bluuebunny/crossref_metadata_2025_split huggingface dataset:
Initial Stages of Interface Formation in the Si/Sn System
Authors: Zinke-Allmang M. , Gossmann H.-J. , Feldman L. C. , Fisanick G. J. 
Published: March 2011

ABSTRACTGroup IV-IV heterostructures with Sn as one constituent have potentially important applications. We report on an investigation of the initial stages of interface formation for deposition of Sn on Si(100)2×1 and Si(111)7×7. We find that simple growth occurs up to a critical coverage θc. (α1.25×1015 cm-2), independent of temperature. Beyond θc. growth continues to be laminar for deposition at 150 K only, while island formation is observed at temperatures at and above room temperature. The Si(111)7×7 reconstruction seems unperturbed by Sn deposition at room temperature while the Si(100)2×1 begins to order. However, the reordering, a necessary condition for perfect growth, is incomplete.
Compositional Determination of Silicon Oxynitride Films
Authors: Hatton Kenneth S. , Wachtman John B. , Haber Richard A. , Wilkens Barry 
Published: March 2011

ABSTRACTSilicon oxynitride thin films made by RF reactive sputtering can be made with varying composition along the silicon dioxide - silicon nitride tie line by control of the sputtering gases. Compositional determination was made by the Rutherford backscattering technique. A simple model relating film composition to the composition of the reactive gases is proposed which fits the experimental results.
Elastic Stresses in InGaAsP Heterostructures with Alloyed Contact Metallizations
Authors: Swaminathan V. , Lopata J. , Lee J. W. 
Published: March 2011

ABSTRACTWe have measured the radius of curvature of InGaAsP/InP heterostruc-ture wafers grown by liquid phase epitaxy, after growth and after broad area p-and n-metallizations used in the fabrication of 1.3vm lasers, by the x-ray automatic Bragg angle control technique. The heterostructure consisted of an n-InP buffer layer (0.2μm), an InGaAsP active layer (0.3 – 0.4μm), a p-InP layer (0.7μm) and either a p-InGaAsP or a p-InGaAs cap layer (0.6 – 0.7μm) grown on a 250 μm thick n-Inp substrate. The radius of curvature measured after growth was found to be in good agreement with the value calculated using the lattice mismatch strains. The changes in the radius of curvature after deposition and alloying of a 1000 Å thick AuZnAu p-metallization and after thinning the substrate to 86μu followed by 2900 Å thick alloyed GeAu n-metallization are such that the metal films are under a tensile strain. The value of the strain is calculated to be 8 × 10-3 and 1.6 × 10-3 respectively for the p- and n-metals. The radius of curvature was measured after the final metallization and annealing of 2500 A thick TiPt layer on the p-side. The annealed TiPt layer was found to have a compressive strain of 6 × 10-3. The stress in the active layer remained tensile at all times for both wafers and it was in the range 9 × 10 – 1.4 × 10 dyne cm-2. These values are less than the estimated fracture stress of InGaAsP by an order of magnitude.
Molecular-Dynamics Simulation of Thin-Film Growth
Authors: Schneider Matthias , Schuller Ivan K. , Rahman A. 
Published: March 2011

ABSTRACTThe epitaxial growth of thin films has been studied by molecular-dynamics computer simulation. In these simulations atoms are projected towards a temperature-controlled substrate, and the equations of motion of all atoms are solved for a given interaction potential. The calculations give insight into the microscopic structure of thin films, the dynamics of the adsorption process, and they help answer the way in which substrate temperature, form of the substrate, flux of impinging atoms, and form of the interaction potential, affect epitaxial growth. Simulations were performed for monatomic and binary systems with spherically symmetric atomic interactions, and for systems in which the atoms are interacting via a three-body potential to simulate the epitaxial growth of silicon.
Strength Improvement in Transformation Toughened Ceramics using Compressive Residual Surface Stresses
Authors: Cutler R. A. , Hansen J. J. , Virkar A. V. , Shetty D. K. , Winterton R. C. 
Published: March 2011

ABSTRACTA1 2 03–15 vol. % ZrO2 bar shaped composite specimens were fabricated by pressing three layers. The two outer layers consisted of Al2O3 and unstabilized ZrO2 (primarily in the monoclinic polymorph), and the inner layer consisted of Al2O3 and partially stabilized zirconia in the tetragonal polymorph. The transformation of ZrO2 from tetragonal to monoclinic, upon cooling from sintering temperature, led to the establishment of residual compressive stresses in the outer layers. Flexural tests at room temperature showed that residual stresses contributed to strength increasing from 450 to 825 MPa. The existence of these stresses was verified by measuring apparent fracture toughness, as well as using strain gages. Strength and toughness data were obtained at 500, 750, and 1000°C. X-ray diffraction was used to explain the elevated temperature data by monitoring the monoclinic to tetragonal transformation upon heating to 1000°C.
The Strength of Fibres in All-Ceramic Composites
Authors: Kendall Kevin , Alford N. Mcn. , Birchall J. D. 
Published: March 2011

ABSTRACTWhen 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

ABSTRACTA 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

ABSTRACTWhisker 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

ABSTRACTThe 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

ABSTRACTPreviously, 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

ABSTRACTRecent 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

ABSTRACTThe 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

AbstractWe 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

AbstractAn 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

AbstractThe 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

AbstractThe 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

AbstractSpark 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

AbstractThe 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

AbstractMartensitic 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

AbstractIn 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

AbstractAmorphous 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

AbstractFatigue 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.