bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of some Microstructural and Test Parameters on the Tensile Stress and Ductility Behaviour of a MA FeAl Intermetallic
Authors: Chao J. , Muñoz-Morris M.A. , Gonzalez-Carrasco J.L. , Morris D.G. 
Published: April 2011

ABSTRACTThis study examines the influence of microstructural parameters (grain and dispersoid size, vacancy content) and some test parameters (strain rate, protective oxide coatings, air and water vapour excluding films, and surface geometrical quality) on the tensile behaviour (yield stress, work hardening rate, tensile stress, ductility) of a mechanically-alloyed, fine-grained Fe-40Al intermetallic. Major changes of strength and ductility are obtained by changing grain size (1% and 10% for grain sizes of 100μm and 1μm) and by avoiding premature stress/strain concentrators (ductility increased from 5% to 10% for imperfectly machined to prepolished samples). Ductility variations are interpreted using a slow-crack-propagation-to-instability model, where the roles of environment, surface state, deformation processes, and fracture mechanisms can be distinguished.
Microstructure and Plastic Deformation in Unidirectionally Solidified NbSi2 (C40) /MoSi2 (C11b) Crystals
Authors: Nakano Takayoshi , Nakai Yasuhiro , Umakoshi Yukichi 
Published: April 2011

ABSTRACTMicrostructure and plastic deformation behavior in duplex-phase silicides composed of the C40 and C11b phases were examined using pseudo-binary (Nb,Mo)Si2 crystals with a single set of lamellae. Single crystals of the C40 single-phase were grown from the master ingot with a composition of (Nb0.15Mo0.85)Si2 by a floating zone method and duplex-phase microstructure containing a single set of lamellae was obtained by subsequent heat treatment at 1400°C for no less than 6h. During the heat treatment, the C11b phase was precipitated from the C40 matrix by satisfying the crystallographic relationship of (0001)C40//(110)C11b, <1210]C40//[110]C11b and < [1010]C40//[001]C11b at the lamellar boundary, while randomly oriented C11b grains also appeared at further annealing. As a result, the duplex-phase silicides with a single set of lamellae contained the C40 phase with a single orientation and three variants of the C11b phase. The lamellar spacing and the volume fraction of their phases depended strongly on annealing time.In compression tests, yield stress and fracture strain of the duplex-phase silicides depended strongly on angle (φ) between the loading axis and lamellar boundaries, similar to TiAl-PST crystals. At φ=0°, specimens fractured just after showing high fracture stress even at 1400°C. In contrast, at φ=45° where shear deformation in the C11b phase of lamellae occurred parallel to lamellar boundaries, low yield stress and significant plastic strain were achieved at 1400°C.
C11b/C40 Lamellar Structure in a Ta-added Molybdenum Disilicide
Authors: Wei Fu-Gao , Kimura Yoshisato , Mishima Yoshinao 
Published: April 2011

ABSTRACTC11b/C40 fully lamellar microstructures, similar to the well-known TiAl/Ti3Al lamellae, were obtained in Ta- and Nb-added MoSi2 polycrystalline alloys in a previous work. In the present study, the crystallography of the lamellar structure is investigated in a MoSi2-15mol%TaSi2 pseudo-binary alloy after homogenized at 1400°C for 168h, in order to provide some useful parameters for microstructural control to improve mechanical properties. The orientation relationship between C11b and C40 phases and its three distinct variants were identified. Coherency of the lamellar interface is analyzed in comparison with the TiAl/Ti3Al lamellae. Approach to modify the C11b/C40 lamellar microstructure to increase its coherency is discussed based on the results obtained.
Dislocation Processes and Deformation Behavior in <001>-Oriented FeX-Ni60–X-Al40 Single Crystals
Authors: Brenner P. S. , Srinivasan R. , Noebe R. D. , Lograsso T. , Mills M. J. 
Published: April 2011

ABSTRACTThe mechanical properties and dislocation microstructure of single crystals with a range of compositions within the Fex-Ni60–x-Al40 pseudobinary system have been investigated, with the purpose of bridging the behavior from FeAl to NiAl. Experiments are focused on the compression testing of <001> oriented single crystals with compositions where x = 10, 20, 30, 40, and 50 (in atomic percent). Observations of a<111> dislocation morphologies at room temperature and both a<111> and non-a<111> dislocation activity at elevated temperatures are reported and discussed. Measurements of the yield strength, elastic modulus and strain hardening rates are reported, and the variation of strength with composition is correlated with dislocation dissociation and overall dislocation morphology.
Nonstoichiometry and Defect Mechanism in Intermetallics with L12-Structure
Authors: Ipser Herbert , Semenova Olga P. , Krachler Regina , Schweitzer Agnes , Yuan Wenxia , Peng Ming , Qiao Zhiyu 
Published: April 2011

ABSTRACTA statistical-thermodynamic model was derived which allows to describe thermodynamic activities in intermetallic compounds with L12-structure as a function of composition and temperature. The energies of formation of the four types of point defects (anti-structure atoms and vacancies on both sublattices) were used as adjustable parameters. The model was applied to the three compounds Ni3Al, Ni3Ga, and Pt3Ga, and it permitted to estimate for the first time the defect formation energies for Ni3Ga and to provide initial estimates for Pt3Ga.
Synthesis of Spatially Controlled Nanostructures by Ion Implantation in V-Grooves on (001) Si Surfaces
Authors: Müller Torsten , Heinig Karl-Heinz , Schmidt Bernd , Mücklich Arndt , Möller Wolfhard 
Published: April 2011

AbstractThe synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxidation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm−2. Ge accumulates within the SiO2 at the bottom of the V-groove, which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that the Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalescence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.
Mechanical Properties of AlN Thin Films Prepared by Ion Beam Assisted Deposition
Authors: Miyabe Shuichi , Okawa Toshiyuki , Kitazawa Nobuaki , Watanabe Yoshihisa , Nakamura Yoshikazu 
Published: April 2011

AbstractAluminum nitride (AlN) thin films were prepared by ion-beam assisted deposition method, and the influence of the nitrogen ion beam energy on their microstructure and mechanical properties was studied by changing the ion beam energy from 0.1 to 1.5 keV. Films prepared with a low-energy ion beam show a columnar structure, while films prepared with a high-energy ion beam show a granular structure. The film hardness is found to decrease with increasing nitrogen ion beam energy. It is also found that the film hardness does not change drastically after annealing in nitrogen atmosphere at 500 °C, yielding the residual stress relaxation. It is proposed that the film hardness is dependent on the film microstructure, which can be controlled with the nitrogen ion beam energy, rather than the residual stress in the films.
synthesis of III-Nx-V1-x Thin Films by N Ion Implantation
Authors: Yu K. M. , Walukiewicz W. , Shan W. , Wu J. , Beeman J. W. , Ager J. W. , Haller E. E. , Ridgway M.C. 
Published: April 2011

AbstractDilute III-Nx-V1-x alloys were successfully synthesized by nitrogen implantation in GaAs and InP. The fundamental band gap energy for the ion beam synthesized III-Nx-V1-x alloys was found to decrease with increasing N implantation dose in a manner similar to that commonly observed in epitaxially grown GaNxAs1-x and InNxP1-xthin films. The fraction of N occupying anion sites ("active" N) in the GaNxAs1-x layers formed by N implantation was thermally unstable and decreased with increasing annealing temperature. In contrast, thermally stable InNxP1-x alloys with N mole fraction as high as 0.012 were synthesized by N implantation in InP. Moreover, the N activation efficiency in InP was at least a factor of two higher than in GaAs under similar processing conditions. The low N activation efficiency (<20%) in GaAs can be improved by co-implanting Ga and N in GaAs.
Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation
Authors: Heinig K.-H. , Schmidt B. , Strobel M. , Bernas H. 
Published: April 2011

AbstractUnder ion irradiation collisional mixing competes with phase separation if the irradiated solid consists of immiscible components. If a component is a chemical compound, there is another competition between the collisional forced chemical dissociation of the compound and its thermally activated re-formation. Especially at interfaces between immiscible components, irradiation processes far from thermodynamical equilibrium may lead to new phenomena. If the formation of nanoclusters (NCs) occurs during ion implantation, the phase separation caused by ion implantation induced supersaturation can be superimposed by phenomena caused by collisional mixing. In this contribution it will be studied how collisional mixing during high-fluence ion implantation affects NC synthesis and how ion irradiation through a layer of NCs modifies their size and size distribution. Inverse Ostwald ripening of NCs will be predicted theoretically and by kinetic lattice Monte-Carlo simulations. The mathematical treatment of the competition between irradiation-induced detachment of atoms from clusters and their thermally activated diffusion leads to a Gibbs-Thomson relation with modified parameters. The predictions have been confirmed by experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The unusual behavior results from an effective negative capillary length, which will be shown to be the reason for inverse Ostwald ripening. Another new phenomenon to be addressed is self-organization of NCs in a d-layer parallel to the Si/SiO2 interface. Such d-layers were found when the damage level at the interface was of the order of 1-3 dpa. It will be discussed that the origin of the d-layer of NCs can be assigned to two different mechanisms: (i) The negative interface energy due to collisional mixing gives rise to the formation of tiny clusters of substrate material in front of the interface, which promotes heteronucleation of the implanted impurities. (ii) Collisional mixing in the SiO2produces diffusing oxygen, which may be consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si excess promotes heteronucleation too. Independent of the dominating mechanism of self-organization of a d-layer of NCs, its location in SiO2 close to the SiO2/Si interface makes it interesting for non-volatile memory application.
Characterization of Thin Layers of Metal Clusters Embedded in Silica Glass Formed by High Dose Ion Implantation
Authors: Chung P.S. , Wong S.P. , Cheung W.Y. , Ke N. , Lee W.K. , Chan C.W. 
Published: April 2011

AbstractThin layers of metal clusters in silica glass were formed by high dose ion implantation of Ag, Ni and Cu using a metal vapor vacuum arc (MEVVA) ion source. Characterization of the implanted layers was performed using Rutherford backscattering spectroscopy, transmission electron microscopy, x-ray diffraction, and optical measurements. The nonlinear optical properties of the implanted samples were studied by the z-scan method, using a self mode-locked Ti: sapphire laser delivering linearly polarized pulses of 130fs long at a wavelength of 790nm at 76MHz. The variation of the intensity-dependent refractive index n2 with the ion species and the implantation conditions were studied. An n2 value of about 0.6 cm2/GW was measured for one of the Cu and Ni co-implanted samples. The correlation between n2 and the cluster size was also analyzed. Ellipsometry spectra of the samples were measured in the visible range from 0.4 to 0.7 [.proportional]m and in the near infrared range from 0.9 to 1.6 [.proportional]m. Preliminary results are reported on our attempt to deduce the effective complex refractive indices of the implanted layers by fitting of the ellipsometry spectra using a simple single uniform layer on substrate model and the Maxwell-Garnett effective medium approximation.
Gold Nanoclusters Formed by Ion-Implantation into Bi2TeO5
Authors: Kling A. , da Silva M.F. , Soares J.C. , Fichtner P.F.P. , Amaral L. , Zawislak F.C. , Földvári I. , Péter Á. 
Published: April 2011

AbstractSingle crystalline samples of bismuth tellurite (Bi2TeO5) were implanted with 800 keV Au+ions to a fluence of 1×1016 cm-2 at room temperature. The samples were subjected to heat treatments in two different ambients (air and high vacuum) at temperatures ranging from 400 - 700°C in a conventional furnace. Strong absorption maxima in the range from 600 - 630 nm in the optical absorption spectra and an intense blue-green color in the samples were observed for annealings performed in air at temperatures between 500 and 700°C indicating the formation of gold colloids. The average radii of the Au clusters formed were estimated to be in the range of 3-4 nm. Samples annealed under vacuum showed distinct changes in color for different annealing temperatures. Studies using the RBS/channeling technique indicate that no full recrystallization of the samples was achieved under both annealing regimes although heat treatment under vacuum provides a significantly better lattice recovery than for air ambient.
Chemical Effects in Ion Implantation Induced Quantum Well Intermixing
Authors: Simpson Todd W. , Piva Paul G. , Mitchell Ian V. 
Published: April 2011

AbstractIon implantation followed by rapid thermal annealing is used to induce layer intermixing and thus selectively blue-shift the emission wavelength of InP-based quantum well hetero- structures. The intermixing is greatly enhanced over thermal intermixing due to the supersaturation of defects. The magnitude of the observed blue-shift has been studied previously as a function of ion fluence and ion mass: the dependence on ion mass is well established, with heavier ions producing a larger shift. We show here that chemical effects can also play a significant role in determining the induced blue-shift. Data are presented from the implantation of the similar mass ions; aluminum (m~27), silicon (m~28) and phosphorus (m~31). The P- induced blue shift displays a monotonic increase with fluence, consistent with previous studies; however, the fluence dependence of Al- and Si-induced blue-shifts both deviate significantly from the behaviour for P. These results have important implications for attempts to scale intermixing behaviour with ion mass.
Simulations and Argon-Cluster-Ion Smoothing of Surfaces
Authors: Fenner D. B. , Dean D. W. , DiFilippo V. , Allen L. P. , Hautala J. , Mirkarimi P. B. 
Published: April 2011

AbstractBombardment of slightly rough, planar surfaces with an energetic gas-cluster ion beam (GCIB) is known to result in a decrease in roughness. We report comparison of measured surface evolution with simulations based on a simple phenomenological model. The model consists of a continuum rate equation for the surface height undergoing multiple cluster impacts. With suitable assumptions the main features observed in the evolution of an initially nonplanar surface can be simulated. Qualitatively, both experiment and simulation show that sharp features and asperities are rapidly eroded. Examples are given of initial surfaces that are either randomly rough and scratched, or very smooth with added nanoscale engineered features. Both types of surfaces show smoothing in microscopy evaluations of the GCIB and in the simulations, thereby identifying impact-transient surface diffusion as the primary cluster smoothing mechanism.
On the Measurement of Stress-Strain Curves by Spherical Indentation
Authors: Herbert E. G. , Pharr G. M. , Oliver W. C. , Lucas B. N. , Hay J. L. 
Published: April 2011

AbstractIt has been proposed that with the appropriate models, instrumented indentation test (IIT) data can be reduced to yield the uniaxial stress-strain behavior of the test material. However, very little work has been done to directly compare the results from uniaxial tension and spherical indentation experiments. In this work, indentation and uniaxial tension experiments have been performed on the aluminum alloy 6061-T6. The purpose of these experiments was to specifically explore the accuracy with which the analytical models can be applied to IIT data to predict the uniaxial stress-strain behavior of the aluminum alloy.
Nanoindentation Measurements of Mechanical Properties of Polystyrene Thin Films
Authors: Li Min , Carter C. Barry , Gerberich William W. 
Published: April 2011

ABSTRACTThe elastic modulus and work of adhesion of thin polystyrene (PS) films have been evaluated from nanoindentation load-displacement curves. The modulus was calculated using two methods: an unloading stiffness analysis and an elastoplastic unloading analysis. Results indicate that the latter analysis gives better modulus evaluation for the polymers. Two methods were also utilized in determining the work of adhesion, one using the pull-off forces and one using the displacement difference at zero force and pull-off force. The values given by the two methods are close. The effects of surface roughness and maximum load on the adhesion measurements are discussed. Different molecular weights were also chosen to compare the characteristics of the polymers during use under the same conditions. No significant difference in either modulus or adhesion energy was shown between the PSs of very low, moderate, and high molecular weights at room temperature.
Identification of Pressure-Induced Phase Transformations Using Nanoindentation
Authors: Domnich Vladislav , Gogotsi Yury , Trenary Michael 
Published: April 2011

ABSTRACTA combination of depth-sensing indentation and Raman microspectroscopy has been used for the identification of pressure-induced phase transformations in silicon, germanium, boron carbide and partially stabilized zirconia single crystals. Phase transformations during nanoindentation may be revealed through deviations in the shape of the load-displacement curves from that of a perfect elastoplastic material. Such deviations are often more readily identified if the nanoindentation data are presented as average contact pressure vs. contact depth curves, allowing assessment of the corresponding transformation pressures.
Irradiation-Induced Recrystallization of Cellular Dislocation Networks in Uranium-Molybdenum Alloys
Authors: Rest J. , Hofman G. L. 
Published: April 2011

ABSTRACTWe developed a rate-theory-based model to investigate the nucleation and growth of interstitial loops and cavities during low-temperature in-reactor irradiation of uranium-molybdenum alloys. Consolidation of the dislocation structure takes into account the generation of forest dislocations and capture of interstitial dislocation loops. The theoretical description includes stress-induced glide of dislocation loops and accumulation of dislocations on cell walls. The loops accumulate and ultimately evolve into a low-energy cellular dislocation structure. Calculations indicate that nanometer-size bubbles are associated with the walls of the cellular dislocation structure. The accumulation of interstitial loops within the cells and of dislocations on the cell walls leads to increasing values for the rotation (misfit) of the cell wall into a subgrain boundary and a change in the lattice parameter as a function of dose. Subsequently, increasing values for the stored energy in the material are shown to be sufficient for the material to undergo recrystallization. Results of the calculations are compared with SEM photomicrographs of irradiated U- 10Mo, as well as with data from irradiated UO2.
Influence of Interatomic Potentials in MD Investigation of Ordering in a-SiC
Authors: Yuan Xianglong , Hobbs Linn W. 
Published: April 2011

ABSTRACTMolecular dynamics (MD) simulations of a-SiC using several Tersoff potentials have been performed and their influences on structure ordering were studied. It was found that using different potential cutoffs leads to remarkably different structures. An abrupt cutoff at 2.5 Å greatly increases the chemical ordering of a-SiC by disfavoring the formation of Si-Si bonds. In addition, annealing of SiC cascades embedded in β-SiC was simulated, and the final structures were compared. Again, much stronger topological and chemical ordering was observed in the structure modeled with the 2.5 Å potential cutoff.
Computer Simulation of Energy Dependence of Primary Damage States in SiC
Authors: Devanathan R. , Gao F. , Weber W. J. 
Published: April 2011

ABSTRACTThe primary damage state in 3C-SiC has been comprehensively studied by molecular dynamics using a modified Tersoff potential. The simulations examined damage produced by Si and C primary knock-on atoms (PKA) with energies from 0.25 to 30 keV. The study also generated statistics of defect production by simulating a number of PKAs at each energy. The defect production efficiency decreases with increasing PKA energy, as observed previously in metals. However, the cascade lifetime is very short (less than 1 ps), localized melting does not occur, the defect arrangements are highly dispersed, and the tendency for defects to form clusters is much less compared to the case of metals. Frenkel pairs on the C sublattice are more numerous than Si Frenkel pairs, and 10-20% of the displacements are in the form of anti-site defects.
Hydrogen Passivation of Si Nanocrystals in Silica
Authors: Cheylan Stephanie , Elliman Robert G. 
Published: April 2011

ABSTRACTThis paper explores the effect of hydrogen on the luminescence properties of silicon nanocrystals formed in silica by high-dose ion-implantation and thermal annealing. For samples implanted to low fluence (small nanocrystals), passivation is shown to result in a uniform enhancement of the PL emission for all wavelengths. However, for samples implanted to high fluence, preferential enhancement of the emission from larger nanocrystals is evident, resulting in a red-shift of emission spectra. Both the intensity enhancement and the red-shift are shown to be reversible, with spectra returning to their pre-passivation form when H is removed from the samples by annealing. The luminescence lifetime is also shown to increase after passivation, confirming that defect-containing nanocrystals luminesce.
Irradiation-Induced Amorphization Of Titanite
Authors: Meldrum A. 
Published: April 2011

ABSTRACTTitanite (CaTiSiO5) is a widely occurring accessory mineral that contains ppm-level concentrations of U and Th. Radiation effects in titanite are important because this phase is commonly-used for U-Pb age dating of rock formations, and it is also the main crystalline constituent of certain glass-ceramic nuclear waste forms. Previous work suggested that titanite is highly susceptible to natural alpha-decay-induced amorphization, but ion irradiation experiments have so far been reported only at room temperature. In this work, the first temperature-dependent amorphization data for titanite are reported. High-purity single-crystal specimens from the Khan Mine, Namibia were characterized by analytical electron microscopy and powder XRD. Suitable specimens were then irradiated in-situ at the IVEM Facility using 800 keV Kr ions at temperatures ranging from 30 to 1100 K. Conventional imaging and diffraction techniques were used to monitor the transformation to the amorphous state. Titanite was amorphized at a relatively low dose over the entire temperature range investigated. Limited crystallization of ion-beam-amorphized titanite was observed at temperatures above 1100 K.