bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fracture and Fatigue Crack Growth of Bulk Metallic Glass Alloys and their Composites
Authors: Flores Katharine M. , Dauskardt Reinhold H. 
Published: April 2011

AbstractBulk metallic glasses exhibit extraordinary strength and elastic properties, but the lack of extensive plastic deformation and the catastrophic nature of failure limit the usefulness of the monolithic alloy. This work presents an overview of the results of fracture and fatigue crack growth experiments for a bulk metallic glass matrix composite with a Zr-Ti-Nb reinforcement phase precipitated in situ. The composite exhibits stable crack growth at stress intensities nearly double the fracture toughness of the monolithic glass. This is associated with the formation of a distributed damage zone at the crack tip. While the second phase had a marked effect on the fracture behavior, there was very little change to the fatigue crack growth results. Fractography suggests that the second phase particles are too small to cause crack bridging or significantly change the crack path.
Quality Assurance Evaluation of Thermal Barrier Coatings by Electrochemical Impedance Spectroscopy
Authors: Zhang Jianqi , Tamboli Danyash , Desai Vimal 
Published: April 2011

ABSTRACTThe technique of electrochemical impedance spectroscopy (EIS) was used to examine the behavior of intact thermal barrier coatings (TBC) at ambient temperature. Cross-sectional morphological examination of TBC was conducted by scanning electron microscope (SEM). By correlating the SEM visual examination with EIS data, TBC was characterized non-destructively. A model of EIS alternative current (AC) equivalent circuit was proposed to establish the relationship between the EIS elemental parameters in the circuit and the microstructural characteristics of TBC. A linear relationship was found to exist between the electrical impedance of TBC topcoat and the thickness of the topcoat. The porosity of TBC top coat showed a linear relationship with the capacitance of ceramic TBC, and the pore shape in the TBC topcoat was represented by the value of the electrical impedance of the pore. The result in the study has demonstrated that EIS can be used as a non-destructive evaluation (NDE) technique for quality assurance of TBC.
An In-Situ Study of Crack Propagation in Binary Lamellar TiAl
Authors: Wang P. , Bhate N. , Chan K.S. , Kumar K.S. 
Published: April 2011

ABSTRACTSingle-colony thick compact tension specimens of binary lamellar Ti-46.5%Al were tested within a scanning electron microscope to examine the contribution of colony boundaries to crack growth resistance under monotonic loads. These specimens were obtained by machining slices from bulk material that had been heat treated to grow the colony size. Thus, the lamellae in adjacent colonies exhibit significant misorientation across the boundary. The orientation of the lamellae within a colony has been characterized in terms of two angles defined with respect to the notch orientation: an in-plane angle β and a through thickness angle β. The change in these two angles across the colony boundary quantifies the misorientation. In addition a third angle, ö, defines the colony boundary tilt to the vertical plane. These parameters were measured in several specimens and the crack growth resistance across the boundary was qualitatively and quantitatively characterized. The importance of the through-thickness angle β in providing resistance to crack growth is illustrated.
Interaction of boron with crystal defects in B2-ordered FeAl alloys
Authors: Fraczkiewicz Anna , Gay Anne-Sophie , Cadel Emmanuel , Blavette Didier 
Published: April 2011

ABSTRACTIntermetallic alloys are often doped with boron to suppress their intrinsic room-temperature intergranular brittleness. The commonly admitted mechanism of this effect, i.e. an intergranular segregation of boron, seems not to be the only important feature. In this work, boron interactions with numerous kinds of crystal defects (point defects, dislocations, grain boundaries) are studied in B-doped FeAl (B2) alloys containing 40 at. % Al. The intergranular segregation of boron is first characterized. Both an equilibrium and a non-equilibrium (due to a solute atom / thermal vacancy interaction) segregation mechanisms are identified. Strong tendency of boron to segregate to the dislocations lines is shown by direct measurements by atom probe field ion microscopy (AP FIM). This segregation is shown to induce a local depletion in Al in the vicinity of defects.
Plastic deformation of single crystals with the C11b structure : Effect of the c/a axial ratio
Authors: Ito Kazuhiro , Yoshioka Hironori , Yamaguchi Masaharu 
Published: April 2011

ABSTRACTMoSi2 has a great potential for very high temperature structural applications. Plastic deformation of MoSi2 single crystals with the C11b structure is extremely anisotropic. It is caused by non-Schmid behavior of slip on {013}<331> with the higher CRSS values for orientations closer to [001]. In order to provide better understanding of key factors on such non-Schmid behavior in MoSi2 (c/a=2.45), we chose PdZr2 with a c/a axial ratio higher than 3 (c/a=3.30) and characterized the plastic deformation. Compression tests were conducted at various temperatures along [001], [010] and [110] axes. Slip on {013}<100> has the shortest Burgers vector and the largest interplanar spacing in PdZr2 and was observed to be activated for [110] with the lowest CRSS. While slip on {013}<331> can be activated even at -196°C for [001]. Although {013}<331> slip has the same Schmid factors for [001] and [010], the yield stress of the [010]-oriented crystals is about twice higher than that of the [001]-oriented crystals. Thus non-Schmid behavior of slip on {013}<331> is also observed in PdZr2, and the manner is opposite to that in MoSi2. Plastic anisotropy in the C11b structure will be discussed in terms of the c/a axial ratio.
Ab initio simulation of a tensile test in MoSi2 and WSi2
Authors: Friák M. , Šob M. , Vitek V. 
Published: April 2011

ABSTRACTThe tensile test in transition metal disilicides with C113 structure is simulated by ab initio electronic structure calculations using full potential linearized augmented plane wave method (FLAPW). Full relaxation of both external and internal parameters is performed. The theoretical tensile strength of MOS12 and WSi2 for [001] loading is determined and compared with those of other materials.
Transient creep behaviour of Ni3Al polycrystals
Authors: Kruml Tomas , Piccolo Birgit Lo , Martin Jean-Luc 
Published: April 2011

ABSTRACTRepeated creep tests were used for measuring various constant strain-rate deformation parameters. The results are consistent with those of repeated stress relaxations, although the precision is lower for creep in the present case. The small yield point observed in reloading after the transient is directly related to the amount of exhausted mobile dislocations, i.e. it originates from multiplication processes. During the transient test (180s total), the total exhaustion rate of mobile dislocations can be as high as 99%. It exhibits a maximum at the same T (about 500 K) as the work hardening. This supports the validity of a model which considers the work-hardening peak temperature to correspond to the stress under which incomplete Kear-Wilsdorf locks yield.
Slip trace characterisation of Ni3Al by atomic force microscopy.
Authors: Coupeau Christophe , Kruml Tomas , Bonneville Joël 
Published: April 2011

ABSTRACTWe examined by atomic force microscope the slip traces produced on Ni3Al single crystals pre-deformed up to nearly 1% plastic strain at three temperatures in the anomaly domain: 293K, 500K and 720K. It is observed that, whatever the deformation temperature, the slip traces essentially belong to the primary octahedral slip system. The lengths of the slip lines become shorter and shorter with increasing temperature, while the number of dislocations that constitutes the lines is approximately constant. These results are interpreted in terms of a decreasing mean free path of the mobile dislocations when the temperature is raised. The implications of these results in the understanding of the flow stress anomaly are underscored.
Growing Cobalt Triantimonide Using Vertical Bridgman Method and Effects of Post Annealing
Authors: Akasaka M. , Sakuragi G. , Suzuki H. , Iida T. , Takanashi Y. , Sakuragi S. 
Published: April 2011

ABSTRACTCrystals of CoSb3 were grown using the vertical Bridgman method at growth rates that varied from 0.4 to 2.8 mm/h. Thermoelectric properties were analyzed for both as-grown and post-annealed samples. Polycrystalline CoSb3 surrounded by Sb was obtained. Samples grown at the rate of 0.4 mm/h had larger CoSb3 grains than samples grown at the 2.8 mm/h rate. For the as-grown samples, the Seebeck coefficient was smaller than 200 μ/K, which is a nominal value [1–3]. The presence of residual Sb resulted in a decrease in the Seebeck coefficient and an increase in the samples' electrical conductivity. A subsequent heat treatment at 800 °C for 20 h eliminated the residual Sb, resulting in a significant increase in the Seebeck coefficients (ranging from > 200 μV/K) in the annealed samples, as compared with the as-grown samples. The samples with a higher growth rate had larger Seebeck coefficients of ∼500 μ/K after annealing.
Growth of The Mo5SiB2 Phase in A Mo5Si3/Mo2B Diffusion Couple
Authors: Kim Sungtae , Sakidja R. , Dong Z. F. , Perepezko J. H. , Kim Yeon Wook 
Published: April 2011

ABSTRACTThe high melting temperature and oxidation resistance of the Mo5SiB2 (T2) phase and multiphase microstructures incorporating the T2 phase in the Mo-Si-B system have motivated further studies for applications in very high temperature environments. Since the long term microstructural stability is determined by diffusional processes, diffusion couples consisting of binary boride and silicide phases have been examined in order to evaluate the kinetics of T2 phase development and the relative diffusivities controlling the kinetics. Long term annealing (500 hrs) of the Mo5Si3/Mo2B diffusion couple yields the phase sequence of Mo5Si3/Mo3Si/T2/Mo2B at 1600°C. This indicates that the T2 phase initiates and grows from the Mo2B side to a thickness of about 32μm and the Mo3Si phase initiates and grows from the Mo5Si3 side to a thickness of about 15μm. Other annealing treatments allow for an analysis of the diffusion kinetics based upon the layer thickening and composition profile measurements. To identify the crystallographic growth direction of T2 on Mo2B, a wedge shaped TEM sample with very thin leading edge was prepared. Microstructure images indicate that the growth mode of the T2 phase is columnar. There is a clear tendency for the growth of T2 to be approximately normal to c-axis.
The generation of faulted dipoles and dislocation activity in γ-TiAl
Authors: Grégori Fabienne , Veyssière Patrick 
Published: April 2011

ABSTRACTFaulted dipoles (FDs) nucleates at the tip of a <011] screw lock while the latter is unzipped by the connecting mixed segment. The transformation is favoured by the asymmetrical dissociation mode of the <011] dislocation, into two partials with 1/6<112] and 1/6<154] Burgers vectors bordering an intrinsic stacking fault. Where the parent <011] dislocation switches from a locked, 3D non planar to a fully coplanar core configuration at the connecting mixed segment, the 1/6<154] partial assumes a zonal form capable of expelling a partial dislocation with 1/6<112] Burgers vector. The latter transforms the fault from intrinsic to extrinsic and leaves a 1/3<121] partial with a zonal core on the other side of the fault. The presence of FDs reflects the propensity of <011] dislocations to form screw locks and thus attests to the operation of <011] dislocations during deformation.
High temperature gas nitridation and wear resistance of TiAl based alloys
Authors: Zhao Bin , Sun Jian , Wu Jiansheng , Wang Fei 
Published: April 2011

ABSTRACTGas nitridation of TiAl based alloys in an ammonia atmosphere was carried out in the present work. The nitride layers were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The evaluation of the surface hardness and wear resistance was performed to compare with those of the non-nitrided alloys. It is concluded that the nitride layers are composed of Ti2AlN as the inward-growing layer and TiN as the outward-growing layer. The nitridation temperature and time were two major factors influencing the thickness of the nitride layers of the alloys. The high temperature nitridation raised the surface hardness and the wear resistance of the TiAl based alloys markedly. The tribological behaviors of the nitrided alloys were also discussed.
Mechanisms contributing to the pinning of ordinary dislocations in γ-TiAl
Authors: Grégori Fabienne , Veyssière Patrick 
Published: April 2011

ABSTRACTProperties of ordinary dislocations and related debris are investigated in single crystals of γ-TiAl deformed in single slip at 20°C and 400°C. Typical of this temperature range are prismatic loops isolated or belonging to arrays, together with multipoles. The interaction of these with mobile ordinary dislocations generates various configurations including trailing-like hairpins. Certain features are consistent with an extrinsic origin for point pinning.
Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers
Authors: Spiga Sabina , Ferrari Sandro , Fanciulli Marco , Schmidt Bernd , Heinig Karl-Heinz , Grötzschel Rainer , Mücklich Arndt , Pavia Giuseppe 
Published: April 2011

AbstractIn this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (fluences of 0.1-1 × 1016 cm−2) Sn implantation in 85 nm thick SiO2, followed by annealing (800-1000°C for 30-300 sec under Ar or N 2 dry ambient) in a rapid thermal processing (RTP) system, leads to the formation of two cluster bands, near the middle of the SiO2 layer and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed between the two bands. Cluster-size distribution and cluster-crystallinity are related to implantation fluence and annealing time. Low energy (10-12 keV) Sb and Sn implantation (fluences 2-5 × 1015 cm−2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.
Ion beam radiation effects on InAs semiconductor quantum dots
Authors: Zhu J. , Thaik M. , Yakimov M. , Oktyabrsky S. , Kaloyeros A. E. , Huang M. B. 
Published: April 2011

AbstractSelf-assembled quantum dots (QDs) have attracted significant attention because of their potential applications in novel semiconductor devices. In this work, we investigated radiation effects induced by 1.0 MeV proton ion beams on InAs self-assembled quantum dots. In particular, we emphasized the effects of lattice environments of QDs on their luminescence emission after ion beam irradiation. Photoluminescence (PL) spectroscopy was used to characterize the optical properties of QDs subjected to proton irradiation and post-irradiation annealing. Compared to the single-layer QDs grown in GaAs films, the QDs embedded in an AlAs/GaAs superlattice exhibited much higher PL degradation resistance to proton beam bombardment, e.g., at the highest dose (1.0×1014 cm−2) used in this work, a difference of ~ 20-fold in PL intensity was found between the QDs configured in these two different lattice structures. After thermal annealing of irradiated QD samples, ion beam enhanced blueshift of PL was observed to be much more pronounced for the single-layer QDs. We discuss mechanisms that may result in the differences in optical response to ion beams between QDs with different lattice surroundings.
Effect of Substrate Materials on Mechanical Properties and Microstructure of Carbon Nitride Films Prepared by Ion-beam-assisted deposition
Authors: Ohta Hidenobu , Matsumuro Akihito , Takahashi Yutaka 
Published: April 2011

AbstractCarbon nitride (C-N) thin films were prepared on several substrates by ion-beam-assisted deposition technique. In this experiment, carbon was evaporated by electron beam. Nitrogen and argon ion beams were bombarded simultaneously. Aluminum alloy (7075), high-carbon chrome bearing steel (SUJ2), pure titanium plates (99.5%) and Si(100) wafer were used as substrates. Here, mechanical properties, such as hardness, adhesion, friction coefficient and wear resistance were investigated. These results show the adhesion between the films and substrates were improved by formation of the carbon layer. The microstructure of the carbon nitride films were investigated by cross sectional high-resolution transmission electron microscopy (HRTEM).
Nanophase Composites Produced by Ion Implantation: Properties, Problems, and Potential
Authors: Meldrum A. , Boatner L. A. , White C. W. , Haglund R. F. 
Published: April 2011

AbstractIon implantation has become a versatile and powerful technique for synthesizing nanometer-scale clusters and crystals embedded in the near-surface region of a variety of hosts. The resulting nanocomposite materials often show unique optical, magnetic, and electronic properties. Here we review some of the principal features of this nanophase materials synthesis technique and discuss the outstanding experimental difficulties that currently hamper the development of devices based on the many unique properties of these nanocomposite materials. Possible solutions to these problems and future research directions are discussed.
A Damage Model for Disordered Structures in Ion Irradiated Silicon
Authors: Cheng Ju-Yin , Gibson J. Murray 
Published: April 2011

AbstractMedium-range order has been observed in ion-implanted amorphous silicon, suggesting a paracrystalline structure for this material. The origin of a paracrystalline structure may be due to an energy spike phenomenon. To evaluate the influence of energy spikes on a particular process, we have attempted to calculate the characteristic energy in a spike. However, the observed depth dependence of amorphous structures in as-implanted silicon is puzzling. To explain this, we simulated the depth distribution of cascade events in a particular energy range. We found a great increase of point defect concentration and cascade events as the depth increases. This result could explain the experimental depth dependence.
Impact of Boron and Gallium on Defects Production in Silicon
Authors: Khan Aurangzeb , Dharmarasu Nethaji , Yamaguchi Masafumi , Araki Kenji , Vu Tuong K. , Saga Tatsuo , Abe Takao , Annzawa Osamu , Imaizumi M. , Matsuda Sumio 
Published: April 2011

AbstractWe report the results of comparison of radiation-induced defects (1 MeV electrons) in n+-p-p+ Si diodes doped with gallium or boron ranging in concentration from 8 × 1014 to 5 × 1016 cm−3, together with the impact of oxygen on radiation –induced defects. Present results provide evidence for new defects states in addition to those previously reported in gallium- and boron-doped Si. The combined boron and gallium data provide enough information to gain valuable insight into the role of the dopants on radiation-induced defects in Si. The interesting new future of our results is that the gallium appears to strongly suppress the radiation induced defect, especially hole level EV+0.36 eV, which is thought to act as a recombination center. Similarly the dominant electron level at EC-0.18 eV in B-doped Si (which act as a donor) has not been observed in Ga-doped CZ-grown Si.
Post Annealing Studies Of C60 Ion Implanted Thin Films
Authors: Dharmarasu Nethaji , Narayanan Kannan L. , Kojima Nabuaki , Ohshita Yoshio , Yamaguchi Masafumi 
Published: April 2011

AbstractPhysical properties of multiple-energy B-ion implanted C60 thin films were investigated for various doses. Fourier Transform Infra-red Spectroscopy (FTIR) results indicate the structural transformation of C60 to amorphous carbon phase during implantation. The conductivity type of the implanted films is found to be p-type and the conductivity measurements reveal a dramatic increase in the conductivity with ion implantation. Temperature dependent conductivity shows the semiconducting nature of the B-ion implanted films. The optical absorption coefficient and optical gap of the implanted films have been observed as a function of B-ion dose. Measurements on implanted films subjected to thermal annealing indicate the removal of the defects caused during the implantation. Ion implantation-induced defects are found to partially annihilate with the annealing temperature. Electrical conductivity and optical gap are determined in the post-implanted films. The observation of the systematic increase in the conductivity of the annealed films is due to the removal of the defects and the formation of defect free boron impurity acceptor.
Unusual Change in Columnar Defect Morphology in YBCO upon Annealing
Authors: Yan Y. , Kirk M. A. , Petrean A. , Paulius L. 
Published: April 2011

AbstractWe show evidence from transmission electron microscopy of an unusual change in columnar defect morphology in YBCO upon annealing to 600°C. The disappearance of the nanotwinned, but not the larger scaled thermal twinned, structure is found. A removal of the large fluctuations in the diameter of the amorphous column, preserving a narrow continuous column, is surprisingly discovered. Correlations with magnetization measurements demonstrate the greater efficiency of vortex pinning at 77 K by the annealed defect structure.
Understanding ion beam synthesis of nanostructures: Modeling and atomistic simulations
Authors: Strobel M. , Heinig K.-H. , Möller W. 
Published: April 2011

AbstractIon implantation, specified by parameters like ion energy, ion fluence, ion flux and sub-strate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced, which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient in understanding nanocluster evolution. Various aspects of precipitate evolution during implantation, formation of ordered arrays of nanophase domains by focused ion implantation and compound nanocluster synthesis are discussed.
Co-Implantation and the Role of Implant Damage in the Thermal Stability of Implanted Helium in Indium Phosphide
Authors: Simpson Todd W. , Mitchell Ian V. 
Published: April 2011

AbstractThe thermal stability of 3He implanted into single crystal indium phosphide has been studied. Helium diffuses in the 200°C-300°C temperature range unless stabilized by bubbles which trap helium up to the 400°C-500°C temperature range. The efficiency of bubble formation, as measured by the fraction of implanted helium retained to 400°C is increased by: 1) increasing the helium fluence, 2) increasing the temperature ramp rate, 3) co-implantation with a second ion species, or 4) implanting at elevated temperature. The mechanism by which these processes enhance bubble formation can be understood in terms of a model where the nucleation of bubbles occurs at elevated temperature in the presence of both lattice defects and helium atoms.