of Heterojunction Layers by Ellipsometric, RBS, and XTEM Analysis
Authors: Woollam J. A. , Snyder P. G. , McCOrmick A. W. , Rai A. K. , Ingram D. C. , Pronko P. P. , Geddes J. J.
Published: March 2011

Variable Angle of incidence Spectroscopie Ellipsometry (VASE), Rutherford Backscattering (RBS) and Cross-sectional Transmission Electron Microscopy (XTEM), are used to measure heterojunction layer thicknesses in an AlGaAs/GaAs sample. All three techniques yield the same thickness values within error limits.
Variable Angle of Incidence Spectroscopic Ellipsometric Measurement of the Franz-Keloysh Effect in Modfet Structures
Authors: Snyder P. G. , Oh J. E. , Woollam J. A.
Published: March 2011

It has been shown recently that variable angle of incidence spectroscopie ellipsometry (VASE) is a sensitive technique for determining semiconductor multilayer model parameters, e.g. layer thicknesses and ternary compositions. In this paper we show that VASE is, in addition, sensitive to the Franz-Keldysh effect induced by band bending in the barrier layer of a GaAs-AlGaAs-GaAs (MODFET) structure. VASE measurements differ from electro-reflectance and photoreflectance, in that the internal heterojunction region electric field is directly probed, without the application of a modulating field. The Franz-Keldysh effect appears in the VASE spectra near the AlGaAs bandgap energy. Data for two samples, with different doping profiles, are quantitatively modeled to determine the internal electric field amplitudes.
Surface Structure Investigation of Epitaxial Nickel Silicides on Si(001)
Authors: Huang Judy H. , Stanley Williams R.
Published: March 2011

Low Energy Ion Scattering (LEIS) techniques have been used to examine epitaxial NiS2 films grown on the (001) surface of Si. The experimental results support a model of a NiSi2(001) surface that is a bulk-like but relaxed (001) Si plane with a 25%-30% concentration of vacancies. The 1/3-, 1/4-, and 1/5-order LEED spots observed for these surfaces may be the result of ordering of the vacancies, such that there are domains in which every 3rd, 4th, or 5th [110]-type atomic rows are missing in the Si terminated (001) plane.
TEM Investigation of Epitaxial Growth of Semiconductor Superlattices on Structured Substrates
Authors: Hwang D. M. , Kapon E. , Tamargo M. C. , Bhat R.
Published: March 2011

In exploring new techniques to produce controllable lateral variations in the physical properties of semiconductor superiattices, substrates containing etched patterns were used for epitaxial crystal growth. High resolution TEM was used for the first time to study this kind of structures. It was found that the resultant superlattices exhibit wavy or zigzag layers which register the history of the topographic evolution of the crystal surfaces during growth and reveal useful information on the fundamental mechanism of the epitaxial process.

Alternate layers of Al0.3Ga0.7As and GaAs were grown by MBE and OMCVD on (100) GaAs substrates patterned with grooves and mesas along the [011] and [011] directions. The morphology of the superlattices grown on the grooves and mesas was analyzed with TEM cross-sectional imaging. It was found that the evolution of non-planar crystal surfaces depends not only on the source flux and surface affinity, but also on the lateral diffusion of the adsorbed atoms or molecules on the crystal surfaces. Several growth features at the intersections of adjacent facets are illustrated in this work. Implications on the epitaxial process are discussed.
Electrical and Optical Properties of GaAs Heteroepitaxial Films on Si Substrates
Authors: Nishioka Takashi , Itoh Yoshio , Yamaguchi Masafumi
Published: March 2011

Electrical and optical properties of single-domain GaAs heteroepitaxial films grown on Si(100) by using metalorganic chemical vapor deposition have been investigated. Cathodolumi-nescence and electron-beam induced current experiments have revealed that signal nonuniformities on the film surface agree in number with GaAs microdefect densities observed through chemical etching, rather than conventional aligned etch-pit densities. The cathodoluminescence experiments also indicate that GaAs properties are improved with increases in film thickness. This nonuniformity and the film-thickness dependence are related to GaAs solar cell characteristics fabricated on the Si substrate. A GaAs/Si interface study proves that p-type Si substrates cause type conversions near the interface due to GaAs growth. Evidence of positive interface charges in the GaAs/Si system is determined by using Hall effect measurements, secondary-ion mass spectroscopy and electron-beam induced current experiments.
Crack Propagation in MG-PSZ
Authors: Readey M. J. , Heuer A. H. , Steinbrech R. W.
Published: March 2011

Certain coarse-grained Mg-PSZ's exhibit marked R-curve behavior, e.g., the crack resistance increases from ∼5 to ∼15 MPam1/2 with the first 500 microns of crack extension. These high toughness materials also show unusually-good flaw tolerance.

Crack propagation and crack path development in Mg-PSZ were investigated during stable crack growth using a modified DCB specimen geometry. Crack extension was monitored with a traveling microscope equipped with a video recording system. PSZ's with various heat-treatments were tested to determine the effect of microstructure on R-curve behavior.

Cracks were found to propagate discontinuously and to arrest. Smaller microcracks would develop around the arrested crack, and link together to form the macrocrack which led to eventual failure.
Mechanical Properties and Thermal Stability of Yttria-Doped Tetragonal Zirconia Polycrystals with Diffused Ceria in the Surface
Authors: Sato T. , Ohtaki S. , Fukushima T. , Endo T. , Shimada M.
Published: March 2011

Yttria-doped tetragonal zirconia polycrystals (Y-TZP) containing 2 and 3 mol% of Y2O3 uniformly alloyed by 0-15 mol% of CeO2 or diffusing CeO2 on the surface were fabricated, and the mechanical properties and thermal stability of the sintered bodies were evaluated by annealing in humidity conditions at 50–600° C. The tetragonal-to-monoclinic phase transformation proceeded at 100–500°C in air, and accompanied microcracks. The phase transformation proceeded rapidly on the surface, but slowly inside the body. The bending strength of the annealed specimens depended on the depth of the transformation layer thickness, but not on the degree of the phase transformation on the surface. Alloying CeO2 was useful to improve the thermal stability of Y-TZP, but noticeably decreased the fracture strength. Diffusing CeO2 on the suface of Y-TZP seemed to be useful to improve the thermal stability without loss of the fracture strength.
Zirconia Dispersed Mullite Ceramics Through Hot-Pressing Of Amorphous ZrO 2 -SiO 2 -Al 2 O 3 Obtained by Rapid Quenching
Authors: Yoshimura Masahiro , Noma Tatsuo , Hanaue Yasuhiro , Sōmiva Shigeyuki
Published: March 2011

Zirconia dispersed mullite ceramics were fabricated through hot-pressinq at a pressure of 25 MPa from the amorphous material of 2Owt%ZrO2-8Owt%(3Al2O3 2SiO2) obtained by rapid quenching of the melts. The densification was initiated at ∼950°C and accelerated by crystallization of mullite and t-ZrO2 to yield almost pore free samples about 1050°C. This sample seemed to contain Si02-rich glassy phase in addition to A12O3-rich mullite and t-ZrO2 The further heat-treatments with/without pressing brought about the reaction between the Si02-rich glassy phase and the A1203-rich mullite phase to yield nearly stoichiometric mullite. and growth of the mullite grains and the t-ZrO2 particles up to 1 u m in size at 1600°C. The TEM observation revealed a duplex microstructure of twinned m-ZrO2 at the triple points and fine t-ZrO2 in the center of the mullite grains. The fracture toughness of the specimen increased with hot-pressing temperatures up to 2.2 MPam1/2 in the samples at 1600°C.
A Study of Rhombohedral Phase in Y2 O3 -Partially Stabilized Zirconia
Authors: Kitano Jukishige , Mori Y. , Ishitani A. , Masaki T.
Published: March 2011

Tetragonal to rhombohedral phase transformation was studied by X-ray diffraction technique on the ground surfaces of tetragonal zirconia polycrystals (Y-TZP) and partially stabilized zirconia (Y-PSZ) with 2.0 to 5.0 mol% Y2 O3 contents prepared by hot isostatic pressing. The rhombohedral phase increased with increase of Y2 O3 content from 2.0 to 5.0 mol%, and also with the increase of HIPing temperature from 1400 to 1600°C. The stability of the phase was also studied with regard to the surface finish and annealing. The subsequent heat treatment of the samples was found to promote the reverse rhombohedral to tetragonal transformation.
Analysis by Sims and by Eels-Edx in a Stem of Sic Fibers Reinforced Composites
Authors: Lancin M. , Anxionnaz F. , Schuhmacher M. , Duone O. , Trebbia P.
Published: March 2011

A series of Nicalon SiC fibers (202) coated by CVD with C and SiC were analysed by Secondary Ion Mass Spectrometry (SIMS). Results (i) give the composition of the material, (ii) show its heterogeneity of composition, and (iii) demonstrate the limit of application of the method for the fibers analyses. SIMS and Electron Energy Loss Spectroscopy (EELS) analyses of one coated fiber segment were done. When elements are detected by both techniques, reasonable agreement is observed between the results. SiC - CVD deposits are not uniform: they are rich in carbon close to the fiber and tend towards stoechiometry after a few microns. The coated fibers are rich in oxygen and in free carbon. Analyses of a glass-ceramic matrix/ Nicalon SiC fiber (202) composite were performed using SIMS, EELS and Energy Dispersive X-Ray Spectroscopy (EDX).
The Temperature Dependence of Yield Stress and Fracture Toughness in Unstabilized Zirconia Crystals
Authors: Coyle T. W. , Ingel R. P. , Willging P. A.
Published: March 2011

The flexural strength and the single edge notch beam fracture toughness of undoped ZrO2 crystals, grown by the skull melting technique, were examined from room temperature to 1400°C. On heating the toughness increased with test temperature to a maximum of 4.0 MPajm at 1225°C then gradually decreased to 2.6 MPa/m. Upon cooling after a 20 minute hold at 1250°C an increase in toughness to 5 MPa/m was observed at 1200°C; upon cooling to lower temperatures Kic gradually diminished. The loaddeflection curves for the flexural strength tests showed marked nonlinearity before failure for samples tested on cooling. The temperature dependence of the apparent yield stress suggests that initial yielding occurs by slip above 1200°C but that from 1200°C to 1050°C the observed yielding is due to stress induced tetragonal to monoclinic transformation.
Comparison of the Thermal Stabilities of Amorphous Hydrides Formed by Zr-Based Metallic Glasses
Authors: Cantrell J. S. , Bowman R. C.
Published: March 2011

Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) measurements were performed on a-Zr2 PdHx, a-Zr3 RhHx, a-Zr76 Fe24 Hx, and a- Zr2NiHx to assess the effects of hydrogen on their thermal stabilities. Only exothermic DSC peaks were observed for the hydrogen-free glasses and are shown to correspond to the formation of crystalline intermetallic phases. On the other hand, heating of the amorphous hydrides gives decomposition reactions with the generation of ZrHx (1.5 <x < 2.0) and either free metal (e.g., Rh) or a Zr-depleted intermetallic (e.g., ZrPd). With the exception of the Zr2 PdHx samples, hydrogenation significantly decreases the thermal stabilities (i.e., the exothermic transitions occur at lower temperatures in the amorphous hydrides). Endothermic peaks, which are associated with hydrogen evolution from the glass, are observed when the hydrogen-to-metal ratios approach unity.
Electrochemical Study of the Passivation and Passive Film Breakdown of Mg70 Zn30 Metallic Glass
Authors: Hagans Patrick L.
Published: March 2011

Anodic dc polarization measurements of glassy Mg70 Zn30 in pH=9.3 boric-borate electrolyte with and without the presence of Cl− were used to study both passive film formation and breakdown. In the absence of C− a single, broad passivation peak is observed which is very similar to that found with triply distilled Mg except that the large increase in peak potential and reduction in peak current density indicates that a more stable film has formed on Mg70 Zn30. Also observed with Mg70 Zn30 but not with Mg, Zn or other different types of crystalline Mg alloys is a large, narrow peak in the transpassive region (i.e., the region where the passive film begins to break down and/or O2 evolution commences). This process of breakdown of the passive film and further oxidation of the base metal is totally irreversible and is almost completely missing on the second and subsequent voltage sweeps. Although speculative in nature, existing evidence suggests that a phase transition has occurred within the passive film itself. In the presence of Cl− this process does not occur as passive film breakdown is initiated via a pitting mechanism at a potential nearly 2.5 Volts more negative than the onset of O2 evolution. Nevertheless, the onset of pitting is still 0.4 Volts more positive than that found for Mg indicating again that a much more protective film has formed on Mg70 Zn30
Fatigue Corrosion of Amorphous Fe75-xCrxB15 Si10 Wires
Authors: Le Anh , Kabacoff Lawrence T. , Martinez Nancy Y.
Published: March 2011

Measurements have been made of the corrosion and fatigue properties of metallic glass wires of composition Fe75-xCrxB15Si10 (X = 5, 8, 11) in air, deionized water, 3.5 w/o NaCl and 1.0 N H2SO4. A clear inverse relationship was observed between the corrosion rate and the number of cycles to failure. Fatigue limits were observed for those cases where spontaneous passivation occurs (all compositions in air and deionized water, and 8 and 11 a/o Cr in chloride solution). It was found that the mechanism for the fatigue failure of specimens which spontaneously passivate differs from that of metallic glasses in an acidified chloride environment where active/passive behavior is observed. A model is proposed to explain this observation.
Confined Gas Atomization: The Role of the Melt Delivery Tube in Particle Size Control
Authors: Raman R. V.
Published: March 2011

Gas atomization is one of the key processes used for the production of rapidly solidified materials. The unique feature of the gas atomization process is its capability to form spherical powders of multicomponent alloys containing reactive elements. Spherically shaped powder is specified in the secondary processing operations used in a number of applications. This requirement has resulted from the higher flow rate, better packing density, and lower surface area obtained in spherical particles compared to irregularly shaped particles.
Stabilization of Metallic Glasses by Irradiation with Picosecond Laser Pulses.
Authors: Radliński A. P. , Calka A. , Davies B. Luther
Published: March 2011

Introduction

Glassy metallic alloys are usually formed by bringing a small amount of the melt mechanically into good thermal contact with a heat conducting medium. Cooling rates of the order of 106K/sec can thereby be obtained. Despite the extensive use of laser treatment in many areas of technology the idea of using ultra short laser pulses to increase the cooling rate by many orders of magnitude is relatively new. The rates obtainable in metals as a result of laser irradiation have been estimated to be of the order of 1010 K/sec (for nanosecond laser pulses) in the critical temperature region of high nucleation rate and low viscosity. Some less sophisticated estimates for laser annealing of silicon with picosecond pulses yield values of 1012 – 1013 K/sec.. The recent measurements of the surface colour temperature in laser irradiated metals suggest cooling rates of the order of 1010K/sec in both nanosecond and picosecond regimes.
Nucleation During the Solidification of Atomized Droplets Catalyzed by Spherically-Shaped Oxide Particles
Authors: Libera Matthew R. , Olson Gregory B. , Sande John B. Vander
Published: March 2011

Nucleation temperatures are calculated for the case of solidification in atomized metal droplets where spherical substrate particles act as nucleation catalysts. Following the method of Fletcher, the effect of substrate size on catalytic potency is illustrated, and the model is applied to the nucleation of bcc solid from pure, liquid iron containing oxide substrate particles as catalysts. Supercooling data from the literature are used to determine wetting angles for alumina, silica, and rare-earth oxide. Oxide particle-size distributions are then used to predict the supercooling behavior of atomized liquid droplets based on the probability that a given size of droplet will contain a particular size of substrate particle. A transition size regime is found separating droplet sizes undergoing very small and very large supercoolings, respectively. This is discussed in terms of the types and number densities of inclusions present during atomization of the melt.
Nonequilibrium Interface Kinetics During Rapid Solidification
Authors: Aziz Michael J.
Published: March 2011

Abstrat

The deviations from local equilibrium at a rapidly moving solid-liquid interface are well documented. The fraction of solute atoms in the liquid at the interface that joins the crystal during rapid solidification approaches unity and the interface temperature drops. Experimental and theoretical work on impurity incorporation and interfacial undercooling is reviewed. Past and future experiments to test the theories are discussed.
Grain Growth Behavior of a Rapidly Solidified Fe-10Cr-8A1 Alloy
Authors: Maloney M. J. , Garratt-Reed A. J. , Yurek G. J.
Published: March 2011

A rapidly solidified Fe-10Cr-8Al alloy that contained a dispersion of very fine MnS and Al203 particles was produced by a gas atomization/twin-roll quenching technique. The RS particulates were consolidated by hot isostatic pressing, and the consolidated alloy was hot forged, and then hot and cold rolled. Grain growth took place during primary recrystallization of the alloy; however, once primary recrystallization was complete, the dispersion of second phase particles was effective in pinning alloy grain boundaries.
Microstructure of Metastable Metallic Alloy Films Produced by Laser Breakdown Chemical Vapor Deposition and Ion Implantation
Authors: Henon S. K. , Jervis T. R. , Nastasi M.
Published: March 2011

Thin films produced by laser breakdown chemical vapor deposition from nickel and iron carbonyls and by implanting Ni foils with varying levels of C have been characterizea by transmission electron microscopy. Decomposition of Ni(CO)4 produces polycrystalline films of fcc Ni and metastable ordered nexaogonal Ni3C. This metastable phase is identical to that produced by gas carburization, rapid solidification of Ni-C melts, and ion implantation ot C into Ni at low;co ncentrations. Increasing the H2 content in the gas mixture during laser deposition reduces the grain size of the films significantly witn grain sizes smaller than 10 nanometers produced. Laser uecomposition of Fe(CO)5 produces films with islands of fcc gamma-Fe and finely dispersed metastable Fe3C (Cementite). In addition, the ferrous oxides Fe2O3 and Fe3O4 were found in these samples. Implants of C into pure Ni foils at 77°K and at a concentration of 35 at.% produced amorphous layers. Implants at the same dose at room temperature did not proouce amorphous layers.
Microstructure & Phase Transformation in Rapidly Solidified V-Ga Alloys
Authors: Park M. W. , Whang S. H. , Karmarkar S. , Divecha D.
Published: March 2011

The A15 Phase forming V-Ga alloys were processed into ribbons and foils by rapid solidification techniques. Microstructures and phase transformation in these alloys by rapid solidification and succeeding heat treatment were investigated by x-ray diffraction and TEM. It is shown that equilibrium A15 phases can readily be suppressed by rapid quenching in these alloys. A significant grain refinement resulting from the rapid solidification also was observed. Microhardnesses of these alloys as a function of Ga concentration were determined.
Microstructure of Rapidly Solidified W-Ni Alloys
Authors: Vujic Dinko , Whang Sung H. , Cytron Sheldon
Published: March 2011

Binary W-Ni alloys of four different compositions were rapidly quenched into thin foils. Microstructures and hardnesses of the as-quenched alloys were studied by TEM and hardness measurements. The results from the microstructural study show that the W grains and particles undergo extensive refinement and that the grain size is much smaller than that obtained in conventional alloys. In addition, the formation of WNi and W2Ni, the low melting temperature intermetallic compounds in the W-Ni system, was readily suppressed by rapid quenching. The hardness increase in rapidly solidified W-Ni alloys appears to have originated from the microstructural refinement.
Microstructure and Wear Behavior of Laser Processed Co-Cr-W/Steel Surface Alloys
Authors: Xiaoping Jiang , Zhuangqi Hu , Yunlong Ge , Ming Jiang , Changxu Shih
Published: March 2011

Surface alloys with various compositions of Co, Cr and W on 20CrMo steel have been processed by controlling the ratio of thickness of plasma sprayed Co-Cr-W coating to laser melting depth. A formula has been suggested to evaluate the contents of surface alloying elements. With increasing the contents of Co, Cr and W in the surface alloy system, two hardness peaks occur at about 17Co7Cr3W and 52Co22CrgW corresponding to microstructure of M and γ-Co + M23C6 respectively. Wear experiments in media of air, 1N H2SO4 and 1% NaCl indicate that 17Co7Cr3W surface alloy has higher wear resistance in air, while 52Co22Cr9W better in the corrosive media under high load. In any case, wear resistance of the above two surface alloys are much better than that of plasma sprayed coating of Co-Cr-W.
Melt-Spun Permanent Magnet Alloy with Enhanced Isotropic Remanence
Authors: Kadin A. M. , McCallum R. W. , Clemente G. B. , Keem J. E.
Published: March 2011

Rapid solidification onto a copper quench surface (melt-spinning) has been used to fabricate a high-performance permanent magnet alloy (Ovonic Hi-Rem™) based on the Nd-Fe-B class of materials. Crucial idditions of alloying elements are combined with careful control over quench parameters to yield a random assembly of microcrystallites, with macrosconically isotropic magnetic properties including values of remanent induction that can exceed 10 kG and maximum energy products greater than 20 MGOe. These values exceed those expected from conventional randomly oriented magnets. The enhanced magnetic performance is related to results of x-ray diffraction and electron microscopy.
Magnetic Percolation in New Crystalline FCC Fe-Cu Alloys
Authors: Chien C. L. , Liou S. H. , Xiao Gang , Gatzke M. A.
Published: March 2011

Magnetic percolation has rarely been realized in Fe-based binary alloys either because Fe does not retain its moment in the dilute limit or because the solubility is too low. By using a vapor quenching method, which in our case is highrate sputtering, we have succeeded in making new metastable crystalline alloys of fcc FexCu1−x which do not appear in the equilibrium phase diagram. These alloys spanning the percolation threshold allow magnetic percolation phenomena on an fcc lattice to be observed by SQUID magnetometry and Mössbauer spectroscopy. Above xc, the magnetic ordering temperature varies as (x−xc)γ with xc = 0.185 and γ = 0.63. Below xc, spin glass ordering has been observed.
Reversible Structural Relaxation in Fe-Ni-B-Si Metallic Glasses
Authors: Brüning R. , Altounian Z. , Ström-Olsen J. O.
Published: March 2011

Reversible structural relaxation has been studied in (Fe1-xNix)80B10Si10 by differential scanning calorimetry and X-ray diffraction. It is found that surface crystallization plays a major role in inhibiting reversibility. In consequence previously published data have presented a misleading picture about the composition dependence of the reversible effect in Fe-Ni-B-Si, which simply increases monotonically with Ni composition. There is no evidence that chemical short range order plays any role in reversibility.
Comparison of Miogtiwiures and Magnetic Properties of Melt Spun and Plasmla Sprayed Alloys of Fe-Rare Earti-B
Authors: Anderson C. D. , Overfelt R. A. , Flanagan W. F.
Published: March 2011

Samples of Fe76RE16B8 have been prepared by melt spinning and plasma deposition. The samples were fully saturated by cooling fran 350°C in a 5 kOe field. The room temperature coercivities of these samples are reported and correlated to the microstructures revealed by scanning electron microscopy. Subsequent heat treatments are shown to either increase or decrease the intrinsic coercivities depending upon the solidification rate that each sample experienced.
Structural Relaxation and Interdiffusion in Amorphous Fe-Ti Compositionally Modulated Films
Authors: Chason Eric H. , Mizoguchi Tadashi
Published: March 2011

Interdiffusion and structural relaxation in amorphous compositionally modulated films of Fe-Ti have been measured simultaneously. Interdiffusivity is determined by the change in X-ray modulation peak intensity upon annealing and structural relaxation is determined by the shift in X-ray peak position corresponding to the densification. The relaxation kinetics of the densification are explained by the free volume model of structural relaxation. The relaxation kinetics of the inverse diffusivity are shown to be the same as for viscosity relaxation.
Deformation-Induced Amorphization of Crystalline Particles in a Cu-Ti Metallic Glass
Authors: Kamenetzky Eduardo A. , Asikenazy Philip D. , Tanner Lee E. , Johnson William L.
Published: March 2011

Crystalline particles and grains embedded in Cu35Ti65 glass ribbons have been amorphized by isothermal cold rolling. The structural evolution has been studied by X-ray diffraction and TEM techniques. Initial particle morphologies are spherulitic and spherical, the latter with sizes ranging between 10 and 100 nm. The new amorphous phase seems to nucleate at crystalline-amorphous matrix interfaces. Initially there is a well defined interface between the new and the existing amorphous phases but it disappears as rolling progresses. Crystallites on a nanoscale still present in the final stages of particle amorphization have been observed by convergent beam electron diffraction. After sufficient deformation the consolidated ribbon becomes completely glassy. A morphological description of the transformation process in terms of crystal destabilization and solid-state particle melting is presented.
Kinetics and Mechanisms of Formation of Al-Ni Intermetallics
Authors: Patchett J. A. , Abbaschian G. J.
Published: March 2011

The effects of cooling rate and composition on the nucleation and growth kinetics of NiAl, Ni2Al3, and NiAl3 intermetallics were studied for alloys containing 25 and 31.5 ht.% Ni. Fgr the former composition, the peritectic regction Ni Al + Liquid → NiAl3 was studied over cooling rates from 20 to 105 K/s. For the latter composhtion, the reaction NiAl + Liquid → Ni2Al3 was studied at cooling rates ranging form 10 to 600 K/sec. The amounis of constituent phases are shown to depend on the cooling rate, and for the peritectic phases, on the surface area of the primary phase. The nucleation of Ni2Al3 and NiAl3, and the ordering of the aluminum-rich NiAl were also examines uding trans ission electron microscopy. Cooling the NiAl + liquid below the peritectic temperature results in a metastable extension of NiAl with a high dislocation and stacking fault density, followed by the epitaxial nucleation and almost dislocation-free growth of Ni2Al3 In contrast, the nucleation of the NiAl3 on Ni2Al3 occurs directly witgoud the formationof an intermediate region.
Long—Range Ordering in Rapidly Quenched Llo TiAl Compound Alloys
Authors: Whang S.H. , Li Z.X. , Vujic D.
Published: March 2011

Rapid solidification has an effect on lattice parameters and long&range order parameter in L1o TiAl compound alloys. In these compounds rapid quenching from the liquid state significantly decreases the long—range order parameter while the tetragonal distortion c/a decreases as a result of rapid quenching. The lattice parameter change due to rapid quenching becomes pronounced with increasing aluminum concentration beyond the stoichiometric alloy composition. The recovery from the disordered state and the relaxation from the tetragonal distortion were found to be two different kinetic processes.

The long—range ordering requires low temperature and long annealing time in comparison with high temperature and short annealing time for the recovery of the tetragonal distortion.
Two—Phase Nickel Aurunides
Authors: Khadkikar P. S. , Veduia K. , Shabel B. S.
Published: March 2011

The as—extruded microstructures of two alloys in the two phase field consisting of Ni3Al and NiAl in the Ni—Al phase diagram exhibit fibrous morphologyand consist of Ll2 Ni3Al and B2 NiAl. These as—extruded microstructures can be modified dramatically by suitable heat treatments. Martensite plus NiAl or martensite plus Ni3Al microstructures are obtained upon quenching from1523 K. Aging of martensite at 873 K results in the recently identified phase Ni5Al3 whereas aging at 1123 K reverts the microstructures to Ni Al plui NAl. The microstructures with predominantly martensite or Ni5Al3 phases are brittle in tension at room temperature. The latter microstructure does not deformplastically even in compression at room temperature. However, some promise of room temperature tensile ductility is indicated by the Ni3Al plus NiAl phase mixtures.
Creep in Ternary B2 Aluminides and Other Intermetallic Phases
Authors: Jung I. , Rudy M. , Sauthoff G.
Published: March 2011

This paper examines the possibilities for obtaining a high creep resistance in intermetallic phases. In a first section, the creep mechanisms are discussed with respect to the effects of stress, temperature and composition in the light of recent experimental results on the creep behaviour of the B2 phase (Fe,Ni) Al between 650 °C and 1100 °C. The familiar models for describing the creep of conventional disordered alloys apply to intermetallic phases, too, and describe the observed behaviour in a quantitative way. In the second section the creep of various ordered bcc phases - (Fe,Ni)Al and (Co,Ni)Al with B2 structure and the Heusler-type Ni2AlTi with L21structure - and ordered fcc phases - Ni3Al with L12structure, Fe3AlC and Ni3AlC with E21structure and NbAl3with DO22structure - are examined. Large increases in creep strength are possible by the transition to phases with more complex structures as well as by appropriate alloying. Much further work is necessary for making more reliable predictions on the obtainable creep strengths.
Antiphase Domains, Disordered Films and the Ductility of Ordered Alloys Based on Ni3Ai
Authors: Cahn R. W.
Published: March 2011

In elements and intermetallic compounds alike, tensile ductility is favoured by a small spacing of obstacles to dislocation movement, whether these obstacles be grain boundaries or other structural features. The evidence for this generalisation is reviewed.

Antiphase domains (APD) form only when Tt is below the freezing temperature, Tf: this isa rule which has not hitherto been recognized. In Ni-Al, Tt < Tf when the Al content is less than ≈23.5at.%. APD's can serve as heterogeneous nuclei where films of disordered (γ) phase deposit. Domains, especially if decorated by γ films, are associated with enhanced ductility, and there is circumstantial evidence that the ductility is indeed caused by these microstructural features.
The Microstructure and Tensile Properties of Extruded Melt-Spun Ribbons of Iron-Rich B2 FeAl
Authors: Baker I. , Gaydosh D.J.
Published: March 2011

The microstructure of extruded rods of iron-rich FeAl (B2-structure), as characterized by TEM, SEM, optical microscopy and x-ray diffractometry, consisted of elongated grains with a <111> fibre texture containing a high dislocation density. Numerous oxide particles were found, mostly in lines which reflected the matrix flow during extrusion. In addition, some large inclusions were present. Tensile testing of annealed, relatively dislocation-free specimens as a function of increasing temperature found increasing ductility up to 900K, above which a ductility drop occurred accompanied by a change in fracture mode, from transgranular cleavage to intergranular fracture. The yield strength, which was independent of temperature up to 800K (at ∼500MPa), also decreased rapidly as diffusion became more important. The predominant slip vector changed from <111> to <100> around 700K
High Temperature Strength of Ordered and Disordered Ni4Mo
Authors: Kao H. P. , Brooks C. R. , Vasudevan K.
Published: March 2011

The alloy Ni−20 at. % Mo is FCC and disordered at high temperatures, but below 868°C forms a superlattice of the D1a type. The disordered structure can be retained by quenching, and subsequent aging below 868°C can develop a variety of ordered domain structures. In the disordered condition, the yield stength at 25°C is typically 140– The tensile properties were measured for two ordered domain sizes: 24 nm and 3,000 nm. For the 24 nm domain size, the yield strength at 25°C was 862 MPa (125,000 psi). This decreased with increasing test temperature to about 690 MPa (100,000 psi) at 800°C, then decreased greatly to about 210 MPa (30,000 psi) at 1000°C. In the ordered condition, the alloy had a very low ductility (1% elongation or less) from 25°C to the disordering temperature of 868°C, above which it increased considerably (e.g., 30% elongation). The alloy with the 3,000 nm domain size showed similar behavior, although the strength was less. (The ordered alloy with 24 nm domain size had a yield strength-temperature curve similar to that of Waspaloy.) These results are correlated with fractography of the tensile samples.
Grain Boundary Chemistry and Ductility in Ni-Base LI2 Intermetallic Compounds
Authors: Taub A. I. , Briant C. L.
Published: March 2011

The available experimental data for the Ni3X, LI2 intermetallics indicate a strong effect of chemistry on the tendency for brittle intergranular fracture. Combining the data for the binary compounds with the effects of macroalloying with × substituents and microalloying with boron, the resistance to intergranular fracture varies as Fe ~ Mn > Al ~ Ga > Si > Ge. Two models have been proposed to explain these chemistry effects. The basis for both models is that electronic charge localization is responsible for the brittle behavior of the ordered intermetallics. The models differ in the measure of charge redistribution; one uses valency differences whereas the other uses electronegativity differences.
Ductility and Fracture Behavior of Polycrystalline Ni3Al Alloys
Authors: Liu C. T.
Published: March 2011

This paper provides a comprehensive review of the recent work on tensile ductility and fracture behavior of Ni3AI alloys tested at ambient and elevated temperatures. Polycrystalline Ni3Al is intrinsically brittle along grain boundaries, and the brittleness has been attributed to the large difference in valency, electronegativity, and atom size between nickel and aluminum atoms. Alloying with B, Mn, Fe, and Be significantly increases the ductility and reduces the propensity for intergranular fracture in Ni3Al alloys. Boron is found to be most effective in improving room-temperature ductility of Ni3Al with <24.5 at. % Al.

The tensile ductility of Ni3Al alloys depends strongly on test environments at elevated temperatures, with much lower ductilities observed in air than in vacuum. The loss in ductility is accompanied by a change in fracture mode from transgranular to intergranular. This embrittlement is due to a dynamic effect involving simultaneously high localized stress, elevated temperature, and gaseous oxygen. The embrittlement can be alleviated by control of grain shape or alloying with chromium additions. All the results are discussed in terms of localized stress concentration and grain-boundary cohesive strength.
A Review of Recent Developments in Iron Aluminides
Authors: Mendiratta Madan G. , Ehlers Sandra K. , Dimiduk Dennis M. , Kerr William R. , Mazdiyasni Siamack , Lipsitt Harry A.
Published: March 2011

This paper presents a review of recent research conducted at the Air Force Wright Aeronautical Laboratories (AFWAL)/Materials Laboratory to develop iron-aluminides as elevated temperature structural materials. The research consisted of investigations on the microstructure, tensile behavior, deformation, and fracture mechanisms of the DO3 and B2 ironaluminides. Binary Fe-Al alloys with a wide range of Al contents, solidsolution ternary alloys and precipitation- and dispersion-strengthened two-phase alloys have been investigated. It is shown that iron-aluminides have a potential to be structural materials at least up to 650°C.
Atomistic Simulations of [001] Symmetric Tilt Boundaries in Ni3Al
Authors: Chen S. P. , Voter A. F. , Srolovitz D. J.
Published: March 2011

We report a systematic atomistic simulation study of [001] symmetric tilt grain boundaries (GB) in Ni3Al, Ni, and Al. We found that the grain boundary energies and cohesive energies of Ni3Al and pure fcc Ni are approximately thesame. Grain boundary energies aid cohesive energies in Ni3Al depends stronglyon the grain boundary composition. The Al-rich boundaries have highest grain boundary energies and lowest cohesive energies. This offers an explanation for the stoichiometric effect on the boron ductilization
Kinetics of Oxidation of Ni Aluminide Exposed to Oxygen-Sulfur Atmospheres
Authors: Natesan K.
Published: March 2011

As part of a development effort on nickel aluminides based on Ni3Al as structural materials for fossil energy applications, oxidation/sulfidation studies are being conducted at Argonne National Laboratory on materials that are being developed at Oak Ridge National Laboratory. Sheet samples of nickel aluminide, containing 23.5 at, % Al, 0.5 at. % Hf, and 0.2 at. % B were tested in an annealed condition and after preoxidation treatments. Continuous weight-change measurements were made at 875°C by a thermogravimetric technique in exposure atmospheres of air, a low-p02 gas mixture, and low-p02 gas mixtures with several levels of sulfur. getailed analyses of the corhosion product scale layers were conducted using a scanning electron microscope equipped with an energy dispersive x-ray analyzer and an electron microprobe. The air-exposed specimens developed predominantly nickel oxide; the specimen exposed to a low-p02 environment developed an aluminum oxide scale. As the sulfur content of the gas mixture increased, the alumina scale exhibited spallation and the alloy tended to form nickel sulfide as the reaction phase. The results indicated that the sulfidation reaction in nickel aluminide specimens (both bare and preoxidized) was determined by the rate of transport of nickel from the substrate through the scale to the gas/alumina scale interface, mechanical integrity of the scale, and the H2S concentration in the exposure environment.
Temperature and Orientation Dependence of Surface Film Effects in Single Crystal Nial
Authors: Noebe R.D. , Kim J.T. , Gibala R.
Published: March 2011

During deformation of bcc metals and bcc-based ordered alloys, conditions of elastic and plastic constraint associated with the presence of thin adherent surface films can be responsible for introducing increased densities of mobile dislocations in the metal, resulting in enhanced ductility and reduced yield and flow stresses of the film-coated materials. In the present paper, surface film effects were investigated as a function of temperature and crystallographic orientation for single crystal β-NiAl. Appreciable temperature-dependent and orientation-dependent surface film effects were observed, as were significant effects of film adherence on the observation of surface film softening.
Dislocation Reactions at Grain Boundaries in Li2Ordered Alloys
Authors: King A.H. , Yoo M.H.
Published: March 2011

The characteristics of perfect grain boundary dislocations in ordered alloys are discussed, and consideration is given to the possible formation of perfect and imperfect grain boundary dislocations by the impingement of crystal lattice dislocations. It is shown that many dislocation reactions at grain boundaries in ordered alloys are made unfavorableif chemical co—ordination must be maintained in the structure of the grain boundary. This leads to a suggestion that the effect of boron in the grain boundaries of Ni3AI is to reduce the importance of chemical ordering, and thus to promote deformation by allowing greater freedom for dislocation reactions to occur.