bluuebunny/crossref_metadata_2025 huggingface dataset:
The Strength of Fibres in All-Ceramic Composites
Authors: Kendall Kevin , Alford N. Mcn. , Birchall J. D.
Published: March 2011

When considering the strength of a fibre reinforced ceramic composite, it is often assumed that the fibres retain their full strength of several GPa after cracking of the weaker matrix. The strength of the composite after matrix cracking is then calculated by the rule of mixtures as the product of fibre volume fraction and fibre strength. This paper demonstrates that such a calculation is not consistent with the principles of fracture mechanics for an isolated fibre embedded in an elastic matrix of the same elastic modulus, because the strength of the fibre is much reduced by the stress concentration arising from the matrix crack. Experimental measurements of the strength of a glass fibre embedded in a brittle matrix support the theory. The case of a fibre in a matrix of different elastic modulus is also considered, together with the proDlem of cracking along the fibre-matrix interface.
Interfacial Characterizations of Fiber-Reinforced Sic Composites Exhibiting Brittle and Toughened Fracture Behavior
Authors: Rawlins M. H. , Nolan T. A. , Stinton D. P. , Lowden R. A.
Published: March 2011

A process has been developed for the fabrication of a ceramic composite of SiC fibers in a chemical vapor infiltrated (CVI) SiC matrix. Early specimens produced by this technique exhibited nonuniform fracture toughness behavior; regions of brittle fracture with no fiber pullout were interspersed with regions of good toughness where fiber pullout predominated. Microscopic and spectroscopic analyses of fiber surfaces revealed that this behavior may have been related to a thin, discontinuous layer of predominantly silica which, when present, prevented tight bonding of fibers and CVI matrix. Consequently, efforts to control interfacial bond strengths and enhance fracture toughness via fiber pretreatment with CVI overcoatings have had mixed success depending upon the overcoating specie. Chemical and microstructural characterizations by analytical electron microscopy of these composites are presented and correlated with composite mechanical property data.
Strain and Fracture in Whisker Reinforced Ceramics [1]
Authors: Angelini Peter , Mader W. , Becher P. F.
Published: March 2011

Whisker reinforced ceramics offer the potential for increased fracture strength and toughness [2]. However, residual strain due to the thermal expansion mismatch between Al2O3 and SiC may affect mechanical properties of such composites. Crack tip interaction with the whisker/matrix may lead to changes in debonding behavior or influence other toughening mechanisms. The strain field in the Al2O3 matrix surrounding SiC whiskers was analyzed with a High Voltage Transmission Electron Microscope (HVEM). Strain contrast oscillations indicating the presence of residual stress in the specimen were observed in a Al2O3-5 vol % SiC composite having ≃15 μ grain size.The strain field was found to have both radial (perpendicular to whisker axis) and axial (parallel to whisker axis) components. A strain field was also present near the end faces of SiC whiskers. In situ thermal annealing to 573, 873, and 1173 K showed a decrease in the residual strain while in situ cooling to ≃77 K revealed little change in the strain. These results show that residual stresses in the compacts result from differences in thermal expansion and elastic constants of the matrix and whisker materials. Dynamic in situ fracture experiments performed in an HVEM on the Al2O3-5 vol % SiC having ≃1 μm as well as on Al2O3-20 vol % SiC having ≃1 μm grain size revealed that fracture resistance is due to a number of mechanisms including debonding near the whisker matrix interface, crack deflection, pinning, and bridging by SiC whiskers. Formation of secondary fractures and rocracks near and in front of propogating crack tips was also observed in the larger grain size composite.
Microstructure Development in SI3N4-Based Composites
Authors: Buljan S. T. , Zilberstein G.
Published: March 2011

The success and predictability of mechanical property improvements in ceramic matrix composites strongly depends on the ability to generate specific spacial arrangements and maintain the properties of the constituents. Dispersoids added to improve the toughness and strength of the ceramic base can mechanically or chemically alter the development of the matrix microstructure during consolidation and cause the properties to deviate from expected values. The present study examines and compares the development of a Si3N4 based composite microstructure with the chemically “active” TiC and “inert” SiC dispersoids; it further examines the effect of the resulting microstructures on the composite fracture toughness.
Reversible Transformation Plasticity in Uniaxial Tensioncompression Cycling of Mg-PSZ
Authors: Bowman K. J. , Reyes-Morel P. E. , Chen I-W.
Published: March 2011

Previously, the pressure, temperature and strain rate sensitivities of transformation plasticity have been investigated for monotonic loading of Mg- PSZ. Research in this area has been extended to fully reversed cyclic loading of the type used in plastic strain control fatigue. Cyclic deformation experiments were performed to permit investigation of constitutive behavior under stable deformation conditions at microstrain levels. It was found that cyclic microstrains over a range of temperatures and strain rates were associated with reversible transformation plasticity in the strongly thermally-activated regime. These results are compared to the constitutive relations of transformation plasticity which have been previously developed to explain macrostrain observations.
Deformation of Transformation Toughened Zirconia
Authors: Lankford James
Published: March 2011

Recent experimental work on the yield and flow behavior of both single crystal and polycrystalline transformation toughened zirconia is presented. In addition, related work by other researchers is reviewed. The resulting picture is used to assess the relative plastic deformation contributions of phase transformations, dislocation activity, and grain boundary sliding. Particular emphasis is placed on the effects of stabilizer chemistry, grain size, temperature, strain rate, and state of stress. The results are shown to reflect the strong role of shear stresses in selecting, and controlling the operation of, each deformation mode.
Transformation Plasticity and Transformation Toughening in Mg-PSZ and Ce-TZP
Authors: Chen I-Wei , Reyes-Morel P. E.
Published: March 2011

The constitutive behavior of transformation plasticity in single phase fine grain Ce-TZP and polyphase coarse grain Mg-PSZ was studied. A material independent pressure sensitivity and a microstructure dependent strain rate sensitivity and temperature sensitivity were found to be associated with the transformation yield stress. Autocatalysis of various extent operates in all cases, forming broad macroscopic shear bands in TZP and fine crystallographic slip bands which terminate at grain boundaries in PSZ. Transformation plasticity is apparently athermal near the Mb temperature in TZP, but not in PSZ except in brittle fracture. A strong crystallographic texture of the transformed phase develops during deformation. These results are analyzed in terms of a shear-dilatant yield criterion and a rate equation which account for stress assistance in martensitic transformation. An elastic-plastic fracture mechanical model is developed to estimate both the shear and dilatation contributions to the transformation plastic work in the crack tip plastic zone. On the basis of approximately equal shear and dilatation contributions to transformation plasticity, the model predicts a transformation zone height which is four times that of the previous model, and a toughness increment which is two times that of the previous model. These predictions are found in good agreement with the reported toughness-zone size relationship. The effect of temperature and chemical stability on toughness is also rationalized.
Atomic Size Effects on the Composition Range of Binary Amorphous Alloys
Authors: Liou S. H. , Chien C. L.
Published: March 2011

We have studied a number of binary metal-metal and metalloid alloy systems made by a single vapor quench method under very consistent conditions. In each case, amorphous alloys are found in one continuous composition range (Xmin<x<xXmax) regardless of the number of eutectic points in the equilibrium phase diagrams. It is found that the atomic size difference is the single most important factor in the quantitative determination of the composition range.
An Electrochemical and XPS Investigation of Sputter Deposited Ni44 Fe32Cr11P8B5 on 304 Stainless Steel
Authors: Nagarkar P. V. , Latanision R. M.
Published: March 2011

An Ni44 Fe32Cr11P8B5 (at.%) alloy was sputter deposited on to water cooled 304 stainless steel substrates. Electrochemical testing was performed in 0.1N H2So4 with and without the addition of O.06N NaCI. The surface layers of specimens polarized into the active and passive regions of the anodic polarization curves were analyzed using x-ray photoelectron spectroscopy (XPS) to check for preferential dissolution and possible segregation of the constituent elements. A significant improvement in the overall corrosion behaviour of 304 stainless steel was observed due to the sputter deposited layer.
Chemically Produced Precursors for the Synthesis of Amorphous Metal Alloy Powders
Authors: Henderson Richard S. , Tenhover M. , Fox Joseph R. , Grasselli R. K.
Published: March 2011

The classical formation of metallic glasses by rapid quenching requires the suppression of the nucleation and growth of crystalline phases during cooling from the liquid alloy melt. More recently a variety of techniques have been described in the literature wherein amorphous metal alloys have been prepared by diffusion reactions under solid state conditions. These include hydrogen glass forming reactions, multilayer diffusion couples, and mechanical alloying.

Wet chemical and thermal synthetic methods are described which allow the preparation of a wide variety of multi-component amorphous metal alloy precursors. Subsequent heat-treatment of these precursor materials serves to transform them into a substantially amorphous metal alloy powder. In the parent process, at least one metal-bearing compound is disposed in a liquid medium then reduced so as to obtain an intimate molecular mixture of the elements of the amorphous metal alloy to be synthesized. Specific examples of typical reduction procedures and variations are included. The modification of the chemical reaction schemes with respect to the parent process will be addressed in terms of the variability of intermediate precursor mixtures that can be isolated. In all cases, the critical step for the production of the amorphous metal alloy is the synthesis of a homogeneous, intimate mixture in the precursor powder. The solid-state reaction which occurs to alloy this intimate mixture is discussed in terms of the relative free energy difference between the intimate mixture and the resultant amorphous alloy.
Influence of Phosphorus on the Calorimetric, Magnetic and Mechanical Properties of Amorphous Fe78 Si9B13 Alloys
Authors: Rudkowski P. , Strom-Olsen J. O. , Schulz R. , Roberge R.
Published: March 2011

The effects of adding small amounts of phosphorus to amorphous Fe78Si9B13 alloys have been investigated. Substituting boron atoms by phosphorus improves the thermal stability of the glassy alloys. The optimum stability is reached at about 1.2 at. % phosphorus concentration. With respect to the soft ferromagnetic properties, the saturation induction increases rapidly with increasing phosphorus concentration, reaches a maximum around 0.1–0.2 at. % and then decreases upon further addition. The highest induction value was achieved with 0.1 at. % phosphorus after field annealing for 2 hours around 633K. The mechanical strength of the amorphous alloy is greatly reduced for phosphorus concentrations larger than 0.4 at. %.
Some Effects of Quench Rate on The Properties and Microstructures of Amorpous and Crystalline Materials Produced by Spark Erosion
Authors: Walter John L. , Berkowitz Ami E.
Published: March 2011

Spark erosion provides a means for producing fine particles (5 nm to 75 um) of metals, alloys, and semiconductors. Since the powders are formed from liquid droplets solidified in a liquid dielectric, the rate of solidification of the particles can be very high, varying according to particle size and the dielectric used. This paper examines some effects of different dielectrics on the microstructures, magnetic properties,and crystallization characteristics of amorphous and crystalline metals. It is seen that these properties depend upon the quench rate provided by the dielectric. In the case of the organic dielectrics, the quench rate appears to be associated with specific properties of the dielectric.
Characterization of Amorphous and Crystalline TiCuDx By Deuteron Magnetic Resonance
Authors: Volz M. P. , Bork V. P. , Fedders P. A. , Norberg R. E. , Bowman R. C. , Maeland A. J. , Cantrell J. S.
Published: March 2011

The structure and dynamics of a-TiCu(D,H)1.7 and a-TiCu(D,H)1.4 have been examined by Fourier transform quadrupole echo DMR line shape and relaxation time measurements at 30.7 MHz. The quadrupole-broadened a-TiCu(D,H)x line widths narrowed appreciably above 300 K because of increased D mobility. Low temperature DMR spectra show that static quadrupolar broadening is larger for amorphous samples than for crystalline samples. Deuteron spin lattice relaxation is attributed to conduction electrons below 200 K and to quadrupolar interactions at higher temperatures where deuteron hopping becomes significant. The spin lattice relaxation times indicate that the deuteron mobility is larger by an order of magnitude in the amorphous material than in the crystalline counterparts. Results are compared with those from proton magnetic resonance in corresponding hydrides.
Integrated Rapid Solidification and Heat Treatment using Computerized Electron Beam Processing
Authors: Iwata Atsushi , Tauqir Anjum , Strutt Peter R.
Published: March 2011

Martensitic refinement is observed in rapidly solidified high speed steel (M7) by introducing a short ‘thermal arrest’ during cooling. This is accomplished using microcomputer controlled electron beam deflection for the generation of preselectcd scanning patterns. Such a tcchnique provides a high degree of control over short-duration heating at high temperatures and thus facilitates the use of fast reaction rate kinetics. By programming a ‘thermal arrest’ in the austenite range it has been found possible to obtain a distribution of fine carbides within the solidification cells. These carbides, it was found, result in refinement of the martensitic structure.
A Long-Period Close-Packed Phase of the PuGa3 Type Prepared by RSP: m-Nb (Rh.75 Pd.25)3
Authors: Quan M. X. , Haldar P. , Giessen B. C.
Published: March 2011

In the pseudobinary system Nb(Rh1−xPdx)3, as in other similar alloy systems, a series of polytypic phases occurs which have related, closepacked structures with systematically varying stacking sequences. After rapid quenching from the melt, the stacking sequence of these polytypes is often changed.

A phase m-Nb(Rh.75Pd.25)3 of the PuGa3 type with a 12-layer stacking sequence has been prepared by RSP; this phase is probably metastable and displaces an equilibrium phase of the VCo3 type with a 6-layer structure. Occurrence of the m phase can be rationalized in terms of the sequence of the Jagodzinski notation (fraction of h-like packing) and the variation of the diffraction pattern with composition.
Glass Formation By Mechanical Alloying
Authors: Schultz L. , Hellstern E.
Published: March 2011

Amorphous metallic powders can be formed by mechanical alloying in a high-energy ball mill. Starting from the elemental, crystalline powders, ball milling first produces powder particles with a characteristically layered microstructure. Further milling leads to an ultrafine composite in which amorphization by solid state reaction takes place. The glass-forming range has been determined in detail for Fe-Zr and Ni-Zr. In Fe-Zr it differs completely from rapidly quenched amorphous samples. A systematic study of alloys of 3d transition metals with Zr and Ti shows that the glass-forming ability depends critically on a large negative free enthalpy of mixing. The results lead to the conclusion that amorphization by mechanical alloying is based on a solid state reaction and occurs under a metastable thermodynamic equilibrium neglecting the existence of intermetallic phases. Measurements of the superconducting transition temperature and Möβbauer studies show the structural similarity of mechanically alloyed and rapidly quenched amorphous samples. Finally mechanical alloying of FeZrB and NdFeB is described. Whereas FeZrB becomes amorphous after an additional annealing, a microcrystalline powder with very high coercivity is formed for NdFeB.
Fatigue Properties of a Ni-Base Superalloy Treated by Laserolazing
Authors: Xiaoping Jiang , Qi Hu Zhuang , Changxu Shih , Guizeng Zhu , Qinglin Meng , Xiaode Zhao
Published: March 2011

Fatigue properties of a wrought Ni-base superalloy treated by laserglazing and post heat treatments have been investigated. Tests have been run both by the rotating bend fatigue at 700°C and the vibration fatigue of turbine blades at room temperature. The results showed that the fatigue property of laserglazed specimens was obviously deteriorated because of resolution of γ′ phase and grain boundary carbide, interdendritic segregation of TiC and microcrack caused by thermal stress. However, suitable preheating and post heat treatment added before and after laserglazing can eliminate these defects and recover the fatigue life of this superalloy. Selected laser processing technology was applied to repairing blades rejected due to microcracks at trailing edge. The vibration fatigue life of blades repaired by laserglazing and post heat treatment was over two times as high as that of normal used blades with same service time.
Dielectric Tensor Characterization for Overcoated Amorphous TbFe Alloys
Authors: Ruane M. , Jain A. , Rosenvold R. , Mansuripur M.
Published: March 2011

Amorphous thin films of TbFe. sputter-deposited on quartz substrates with compositions supporting polar Kerr magneto-optical behavior, and overcoated with a transparent protective layer, are studied to determine their dielectric tensor elements. Refleetivity measurements over a range of angles of incidence are made in an apparatus that corrects for the overcoat layer and exploits magnetization reversal to enhance the measurement of r⊥, the complex reflectivity associated with the magneto-optical signal. Conventional Fresnel reflectivities are also found. The theoretical model for reflectivities from a thick film magneto-optical medium at oblique incidenci is developed and used within a Levenberg-Marquardt nonlinear estimation algorithm to estimate sequentially the dielectric tensor elements, considering their widely varying magnitudes and sensitivities to errors in reflectivity data. The interpretation of the dielectric elements in terms of magneto-optical performance and structural perpendicular anisotropy is discussed.
Lattice Location of Boron and Hafnium Dopants in an Aluminide by Use of Ion Channeling/Nuclear Reaactnio Analyses
Authors: Bohn H. G. , Williams J.M. , Barrett J.H. , Liu C.T.
Published: March 2011

Experiments have made use of Rutherford backscattering (RBS), ion channeling techniques and analyses for nuclear reaction products to study lattice location of B and Hf dopantsin an ordered nickel aluminide. Studies were of an alloy single crystal of composition Ni76A123Hf1 with about 0.1 at. % of B added. Analysis for B was accomplished by detection of alpha particles resulting from the reaction 11B(p,αi)8 Be, in ion channeling experiments in which RBS from the Ni constituent was used to control channeling in the host lattice. Yield of the reaction product from proton interaction with B decreased relative to random for channeling in a <100> direction, but increased relative to random for channeling in a <110= direction. It was concluded that B occupies primarily octahedral interstitial sites. RBS/channeling half-angles for Hf in a <100> direction are somewhat smaller than those for Ni, but nevertheless considerably larger than half-angles expected for Al. It is concluded that the majority of Hf atoms are on the Ni sublattice.
Ab Initio Theory of the Ground State Properties of Ordered and Disordered Alloys and the Theory of Ordering Processes in Alloys
Authors: Stocks G. Malcolm , Nicholson D.M. , Pinski F.J. , Butler W.H. , Sterne P. , Temmerman W.M. , Gyorffy B.L. , Johnson D.D. , Gonis A. , Zhang X.-G. , Turchi P.E.A.
Published: March 2011

We review some of the advances in the calculation of the electronic structure and energetics of ordered and disordered alloys that hold out the possibility of obtaining, in thenot-too-distant future, an ab initio theory of ordering and phase stability in alloys. In particular, we focus on the calculation of the ground state properties of Ni3Al and discuss the competition between the Li2 and D022 ordered structures. We review the ab initio concentration functional theory of ordering developed by Gyorffy and Stocks and its application to the short-range-ordered solid-solution state in CucPd1-c alloys. Finally, we review the generalized perturbation method approach to calculation of multisite interchange potentials in Ni3Al, Pd3V, and Al3Ti and again discuss L12/D022 competition as well as antiphase boundary energies in Ni3Al.
Deformability Improvements of Li2-Type Intermetallic Compounds
Authors: Izumi Osamu , Takasugi Takayuki
Published: March 2011

Intermetallic compounds are usually so brittle that they simply cannot be efabricated into useful shape components. Recent developments of physical and metallurgical principles for the structural materials have led to the conclusion that the deformability of several intermetallic systems can be substantially improved. Among them, in this lecture, the nature of grain boundary structure in L12-type intermetallics is first discussed.

Then, the possibilities and instances to overcome the brittleness are shown. Polycrystalline L12 -type Ni3Al, even prepared from high purity metals, exhibits brittle intergranular fracture. On the other hand, single crystals of Ni3Al are ductile even at room temperature. Thus, it is said that the grain boundaries of this alloy are intrinsically weak. Our recent analyses showed that there exist several configurations of atomic bonds, resulting in the heterogeneous electronic environments which can be regarded as “cavities”. The drastic ductility improvement of Ni3Al alloy by a small boron addition, which was found in 1979, can be interpreted as segregated boron atoms at grain boundaries to modify the electronic environments of boundaries and to reinforce boundary cohesion, thus suppressing intergranular fracture. From a quite similar point of view, modification of boundary structures can be achieved by substituting proper elements for the constituents of compounds or by selecting atom combinations of compounds. Thus, the ductility of Ni3Al could be improved by substituting a few percent of Mn or Fe for Al. Also, by selecting atom combination, several L12-type alloys such as Co3Ti, Cu3Pd, Ni3Mn and Ni3Fe have been found as ductile intermetallics.
An Overview of the Temperature Dependence of the Strength of the Ni3Al System
Authors: Tien John K. , Eng Sandra , Sanchez Juan M.
Published: March 2011

Many L12ordered alloys including the Ni3Al intermetallic system are noted for their anomalous temperature dependence of strength. It is also generally accepted that this dependence is due to a thermally assisted cross-slip, work hardening based model [1,2]. An alternative antiphase boundary (APB) based model has long been dismissed by the research community because prior calculations of APB energy, and some measurements, have shown that the appropriate APB energy of Ni3Al should remain constant with temperature [3]. These aspects will be reviewed briefly and will serve as a basis for a presentation of some more recent results. These will include the strain rate insensitivity of strength versus temperature in the increasing strength temperature region, a result that is, in our view, rather contradictory to the thermally assisted cross-slip model. Some very recent calculations of equilibrium APB energies will also be reviewed in the context of the strength dependence issue. These results show that the equilibrium APB energy increases with temperature. The question of what role, if any, equilibrium APB plays in the deformation and strengthening process will be discussed.
Strengthening of Ni3Al by Ternary Additions
Authors: Heredia F. , Pope D. P.
Published: March 2011

It is important for a number of reasons to have a basic understanding of the mechanisms by which ternary additions strengthen Ni3Al. First of all, since the basic strength-controlling mechanisms in pure Ni3Al are different from those in pure metals and substitutional solid solutions, it is expected that the mechanisms of solid solution strengthening will also be different in Ni3Al. Secondly, such an understanding will provide valuable insights into the properties of nickel-base superalloys in which Ni3Al is a key constituent. In addition, since new alloys based on an ordered Ni3Al matrix are being developed, it is important to understand the strengthening mechanisms in such alloys. In the present study, flow stress measurements have been performed on single crystals of Ni3Al containing additions of Hf and Ta, and on binary Ni rich, Ni3A1 used as a reference alloy. The data have been collected over a wide range of temperatures, for different orientations within the unit triangle, and as a function of the sense of the applied uniaxial stress. The effect of such additions on the critical resolved shear stress (CRSS) for octahedral slip has been determined and combined with previous data. An attempt is then made to clarify whether a lattice parameter/modulus mismatch effect or a dislocation core effect is the dominant mechanism for the strength increase with compositional changes. It appears that a lattice parameter/modulus mismatch is the dominant mechanism for orientations in which the tension/compression flow stress asymmetry disappears.
Creep Cavitation in a Nickel Aluminide
Authors: Schneibel J. H. , Martinez L.
Published: March 2011

A nickel aluminide with the composition Ni-23.5 Al-O.5 Hf-O.2 B (at. %) was creep-tested in tension at constant load (initial stress 250 MPa, temperature 1033 K). The creep rate reaches a minimum at a strain of approximately 0.3%. Its increase at larger strains is partly caused by grain boundary cavitation. Cavity size distributions corresponding to different creep times and strains were determined metallographically and evaluated in order to obtain the cavity growth rate as a function of cavity size. Contrary to a newly developed model for crack-like diffusive growth the cavity tip velocity increases with cavity size. This discrepancy is attributed to cavity coalescence. Sintering at elevated temperatures (1473 K) reduces the diameter and increases the thickness of the disc-shaped cavities. Sintering of such cavities might be exploited to measure surface diffusivities.
Effective-Pair-Interactions from Supercell Total Energy Calculations: Al-Transition Metal Alloys
Authors: Carlsson Anders E.
Published: March 2011

Effective-pair-interactions (EPI) are computed for alloys of Al with transition metals, Li, and Zn, using a method in which concentration-independent cluster interactions are resummed to obtain the concentration-dependent EPI. The method includes alloy fluctuations in the interatomic charge transfer, enables one to transcend the muffin-tin approximation and thus treat surfaces and layered structures, and allows the inclusion of lattice strain effects. The calculated EPI have a large magnitude when d-bonding effects are important. For transition metals the EPI are strongly concentration-dependent. In Ni-Al, results for bcc and fcc lattices are similar and exhibit a quick decay of the EPI with interatomic separations. The concentration dependence of the transition metalEPI exhibits rapid oscillations with the number of valence electrons. The concentration-averaged EPI varies less dramatically. The oscillations in the concentration dependence of the EPI are interpreted in terms of the position of the Fermi level relative to peaksand valleys in the one-electron density of states.
Rolling Anisotropy of Ni3Al Single Crystals
Authors: Watanabe Katsuya , Fukuchi Masaaki
Published: March 2011

The rolling anisotropy of Ni3Al single crystals was studied. A single crystal sheet in the (011) plane showed remarkable anisotropy. Rolling the sheet in the [100] direction was simple but was almost impossible in the [011] direction. Substantial anisotropy was not observed in the (111) and (001) sheets. The texture of the rolled (011) and (111) sheets were {011}<011>. It is concluded that the rolling anisotropy of single crystal sheets is determined by the presence of active slip system related to compressive strain normal to the sheet plane, and tensile strain parallel to the rolling direction.
Rutherford Backscattering (RBS) and Channeling Studies of Defects in Arsenic Implanted Silicon Induced by Arsenic Clustering
Authors: Baiocchi Frank A. , Kamgar Avid
Published: March 2011

RBS/Channeling measurements have been used to characterize the Si recrystallization and As substitutionality of <100> Si wafers implanted with 100 keV As at two doses after multiple thermal anneals. It is found that low temperature thermal treatment after a high temperature rapid thermal anneal results in deactivation of the implant, presumably due to Arsenic clustering. The ion channeling results indicate the growth of a disordered layer in the silicon after the second anneal at a depth corresponding to the peak of the Arsenic implant concentration. The number of displaced Si atoms is found to be 5-10 times greater than the number of displaced As atoms. This indicates that both As clustering and growth of Si defects should be considered as possible mechanisms for the electrical deactivation of the implanted Si after post anneal.
Characterization of Structural Changes and Defects in Ion Bombarded GaAs
Authors: Johnson Stephen T. , Williams J.S. , Elliman R.G. , Pogany A.P. , Nygren E. , Olson G.L.
Published: March 2011

In-situ time resolved reflectivity, Rutherford backscattering and channeling and transmission electron microscopy have been employed to characterise the evolution of Ar+ ion implantation damage in GaAs as a function of ion dose at various irradiation temperatures. Specific reflectivity signatures have been identified and characterised in terms of observed structural changes to the GaAs. Reflectivity provides a simple and convenient means of monitoring damage build up during ion implantation. In contrast to accepted models for amorphous phase formation in semiconductors, GaAs has been observed to undergo a sudden transformation from a crystal containing a dense network of extended defects to an amorphous phase under elevated temperature irradiation conditions.
Determination of Electrically Active Defect Profiles in Semiconductors Using a Photoelectrochemical Technique
Authors: Gealy F.D. , Tuller H.L.
Published: March 2011

Electrically active defects are common in semiconductors. Such defects include easily ionized substitutional impurities, vacancies, and interstitials which can act as shallow donors or acceptors. If one type of defect predominates, its concentration corresponds directly to the local donor or acceptor concentration. Consequently, measurement of a carrier profile in a nonhomogeneous semiconductor is effectively the same as measurement of the defect profile.

The photoelectrochemical profiling technique allows for carrier profile measurement with submicrometer spatial resolution. The sample is profiled by photoetching, then carrier measurement, and iterating this procedure until the desired profile depth is obtained.

Derivation of the space charge capacitance by impedance spectroscopy is discussed. An analysis of the P-doped Si-liquid electrolyte interface is presented. Phosphorous diffusivity coefficients in good agreement with literature values are derived from photoelectrochemical derived profiles.
Combined Use of Small Angle Neutron Scattering (Sans) and (Conventional and High Resolution) Electron Microscopy for the Characterization of Early Stages of Ordering and Phase Separation in Ni-Ti
Authors: Cerri A. , Schmelczer R. , Schwander P. , Kostorz G. , Wright A.F.
Published: March 2011

The decomposition of Ni ∼ 11.5 at.% Ti single crystals was studied for an ageing temperature of 540°C. In this alloy, coherent ordered zones of γ′-Ni3Ti (Cu3Au structure) are formed prior to the stable n precipitates. The early stages of zone formation were investigated by in-beam SANS and transmission electron microscopy (TEM). Electron diffraction, high resolution electron microscopy, TEM analysis of dislocation arrangements in samples deformed after ageing and X-ray measurements of the integrated intensity at L12 superstructure positions show that ordered regions already appear in quenched samples, whereas compositional changes, as determined by SANS measurements, occur only upon ageing.
Accurate Interatomic Potentials for Ni, Al and Ni3Al
Authors: Voter Arthur F. , Chen Shao Ping
Published: March 2011

To obtain meaningful results from atomistic simulations of materials, the interatomic potentials must be capable of reproducing the thermodynamic properties of the system of interest. Pairwise potentials have known deficiencies that make them unsuitable for quantitative investigations of defective regions such as crack tips and free surfaces. Daw and Baskes [Phys. Rev. B 29, 6443 (1984)] have shown that including a local “volume” term for each atom gives the necessary many-body character without the severe computational dependence of explicit n-body potential terms. Using a similar approach, we have fit an interatomic potential to the Ni3Al alloy system. This potential can treat diatomic Ni2, diatomic Al2, fcc Ni, fcc Al and L12 Ni3Al on an equal footing. Details of the fitting procedure are presented, along with the calculation of some properties not included in the fit.
Theoretical Studies of Defects in Binary and Ternary Oxides
Authors: Ching W. Y. , Ellis D. E. , Lam D. J.
Published: March 2011

In the past decade, there has been an explosive development of computational techniques utilizing high-speed computers to study the electronic and atomic structural properties of solids. These techniques form an important compliment to laboratory experiments for providing a better understanding of spectroscopic properties, as well as the energetics of the solid systems. For ideal metallic and semiconducting crystal lattice with translational symmetry, the conventional energy band structure approaches are capable to provide a good degree of precision in both electronic structure and system energies. On the other hand the molecular-cluster model represents a convenient method of studying those properties that are primarily a function of the local environment of the system, such as vacancy, substitutional and interstitial defects.
Synchrotron X-Ray Topography of Dislocation Arrays
Authors: Bilello J. C.
Published: March 2011

The application of relatively low resolution x-ray topography methods, typically ∿ 1 micrometer, is limited in studies which involve large scale dislocation networks. However, the ability to non-destructively image wide areas for “thick” specimens at high intensity with a tunable x-ray source makes the synchrotron an ideal probe for a range of problems previously inaccessible by other methods. Some examples will be discussed such as: (a) crack initiation and propagation in fatigued bicrystals, (b) real-time in situ plastic deformation studies in strain-annealed Mo crystals, and (c) strain distributions in vapor deposited and LPE thin films on Si and GaAs substrates.
X-Ray Double Crystal Topography of Processed Silicon Wafers
Authors: Loxley Neil , Tanner Brian K.
Published: March 2011

Double crystal topographs of a processed silicon device wafer, taken in highly asymmetric reflection conditions using synchrotron radiation are presented. By using a variety of wavelengths and reflections the depth and distribution of defects generated by the fabrication process are explored. Examples of several reflections are given, with a spatial resolution of better than 5 microns and extremely high device and defect visibility. Results suggest that a high mismatch of lattice parameter at device edges leads to the formation of dislocation loops penetrating junctions.
Atomic Structure of Dislocations and Dipoles in Silicon
Authors: Nandedkar A. S. , Narayan J.
Published: March 2011

Dislocations of a/2<110> Burgers vectors lying in {001} and {111} planes in the form of cross-grids are often observed in ion implanted and thermally annealed specimens. In order to asses the mechanism of formation of these dislocations, we have calculated energies and determined atomic core structuresof a/2<110>{001} edge dislocations and their dipoles,and of a/2<110>{111} dislocations in silicon by minimizing the total configurational energy.
Positron Annihilation Spectroscopy of Defects in Solid
Authors: Hautojärvi P.
Published: March 2011

The use of positron annihilation to study vacancy defects and some recent results are reviewed. For metals, theoretical calculations have reached the leyel where they can reliably predict lifetime values of positrons trapped at vacancy defects of various size, geometry and impurity environment. Experimental results are shown on vacancy recovery and vacancysolute interaction in electron irradiated Fe, Nb, and Ta. During last years the technique has been applied also to semiconductors. Positron trapping in Si is discussed and some results are given on native and irradiation induced vacancies in GaAs. A beam of slow positrons is a new tool to probe nearsurface regions and thin films. Examples are shown on Mo(111) surface sputtered with Ar+ ions and on Si(100) implanted with 35 keV H+ ions.
Imaging of Dislocations and SUB–Grain Boundaries in Alumina Through Chromia – Vacancy and Molybdenum Solute Atmospheres
Authors: Raman S.V.
Published: March 2011

The phenomenon of plastic flow in alumina was previously [1 and 2] characterized using sintering models and transmission electron microscopy. Some of the findingsof the work were (a) near equality in the activation energy for volume diffusion and surface area reduction (82 kJ/mol), (b) a higher activation energy (440 kJ/mol) for Coble creep mechanism in the absence of gamma/alpha phase transformation and a lower activation energy (250 kJ/mol) when phase transformation was a part ofthe sintering process and, (c) presence of extended dislocations and deformed electron diffraction spots.

In view of these results it was of interest to follow the effect of solute addition on plastic flow [ 3 ]. The solutes were incorporated in alumina through gel synthesis route and formed solid—solution systems of Cr203— A1203 and MoO3 — A12O3 at 1000°C. In the course of sintering there is partiai vaporization of caromiaand reduction of MoO3. The chromiavacancy and Mo metal thus impart an impurity decoration to the lattice. The scanning electron micrographs seem to show that they are segregated along grain boundaries, sub—grain boundaries and dislocations. With increase in temperature the linear vacancy segregations and the scattered vacancy clusters annihilate to form pores. These pores transform to creep cavities that extend from grain boundary to volume. The clustered occurrence of Mo at grain boundaries and its extended spacing in the subgrain boundary is perhaps indicative of a dislocation pipe model for its segregation. On the basis of these modeling and microstructural results a heuristic argument is presented in favor of kinetic equality among self diffusion, dislocation pipe diffusion and dislocation climb, and in favor of the commencement of Coble and Nabarros—Herring creep with severance of these equalities.
Characterization of Defect Structures by Perturbed Angular Correlation Technique
Authors: Wichert Thomas
Published: March 2011

In applications of the perturbed angular correlation (PAC) technique to the characterization of defect structures in materials conclusions are drawn from the local electric field gradient measured at the site of a radioactive probe atom. In metals, PAC has been very successful in labeling and identifying simple probe atom-defect pairs. Based on these results, new experiments were performed on defect structures in cold-worked samples, on the dynamics of He-defect interactions and on the growth of vacancy clusters. Recent results on interactions between the acceptor atom In and different donor atoms or intrinsic defects in Si indicate that PAC may provide atomistic information also in the case of semiconductor materials.
In Stlo High Resolution Electron Microscopy for Interface Studies
Authors: Parker M. A. , Sinclair R.
Published: March 2011

In situ kinetic measurements on the rate of solid—phase epitaxial regrowth of silicon in a conventional transmission electron microscope are described. The data compare well with those established for the sane material by high voltage electron microscopy and by Rutherford backscattering spectroscopy. High—resolution imaging at the same time provides direct information on atomic mechanisms. It is anticipated that this will beccme a more highly developed procedure in due course, especially for studies of interface reactions.
The Behavior of Oxidation Stacking Faults During O2/NF3 Oxidation of Silicon
Authors: Kim U. S. , Jaccodine R. J.
Published: March 2011

The behavior of oxidation—induced stacking faults(OSFs) during the O2 /NF3 oxidation of silicon has been investigated in the temperature range of 850–1100°C with varying concentration of NF 3 (0.011—0.044 vol%). In this study, we report the rapid and non-linear shrinkage of pregrown OSFs with time by a new oxidation process including small(ppm) additions of fluorine compound to the oxidant. It is also found that the shrinkage rate of OSF decreases as the oxidation time is increased. It is proposed that the fast OSF shrinkage is due to excessive vacancy flux as a result of the reaction of fluorine at the Si/SiO2 interface during the initial transient state, and subsequently the shrinkage rate is reduced as the steady—state condition of vacancy—interstitial recombination is approached.
Characterization of Sub-Surface Structures by Double Crystal X-Ray Diffraction
Authors: Bowen D.K. , Hill M.J. , Tanner B.K.
Published: March 2011

The application of double crystal X-ray diffractometry and computer simulation to the characterization of lattice parameter variations through the thickness of heteroepitaxial layers is reviewed. The sensitivity is demonstrated in studies of graded layers grown by vapour phase epitaxy. Capping layers significantly affect rocking curves from superlattice structures. The use of glancing angle diffraction to characterize thin, low period multilayers is examined.
Beam-Metal Surface Interactions Using an Excimer Laser
Authors: Pellegrino Joseph , Partridge Julian P. , Magee A. , Strutt P.
Published: March 2011

In view of material technological developments, studies have been made of the interactive processes involved in irradiation of metals with an excimer laser. These studies involved single-pulse irradiation of Al, Ni, Ti, and Zn at various powers up to about 5 MW. Systematic studies at widely differing, yet reproducible, power densities were facilitated using numerically controlled beam focusing. By changing the incident intensity, different plasma pressures were produced during surface melting. These created various types of unstable ripple patterns which emanated radially from the center of beam incidence and were enhanced by immersion in liquid nitrogen.

The results showed only minor differences between substrates possessing different physical properties and the influence of crystallographic orientation was also found to be minimal. An elliptical disturbance zone was produced on the substrates when the beam was defocused and this is attributed to astigmatic effects associated with a lens system incorporating spherical refracting surfaces.
Surface Concentration of Defects on a Constrained System: a Molecular Dynamics Approach
Authors: Rosato Vittorio , Guillope Michel
Published: March 2011

We have performed a systematic study to evaluate the structural response of a {110} fcc surface to an externally imposed elastic deformation, by Molecular Dynamics at a fixed temperature T=0.48T and T=0.68T (T melting point). For high contractions along the dense axis [110], surface concentration of defects (SCD) and diffusion coefficient increase with respect to the equilibrium values. The resulting surface disorder is similar to the one found, at equilibrium, at higher temperatures.
The Nature of the Surface of a Metal-Metalloid Metallic Glass
Authors: Brower W. E. , Tlomak P. , Kowbel W. , Pierz S. J.
Published: March 2011

The surface of a metallic glass has been characterized at the atomic and microstructural levels. On the atomic scale, the glassy surface hal been previously characterized via a model which allows the calculation of surface coordination numbers and the fractal dimension. Catalytic experiments and LEIS measurements appear to confirm the model's prediction of surface roughness on the atomic scale. In this work, the glassy surface has been characterized on the microstructural level via RHEED patterns. In addition, the fresh glassy surface produced by comminution of Fe-B glass has been characterized with respect to the relative stability of the comminuted glass as compared to as-quenched glass.
Defects in Laser Surface-Melted Metals Studied by Pac
Authors: Collins Gary S. , Aliard Carl , Hohenemser Christoph , Draper Clifton W.
Published: March 2011

Following nanosecond-duration laser surface-melting, lattice locations of illIn probe atoms in Ni and Pt samples were studied using the technique of perturbed gamma-gamma angular correlations (PAC). After melting and annealing, no probe atoms were observed to become associated with unique vacancy clusters observed after other methods of damaging, while many probe atoms were found on non-unique sites. 111In probe atoms were observed to move to the surface and to be expelled at anomalously low temperatures. These observations are partially reconciled by the hypothesis that probe atoms diffusing in the molten surface layer become trapped on dislocations during resolidification, and during later annealing return to the surface via pipe diffusion.
Adsorption of Oxygen on Sodium Saturated Cu{110}
Authors: Grider D. E. , Wendelken J. F.
Published: March 2011

The adsorption of oxygen on a sodium saturated Cu{110} surface is examined with x-ray photoelectron spectroscopy (XPS) in an extension of a previous study of this system which utilized low energy electron diffraction (LEED), and high resolution electron energy loss spectroscopy (HREELS). The sodium overlayer, despite the presence of an initial oxide contaminant, shows metallic character. Intentionally adsorbed oxygen is in a different chemical state than the initial oxygen contaminant and causes a reduction in the metallic character of the sodium. The sticking coefficient for oxygen on the sodium saturated surface is almost three times greater than for the bare Cu{11O} surface.