bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Single-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

Intermetallic 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

MoSi2 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

The 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

Repeated 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

We 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

Crystals 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

The 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

Faulted 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

Gas 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

Properties 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

In 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

Self-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

Carbon 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

Ion 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.
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

We 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

Physical 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.
Understanding ion beam synthesis of nanostructures: Modeling and atomistic simulations
Authors: Strobel M. , Heinig K.-H. , Möller W.
Published: April 2011

Ion 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

The 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.
Spontaneous Crystalline Multilayer Formation in Ni Implanted Al at 100 K
Authors: Cuenat Alexandre , Hessler-Wyser Aicha , Döbeli Max , Gotthardt Rolf
Published: April 2011

The microstructure evolution of aluminum implanted with nickel at 5 MeV and at 100 K to a local concentration of 25 at. % is described. Transmission Electron Microscopy (TEM) observa- tions and Rutherford Backscattering Spectrometry (RBS) experiments are conducted to deter-mine the Ni profile and the microstructure of the implanted samples. For lower Ni concentration, it has been previously observed that Al0.75Ni0.25 amorphous precipitates are formed together with a high dislocation density. When the Ni concentration reaches 25 at. %, a new crystalline multi-layered microstructure is observed: the TEM observations reveal the presence of well-defined crystalline layers separated by sharp interfaces. To our knowledge, it is the first time that such a structure is observed without further annealing of the implanted sample. A series of mechanisms describing the formation of the crystalline multilayer are briefly discussed. It is argued that its formation is the result of a recrystallization front produced by the exothermal amorphous to crystal transformation.
Time-Resolved X-Ray Scattering Study of Co Surface Evolution during Low-Energy Ion Irradiation
Authors: Malis O. , Pomeroy J. M. , Headrick R. L. , Brock J. D.
Published: April 2011

The sputter-erosion of hcp Co (0001) single crystal with Ar+ ions in the 100 to 700 eV energy range was investigated using in-situ time-resolved x-ray scattering. At temperatures above 300°C the surface remains relatively smooth, erosion evolving through a layer-by-layer or step flow mechanism. In this regime the ions have a smoothening effect on the surface and the resulting roughness decreases with increasing ion energy. Below 300°C the surface develops a pattern of mounds or pits with a characteristic wavelength. The time, ion energy and temperature dependence of this wavelength were studied in detail. Epitaxial Co thin films thermally evaporated on sapphire were also sputtered through in order to synthesize self-assembled arrays of Co nanoclusters with a narrow size distribution. The degree of local order within the Co dot arrays was examined using atomic force microscopy.
Shear Modulation Force Microscopy Studies on Cross-linked Elastomer Thin Films
Authors: Zhang Y. , Ge S. , Rafailovich M.H. , Sokolov J.C. , Peiffer D.G. , Dias A.J.
Published: April 2011

The atomic force microscope in the shear force modulation microscopy (SMFM) mode has been used to characterize the surface modulus and cross-link density of elastomer thin films, where standard rheological methods cannot be applied. Brominated poly(isobutylene-co-4-methylstyrene) (BIMS) is a synthetic terpolymer which can be stoichiometrically cross-linked by N, N'-dicinnamylidene-1,6-hexanediamine. The results on several types of BIMS elastomers with different bromide content are reported. The cross-linking reaction at the surface is found to be significantly faster than that of bulk. The estimated shear moduli of the thin films were found to be proportional to the cross-link density, as expected from the rubber elasticity theory for bulk materials.
3D FIB and AFM mapping of Nanoindentation Zones
Authors: Steer T.J. , Möbus G. , Kraft O. , Wagner T. , Inkson B.J.
Published: April 2011

A novel technique has been developed to examine site-specific, subsurface microstructures in three dimensions. A 3D data set is collected by successive cross-sectional slicing using a gallium focused ion beam (FIB) and imaging using ion-induced secondary electrons, enabling a 3D microstructure map to be generated using computer-based reconstruction techniques. In the first instance, this 3D FIB mapping technique has been applied to copper-based epitaxial metal multilayer coatings which have been deformed by nanoindentation. It is possible to produce 3D profiles of the deformed subsurface interfaces. These individual interface maps allow analysis of the deformation in terms of both the thickness of individual layers and that of the entire film. Material flow, which is seen as pile-up and residual indent zones around the indent, can thus be precisely characterised. The site at which the sectioning is to be carried out can be chosen with high spatial resolution; consequently, nanoscale mechanical properties can be linked directly with an area's microstructure.

In an attempt to examine the errors involved in this 3D mapping method the 3D FIB map of the surface of a residual indent has been compared to an atomic force microscopy (AFM) scan of the same region. The sources and significance of the errors are discussed with reference to ways in which they might be reduced.
Spherical Indentation and Flow Property Measurement-Finite Element Simulation
Authors: He Ming Y. , Odette G. R. , Lucas G. E.
Published: April 2011

Finite element simulations of ball indentation tests were performed and analyzed using the automated ball indentation method. The accuracy and reliability of this methods were assessed.
Mechanical Deformation of Crystalline Silicon During Nanoindentation
Authors: Bradby J.E. , Williams J.S. , Wong-Leung J. , Swain M.V. , Munroe P.
Published: April 2011

Deformation during spherical and pointed indentation in (100) crystalline silicon usig a UMIS-2000 nanoindenter has been studied using cross-sectional transmission electron microscopy (XTEM), atomic force microscopy (XTEM), atomic force microscopy and Raman microspectroscopy. XTEM samples were prepard by focused ion beam milling to accurately position the cross-section through the indentations. Indentation loads were chosen below an above the yield point for silicon to investigate the modes of plastic deformation. Slip planes are visible in XTEm micrographs for all indentation loads studied but slip is not the main avenue for plastic deformation. A thin layer of poly-crystalline material has been identified (indexed as Si-XII from diffraction patterns) on the low load indentation, just prior to yield (pop-in during loading). For loading above the yield point, a large region of amorphous silicon was observed directly under the indenter when fast unloading conditions were used. The various microstructures and phase observed below indentations are correlated with load/unload data.
Nanomechanics Using an Ultra-Small Amplitude AFM
Authors: Hoffmann Peter M. , Jeffery Steve , Oral Ahmet , Grimble Ralph A. , Özer H. özgür , Pethica John B.
Published: April 2011

A new type of AFM is presented which allows for direct measurements of nanomechanical properties in ultra-high vacuum and liquid environments. The AFM is also capable of atomic-scale imaging of force gradients. This is achieved by vibrating a stiff lever at very small amplitudes of less than 1 Å (peak-to-peak) at a sub-resonance amplitude. This linearizes the measurement and makes the interpretation of the data straight-forward. At the atomic scale, interaction force gradients are measured which are consistent with the observation of single atomic bonds. Also, atomic scale damping is observed which rapidly rises with the tip-sample separation. A mechanism is proposed to explain this damping in terms of atomic relaxation in the tip. We also present recent results in water where we were able to measure the mechanical response due to the molecular ordering of water close to an atomically flat surface.
Matrix Damage in Iron
Authors: Nicol A C , Jenkins M L , Kirk M A
Published: April 2011

We present results of a weak-beam transmission electron microscopy study of “matrix damage” in two nearly-pure irons (designated alloys 1A and 2A) produced by neutron irradiation to a fluence of 0.06 dpa at 280°C. The matrix damage in both materials was found to consist of small (2-6 nm) dislocation loops. About 80 % have Burgers vectors b = a<100>, and the remainder have b = a/2<111>. The loops in alloy 1A have a mean image size dmean = 2.8± 0.1 nm and a mean maximum image size dmax = 4.2± 0.3 nm, while those in 2A have d mean = 3.4± 0.1 nm and d max = 4.5± 0.3 nm. The number densities are about 8.5 × 1021 m−3 in alloy 1A, and 6.6 × 1021 m−3 in 2A. It can be shown that the loops can account for the observed irradiation hardening. At least some loops are stable under thermal annealing to temperatures of at least 430°C. This and other indirect evidence suggests that their nature is interstitial.
Identification of Defects In Ferritic/Martensitic Steels Induced by Low Dose Irradiation
Authors: Schäublin R. , Victoria M.
Published: April 2011

The ferritic/martensitic steels which are candidates for the first wall of the future fusion reactor are investigated in TEM. While the irradiation doses expected in this reactor are in the range of 100 dpa per year, there is still a lack of knowledge on the nature of the irradiation induced defects for the low doses at which hardening is already occuring. This hardening depends strongly on the type of interaction between the moving dislocations and the defects. The early defects, which start to appear as black dots in TEM, are expected to be either three dimensional clusters of interstitials or vacancies, or dislocation loops. The nature and size of these defects is carefully studied in the F82H steel for doses ranging from about 0.5 dpa to 9 dpa and irradiation temperatures ranging from 40°C to 330°C. For that purpose, various weak beam techniques are explored at the limit of resolution of a TEM used in diffraction mode. Results are presented here for the cases of a 1.7 dpa and a 8.8 dpa irradiation.
High Energy Proton Irradiation of Pure Titanium
Authors: Leguey Teresa , Bailat Claude , Baluc Nadine , Victoria Max
Published: April 2011

Polycrystalline specimens of hcp pure titanium have been irradiated at 300-320 K with 590 MeV protons to doses ranging between 10-3 and 3×10-2 dpa. Combination of tensile deformation experiments and transmission electron microscopy observations revealed that irradiation produces slight hardening of the material, related to the irradiation-induced formation of defect clusters, but not significant loss of ductility. Plastic deformation of irradiated titanium is homogeneous. It occurs via propagation of dislocations through a cloud of defect clusters, leading to their annihilation and the formation of a cellular dislocation structure together with twins. This mechanical behavior is similar to what was previously observed for pure fcc metals, the formation of twins being however intrinsic to deformation of hcp titanium.
Dynamical Behavior of Voids in Neutron-irradiated Copper at Elevated Temperature
Authors: Mukouda Ichiro , Shimomura Yoshiharu
Published: April 2011

We reported previously an experimental result which shows that voids can move in neutron-irradiated copper at elevated temperature. To study the detailed behavior of voids, we carried out annealing experiments and in-situ observations in neutron-irradiated copper. Neutron irradiation was carried out in the temperature controlled capsule at KUR (Kyoto University Reactor). Neutron irradiation was performed at 300°C to damage levels between 10-4 to 10-3 dpa. The annealing temperature was 250°C for 10, 20, 30 min sequentially for neutron- irradiated copper. After annealing TEM observation was carried out at room temperature. Experimental results show that voids moved along the [110] direction. Voids moved during 250°C annealing but small stacking fault tetrahedra (SFT) were not changed. We observed 37 voids and 8 voids moved, the others vanished during annealing. The images of in-situ observation, void contrast images were recorded on VTR tape and analyzed frame by frame. At room temperature observation voids were static and were seen as white circles; however at 300°C the contrast changed to an oval shape and sometimes disappeared. After 7 sec contrast was a white circle and moved slightly and similar phenomena were observed quite frequently at 300°C. It is concluded that void moved with dynamical structural relaxation at elevated temperature.
Effect of Annealing and Re-irradiation on the Copper-enriched Precipitates in a Neutron-irradiated Pressure Vessel Steel Weld
Authors: Miller M. K. , Russell K. F. , Pareige P.
Published: April 2011

An atom probe tomography study has been performed to estimate the matrix composition, and the size, composition and number density of the ultrafine copper-enriched precipitates that formed under neutron irradiation in a submerged arc weld (Weld 73W). This high copper (0.27 at. % Cu) weld was examined after a typical stress relief treatment of 40 h at 607°C, after neutron irradiation to a fluence of 1.8 × 1023 n m-2 (E > 1 MeV) at a temperature of 288°C, after irradiation and thermal annealing for 168 h at 454°C, and after irradiation, thermal annealing and re-irradiation to an additional fluence of 0.8 × 1023 n m-2 (E > 1 MeV). A high number density of ultrafine copper-enriched precipitates were found to form on irradiation. These precipitates were found to coarsen and decrease in number density after the annealing treatment at 454°C. These precipitates were present after re-irradiation and some additional subnanometer diameter copper- enriched precipitates were also observed. Segregation of nickel, manganese, silicon, copper and phosphorus atoms to dislocations was also observed.
The Size Distribution of Ge Nanocrystals in Implanted and Annealed Silica
Authors: Dowd Annette R. , Llewellyn David , Gerald John D. Fitz , Elliman Robert G.
Published: April 2011

This study examines the effect of implantation and annealing parameters on the formation of Ge crystallites in ion-implanted silica. Samples were implanted at room temperature or −196oC with 1.0 MeV Ge+ ions to fluences in the range from 0.6 to 3×1017 Ge.cm−2. Ge nanocrystals were not observed in samples implanted at −196°C but were observed in samples irradiated at room temperature. Nanocrystals were observed in all samples after annealing and their size distribution was found to be almost independent of the implant fluence. The distributions were also shown to be asymmetrical with depth, with smaller nanocrystals located on the near-surface side of the implant distribution.
Molecular Dynamics Simulations of Cluster Ion Impact on Diamond Surface
Authors: Aoki Takaaki , Matsuo Jiro , Takaoka Gikan , Yamada Isao
Published: April 2011

Molecular dynamics (MD) simulations of various cluster ions impacting on solid targets were performed in order to examine the implant and damage formation processes. Ne and Ar rare gas cluster with various cluster sizes, and fullerene (C60) were impacted on diamond (001) surface. It was shown that the impact process of cluster ion depends on the cluster size. When the cluster size is small and incident energy-per-atom is high, such as Ar15 with 800eV/atom, all incident Ar atoms penetrate the surface and reside in the substrate. As the cluster size increases and the incident energy-per-atom decreases, the implant depth decreases and the profile of the displacement becomes shallower. A large cluster, such as Ar60 with 200eV/atom, shows a shallower implant depth and a higher sputtering yield than Ar15. However, Ar240 with 50eV/atom shows a shallower implant depth, but less sputtering yield than Ar60.These results suggest that there is proper cluster size and incident energy where the maximum sputtering yield is achieved.
Microstructural Evolution of Ni-doped Ferritic/martensitic Steels Irradiated in the HFIR
Authors: Hashimoto Naoyuki , Klueh Ronald L. , Robertson Janet P.
Published: April 2011

The microstructures of reduced-activation ferritic/martensitic steels, 9Cr-2WVTa and 9Cr-2WVTa doped with 2% Ni, irradiated at 400oC up to 12 dpa in the High Flux Isotope Reactor (HFIR), were investigated by transmission electron microscopy. Specimens were tempered at two different temperatures in order to investigate the effects of tempering on microstructural evolution during irradiation. Before irradiation, the lath width of Ni-doped 9Cr-2WVTa was somewhat narrower and the dislocation density tended to be higher compared with 9Cr-2WVTa. Dislocation density of specimens tempered at 750°C was lower than that tempered at 700°C. In all steels, precipitates on grain and/or lath boundaries were mainly M23C6, and there were a few TaC along dislocations in the matrices. Irradiation-induced cavities were observed in all the steels. The cavity number density of the Ni-doped 9Cr-2WVTa was higher than that of 9Cr-2WVTa due to the higher concentration of helium; however, swelling in each steels was < 0.1% because cavity sizes were so small. There was no difference of cavity number density between the steels tempered at 700°C and 750°C, but the mean size of the cavities in the steels tempered at 750°C was larger than that tempered at 700°C. Irradiation-induced a0<100> and (a0/2)<111> type dislocation loops were observed in all steels; number density and mean diameter of a0<100> type loops was higher and larger than that of (a0/2)<111> type loops. There was a tendency for the number density of loops in Ni-doped 9Cr-2WVTa to be slightly higher than that in 9Cr-2WVTa. In addition, the mean size of loops in the steels tempered at 750°C was larger than for those tempered at 700°C, while there was not much difference of number density between them. In the steels doped with Ni, irradiation-produced precipitates, identified as M6C(η)-type carbide, were found in the matrices. In this experiment, the change in tensile properties and the δDBTT of the 9Cr-2VWTa-2Ni was greater than for 9Cr-2WVTa. The microstructural evidence suggests that these differences in mechanical behavior are related to the formation of radiation-induced precipitates and cavities in the Ni-doped alloy; further analysis of the data using barrier hardening models is in progress.
Radiation Effects on the Plasticity and Microstructure of Ti-Al-V Alloys Containing β Phase
Authors: Sawai Tomotsugu , Tabuchi Masayuki , Wakai Eiichi , Hishinuma Akimichi
Published: April 2011

Tensile properties of Ti-35Al-15V and Ti-30Al-10V alloys were examined. These alloys contain β phase with ordered bcc structure. The total elongation of Ti-35Al-15V alloy abruptly changes from 10% to 60% around 620 ºC. Many transformation bands were observed in β grains that were highly deformed above this temperature. The hexagonal α2-phase grains in bands and the β–phase grains in bands and matrix were in Burgers type of orientation relationship. The ductility of Ti-30Al-10V alloy was highly affected by neutron irradiation. The specimens irradiated and tested at 400 °C showed almost no ductility. The total elongation of specimens irradiated and tested at 600 °C was about 10 %, while that of unirradiated ones was larger than 60 %. Specimens irradiated at 400 °C were also tested at 600 °C and the elongation was only 6 %, showing little recovery in ductility. This embrittlement suggests phase decomposition during irradiation.
The primary damage in Fe revisited by Molecular Dynamics and its binary collision approximation
Authors: Becquart C.S. , Hou M. , Souidi A.
Published: April 2011

Molecular Dynamics (MD) is a very powerful tool for studying displacement cascades initiated by the neutrons when they interact with matter and thus evaluate the primary damage. The mean number of point defects created can be obtained with a fair standard error with a reasonable number of cascade simulations (10 to 20 [1]), however other cascades characteristics (spatial distribution, size and amount of defect clusters …) display a huge variability. Therefore, they may need to be studied using faster methods such as the Binary Collision Approximation (BCA) which is several order of magnitude less time consuming. We have investigated the point defect distributions subsequent to atomic collision cascades by both MD (using EAM potentials for Fe) and its BCA. MD and its BCA lead to comparable point defect predictions. The significant similarities and differences are discussed.
Effect of Bulk Phosphorus Content on Hardening, Non-Equilibrium Segregation and Embrittlement in Neutron Irradiated Iron-Based Alloys
Authors: Nishiyama Y. , Bloomer T. E. , Kameda J.
Published: April 2011

The effect of bulk P contents on hardening, non-equilibrium intergranular segregation and embrittlement has been studied in Mn-doped ferritic alloys subjected to neutron irradiation (E>0.1MeV: fluence of 1 × 1025 n/m2 at 711K for 2120 h) or irradiation-equivalent thermal aging. Neutron irradiation-induced intergranular P segregation became more prominent with decreasing bulk P content. Thermal aging slightly enhanced the amount of segregated P independent of the bulk P content. Intergranular C segregation in all the alloys was suppressed by the irradiation. An alloy with low bulk P content showed only moderate irradiation-induced hardening. The ductile-brittle transition temperature (DBTT) in alloys with low and intermediate amounts of P increased by the same shift during the irradiation but not at all during the thermal aging. Doping high bulk P led to a high DBTT in the as-heat-treated alloy while the irradiation decreased the DBTT. The irradiation effect on the DBTT in the model ferritic alloys containing the different levels of P is discussed in light of embrittling or toughening effects caused by the changes in the P or C segregation, and hardness.
Hardening and Microstructure of Model Reactor Pressure Vessel Steel Alloys Using Proton Irradiation
Authors: Yu Q. , Was G. S. , Wang L. M. , Odette R. , Alexander D. E.
Published: April 2011

As part of a broad effort to understand the mechanisms of irradiation embrittlement in reactor pressure vessels steels, irradiation hardening and microstructural evolution in simple model Fe-0.9Cu-1.0Mn, Fe-0.9Cu and Fe alloys irradiated with 3.2 MeV protons at 300°C are compared to the corresponding changes in hardening produced by neutron irradiation over a similar dose range of 0.0004 to 0.015 dpa. In the case of the proton irradiated samples, Vickers hardness was measured at a 25 g load and the microstructures were characterized using small angle x-ray scattering (SAXS). In spite of the much higher dpa rate for protons (3 × 10−7dpa/s compared to neutron rates of about 10−9to 10−10dpa/s) as well as very different primary recoil spectra, the observed hardening-dose response is very similar in both cases. The large increase in hardness in the alloys with 0.9% copper, and the SAXS data are consistent with precipitation of coherent copper-rich features accelerated by irradiation enhanced diffusion, as well as a much smaller contribution presumably from defect clusters that do not require the presence of copper.
Post Annealing Studies of C60 Ion Implanted Thin Films
Authors: Dharmarasu Nethaji , Narayanan Kannan L. , Kojima Nabuaki , Ohshita Yoshio , Yamaguchi Masafumi
Published: April 2011

Physical 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.
Stress Driven Phase Transformations and Recrystallization Processes in Two-Phase Titanium Aluminide Alloys
Authors: Appel Fritz , Oehring Michael
Published: April 2011

The paper presents an electron microscope study of phase transformation and recrystallization in an intermetallic α2(Ti3Al) + γ(TiAl) titanium aluminide alloy, after long-term creep. The mechanisms are closely related to the atomic structure of the α2/γ phase boundaries and are probably driven by a non-equilibrium of the phase composition leading to the dissolution of the α2 phase. The α2 /γ transformation is accompanied by the formation of precipitates, because the γ(TiAl)phase has a significantly lower solubility for interstitial impurities than the α2(Ti3Al) phase.
Morphological Evolution of a Fully Faceted Grain Boundary
Authors: Medlin D.L. , Lucadamo G.
Published: April 2011

We examine the morphological evolution of faceted grain boundaries in gold during annealing. Experiments were performed on <111> oriented gold films composed of two Σ=3 related orientation variants. The boundaries between these variants initially possess a high density of finely spaced (<25 nm) facets on {112} type planes. During annealing a large proportion of these fine-scale corrugations are annihilated, and the facet distribution coarsens significantly. Through in situ transmission electron microscopy (TEM), we directly observe this coarsening process. These results show a more complex behavior than geometric models for facet evolution would suggest and point to the need for an improved understanding of facet-junction properties and the interactions between grain boundary facets and dislocations.
Phase-Field Simulation of Domain Structure Evolution in Ferroelectric Thin Films
Authors: Li Y. L. , Hu S. Y. , Liu Z. K. , Chen L. Q.
Published: April 2011

A phase-field model for predicting the domain structure evolution in constrained ferroelectric thin films is developed. It employs an analytical elastic solution derived for a constrained film with arbitrary eigenstrain distributions. In particular, the model is applied to the domain structure evolution during a cubic→tetragonal proper ferro- electric phase transition. The effect of substrate constraint on the volume fractions of domain variants, domain-wall orientations, and domain shapes is studied. It is shown that the predicted results agree very well with existing experimental observations in ferroelectric thin films.
Interface Structure in Ferritic/Austenitic Stainless Steel Bicrystals
Authors: Taisne Aude , Décamps Brigitte , Priester Louisette
Published: April 2011

Elementary mechanisms of deformation by fatigue in duplex stainless steels bicrystals are studied by transmission electron microscopy (TEM). An attempt is made to correlate the bicrystal macroscopic behaviour with the interphase interface crystallography.
Fracture Toughness of Amorphous Precursor Derived Si-C-N Ceramics
Authors: Bauer A. , Zimmermann A. , Aldinger F.
Published: April 2011

Fully amorphous ceramics in the system silicon-carbon-nitrogen were produced with the polymer precursor route using the commercially available polysilazane CerasetTM. Besides their high temperature thermal stability, these ceramics show excellent high temperature creep resistance. Not many investigations have been dedicated to the fracture mechanics of these materials. This paper provides data on toughness measurements utilizing bulk and indentation techniques. The double cantilever beam method (DCB) was used to study crack propagation. To determine the intrinsic toughness, the crack opening displacements (COD) of indentation cracks were determined.
Interaction of Slip Bands with Grain Boundary - in situ TEM Observation
Authors: Gemperlová Juliana , Jacques Alain , Gemperle Antonín , Zárubová Niva
Published: April 2011

Mechanism of the slip transmission across the grain boundaries was studied on Σ3 bicrystals of Fe-4at%Si by transmission electron microscopy. In situ straining experiments as well as post mortem observations were performed. Three distinct events were observed in dependence on the angle α between the slip and grain boundary planes, namely transformation of the tertiary slip system in one grain into the secondary slip system in the other grain for α ≍ 90°, cross slip of dislocations of the primary slip system into the {112} plane parallel to the grain boundary for α ≍21°, and an abrupt formation of a sub-grain boundary in one grain for α ≍49°. Reasons for these diverse phenomena will be discussed in terms of interactions between the slip dislocations and the grain boundary dislocations.