bluuebunny/crossref_metadata_2025_split huggingface dataset:
High Temperature Compressive Properties and Deformation Microstructure of Fe-25Al-10Ti Intermetallic Alloy
Authors: Zhu Su-Ming , Sakamoto Kazushi , Tamura Makoto , Iwasaki Kunihiko 
Published: April 2011

ABSTRACTThe compressive properties of Fe-25Al-10Ti intermetallic alloy were studied as a function of temperature and strain rate. Optical microscopy and transmission electron microscopy (TEM) were used to examine the deformation microstructure. The alloy exhibited strong tendency of strain hardening at low temperatures. A positive temperature dependence of strength was observed in the 673 – 873 K range. The mechanical behavior was interpreted in terms of dislocation structures. Based on the analysis of the stress-strain response, strain rate sensitivity and deformation microstructure, possible hot working range was proposed.
Mechanical Properties of Fe3Al Intermetallic Matrix Composites
Authors: Park B.G. , Ko S.H. , Park Y.H. 
Published: April 2011

ABSTRACTIron aluminides are of considerable interest due to their low cost, relatively high melting point, relatively low density, and excellent resistance to oxidation, sulfidation and molten salts. However, poor ductility and fracture toughness at room temperature hinder their use as a structural material. Refining of the microstructure is known to be one method to increase the room temperature ductility. Mechanical alloying (MA) is an easy way to obtain fine microstructures. In addition, pulse discharge sintering (PDS) is a new technology which suppresses grain growth during sintering because the sparks generated during sintering break the surface oxide layer of the powder particles and thus speed up the sintering process. Therefore, the combination of MA and PDS processes results in final products with very fine microstructures. Fe-28at.%Al alloy and its composite reinforced with 5vol.% of TiB2particles were fabricated by the MA-PDS process. The mechanical properties of these materials were improved significantly as compared to conventionally processed materials.
Tailoring the thermal expansion anisotropy of Mo5Si3
Authors: Schneibel Joachim H. , Rawn Claudia J. , Fu Chong Long 
Published: April 2011

ABSTRACTThe silicide Mo5Si3, with the W5Si3 structure, exhibits a high anisotropy of its coefficients of thermal expansion (CTEs) in the a and c directions, namely, CTE(c)/CTE(a)=2.2. In order to determine whether the CTE anisotropy can be controlled, molybdenum was partially substituted with Nb. CTEs were determined by high temperature x-ray powder diffraction. Partial substitution with 44 at. % Nb reduced the value of CTE(c)/CTE(a) to a value near 1. For higher Nb concentrations, CTE(c)/CTE(a) increased again. When nearly all the Mo was replaced by Nb, the crystal structure changed to the Cr5B3 structure type and the CTE anisotropy decreased to a value near 1. Our thermal expansion results are interpreted in terms of the site occupation of Nb, the Nb-induced increase in the interatomic spacing of the Mo atom chains along the c-direction, and the reduction in the anisotropy of the lattice anharmonicity in the a and c directions.
High-Temperature Compression Strength of Directionally Solidified Nb-Mo-W-Ti-Si In-Situ Composites
Authors: Hirai Hisatoshi , Tabaru Tatsuo , Sha Jiangbo , Ueno Hidetoshi , Kitahara Akira , Hanada Shuji 
Published: April 2011

ABSTRACTDirectionally solidified Nb-xMo-22Ti-18Si (x = 10, 20 and 30 mol%) and Nb-10Mo-yW-10Ti-18Si (y = 0, 5, 10 and 15 mol%) alloys were prepared. All of the alloys consisted of Nb solid solution and (Nb, Mo, (W,) Ti)5Si3 silicide. In compression tests performed on the Nb-xMo-22Ti-18Si alloys, a sample with x = 10 had the highest maximum stress at 1670 K, but it showed a sharp stress drop after reaching the maximum stress. Samples with x = 20 and 30 showed lower yield and lower maximum stress than that with x = 10, and they showed a small stress drop and an almost constant flow stress of 330 and 400 MPa, respectively. The sample with x = 20 showed a minimum creep rate (εm) of 9.6 × 10-7 s-1 at 1670 K at a stress of 200 MPa. The yield stress of the Nb-10Mo-yW-10Ti-18Si alloys increased with increasing W content, although the stress decreased gradually after reaching the maximum stress and showed no steady state deformation. The εm of the sample with y = 15 was 1.4 × 10-7 s-1 at 1670 K at a stress of 200 MPa, which was much slower than that of Nb-20Mo-22Ti-18Si.
Void Morphology In NiAl
Authors: Zakaria M. , Munroe P.R. 
Published: April 2011

ABSTRACTVoid formation in stoichiometric NiAl was studied through controlled heat treatments and transmission electron microscopy. Voids formed at temperatures as low as 400°C, but dissolved during annealing at 900°C. Both cuboidal and rhombic dodecahedral voids were observed, often at the same annealing temperature. At higher annealing temperatures (>800°C) extensive dislocation climb was noted. The relative incidence of void formation and dislocation climb can be related to the mobility of vacancies at each annealing temperature. Further, differences in void shape can be described in terms of their relative surface energy and mode of nucleation.
Fracture Strength of Grain Boundaries in Ni3Al
Authors: Su Jian-Qing , Demura M. , Hirano T. 
Published: April 2011

ABSTRACTThe fracture strength of grain boundaries in Ni3Al was quantitatively measured by performing tensile tests on miniature bicrystal specimens with various grain boundary types. A fairly good relationship between fracture mode, fracture strength and Σ value was established. The Σ1, Σ3 and Σ9 boundaries were found to be strongly crack-resistant but the adjacent bulk fractured. In contrast, Σ5, Σ7, Σ11, Σ13 and random boundaries were found to be less crack-resistant and fractured at lower stresses than the fracture strength of the bulk. In the latter case, the fracture strength of the Σ11 and Σ13 boundaries was higher than that of the Σ5 and Σ7 boundaries. Most random boundaries were as weak as the Σ5 and Σ7 boundaries, but some exhibited high fracture strength comparable to that of the Σ11 and Σ13 boundaries.
Atomistic Modeling Of Ternary And Quaternary Ordered Intermetallic Alloys
Authors: Bozzolo Guillermo , Khalil Joseph , Bartow Matthew , Noebe Ronald D. 
Published: April 2011

ABSTRACTThe structure of ternary and quaternary NiAl-based ordered intermetallic alloys is studied using the BFS method for alloys. A simple calculational procedure, based on the determination of the energetics of local environments surrounding defect atoms is introduced and applied to the study of the defect structure and phase formation in NiAl-based systems. The procedure is illustrated with two different examples: 1) the phase structure of Ni-Al-Fe alloys, focusing on the concentration dependence of the site preference behavior of Fe in NiAl, and 2) the precipitation of a β′ phase in NiAl(Ti,Hf) alloys, focusing on the role of Hf in lowering the solubility limit of Ti in NiAl, thus enhancing the precipitation of a Heusler Ni2Al(Ti,Hf) phase.
Direct Molecular Dynamics Simulations of Diffusion Mechanisms in NiAl
Authors: Farkas D. , Soulé de Bas B. 
Published: April 2011

ABSTRACTMolecular dynamics simulations of the diffusion process in ordered B2 NiAl at high temperature were performed using an embedded atom interatomic potential. Diffusion occurs through a variety of cyclic mechanisms that accomplish the motion of the vacancy through nearest neighbor jumps restoring order to the alloy at the end of the cycle. The traditionally postulated 6-jump cycle is only one of the various cycles observed and some of these are quite complex. A detailed sequential analysis of the observed 6-jump cycles was performed and the results are analyzed in terms of the activation energies for individual jumps calculated using molecular statics simulations.
Long-Term Creep and Oxidation Behavior of a Laves Phase-Strengthened NiAl-Ta-Cr Alloy for Gas Turbine Applications
Authors: Palm Martin , Sauthoff Gerhard 
Published: April 2011

ABSTRACTA Laves phase strengthened NiAl-Ta-Cr alloy (IP 75) has been developed for structural applications in gas turbines as well as in heat exchangers. It has a lower density and a higher thermal conductivity as well as a higher melting point than conventional superalloys. Different methods for alloy production have been established including investment casting (IC) and a powder metallurgical method (PM). Creep properties have been determined in compression and tension. Tension tests up to 10000 hours were performed at 900 °C and 1000 °C for both PM and IC materials. The oxidation behavior of the PM and IC material was studied for up to 1000 hours by thermogravimetry in air at constant temperature between 600 °C and 1300 °C. The results are compared with results obtained from long-term isothermal and cyclic oxidation experiments in air at 1200 °C for 17900 hours. Microstructures and scales were examined by light optical and scanning microscopy, X-ray powder diffraction and electron probe microanalysis.
Static and Dynamic Strain Ageing in Two-Phase Gamma Titanium Aluminides
Authors: Christoph U. , Appel F. 
Published: April 2011

ABSTRACTThe deformation behaviour of two-phase titanium aluminides was investigated in the intermediate temperature interval 450–750 K where the Portevin-LeChatelier effect occurs. The effect has been studied by static strain ageing experiments. A wide range of alloy compositions was investigated to identify the relevant defect species. Accordingly, dislocation pinning occurs with fast kinetics and is characterized by a relatively small activation energy of 0.7 eV, which is not consistent with a conventional diffusion process. Furthermore, the strain ageing phenomena are most pronounced in Ti-rich alloys. This gives rise to the speculation that antisite defects are involved in the pinning process. The implications of the ageing processes on the deformation behaviour of two-phase titanium aluminide alloys will be discussed.
Metal-Alloy Nanocluster Formation in Silica Glass by Sequential Ion Implantation
Authors: Battaglin G. , Cattaruzza E. , Gonella F. , D'Acapito F. , Fernandez C. de Julian , Mattei G. , Maurizio C. , Mazzoldi P. , Sada C. 
Published: April 2011

AbstractSequential ion implantation of two metal species in silica glass may give rise to the formation of alloy metal nanoclusters. Composite materials with peculiar optical properties can be therefore fabricated, with application in integrated-optical devices. In the presented experiments, different couples of transition elements were sequentially implanted in a silica glass. The resulting systems, in some cases after annealing in either reducing or oxidizing atmosphere, were studied by several analytical techniques, such as transmission electron microscopy and X-ray absorption spectroscopy. The formation of different alloy nanoclusters was evidenced, together with the cluster crystalline structure and the chemical environment of the dopant species.
The control of gold nanocluster sizes in dielectric thin films via ion beam assisted deposition
Authors: Schiestel S. , Carosella C.A. , Hubler G.K. , Qadri S.B. , Knies D. , Stroud R.M. 
Published: April 2011

AbstractGold nanoclusters in silica were deposited by co-evaporation of gold and silica in the presence of an argon ion beam. Gold clusters are formed in-situ during the deposition process. The damage induced by the ion beam controls the cluster size, and clusters with a diameter between 15 – 30 Å are obtained. The Au clusters show a highly compressive strain as measured by X-ray diffraction and lattice parameters up to 3.5 % smaller than in bulk gold are observed. Post- deposition annealing in air leads to cluster growth and release of the strain. Annealing near the melting point of gold causes the clusters to grow exponentially up to 180 Å. This is accompanied by a blue shift of the Mie absorption peak. Furthermore the formation of a superlattice was observed by TEM and confirmed by small angle XRD measurements.
Synthesis of B-C-N Thin Films by Ion-Beam-Assisted Deposition and Their Mechanical Properties
Authors: Matsumuro Akihito , Kato Yoshimasa , Ohta Hidenobu 
Published: April 2011

AbstractB-C-N films have been synthesized by an ion-beam-assisted deposition technique, in which boron and carbon were evaporated by electron beam and a mixed nitrogen and argon ion beam was simulataneously irradiated onto silicon (100) substrates. The ratio of argon ions to nitrogen ions was varied by the flow rate ratio of Ar and N2 gases fed into the ion source. In this experiment, the influence of the ratio on the mechanical properties and the microstructure were investigated. Nano indentation studies show the maximum hardness up to 23 GPa at the gas ratio of 25.50 %. The films prepared under the appropriate conditions indicated low friction coefficients of 0.04-0.08 against a sapphire ball and excellent wear resistance. The existence of a cubic B-C-N like phase in the film, which has been predicted as one of new hard materials, was revealed by various micro-structural analyses. It was concluded that the excellent mechanical properties prepared at the optimum gas ratio could be attributed to the appearnce of the new cubic like phase.
Doping of GaN by ion implantation
Authors: Alves Eduardo J. , Liu C. , Silva Maria F. da , Soares José C. , Correia Rosário , Monteiro Teresa 
Published: April 2011

AbstractIn this work we report the structural and optical properties of ion implanted GaN. Potential acceptors such as Ca and Er were used as dopants. Ion implantation was carried out with the substrate at room temperature and 550 °C, respectively. The lattice site location of the dopants was studied by Rutherford backscattering/channeling combined with particle induced X-ray emission. Angular scans along both [0001] and [1011] directions show that 50% of the Er ions implanted at 550 °C occupy substitutional or near substitutional Ga sites after annealing. For Ca we found only a fraction of 30% located in displaced Ga sites along the [0001] direction. The optical properties of the ion implanted GaN films have been studied by photoluminescence measurements. Er- related luminescence near 1.54 µm is observed under below band gap excitation at liquid helium temperature. The spectra of the annealed samples consist of multiline structures with the sharpest lines found in GaN until now. The green and red emissions were also observed in the Er doped samples after annealing.
Determination of the Distribution of Ion Implantation Boron in Silicon
Authors: Wang Te-Sheng , Cullis A.G. , Collart E.J.H. , Murrell A.J. , Foad M.A. 
Published: April 2011

AbstractBoron is the most important p-type dopant in Si and it is essential that, especially for low energy implantation, both as-implanted B distributions and those produced by annealing should be characterized in very great detail to obtain the required process control for advanced device applications. While secondary ion mass spectrometry (SIMS) is ordinarily employed for this purpose, in the present studies implant concentration profiles have been determined by direct B imaging with approximately nanometer depth and lateral resolution using energy-filtered imaging in the transmission electron microscopy. The as-implanted B impurity profile is correlated with theoretical expectations: differences with respect to the results of SIMS measurements are discussed. Changes in the B distribution and clustering that occur after annealing of the implanted layers are also described.
Crystallization of Isolated Amorphous Zones in Semiconductor Materials
Authors: Hollar Eric P. , Robertson Ian M. , Jenčič Igor 
Published: April 2011

AbstractCrystallization of spatially isolated amorphous zones in Si, Ge, GaP, InP and GaAs was stimulated thermally and by irradiation with electrons and photons. The amorphous zones were created by a 50 keV Xe+ implantation. Significant thermal crystallization occurred at temperatures greater than 425 K, 375 K and 200 K in Si, Ge and GaAs, respectively. Electrons with energies between 25 and 300 keV stimulated crystallization in all materials at temperatures between 90 K and room temperature. For electron energies above the displacement threshold, the crystallization rate decreased as the electron energy decreased. As the electron energy was decreased below approximately 100 keV, the crystallization rate unexpectedly increased. The crystallization rate was independent of temperature for all electron irradiations. Irradiation with a 532 nm green laser (hv= 2.33 eV) caused crystallization in Si (Eg = 1.11 eV) and Ge (Eg = 0.67 eV) at a rate comparable to a thermal anneal at 425 K and 375 K, respectively, and caused minimal crystallization in GaP (Eg = 2.26 eV). The electron and photon irradiation results are consistent with the model that crystallization is controlled by defects (dangling bonds and kinks) created by electronic excitation at the amorphous-crystalline interface.
Optical and Structural Changes of Fe Implanted Sapphire
Authors: Marques Carlos P. , Alves Eduardo J. , McHargue Carl J. , Silva Maria F. da , Soares José C. , Correia Rosário , Soares Manuel J. , Monteiro Teresa 
Published: April 2011

AbstractSingle crystalline colorless α-Al2O3 samples were implanted with several fluences of Fe+ ions in the range of 1×1016 to 5×1017 Fe+ cm-2 at room temperature. Optical absorption and luminescence measurements were carried out before and after annealing in reducing and oxidizing atmospheres. The structural changes were studied with RBS/channeling and x-ray diffraction. After implantation, the damage induces a brownish coloration in the samples for fluences below 2×1017 Fe+ cm-2. The optical spectra are characterized by an absorption band centered at 200 nm. This band is strongly reduced after annealing at 1100 °C in reducing atmosphere and a new well-defined band develops around 350 nm. This new band shifts to lower values with the implanted fluence, which is an indication of its correlation with the dimensions of the iron precipitates formed in the implanted region. The existence of these precipitates was confirmed by x-ray diffraction and TEM. The samples implanted with fluences above 1×1016 Fe+ cm-2 annealed in oxidizing atmosphere display different optical absorption spectra, with respect to those annealed in reducing atmosphere, characterized by an increase in the intensity of the peak at 200 nm. Luminescence measurements show the presence of F and F+ centers in the samples. The existence of these defects can be explained by the need of charge compensation and strain release due to the formation of mixed iron oxide or metallic precipitates.
Modification of the electronic properties of a-Si1-xCx:H by Fe+ ion implantation
Authors: Tsvetkova T. , Balabanov S. , Amov B. , Angelov Ch. , Zuk J. , Maczka D. , Adriaenssens G.J. , Iakoubovskii K. 
Published: April 2011

AbstractThe electrical and optical properties of hydrogenated amorphous silicon-carbide alloy films (a-Si1-xCx:H), modified by Fe+ ion implantation (D = 1×1016 - 1×1017 cm-2), have been investigated. Optical transmission spectra have been measured in the visible range (400-900 nm) and considerable absorption edge shift to the longer wavelength region has been registered, together with well-defined decrease of transmittance in the whole measured range. These effects are increased with the dose and are similar for samples with different carbon content (x1=0.08 and x2=0.15). Room temperature (RT) surface electrical conductivity is also increased by Fe+ implantation and the effect is most pronounced for the highest doses (D ~ 1017cm-2). The temperature dependence of the conductivity was measured in the temperature range from RT to 250 oC. The activation energy is considerably reduced and the effect is again strongest for the highest doses. From the above results we conclude that high doses Fe+ implantation in a-Si1-xCx:H affects both the localised states deep in the gap and the shallow states in the band tails.
Atomistic simulations of the Ostwald ripening of Si nanoparticles ion beam synthesized in SiO2
Authors: Bonafos C. , Carrada M. , Colombeau B. , Altibelli A. , Assayag G. Ben , Garrido B. , Lopez M. , Perez-Rodriguez A. , Morante J. R. , Claverie A. 
Published: April 2011

AbstractMost studies of Si nanocrystals ion beam synthesized in SiO2have shown that a link exists between the observed physical properties and the characteristics of the « populations » of nanoparticles (size-distribution, density, volume fraction). Nevertheless, the direct measurement of these parameters by Transmission Electron Microscopy (TEM) is very difficult and predictive simulations are essential to make the kinetic study complete. This paper presents atomistic simulations aimed at predicting the kinetic evolution of the Si nanoparticles during annealing, taking into account eventual interaction effects. The theoretical results are compared to TEM measurements of the size-distributions observed after high temperature annealing. Experimentally, the growth of these nanoparticles is very slow but their size significantly increases when increasing the initial Si excess. Simulations are in agreement with these experimental results only when taking into account possible interactions between neighboring particles for initial supersaturations larger than 10 at. %.
Effects of Ga-Irradiation On Properties of Materials Processed by A Focused Ion Beam (FIB)
Authors: Wanzenboeck H. D. , Langfischer H. , Lugstein A. , Bertagnolli E. , Grabner U. , Pongratz P. , Basnar B. , Smoliner J. , Gornik E. 
Published: April 2011

AbstractFocused Ion Beam (FIB) technology allows to process various materials within a lateral range below 100 nm. The feasibility to mechanically sputter as well as to direct-write nanostructures and the fact that Ga-ions are utilized is unique for this method. The focused Ga-ions are used to locally induce a chemical vapor deposition of volatile precursor molecules adsorbed on a surface. Local deposition of metals and dielectrics has been achieved on a sub-µm scale utilizing a focused ion beam. This method is highly suitable for advanced microelectronic semiconductor fabrication. However, material specifications are narrow for these tailor-made applications. The effect of the Ga-ions implanted into the material both during sputtering and deposition has been realized as a key parameter for the function of FIB processed microelectronic devices. For Si-based semiconductors Ga can be used as dopant intentionally implanted into a Si substrate to locally modify the conductivity of Si. The results of locally confined ion irradiation on the surface roughness of a Si surface have been exploited by atomic force microscopy (AFM). Both local sputter depletion of the sample surface as well as sub-µm deposition of selected metals or dielectrics by ion-induced chemical vapor deposition (CVD) has been examined. The penetration depth and the distribution of Ga ions during the deposition process have been studied by simulation and experimentally by profiling with secondary ion mass spectroscopy (SIMS). Transmission Electron Microscopy (TEM) of cross-sections of the ion processed materials has revealed amorphisation of the crystalline substrate. For focused ion beam assisted deposition the effects of ion irradiation on the interface to the substrate and the local efficiency of the deposition are illustrated and discussed. The prospects of focused ion beam processing for modification of microelectronic devices in the sub-µm range and the limitations are demonstrated by the examples shown.