bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTNb-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

ABSTRACTThis 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

ABSTRACTRecent 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

ABSTRACTSingle 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

ABSTRACTFor 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

ABSTRACTThe 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

ABSTRACTPlastic 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

ABSTRACTEquiatomic 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

ABSTRACTTemperature 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

ABSTRACTThis 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

ABSTRACTThe 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

ABSTRACTDiffusion 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

ABSTRACTThe 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

ABSTRACTThe 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

AbstractDynamic 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

Abstract200 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

AbstractThe 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

AbstractHigh-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

AbstractErbium 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

AbstractSilica 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

AbstractPlasma 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.