bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of the Texture on the Creep behavior of γ-TiAl Sheet Material
Authors: Bartels Arno , Schillinger Wolfram , Chatterjee Anita , Clemens Helmut
Published: April 2011

In hot rolled Ti-46.5at%Al-4at%(Cr,Nb,Ta,B) sheets a strong modified cube texture is found. The c-axes of the tetragonal unit cells in the grains are aligned with the transverse direction of the sheets. This texture causes an anisotropy of the creep resistance which is improved in transverse direction. Heat treatments with different subsequent cooling rates were performed in order to obtain lamellar microstructures with a different spacing of lamellae. Creep experiments exhibit an increase of the creep resistance which is highest after fast cooling. The texture measurements show no longer an alignment of c-axes after the heat treatment in the α-phase field, but a weak {110}-fiber texture in rolling direction occurs which causes a small improvement of the creep resistance in rolling direction. However, the creep resistance of the lamellar microstructure is more determined by the morphology than by the texture.
Creep Studies of Monolithic Phases in Nb-Silicide Based In-Situ Composites
Authors: Bewlay B.P. , Briant C.L. , Sylven E.T. , Jackson M.R. , Xiao G.
Published: April 2011

Nb-silicide composites combine a ductile Nb-based solid solution with high-strength silicides, and they show great promise for aircraft engine applications. Previous work has shown that the silicide composition has an important effect on the creep rate. If the Nb:(Hf+Ti) ratio is reduced below ∼1.5, the creep rate increases significantly. This observation could be related to the type of silicide present in the material. To understand the effect of each phase on the composite creep resistance, the creep rates of selected monolithic phases were determined. To pursue this goal, monolithic alloys with compositions similar to the Nb-based solid solution and to the silicide phases, Laves, and T2 phases, were prepared. The creep rates were measured under compression at 1100 and 1200°C. The stress sensitivities of the creep rates of the monolithic phases were also determined. These results allow quantification of the load bearing capability of the individual phases in the Nb-silicide based in-situ composites.
The Effect of Silicide Volume Fraction on the Creep Behavior of Nb-Silicide Based In-Situ Composites
Authors: Bewlay B.P. , Briant C.L. , Davis A.W. , Jackson M.R.
Published: April 2011

This paper will describe the creep behavior of high-temperature Nb-silicide in-situ composites based on quaternary Nb-Hf-Ti-Si alloys. The effect of volume fraction of silicide on creep behavior, and the effects of Hf and Ti additions, will be described. The composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280 MPa. At high (Nb) phase volume fractions the creep behavior is controlled by deformation of the (Nb) and, as the volume fraction of silicide is increased, the creep rate is reduced. However, at large silicide volume fractions (>0.7) damage in the silicide begins to degrade the creep performance. The creep rate has a minimum at a volume fraction of ∼0.6 silicide. The creep performance of the monolithic and silicide phases will also be discussed.
Strain-Induced Ferromagnetism in Fe-40Al Single Crystals
Authors: Wu D. , Baker I.
Published: April 2011

Recent research [1–3] suggests that strain-induced ferromagnetism in lightly-strained FeAl arises chiefly from anti-phase boundary tubes. Magnetic and calorimetric measurements have been performed on two different orientations of B2-structured Fe-40Al single crystals that had been cold rolled to a variety of strains. The saturation magnetization and magnetic susceptibility are related to the enthalpy associated with the annealing out of antiphase boundary tubes and, hence, to the degree of deformation and crystal orientation.
Elastic and Plastic Properties of Mo3Si Measured by Nanoindentation
Authors: Swadener J. G. , Rosales Isa , Schneibel Joachim H.
Published: April 2011

Single crystal Mo3Si specimens were grown and tested at room temperature using established nanoindentation techniques at various crystallographic orientations. The indentation modulus and hardness were obtained for loads that were large enough to determine bulk properties, yet small enough to avoid cracking in the specimens. From the indentation modulus results, anisotropic elastic constants were determined. As load was initially increased to approximately 1.5 mN, the hardness exhibited a sudden drop that corresponded to a jump in displacement. The resolved shear stress that was determined from initial yielding was 10–15% of the shear modulus, but 3 to 4 times the value obtained from the bulk hardness. Non-contact atomic force microscopy images in the vicinity of indents revealed features consistent with {100}(010) slip.
Phase Stability in Processing and Microstructure Control in High Temperature Mo-Si-B Alloys
Authors: Perepezko J.H. , Sakidja R. , Kim S.
Published: April 2011

For applications at ultrahigh temperatures the multiphase microstructural options that can be developed in the Mo-Si-B system have demonstrated an effective and attractive balance of essential characteristics. The coexistence of the high melting point (>2100°C) ternary intermetallic Mo5SiB2(T2) phase with Mo provides a useful option for in-situ toughening. A further enhancement is available from a precipitation reaction of Mo within the T2phase that develops due to the temperature dependence of the solubility behavior of the T2phase. However, direct access to Mo+T2microstructures is not possible in ingot castings due to solidification segregation reactions that yield nonequilibrium boride and silicide phases with sluggish dissolution. Alternate routes involving rapid solidification of powders are effective in suppressing the segregation induced phases. The processing and microstructure options can also be augmented by selected refractory metal substitutional alloying, such as the incorporation of Nb, that alters the solubility of the T2phase and the relative phase stability to yield solidification of two phase refractory solid solution + T2structures directly. The observed alloying trends highlight the role of atomic size in influencing the relative stability of the T2phase. A key component of the overall microstructural control and long term microstructural stability is determined by the kinetics of diffusional processes. The analysis of selected diffusion couples involving binary boride and silicide phases has been used to assess the relative diffusivities in the T2phase and coexisting phases over the range of solubility and to provide a basis for the examination of the kinetics of reactions involved in coatings and oxidation.
The Effects Of Environment On The Room Temperature Deformation Of B2-Structured Fe-43Al Single-Crystals
Authors: Baker I. , Wu D. , George E. P.
Published: April 2011

The effects of the environment on the room temperature mechanical behavior of Fe-43Al single crystals have been studied. In both single slip and duplex slip crystals, fracture strains greater than 40% were obtained in specimens tested in oxygen, whereas elongations of ∼10% and ∼20% were obtained in air and vacuum, respectively. By comparison, similar elongations were obtained in boron-doped single-slip-oriented single crystals in both air and vacuum, but more ductility was obtained in air at slow strain rate. Fractography showed that testing in different environments produced marked differences in the fracture surfaces. Alternate loading of tensile specimens in air and under vacuum was performed at slow strain rates and showed changes in the flow stress between the two environments. The results are discussed in terms of the effects of moisture-produced hydrogen on the flow and fracture of FeAl.
Deformation Twins in Ni3Nb Single Crystals with DOaStructure
Authors: Hagihara Kouji , Nakano Takayoshi , Umakoshi Yukichi
Published: April 2011

Plastic deformation behavior and substructures in Ni3Nb single crystals were examined focusing on the operative deformation twin systems. Three twinning systems were operative depending on crystal orientation. The twinning behavior was discussed comparing with that in pure hcp metals. Microcracks initiated at the twin intersection. A large number of twin intersections were analyzed and classified into several types.
Thermoelastic Properties of Super High Temperature Ru-Ta Shape Memory Alloy
Authors: Furuya Y. , Zhirong H.
Published: April 2011

Equiatomic Ru-Ta alloy can show a thermoelastic phase transformation at super high temperatures above 1000°C. The temperature of shape memory effect of this alloy seems to be remarkably higher by two times than those of the formerly reported high temperature NiMnAl alloy and it seems very interesting as one of the new high temperature SMAs, however, detailed thermoelastic properties of Ru-Ta system alloy have not been clarified. The present paper investigates the basic material properties of Ru-Ta alloy, i.e. each transformation temperature, temperature hysteresis range, heat absorption by DSC measurement and metallurgical compounds by X-ray diffraction that depend on alloy composition by changing the Ru content from 46–5 4at%. Effect of heat treatment at solution temperature and aging temperature on thermoelastic phase transformation points is investigated and the thermal cyclic stability is also studied for engineering applications as high temperature actuator/sensor materials.
The β-FeSi2 Formation and Thermoelectric Power of the FeSi2+Co Base Alloys
Authors: Kimura Yoshisato , Shindo Kentaro , Mishima Yoshinao
Published: April 2011

Temperature dependence of thermoelectric power and resistivity was measured for the β-FeSi2 based cast alloys on which n-type Co doping was performed with or without Cu addition. The Cu-free alloy shows a homogeneous eutectic microstructure consisting of metallic phases α-FeSi2 and ε-FeSi, while the Cu-doped alloy has a quite heterogeneous microstructure dominated by coarse ε-FeSi dendrites in the α-FeSi2 matrix. Adequate heat treatment condition for the semiconductor β-FeSi2 phase formation has been evaluated as annealing at 923 K for less than 50 h, which is lower in temperature and shorter in duration than previously reported for alloys prepared by powder metallurgy. The resistivity measurement with the aid of microstructure observation has revealed that the β-FeSi2 formation takes place and almost finishes at very early stage of annealing process. Addition of Cu effectively promotes the β-FeSi2 formation rate of the present cast alloys.
Microstructures and High-temperature Strength of Silicide-reinforced Nb Alloys
Authors: Ma C.L. , Tan Y. , Tanaka H. , Kasama A. , Tanaka R. , Mishima Y. , Hanada S.
Published: April 2011

This article describes the phase stability, microstructures and mechanical properties of silicide-reinforced Nb alloys in Nb-Mo-W-Si quaternary system prepared by arc melting and heat treatment. There exists an equilibrium two-phase field of Nb solid solution (Nbss) and α(Nb,Mo,W)5Si3 in a Nb-rich region of this quaternary system. Alloys in this region have a eutectic reaction of L → Nbss+β(Nb,Mo,W)5Si3 during solidification. The β(Nb,Mo,W)5Si3 transforms to the stable α(Nb,Mo,W)5Si3 at very high temperature. The cast and heat treated hypoeutectic alloys consist of dendritic Nbss, network-shaped Nbss matrix and α(Nb,Mo,W)5Si3. These quaternary alloys exhibit excellent high-temperature strength, although the fracture toughness is still unacceptable for practical applications.
Deformation of Ni3Al Polycrystals at Extremely High Pressures
Authors: Vassiliou John K. , Otto J.W. , Frommeyer G. , Viescas A. J. , Bulusu K. , Bellumkonda H.
Published: April 2011

The compression behavior in a multi-anvil apparatus of a foil of Ni3Al embedded in a pressure medium of NaCl has been studied by energy-dispersive X-ray diffraction (EDX). At ambient temperature, the pressure and stresses, determined from line positions of NaCl, were constant throughout the sample chamber. Line positions and line widths of NaCl reflections were reversible on pressure release. Ni3Al polycrystals, in contrast, undergo extensive (ductile) plastic deformation above 4 GPa due to the onset of high non-hydrostatic stresses and the introduction of stacking faults and dislocations. Plastic deformation due to stacking faults leads to a volume incompressibility followed by elastic compression of a fully plastically deformed state. The compression of a fully plastically deformed material is elastic and isotropic, independent of the presence and type of pressure medium. A discontinuity in the compressibility at the transition back from plastic to elastic compression is due to the yield strength of the plastically deformed material and corresponds to the Hugoniot elastic limit.
Interdiffusion and Phase Behavior in Polysynthetically Twinned (PST) TiAl / Ti Diffusion Couples
Authors: Pan Ling , Luzzi David E.
Published: April 2011

Diffusion couples of pure Ti and polysynthetically twinned (PST) TiAl (49.3 at.% Al) were prepared by high vacuum hot-pressing, with the bonding interface perpendicular to the lamellar planes. Diffusion experiments were carried out by annealing the couples in the same furnace at 650, 700 and 850°C for various times. The cross-section of the couple was studied using scanning electron microscopy (SEM) and quantitative wavelength-dispersive x-ray spectroscopy (WDS). A reaction layer whose composition is close to that of the stoichiometric α2-Ti3Al phase formed along the PST TiAl / Ti bonding interface in PST TiAl side. Direct measurements of the thickness of the reaction zone were performed at different phase regions and various boundaries. By assuming the thickness of the reaction zone increases as (Dt)1/2, where D is the diffusion coefficient and t is the annealing time, the diffusion coefficients at these temperatures were calculated. Composition profiles in the reaction zone, along the lamellae and at the lamellar interfaces were obtained by WDS analyses.
Advancement of the Directional Solidification process of a NiAl-Alloy
Authors: Scheppe F. , Wagner I. , Sahm P.R.
Published: April 2011

The directional solidification process of high temperature intermetallic alloys was investigated and discussed for a hypo eutectic NiAl-Cr-alloy. An unexpected solidification behavior was found which may be peculiar to the selected alloy group. The attempts show that due to the required high furnace temperatures only a narrow range of tolerance exists, in which the variation of the process parameters led to directional solidification. Aligned primary NiAl dendrites were then observed, embedded in randomly oriented interdendritic lamellas as known from conventional equiaxed castings. The directional solidification process was basically evaluated for high temperature intermetallics.
1300 K Compressive Properties of Directionally Solidified Ni-33Al-33Cr-1Mo
Authors: Daniel Whittenberger J. , Raj S.V. , Locci Ivan. E.
Published: April 2011

The Ni-33Al-33Cr-1Mo eutectic has been directionally solidified by a modified Bridgeman technique at growth rates ranging from 7.6 to 508 mm/h to produce grain/cellular microstructures containing alternating plates of NiAl and Cr alloyed with Mo. The grains had sharp boundaries for slower growth rates (≤ 12.7 mm/h), while faster growth rates (≥ 25.4 mm/h) lead to cells bounded by intercellular regions. Compressive testing at 1300 K indicated that alloys DS'ed at rates between 25.4 to 254 mm/h possessed the best strengths which exceed that for the as-cast alloy.
Modeling for the Diamond-Like Carbon Film Synthesis by Plasma Based Ion Implantation
Authors: Miyagawa Yoshiko , Djurabekova Flyura , Miyagawa Soji
Published: April 2011

Dynamic Monte Carlo simulations with the binary collision approximation have been applied to the synthesis of hydrogenated amorphous carbon (a-C:H) films by plasma based ion implantation (PBII). We take as representative carbon carriers energetic CH3+ ions and CH3 radicals. The direct chemical incorporation of the radicals, like CH3 reacting with a diamond surface, is too low for the deposition of DLC films, so that the other reaction mechanisms should be responsible. We assumed (a) complete dissociation of CH3+ ions into one C atom and three H atoms with identical velocities upon bombarding the surface, (b) a unity and only one mono-layer sticking of CH3 radicals on the surface, (c) incorporation (stitching) of H and C atoms under the surface induced by binary collisions with energetic CH3+ ions, (d) release of H atoms by the dissociation of CH3 radicals on the surface, and (e) release of a part of displaced H atom after the subsequent collision cascade. We also assumed only the stitched carbon atoms form sp3 states and all other carbon atoms form sp2 states. The effect of the target voltage on the ion dose was also included. The effects of ion/neutral arrival ratio and ion energy on the growth rate, the mixing layer thickness, the hydrogen content, and the sp3/sp2 ratio in the deposited film are presented.
Effect of Iodine and Strontium Ion Implantation on the Microstructure of Cubic Zirconia
Authors: Zhu Sha , Wang Lumin , Wang Shixin , Ewing Rodney C.
Published: April 2011

200 keV iodine and 400 keV strontium ions have been implanted into YSZ in order to study the effects of fission product incorporation in YSZ as an inert fuel matrix. The ion implantation was conducted at room temperature. The ion fluences reached 1×1021 ions/m2 which gives peak displacement damage levels of ~ 290 dpa for I ion implantation and ~ 200 dpa for Sr ion implantation. The peak concentration reaches ~26 at. % for implanted I ions and ~11.6 at.% for Sr ions. Cross-sectional transmission electron microscopy (TEM) was completed to investigate the microstructure changes caused by the implantation. No evidence of amorphization was detected in both samples although a high density of defect clusters was observed by TEM. Cross-sectional TEM revealed formation of iodine containing voids in I- implanted samples and crystalline precipitates of a few tens of nanometers in Sr-implanted samples after annealing of the implanted sample at 1000°C for 0.5 to 2 hours. The void size increased with increasing annealing time. The nano-crystalline precipitates in Sr-implanted YSZ are isometric SrZrO3 (a≅0.41 nm). The orientation relation between the matrix and precipitates, as determined by selected area diffraction pattern, was: [011]YSZ// [111]SrZrO3 and [200]YSZ// [110]SrZrO3.
Evolution of Ion Beam Synthesized Au Nanoclusters in SiO2 under Ion Irradiation
Authors: Schmidt Bernd , Heinig Karl-Heinz , Mücklich Arndt
Published: April 2011

The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO2 layer by 330 keV Au+ implantation and subsequent annealing at T = 1000 °C for 1h in dry O2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range Rp(330keV) = 100 nm, having a mean NC size of 5 nm at Rp, and resembling the broad Lifshiz-Slyozov-Wagner (LSW) size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions was used in order to tailor their size and size distribution. The high-energy Au+ irradiations were performed at 190...210 °C with a fluence of (0.5...1.0)×1016 cm-2. By the post-irradiation no gold was deposited into the SiO2 layer, the Au+ ions come to rest in the (001)Si substrate at Rp(4.5MeV) = 1 [.proportional]m. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.
High-Fluence Implantation of Erbium into Silicon-Germanium Alloys: Structural and Thermal Properties
Authors: Touboltsev V. , Räisänen J. , Johnson E. , Johansen A. , Sarholt L.
Published: April 2011

High-quality crystalline Si1-xGex (x=0.10 and 0.25) alloys were implanted with 70 keV Er+ ions at temperatures of 350°C and 550°C to a fluence of 1015 cm−2. In-situ Rutherford backscattering/channeling (RBS) analysis supplemented with transmission electron microscopy (TEM) showed that as-implanted alloys were in form of ternary solid solutions with a peak Er concentration of 1 at.% without any trace of Er-Si or Er-Ge precipitation.

In the samples implanted at 350°C Er atoms were found to be distributed randomly in the amorphous host matrix. Post-implantation annealing at different temperatures up to 600° showed that the solid phase epitaxial regrowth of the damaged layers strongly depends on both the Ge concentration in the alloys and the temperature of annealing. Along with the recrystallization of the damaged matrix, annealing was observed to induce simultaneous removal of nearly all the implanted Er as the recrystallization front progresses towards the surface.

In contrast, high temperature implantation at 550°C led to spontaneous recovery of the alloy crystallinity and incorporation of considerable fraction of implanted Er atoms on regular tetrahedral interstitial sites in the host lattice.
Growth and Characterization of Erbium Silicides Synthesized by Metal Vapor Vacuum Arc Ion Implantation
Authors: Zhang X. W. , Cheung W. Y. , Wong S. P.
Published: April 2011

Erbium atoms were implanted into p-type Si (111) wafers at an extraction voltage of 60 kV to doses ranging from 5×1016 to 2×1017 cm−2 using a metal vapour vacuum arc (MEVVA) ion source. The implantation was performed with beam current densities from 3 to 26 µA/cm2 corresponding to substrate temperatures ranging from 85 to 245°C. The characterization of the as-implanted and annealed samples was performed using Rutherford backscattering spectrometry, atomic force microscopy and x-ray diffraction. To determine the sputtering yield, masked implantation experiments were performed so that the thickness of the sputtered layer at different substrate temperatures can be obtained directly by an α-step surface profiler. The results showed that ErSi2-xwas directly formed by MEVVA implantation when the substrate temperature was higher than about 160°C. The effects of the implant dose and the beam current density on the retained dose, the sputtering yield and the surface morphology of the implanted samples were also studied.
Effects of ArF Excimer Irradiation on Multi-Energy Ge and Se Ion Implanted Silica
Authors: Magruder R. H. , Weller R. A. , Weeks R. A. , Wehrmeyer J. , Zuhr R. A. , Hensley D. K.
Published: April 2011

Silica samples were implanted at multiple energies with Se and Ge ions producing implanted layers ~ 2.4 µm in depth starting at ~ 0.5 µm below the surface. In each case, the concentration of implanted species was ~ 0.05 atomic %. The optical absorption of the samples was measured from 2.7 to 6.5 eV. In all spectra, local maxima at 5.0 eV with shoulders at 5.9 eV were observed. The spectra have been assumed to be describable as a superposition of Gaussian absorption bands with mean energies taken from the literature of 4.8, 5.01, 5.17, 5.88, and 7.15 eV. The relative strengths of each of these bands have been obtained by linear regression. These fits show that additional bands at 3.7 and 6.4 eV are required to fit the data for the Se samples, while bands at 5.54 and 6.4 eV are needed to fit the data for the Ge samples.
Deposition of Diamond-Like Carbon Films using Plasma Based Ion Implantation with Bipolar Pulses
Authors: Miyagawa S. , Miyagawa Y.
Published: April 2011

Plasma based ion implantation (PBII) with bipolar high voltage pulses has been proposed to improve a dose uniformity in an ion implantation on a three-dimensional target. A pulsed glow discharge plasma is produced around the target by a positive high-voltage pulse, and then ions are implanted into the target from all sides by the subsequent negative high-voltage pulse. A time resolved plasma density and the spatial profiles of the pulsed glow discharge plasma are measured by a Langmuir probe in a boxcar mode, and diamond like carbon (DLC) films are deposited under optimal conditions of the pulsed plasma. It is shown that the PBII with bipolar pulses is a useful method in depositing DLC films on the three-dimensional target. A carbon ion implantation procedure results in the enhanced adherence of DLC coating to the target, and the enhanced adhesion is due to a graded carbon interface produced by carbon implantation.
Correlation between Structural and Optical Properties of Si Nanocrystals in SiO2: Model for the Visible Light Emission
Authors: López M. , Garrido B. , González O. , García C. , Pérez-Rodríguez A. , Morante J.R. , Bonafos C. , Carrada M. , Rodríguez R.J. , Montserrat J.
Published: April 2011

The correlation between the structural and optical properties of Si nanocrystals embedded in SiO2 is the key factor to understand their emission mechanism. However, there is a great difficulty in imaging Si nanocrystals in SiO2 and measuring their size distribution because of the lack of contrast in electron microscopy. We have used here a new method for imaging Si nanocrystals by using high resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Regarding the optical properties, the band-gap energies and photoluminescence have been measured by direct and independent methods. The results have allowed experimental determination, for the first time in this material, of the experimental Stokes shift between absorption and emission as a function of crystallite size. The experimental band-gap versus size correlates well with the most accurate theoretical predictions. Moreover, the photoluminescence energy emission versus crystallite size shows a parallel behaviour to that of band-gap energy. Consequently, the experimental Stokes shift is independent of nanocrystal size and is found to be 0.26±0.03 eV. This value is almost twice the energy of the Si-O vibration (0.134 eV). These results suggest that the dominant emission of Si nanocrystals passivated with SiO2 is a fundamental transition spatially located at the Si-SiO2 interface and with the assistance of a local Si-O vibration.
Ion-implantation Generated Nanovoids in Si and MgO Monitored by High Resolution Positron Beam Analysis
Authors: Eijt S.W.H. , Falub C.V. , van Veen A. , Schut H. , Mijnarends P.E. , van Huis M.A. , Fedorov A.V.
Published: April 2011

The formation of nanovoids in Si(100) and MgO(100) by 3He ion implantation has been studied. Contrary to Si in which the voids are generally almost spherical, in MgO nearly perfectly rectangular nanosize voids are created. Recently, the 2D-ACAR setup at the Delft Positron Research Center has been coupled to the intense reactor-based variable-energy positron beam POSH. This allows a new method of monitoring thin layers containing nanovoids or defects by depth-selective high-resolution positron beam analysis. The 2D-ACAR spectra of Si with a buried layer of nanocavities reveal the presence of two additional components, the first related to para-positronium (p-Ps) formation in the nanovoids, and a second one most likely related to unsaturated Si-bonds at the internal surface of the voids. The positronium is present in excited kinetic states with an average energy of 0.3 eV. Refilling of the cavities by means of low dose 3He implantation (1×1014 cm−2) followed by annealing reduces the formation of Ps and the width of the Ps peak in the ACAR spectrum. This width reduction is due to collisions of Ps with He atoms in the voids. In MgO, p-Ps formed with an initial energy of ~3 eV shows a final average energy of 1.6 eV at annihilation due to collisions with the cavity walls. Possibilities of this new, non-destructive method of monitoring the sizes of cavities and the evolution of nanovoid layers will be discussed.
Interactions of Point Defects and Impurities With Open Volume Defects in Silicon
Authors: Williams J.S. , Ridgway M.C. , Conway M.J. , Wong-Leung J. , Williams B.C. , Petravic M. , Fortuna F. , Ruault M.-O. , Bernas H.
Published: April 2011

Ion implantation can produce open volume defects in silicon by one of two methods, either by H or He implantation followed by annealing to create a band of nanocavities and also by direct implantation to reasonably high doses, which results in a vacancy excess region at depths less than about half the projected ion range. This paper reviews three interesting aspects of open volume defects. In the first case, the very efficient gettering of fast diffusing metals to nanocavities formed by H-implantation is illustrated. In addition, the non-equilibrium behaviour of Cu3Si precipitation and dissolution at cavities is examined. The second example treats the interaction of irradiation-induced defects with nanocavities, particularly preferential amorphisation at open volume defects and subsequent cavity shrinkage. The final example illustrates the coalescence of excess vacancies into small voids on annealing and the use of gettering of Au to detect such open volume defects.
MeV Ion Implantation Doping of Diamond.
Authors: Prawer S. , Jamieson D.N. , Nugent K.W. , Walker R. , Uzan-Saguy C. , Kalish R.
Published: April 2011

Diamond-based semiconductor devices offer the promise of operation at high temperatures and under extreme radiation conditions. An essential step in the drive towards operational diamond-based electronic devices is the ability to controllably and reproducibly dope the diamond. Ion implantation is the method of choice for such doping because it offers precise control of the dopant concentration and spatially selective doping is achievable using standard masking techniques. However, compared to silicon, the doping of diamond is complicated by the tendency of the diamond to relax to graphite upon thermal annealing. Furthermore, even if graphitization can be avoided, the compensation of dopants by residual defects has proved in the past to be a limiting factor in obtaining very high mobility material. In this paper, we present a scheme for the effective doping of diamond using MeV ion-implantation. For MeV ion- implantation the doped layer is deeply buried under a cap of undamaged diamond, and so the scheme includes a method using pulsed laser irradiation for making electrical contact to the buried layer. We show that a boron doped layer fabricated by the MeV implantation scheme has, after suitable annealing and removal of these compensating/trapping defects, very high mobility and low compensation ratio. In fact, its electrical properties are quite similar to those of natural boron-doped type IIb diamond.
Synthesis of Continuous SmSi2 Layers on Si by Samarium Ion Implantation Using A Metal Vapor Vacuum Arc Ion Source
Authors: Cheng X.Q. , Zhu H.N. , Liu B.X.
Published: April 2011

Samarium ion implantation was conducted to synthesize Sm-disilicide films on silicon wafers, using a metal vapor vacuum arc ion source and the continuous SmSi2 films were directly obtained with neither external heating during implantation nor post-annealing. Diffraction and surface morphology analysis confirmed the formed Sm-disilicilde films were of a fine crystalline structure under appropriate experimental conditions. Besides, the formation mechanism of the SmSi2phase is also discussed in terms of the temperature rise caused by ion beam heating and the effect of ion dose on the properties of the SmSi2films.
Load-Displacement Behavior During Sharp Indentation of Viscous-Elastic-Plastic Materials
Authors: Oyen-Tiesma Michelle , Toivola Yvete A. , Cook Robert F.
Published: April 2011

A constitutive equation is developed for geometrically-similar sharp indentation of a material capable of elastic, viscous, and plastic deformation. The equation is based on a series of elements consisting of a quadratic (reversible) spring, a quadratic (time-dependent, reversible) dashpot, and a quadratic (time-independent, irreversible) slider—essentially modifying a model for an elastic-perfectly plastic material by incorporating a creeping component. Load-displacement solutions to the constitutive equation are obtained for load-controlled indentation during constant loading-rate testing. A characteristic of the responses is the appearance of a forward-displacing “nose” during unloading of load-controlled systems (e.g., magnetic-coil-driven “nanoindentation” systems). Even in the absence of this nose, and the associated initial negative unloading tangent, load-displacement traces (and hence inferred modulus and hardness values) are significantly perturbed on the addition of the viscous component. The viscous-elastic-plastic (VEP) model shows promise for obtaining material properties (elastic modulus, hardness, time-dependence) of time-dependent materials during indentation experiments.
Sub-Micrometer Spatially Resolved Measurements of Mechanical Properties and Correlation to Microstructure and Composition
Authors: Kunert M. , Baretzky B. , Baker S. P. , Mittemeijer E. J.
Published: April 2011

The variations of hardness, composition, and microstructure within a carbon implanted region – about 350 nm thick – of a Ti-6Al-4V alloy were measured using nanoindentation, Auger electron spectroscopy and transmission electron microscopy, respectively. Correlations among hardness, composition, and microstructure were made with a spatial resolution of about ±20 nm. The variation in hardness within the implanted regions was quantitatively explained as due to the formation of an almost continuous TiC layer and precipitate hardening. The problems that may arise in measuring and correlating spatial variations in such a complex material on this scale are outlined and a successful method to solve them is proposed. The need for highly spatially resolved measurement techniques is emphasized.
Three-Dimensional Contact Mechanics Studies of Zdol Hard Disk Lubricants
Authors: Lucas Barry N. , Hay Jack C.
Published: April 2011

This paper reports the results of a study of the dynamic 3-dimensional response between a diamond point probe and a commercial hard-disk overcoat/lubricant system. The specific overcoat was CNx with a thickness of 50 Å. The lubricant layer was ZDOL with nominal thicknesses of 11 Å and 24 Å in unbonded and bonded conditions. The experiments were conducted with a constant lateral displacement oscillation in the z, x & y direction of 1 nm at a frequency of 125 Hz. Results of this study show that the bonded lubricant layer increases the lateral force required to maintain a constant lateral displacement oscillation compared to both the unlubricated CNx coating and the CNx coating with the unbonded lubricant.
Mechanical Properties of As-Grown and Ion-Beam-Modified GaN Films
Authors: Kucheyev S.O. , Bradby J.E. , Williams J.S. , Swain M.V. , Toth M. , Phillips M.R. , Jagadish C.
Published: April 2011

The deformation behavior of as-grown and ion-beam-modified wurtzite GaN films is studied by a nanoindentation with a spherical indenter. Atomic force microscopy (AFM) and cathodoluminescence are used to characterize the deformation mode. No systematic dependence of the mechanical properties on the film thickness ( at least for thicknesses from 1.8 to 4 μm) as well as on doping type is observed. Results strongly suggest that (i) slip is the major contributor to the plastic deformatio of crystalline GaN and (ii) slip nucleation (rater than a phae transformation) is responsible for “pop-in” events observed during loading. Indentation with an ∼ 4.2 μm radius spherical indenter at maximum loads up to 900 mN does not produce any cracking visible by AFM in crystalline GaN. Instead, under such loads, indentation results in a pronounced elevation of the material around the impression. Implantation disorder dramatically changes the deformation behaviour of GaN. In particular, implanation-produced defects in crystalline GaN syppress (i) “pop-in” events during loading, (ii) slip bands observed by AFM, and (iii) the plastic component of deformation. GaN amorphized by in bombardment exhibits plastic flow even for very low loads. The values of hardness and elastic modulus of amorphous GaN are dramatically reduced compared to those of as-grown GaN.
Adhesion Quantification of Post-CMP Copper to Amorphous SiN Passivation by NanoIndentation
Authors: Vella J. B. , Smith S. M. , Volinsky A. A. , Adhihetty I. S.
Published: April 2011

In this study, film interfacial fracture is induced by nanoindentation to quantify the practical work of adhesion of a post-CMP copper film to an amorphous silicon nitride passivation film. Poor adhesion of electrodeposited copper to SiN passivation is observed following CMP due to copper oxide growth prior to plasma enhanced silicon nitride deposition. Four point bend testing has shown that failure by brittle fracture of test structures occurs at the Cu/CuO interface. Hydrogen, ammonia, and nitrogen plasma treatments of the post-CMP copper surface can be used to remove the oxide, shown by auger electron spectroscopy, and to increase the surface roughness of copper, shown by atomic force microscopy. Both effects can be used to improve the Cu/SiN adhesion. Nanoindentation with a conical indenter (1.59 μm tip radius) was used to induce SiN film delaminations from Cu, the sizes of which were measured and correlated with the practical work of adhesion.[1,2] In order to more reliably and repeatably produce these delaminations a TiW (10wt% Ti) superlayer was sputter deposited on to the test structures.[2,3] Mechanical properties, including elastic modulus and hardness of SiN, electrodeposited copper, and TiW measured by nanoindentation are also reported here.
Nanoindentation of Poly (Methyl Methacrylate)
Authors: Adams Michael J. , Gorman David M. , Johnson Simon A.
Published: April 2011

For the indentation of an elastic-plastic homogeneous half-space with a pyramidal indenter, the load theoretically increases with the square of the total penetration depth. Experimental data are presented in the current paper that demonstrate the validity of this relationship for an organic polymer and a Berkovich indenter, provided that appropriate account is taken of the tip defect and viscoplasticity. It is also shown that a simple analytical solution exists for the ratio of the contact depth to the total penetration depth. These findings assist in identifying procedures for obtaining the rate-dependent mechanical properties of thin polymer coatings or polymeric materials with depth-dependent mechanical properties.
Fundamental Aspects of Friction and Wear Contacts in <100> Surfaces
Authors: Gerberich William W. , Tymiak Natalia I. , Kramer Donald E.
Published: April 2011

Unexpected friction and wear transitions occur in transition metals associated with dislocation emission, dislocation storage, and oxide break-through phenomena. Both normal nanoindentation and nanoscratch evaluations of conical diamond tips driven into tungsten {100} single crystal surfaces have been conducted. In terms of initiating plasticity undert the contact, this represents a high Peierl's barrier for dislocation motion in transition metals. Both quasi-equilibrium and kinetic aspects are reported along with current but speculative ideas on multiple friction and wear transitions. Preliminary results show that yielding under contacts can produce a 250 nm displacement excursion. Ramifications are seen in terms of friction coefficients which can double during the near-instantaneous yield excursion but then continue to triple from about 0.05 to 0.15 in the pile-up phase in front of the sliding contact. Implications of how nanotribological issues such as adhesion connect through this mesoscale activity to macroscopic friction and wear are discussed.
Deformation Mechanisms in Ferritic/martensitic Steels Irradiated in HFIR
Authors: Hashimoto Naoyuki , Zinkle Steven J. , Klueh Ronald L. , Rowcliffe Arthur F. , Shiba Kiyoyuki
Published: April 2011

A reduced activation ferritic/martensitic steel, F82H (IEA heat), developed for fusion energy applications was irradiated at 300 and 500°C to 5 dpa in the High Flux Isotope Reactor (HFIR). Changes in yield strength, deformation mode, and strain-hardening capacity were seen, with the magnitude of the changes dependent on irradiation temperature. Irradiation at 300°C led to a significant loss of strain-hardening capacity with a large change in yield strength. There was a tendency for a reduction in strain rate to cause a decrease in yield strength and elongation. Irradiation at 500°C had little effect on strength, but a reduction in strain rate caused a decrease in ductility. In order to determine the contributions of different microstructural features to strength and to deformation mode, transmission electron microscopy (TEM) specimens were prepared from the gage sections of the tested (strained) flat tensile specimens and examined; fracture surfaces were examined by scanning electron microscopy (SEM). The fracture surfaces showed a martensitic mixed quasi-cleavage and ductile-dimple fracture in the center at both irradiation temperatures. The microstructure in the necked region irradiated at 300°C showed defect free bands, which may be dislocation channels. This suggests that dislocation channeling could be the dominant deformation mechanism in martensitic steels irradiated at 300°C, resulting in the loss of strain-hardening capacity.
Radiation-Induced Phase Instabilities and Their Effects on Hardening and Solute Segregation in Precipitation-Strengthened Alloy 718
Authors: Thomas Larry E. , Sencer Bulent Hakan , Bruemmer Stephen M.
Published: April 2011

A classic example of radiation-induced phase instability and degraded mechanical properties occurs in γ′-γ″-strengthened alloy 718. During irradiation with neutrons or protons at ∼ 30 to 288°C, the Ni 3Nb γ″ particles disappear after low doses. The γ′ (present only in the matrix) also disappears after <0.6 dpa at 30 to 55°C, but at 288°C it persists to higher doses and eventually reprecipitates as new γ′ with changed composition. Hardness of the alloy is unaffected by disappearance of the γ″, but decreases appreciably at 288°C as the original γ′ particles dissolve. Fine-probe compositional measurements in a TEM showed that the softening coincides with solute redistribution and reprecipitation rather than with the phase disappearance. Compositional changes at grain boundaries included leveling of the thermally segregated Mo as well as strong Ni enrichment and loss of Nb after high doses. The complex phase stability and solute redistribution behavior reflects mainly ballistic mixing at 30-70°C irradiation temperatures and the influence of significant thermal diffusivities at the higher temperatures.
Effects of Proton Irradiation in Zeolite-Y
Authors: Gu Binxi , Wang Lumin , Wang Shixin , Zhao Donggao. , Rotberg Victor H. , Ewing Rodney C.
Published: April 2011

Radiation effects on zeolite-NaY have been investigated by irradiation with a 500 keV H+ beam. The crystalline-to-amorphous transition occurs at a total dose equivalent to an ionizing energy deposition of 3×1010Gy and a displacement damage level of 0.05 dpa. The ion exchange capacity of the irradiated zeolite-NaY with 10 mN SrCl2 or 10 mN AgNO3 solutions varies with the extent of the damage to the crystalline structure. After 25 hours of exchange, the Sr concentration in the amorphous region is nearly zero. This result shows that radiation-induced amorphization can cause a significant loss in ion exchange capacity. The data also suggest that the radiation damage by proton radiation in zeolite-NaY is through both ionizing and displacement processes. The result from Ag-exchange reaction with the irradiated zeolite suggests that higher radiation dose is required to block the penetration of Ag into the supercages. The Ag concentration (∼3 at.%) in the fully damaged region suggests that the cations in the small cages are still exchangeable even when amorphization has been achieved.
Microstructure of Swift Heavy Ion Irradiated SiC, Si3N4 and AlN
Authors: Zinkle S.J. , Jones J.W. , Skuratov V.A.
Published: April 2011

Cross-section transmission electron microscopy was used to investigate the microstructure of single crystal silicon carbide and polycrystalline silicon nitride and aluminum nitride following room temperature irradiation with either 245 MeV Kr or 710 MeV Bi ions. The fluences ranged from 1×1012/cm2 (single track regime) to 1×1013/cm2. Ion track formation was observed in the Bi ion-irradiated Si3N4 specimen in regions where the electronic stopping power exceeded a critical value of ∼15 keV/nm (depths <24 μm). Ion track formation was not observed at any depth in 245 MeV Kr ion-irradiated Si3N4, in which the maximum electronic stopping power was 14.5 keV/nm. There was no evidence for track formation in either SiC or AlN irradiated with 710 MeV Bi ions, which indicates that the threshold electronic stopping power for track formation in these two ceramics is >34 keV/nm. The high resistance of SiC and AlN to track formation may be due to their high thermal conductivity, but further study is needed to quantitatively evaluate the suitability of the various track formation models.
Direct Comparison between Modeling and Experiment: an α-Fe Ion Implantation Study
Authors: Marian Jaime , Wirth Brian D. , Perlado J. Manuel , de la Rubia T. Diaz , Schäublin Robin , Lodi Dario , Hernández Mercedes , de Diego Gonzalo , Briceño Dolores G. , Stoller Roger E.
Published: April 2011

Advances in computational capability and modeling techniques, as well as improvements in experimental characterization methods offer the possibility of directly comparing modeling and experiment investigations of irradiation effects in metals. As part of a collaboration among the Instituto de Fusión Nuclear (DENIM), Lawrence Livermore National Laboratory (LLNL) and CIEMAT, single and polycrystalline α-Fe samples have been irradiated with 150 keV Fe- ions to doses up to several dpa. The irradiated microstructure is to be examined with both transmission electron microscopy (TEM) and positron annihilation spectroscopy (PAS). Concurrently, we have modeled the damage accumulation in Fe under these irradiation conditions using a combination of molecular dynamics (MD) and kinetic Monte Carlo (KMC). We aim to make direct comparison between the simulation results and the experiments by simulating TEM images and estimating positron lifetimes for the predicted microstructures. While the identity of the matrix defect features cannot be determined from TEM observations alone, we propose that both large self-interstitial loops, trapped at impurities within the material, and small, spherical nanovoids form.
Atomistic Simulation of Dislocation-Defect Interactions in Cu
Authors: Wirth B. D. , Bulatov V. V. , de la Rubia T. Diaz
Published: April 2011

The mechanisms of dislocation-defect interactions are of practical importance for developing quantitative structure-property relationships, mechanistic understanding of plastic flow localization and predictive models of mechanical behavior in metals under irradiation. In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiation microstructural examination in Cu reveals that irradiation has produced a high number density of nanometer sized stacking fault tetrahedra. Thus, the resultant irradiation hardening and shear localization is commonly attributed to the interaction between stacking fault tetrahedra and mobile dislocations, although the mechanism of this interaction is unknown. In this work, we present a comprehensive molecular dynamics simulation study that characterizes the interaction and fate of moving dislocations with stacking fault tetrahedra in Cu using an EAM interatomic potential. This work is intended to produce atomistic input into dislocation dynamics simulations of plastic flow localization in irradiated materials.