bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Step Growth and Characterization of BaF2/Si(III) Heterostructures
Authors: Belenchuk A. , Fedorov A. , Lucash V. , Vasilyev A. , Zenchenco V.
Published: April 2011

The influence of growth conditions on structural perfections and epitaxial relation in BaF2 films on Si(111) are considered. It is shown that rotational-twin-free BaF2 films (A-type orientation) can be grown on Si(111) by two step growth method. It is also shown that a mixed (A+B)-type orientation, which usually observed in BaF2 films grown by conventional one step growth method, can be converted into A-type orientation by postgrowth annealing. The correlation between type of epitaxial orientation in BaF2 films and structures of interface is discussed.
Principal Residual Strains as A function of Depth for Sputter Deposited Mo Thin Films
Authors: Malhotra S. G. , Rek Z. U. , Parfitt L. J. , Yalisove S. M. , Bilello J. C.
Published: April 2011

Traditionally, the magnitude of the stress in a thin film is obtained by measuring the curvature of the film-substrate couple; however, these techniques all measure the average stress throughout the film thickness. On a microscopic level, the details of the strain distribution as a function of depth through the thickness of the film can have important consequences in governing film quality and ultimate morphology. A new method for determining the magnitude of principal strains (strain eigenvalues) as a function of x-ray penetration depth using grazing incidence x-ray scattering for a polycrystalline thin film will be described. Results are reported for two Mo metallizations ˜ 500 Å and ˜1000 Å thick sputtered onto Si {100} substrates. The magnitude of the principal strains at several penetration depths was accomplished by an analysis of the diffraction peak shifts of at least six independent {hkl} scattering vectors from the Mo thin films. An out-of-plane strain gradient was identified in both Mo films and the strain eigenvalues were found to be anisotropic in nature. This new methodology should work with a variety of thin films and hence would provide quantitative insight into the evolution of thin film microstructure.
Yield Point Phenomena and Dislocation Velocities Underneath Indentations Into BCC Crystals
Authors: Gerberich W. W. , Venkataraman S. , Nelson J. , Huang H. , Lilleodden E. , Bonin W.
Published: April 2011

In a single material, hardnesses can range from 3σys up to the theoretical strength or approximately E/10 where σys and E are tensile yield strength and modulus. This variation results with decreasing depth of penetration. Such indentation size effects may be associated with surface contamination, passivation films and dislocation phenomena. Even where dislocation nucleation is relatively difficult as in GaAs, the hardness varies from about 1.5 to 15 GPa as the indentation depth decreased from about 100 nm to 10 nm. Similar size effects in BCC metals can give hardnesses which range from about 1 to 30 GPa as the indentations decrease from 1000 nm to 10 nm. Here, there are two types of “yield” phenomena which can be related to an organic contamination film and a dislocation pile-up induced oxide film fracture. As measured in single crystals of Fe, Mo, W, Ta and NiAl, this typically gives lower and upper “yield” points which range from 0.6 to 10 raN. When a dislocation pile-up breaks through the oxide film, velocities can be reasonably large due to the stress at the head of the pile-up. The average dislocation velocity of this avalanche is controlled, to first order, by the Peierls’ energy. A more exhaustive study of NiAl, with a B2/BCC type crystal structure shows that dislocation velocity can be related to the local pile-up stress and a Peierls’ barrier of about 2.2 eV.
An Explanation for the Shape of Nanoindentation Unloading Curves based on Finite Element Simulation
Authors: Bolshakov A. , Oliver W.C. , Pharr G.M.
Published: April 2011

Current methods for measuring hardness and modulus from nanoindentation load-displacement data are based on Sneddon's equations for the indentation of an elastic half-space by an axially symmetric rigid punch. Recent experiments have shown that nanoindentation unloading data are distinctly curved in a manner which is not consistent with either the flat punch or the conical indenter geometries frequently used in modeling, but are more closely approximated by a parabola of revolution. Finite element simulations for conical indentation of an elastic-plastic material are presented which corroborate the experimental observations, and from which a simple explanation for the shape of the unloading curve is derived. The explanation is based on the concept of an effective indenter shape whose geometry is determined by the shape of the plastic hardness impression formed during indentation.
The Indentation Elastic Response - Indentation Shape and the Stress Distribution
Authors: Hendrix B. C. , Xu Ke-Wei , Liu Jun-Hai , He Jia-Wen
Published: April 2011

The unloading of an indentation provides information about the shape of the indentation and the elastic properties of the materials. The assumptions of axisymmetry and material isotropy are critically examined, and a model for transversely isotropic materials is compared to measurements on single crystals. The methods used to infer the area of the indentation from the unloading curve are examined. The area is a fundamental value for the determination of hardness, modulus, and other mechanical properties in the so-called nano-indentor and other continuously monitored indentor techniques. The models of elastic recovery which are currently used are found to lack the flexibility to model the parameters which determine indentation depth. If the current self-consistent model is extended to cover the important aspects of the unloading, the area of the indentation is still not determined uniquely. Guidelines for further development of a unique model are suggested.
Mechanical Properties and Wear Resistance of High Moment thin Film Head Materials
Authors: Deng H. , Inturi V. R. , Barnard J. A.
Published: April 2011

Mechanical and tribological properties of soft magnetic thin films with high permeability and low coercivity are very important for the application of these films in high-density recording heads. This paper reports our experimental observations on these important properties of FeTaN thin film head materials. Hardness(H) and Young’s modulus(E) for FeTaN sputtered films were determined by nanoindentation. Wear resistance of these films against commercial magnetic tapes was measured with a sphere-on-flat wear tester. The experimental results indicate that the FeTa films can be hardened when nitrogen is introduced. It was found in this study that the thermal stability of the mechanical properties such as hardness of thin films containing nitrogen is better than that of the film without nitrogen. However, our experiments also revealed that the wear resistance of FeTaN films decreases when the concentration of nitrogen increases and the hardness of the worn surface at a wear scar is lower than that of the unworn surface.
Measurement of Friction Coefficients Between Diamond-Like Carbon Coated VCR Head Drum And VCR Tapes
Authors: Lee Kwang-Ryeol , Eun Kwang Yong
Published: April 2011

In order to characterize friction and wear behavior between cylindrical specimens and flexible counterface materials such as magnetic tape, a tribometer is suggested. The tribometer is used to investigate the behavior between video cassette recorder (VCR) head drums and VCR tapes. Friction coefficients of uncoated and diamond-like carbon (DLC) film coated head drums of Al alloy are compared before and after a wear test. Before the wear test, an uncoated head drum shows friction coefficients ranging from 0.22 to 0.3 as the applied tension increases from 200 to 600 gf at the sliding speed of 0.16 m/s. The friction coefficients of DLC coated head drum are 14 to 30 % lower than those of uncoated head drums. At the sliding speed of 4.9 m/s, the friction coefficients of both uncoated and DLC coated drums are reduced to less than 0.1. After the wear test, however, the friction coefficients of uncoated head drums increase to the range from 0.3 and 0.47 depending on the applied tensions. Furthermore, the friction coefficients are not reduced even at the high sliding speed of 4.9 m/s. DLC coated head drums, on the other hand, exhibit similar friction coefficients to those before the wear test. Degradation of frictional property in the uncoated head drum is discussed in terms of the surface damages mainly due to magnetic metal oxide particles transferred from VCR tapes. This result shows that the DLC coating of VCR head drum can improve the friction and wear properties. It is also observed that the DLC coating can reduce the damage of VCR tapes.
Micro-Tribological Study of Cobalt Alloys with and Without a Carbon Coating
Authors: Wang Hsin-Fu , Nelson John C. , Gerberich William W.
Published: April 2011

Continuous microscratch tests on an uncoated and a diamond-like carbon coated CoCrMo alloy were performed in air to evaluate the micro-friction and micro-tribology by utilizing a load and depth sensing instrument. By using a diamond-like carbon coating, the friction coefficient for a small applied load was found to decrease compared to the CoCrMo substrate. The hard diamond-like carbon coating prevents the local plastic yielding of the micro-contacts and the adhesion between the metal/metal surfaces during the microscratch tests. However, the effect of the diamond-like carbon coating on the friction was not seen when the applied load is high.
Modeling of Thermal Stresses in Composite Diamond Coatings and Mechanisms of Improvement of Adhesion
Authors: Fan W. D. , Jagannadham K. , Narayan J.
Published: April 2011

Thermal stress influences adhesion of many coatings applied on tool substrates. Management of thermal stresses is important for improvement of coatings and tool life. We have shown that stresses can be controlled by developing a composite layer of diamond with carbides and nitrides such as TiC or TiN. We have modeled the thermal stresses in these composite diamond coatings using finite element analysis. The composite diamond coatings consist of a discontinuous layer of diamond with an embedded layer of TiC or TiN, and a top layer of continuous diamond. For comparison, a single layer of diamond coating has also been used. The thermal stresses in these coatings on WC(Co) and Si3N4 tool substrates were calculated. Results show that the thermal stresses at the interface between the coatings and the substrate are relaxed after introducing the composite layers. This stress relaxation is responsible for the improvement of the adhesion of composite coatings.
Fracture behavior in Amorphous and Ceramic Coatings on Aluminum Alloy Substrate
Authors: Kameda J. , Ranjan R.
Published: April 2011

Fracture behavior in Ni-10 wt.%P amorphous (10 µm thick) and overlay Y2O3 stabilized ZrO2 (0-1.0 µm thick) ceramic coatings on Al alloy substrates has been investigated using small punch (SP) testing and acoustic emission (AE) techniques. SP tests showed that coating cracks extensively propagate along both the radial and tangential directions under the biaxial stress condition. The formation of cracks was more profoundly found in Ni-P amorphous coatings than in amorphous/ceramic coatings. The cumulative AE events were well correlated with the severity of coating cracking independent of the type of coatings. Ceramic coatings with a thickness of 0.25 and 1.0 µm led to a decrease in the fracture toughness by 15–20%, compared with a uncoated alloy. The coating effect on the fracture toughness is discussed in light of residual stresses induced during coating processing and the presence of coating cracks.
Evaluation of Diamond-Like Carbon as a Protective Coating for Holographic Filters
Authors: Yip Pearl W. , Dehmer Peter G.
Published: April 2011

Diamond-like carbon (DLC), a hard, optically transparent, and chemically inert material, is becoming increasingly important for many applications. With the development of low-temperature deposition techniques, DLC can now be applied to many heat-sensitive polymers. This paper will discuss the application of a DLC coating as an abrasion and moisture barrier for three different laser-protective holographic filters. The objective of this investigation is to study the influence of the coating process on the holographic filters, and to determine the effectiveness of the DLC coating as the environmental seal for these filters. The DLC coated filters were characterized by UV/visible spectroscopy, scanning electron microscopy, before and after exposure in an environmental chamber set at 71°C, and 90% humidity. The structure and hardness of the DLC coating were evaluated respectively by Raman spectroscopy and nanoindentation method.
Measuring Methods for High–Power Characteristics of Piezoelectric Materials
Authors: Hirose Seiji , Takahashi Sadayuki , Uchino Kenji , Aoyagi Manabu , Tomikawa Yoshiro
Published: April 2011

Two kinds of measuring method of the high-power characteristics of piezoelectric transducers are described. One is the measurement method at the resonance frequency and another is the measurement method at the antiresonance frequency. The vibrational velocity dependences of the equivalent circuit constants and the temperature rise were measured by using each measurement method under the constant vibrational velocity control. These results are useful for designing the ultrasonic power devices such as the ultrasonic motor, and also useful for investigating the new advanced piezoelectric materials for high power use. Especially, by using the results obtained at the antiresonance frequency, a stable state driving method, named as antiresonance driving, with high-efficiency and low-temperature rise can be achieved.
The Effect of Erbium Additions on the Solidification Behavior of γ-Tial
Authors: Bassler B. Timothy , Kral M. V. , Hofmeister W. H. , Bayuzick R. J.
Published: April 2011

The titanium-aluminum-erbium system has been studied using electromagnetic levitation and ultra high speed imaging in order to quantify the solidification velocity as a function of undercooling. Measurements were made on Ti-60 at% Al alloys with 0.25, 0.5, 1.0, and 2.0 at% Er additions. Boettinger and Aziz1 show that in ordered alloys it is thermodynamically possible at large enough interface velocities, corresponding to large undercoolings, to solidify a disordered phase with the same composition as the liquid. The result of the transition from ordered to disordered solidification is a discontinuity in the relationship between solidification velocity and melt undercooling. The experimental results for the solidification velocity as a function of melt undercooling will be presented and discussed for each alloy.
The Thermal Stability of a TiAl Based Alloy
Authors: Jin C. , Chen W. , Wang J. , Wan X.
Published: April 2011

The thermal stability of a TiAl based alloy was investigated through a series of high temperature exposures in air and vacuum. The microstructures were found to be thermally stable. The bending tests showed that both ductility and strength of air-exposed specimens decreased, but no significant variation was observed in those exposed in vacuum. The influence of alloy microstructure, thermal exposure temperature and time was also taken into account here.
A Study of Fibre/Matrix Interfaces in TiAl/Sic Composites
Authors: Djanarthany S. , Servant C. , Colin C.
Published: April 2011

A continuous fibre reinforced SiC/TiAl composite has been prepared by arc spray and hot pressing. The as-fabricated fibre/matrix interface of monotapes and composites have been examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The arc-spray conditions result in a decohesion at the fibre/matrix interface.
In Situ Straining Tem Observation of Fracture behavior in Pst Crystals of TiAl
Authors: Chen Mingwei , Chen Da , Lin Dongliang
Published: April 2011

Crack propagation process in TiAl alloy PST crystal has been investigated by in situ straining TEM observation. It has been found that the influence of lamellar boundaries on the fracture behaviors is connected with the types of interfaces (twin, pseudo-twin and α2/γ interfaces). Even though secondary microcracks always nucleate at α2/γ interfaces due to stress concentration, the crack growth is cleavage in α2 and γ phases rather than along interlamellae. When a crack meet γ/γ interfaces, its propagation can be inhibited and crack tips blunt by the slide of the interfaces. It also deserves to be mentioned that ductility of PST crystals has connection with the rate of crack propagation..
The Nature of Bonds in New Ternary Zirconium Silicide Intermetallic Compound of 16H Crystal Structure
Authors: Ikarashi Yukinori , Ishizaki K. , Bolsaitis P. , Ohnishi H.
Published: April 2011

The zirconium silicide intermetallic compounds of 16H crystal structure are good materials for high temperature structural applications because of their high melting point and low density. Their shortcoming is low ductility. To increase ductility, new ternary zirconium silicide intermetallic compound of 16H crystal structure, Si3Y3Zr2, has been designed by substituting yttrium atoms into zirconium 6g point set sites.

Near-neighbor diagrams are used to examine the bonds in Si3Y3Zr2, whose bonds are more symmetric than other 16H binary intermetallic compounds.

Melting points of intermetallic compounds of 16H crystal structure depend upon the strain parameters of N4d-N4d(2-2) bonds. The melting point of Si3Y3Zr2 is estimated to be higher than that of Si3Zr5 (2500 K). It is predicted that Si3Y3Zr2 is a good material for high temperature structural applications.
Reaction Synthesis and Densification of MoSi2
Authors: Deevi Seetharama C.
Published: April 2011

In combustion synthesis, and in simultaneous reaction synthesis and hot pressing of Mo + 2 Si powders, a heterogeneous reaction occurs between liquid silicon and molybdenum powder. When the reactant mixture is heated at low-heating rates, Mo5Si3 is observed as a secondary phase along with MoSi2. Application of pressure during the reaction synthesis of MoSi2 eliminates the need to hot press a prealloyed powder. The technique can be applied to obtain composites and alloys of MoSi2 and various other transition metal silicides.
On Phenomenon of Superplasticity in Fe3AL with Large Grains
Authors: Shan Aidang , Lin Dongliang
Published: April 2011

A variety of Fe3Al alloys including Fe-25Al, Fe-28Al, Fe-28Al-4Cr and Fe-28Al-2Ti (all in atomic percent) have been investigated by tensile test to find if these alloys could have superplasticity at elevated temperatures, the results revealed that all these alloys exhibited large elongations when the temperature is higher than 600°C. At 850°C , under appropriate initial strain rate, the elongation is all above 300%. For Fe-28Al-2Ti, the maximum elongation reached 585%. Maximum m values are all above 0.3. Initial grain sizes are bigger than 100μm but became finer after deformation. Fracture happened with necking but no cavities were found under optical microscope. Characteristics of this phenomenon were summarized and discussed.
The Effect of Y and Zr on the Oxidation of NiA1
Authors: Schumann Eckart , Yang J. C. , Rühle M. , Graham M. J.
Published: April 2011

The effect of Y and Zr on the oxidation behaviour of NiAl has been investigated using high resolution SIMS and analytical TEM. 18O tracer experiments in conjunction with SIMS showed that Y and Zr reduce the outward transport of cations during the growth of the AI2O3scale. Complementary STEM-EDS measurements revealed segregation of Y and Zr at the metal/oxide interface as well as the grain boundaries in the AI2O3scale. The amounts of segregation at both the interface and grain boundary were calculated to be less than one monolayer.
Oxidation of Some Intermetallic Compounds and Intermetallic Matrix Composites
Authors: Jackson M. R. , Rowe R. G. , Skelly D. W.
Published: April 2011

Oxidation resistance (1000-1400°C) was characterized for intermetallics M2Al, M3Al, M2Cr, and M5Si3 (M=Nb, Nb+Ti), and metal-toughened intermetallic composite systems. Aluminides were poorest in oxidation, and Laves phases were best. Substitution of Ti for Nb was beneficial for each intermetallic. Addition of metal to produce two-phase castings had differing effects on oxidation, depending on the metal and intermetallic. Modulus and expansion were also measured.
The Microstructure of Nb3Al-Mo Intermetallics
Authors: Passa E. , Tsakiropoulos P.
Published: April 2011

The microstructure of arc melted ingots and melt-spun ribbons of Nb-18A1, Nb-18Al-(20–40) Mo (at%) were studied. Rapid quenching from the melt refined the grain size by at least two orders of magnitude. In the binary alloy ingots and ribbons the Nb3Al (A15) and B2 phases were present. Molybdenum exhibited complete solid solubility in the bcc Nb-Al solid solution as well as in the Nb3Al (A15 phase). The former was the only phase present in the ribbons of the ternary alloys, while Nb3Al was detected only in the ingots. B2 phase was formed in the alloy with 20 at% Mo and the A2 phase was present in the alloy with 40 at% Mo. Furthermore, Mo addition increased the room temperature microhardness of the Nb-Al solid solution by ≈7 Kgmm−2/ at%Mo.
Phase Stability and Mechanical Properties of Multi-Phase Alloys Based on the B2 CoA1 and the E21 Co3AlC
Authors: Kimura Yoshisato , Takahashi Masaru , Miura Seiji , Mishima Yoshinao
Published: April 2011

The Co-Al-C ternary phase diagram has been experimentally examined for the Co-corner with a particular interest in phase relations among B2 type intermetallic compound, the E21 type Co3AlC, and cobalt primary solid solution, denoted as (Co). Reaction scheme, liquidus surface, isothermal sections and isoplethals at constant concentration were determined. Mechanical properties of the B2/E21/(Co) three-phase alloys were investigated by compression tests carried out at a temperature range from 77 to 1273 K, and by tensile tests at room temperature. It has been revealed that both excellent ambient temperature ductility and sufficient high temperature strength can be achieved by proper choice of alloy compositions.
Deformation Microstructures of C15 Cr2Nb Laves Phase Intermetallic Compounds
Authors: Yoshida M. , Takasugi T. , Hanada S.
Published: April 2011

The Cr2Nb intermetallic compounds with C15 Laves structure, which are considered to be attractive candidate as extremely high temperature structural materials, are deformed by compression test. The Cr2Nb intermetallic compounds are deformable at temperatures above 1473 K. The Burgers vector of dislocations activated at temperatures above BDTT are determined to be 1/2<011= which is split into a pair of 1/6<112= (i.e. the Shockley partials) connected by the stacking fault (SF). Also, the morphological feature of the activated dislocations and the SF energy are evaluated.
Effects of Angular Dependent Terms in the Interatomic Potential on Defect Properties in TiAl
Authors: Panova Julia , Farkas Diana
Published: April 2011

Interatomic potentials of the Embedded Atom and Embedded Defect types were used to study the effect of the angular dependent term in the Embedded Defect potential on the properties of defects in TiAl. The defect properties were computed with interatomic potentials developed with and without angular dependent terms. It was found that the inclusion of the angular dependent terms tends to increase the energies of the APB’s and lower the energies of stacking faults. The effects of the angular term on the relaxation around vacancies and antisites in TiAl was also studied, as well as the core structure of several dislocations in this compound.
Ni-Enrichment and its Influence on the Structure Chemistry and Bonding of Grain Boundaries in Ni3Al
Authors: Subramanian S. , Muller D. A. , Silcox J. , Sass S. L.
Published: April 2011

Small angle [001] twist boundaries and [001[(110) tilt boundaries in B-free and B-doped Ni-rich Ni3AI (76 at. pet. Ni) were examined using conventional electron microscopy techniques as well as annular dark field (ADF) imaging, X-ray Fluorescence (XRF) and spatially resolved electron energy loss spectroscopy (EELS) in an UHV scanning transmission electron microscope. The interface structure consists of periodically spaced pairs of a/2<10> partial dislocations, linked by an antiphase boundary (APB). An analysis of the separation of the partials gives APB energies which are lower than in bulk Ni3Al and which decrease with increasing misorientation angle. EELS, XRF and ADF imaging demonstrate that the APBs are Ni-rich. The observations on the APB chemistry and energy taken together lead to the conclusion that Ni-enrichment occurs to lower boundary energy by decreasing the number of high energy Al-Al bonds across the APB. These results on small angle boundaries lead to the suggestion that Ni-enrichment also occurs at large angle boundaries to decrease the number of high energy bonds across the interface.
Some Unusual Properties of the Fine Structure of Dislocations in Ni3Al Deformed at High Temperature
Authors: Veyssiére Patrick , Horton J. A.
Published: April 2011

In Ni3Al polycrystals deformed at 850°C and quenched rapidly, surface defects exhibit two kinds of behaviour. On the one hand, dislocation coupling by antiphase boundary (APB) and complex stacking fault (CSF) is of normal magnitude for this alloy composition. On the other hand, separations are dramatically decreased in both cases. A method to visualize antiphase boundaries using a weakly excited superlattice reflection is introduced.
Grain Boundary Melting and Hot Cracking in Weld Haz of A Two-Phase Ni3Al Alloy Containing Zr
Authors: Li Huaxin , Chaki T.K.
Published: April 2011

Grain boundary melting and its effect on hot cracking in the weld heat-affected zone (HAZ) have been investigated in the investment cast billet of a two-phase (γ + γ′) nickel aluminide alloy (Ni74.48Al16.98Cr8.02Zr0.51B0.10), designated as IC-218. Due to enrichment of Zr, which can form eutectic alloys with Ni, the dendritic boundaries melted incipiently at 1150°C. Under thermal stresses during welding the molten layers often opened up producing liquation cracks at the boundaries in the HAZ. Annealing at 1100°C in argon for 23 h prior to welding reduced the incipient melting temperature to 1125°C and increased the propensity of liquation cracking in the HAZ.
Effect of Crystallographic Orientation on The Fracture Toughness of NiAl Single Crystals
Authors: Shrivastava S. , Ebrahimi F.
Published: April 2011

In the present study, single-edge notched bend specimens of NiAl single crystals were tested in {100}<010>, {101}<101=, and {101}<010} orientations before and after heat-treating the notched specimens at 1000°C for one hour. The fracture toughness data for the non heat-treated specimens were found to be consistent with the previous results. An increase in the fracture toughness of NiAl was observed in all orientations studied upon heat-treating the notched specimens. The toughness ratio for the two orientations obtained from the heat-treated notched specimens was found to be 1.2. This ratio is in agreement with the reported stress analysis considering the crack kinking in {100} oriented specimens. A detailed SEM analysis revealed that the electric discharge machine (EDM) cutting of the notch caused the formation of sharp microcracks at the notch front and also created internal stresses in the vicinity of the notch. The increase in toughness upon heat treatment is attributed to the modification of EDM damage.
Fracture Behaviour of Two-Phase γ-Titanium Aluminides
Authors: Appel Fritz , Lorenz Uwe , Zhang Tao , Wagner Richard
Published: April 2011

Titanium aluminides with a lamellar microstructure consisting of the intermetallic phases ֱ2 (Ti3Al) and γ(TiAl) suffer from brittleness at ambient temperatures but exhibit at the same time a relatively high fracture toughness. This discrepancy indicates particular processes stabilizing crack propagation in the lamellar microstructure. In this context, the toughening mechanisms were investigated in (α2 + γ) TiAl alloys which contained different volume fractions of lamellar colonies. The fracture toughness for crack propagation parallel or across the lamellar interfaces was estimated by using chevron-notched bending bars. Electron microscope studies were performed to characterize the related processes of crack tip plasticity. Special emphasis was paid to the crystallography of crack propagation and to the interaction of crack tips with lamellar interfaces. Accordingly, the lamellar morphology derives some of its toughness from interface-related processes which stabilize crack propagation by deflecting the crack tip and providing the necessary dislocation sources for crack tip shielding in the process zone ahead of the crack tip.
In Situ Straining Experiments On Fe70AL30 Single Crystals
Authors: Molenat G. , Rösner H. , Nembach E.
Published: April 2011

With an aim to contributing to the understanding of the mechanical properties of Fe3Al-based intermetallic alloys, Fe-30 at. % Al single crystals have been strained in a transmission electron microscope below and in the temperature range of the yield stress anomaly (at 300K and 573K respectively).
A Potential Method for Densifying Reactive Sintered NI3AL
Authors: Hu Chen-Ti , Chiou Wen-Chen
Published: April 2011

A potential method to produce Ni3Al+0. 1B PM products of large dimension and as sheets, rods, tubes or other shapes with simple laboratory facilities is presented. The method includes multi-stage sintering and interstage cold deformation to collapse and to eliminate the sintering pores; most important of all, a thermally absorbing material must keep contact with the powder compacts during the preliminary reactive sintering stage to decrease the maximum temperature of the specimen and to develope the Ni2Al3 phase. The found Ni2Al3 regions with some special characteristics can be used to sustain the deformation of cold rolling more than 30% without failure. The monolithic Ni76Al24B0.1 phase is obtained after the second stage of sintering at 1200°C for 4h. At meantime, common reactive sintered specimens without a thermally absorbing material contacting were also studied and compared side by side.
Phase Stability, Point Defects and Site Preference of Feal and Nial with Ternary Additions
Authors: Fu C.L. , Zou J.
Published: April 2011

First-principles calculations have been used to investigate the defect properties and the site preference of FeAl and NiAl with ternary additions. It is found that a “triple-defect” structure model becomes invalid in describing the defect structure of FeAl (which is weakly ordered). The calculated mono-vacancy concentration on the Fe sites is lower than available experimental values by an order of magnitude, which may suggest the formation of defect complexes or the need of sufficiently long annealing time to anneal out quenched-in vacancies. For the site preference of ternary additions in FeAl, Cr and Ti are found to occupy Al sublattices, whereas Ni has a distinct preference for the Fe sites. The substitutional behavior of ternary elements in FeAl is consistent with the trend in the calculated heat-of-formation. For Fe addition in Al-rich NiAl, Fe atoms occupy Ni sublattices exclusively. The site preference of Fe addition in Ni-rich NiAl is dependent on alloy composition and temperature. At low temperatures, Fe atoms are found to preferentially occupy Al sublattices in Ni-rich alloys.
In-Situ Processing and Characterization of Mosi2/Sic Formed by Reactive Low-Pressure Plasma Deposition
Authors: Lawrynowicz D. E. , Wolfenstine J. , Lavernia E. J. , Nutt S. R. , Bailey D. E. , Sickinger A. , Hirt A. M.
Published: April 2011

Low-pressure plasma deposition (LPPD) was used to synthesize an in-situ MoSi2/SiC composite using 100% methane (CH4) as a powder carrier gas. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) identified MoSi2, Mo5Si3, Mo5Si3C, Si02, and SiC as the phases present in the composite. XRD and XPS revealed ∼6 vol% SiC in the as-sprayed material. Annealing of the as-sprayed composite increased the SiC content to ∼8 vol% while reducing the Si02 volume fraction. Transmission electron microscopy studies revealed a fine homogeneous distribution of SiC and/or carbide particles at prior splat boundaries in the MoSi2 matrix. Wavelength dispersive spectroscopy (WDS) confirmed the increased presence of carbon in the in-situ materials. Fracture toughness measurements yielded values on the order of 10 MPa m½ for annealed composites. The creep behavior of the LPPD reactive spray composite dramatically improved compared to unreinforced LPPD MoSi2. Additionally, the creep behavior was shown to be equal to or better than that of powder metallurgy MoSi2/SiC composites containing higher percentages of SiC.
Particles Cellulation Composite (PCC): Dispersion Morphology of SiC Particles in Si3N4/SiC Composites
Authors: Yamada K. , Kamiya N.
Published: April 2011

Dispersion morphology of fine SiC particles in Si3N4/xSiC (x=0, 10, 20, 30wt%, average size: 0.03/µ m) composites was statistically analyzed, and typical properties of the composites such as creep, electric and thermal conductivity were investigated. The dispersion morphology of SiC particles was analyzed by observing the ECR-plasma etched surface of the sintered composites using scanning electron microscopy. SiC particles in Si3N4/SiC composites were distributed both within Si3N4 grains and on Si3N4 grain boundary, but 90% or more of them was located on the grain boundary. For the composites with 20-30wt%SiC, the SiC particles on the grain boundary clearly formed a three-dimensional network structure surrounding a few or more Si3N4 crystalline grains.

A Si3N4/SiC composite with a three-dimensional network structure of SiC particles, named particles cellulation composite (PCC), was artificially made by pressing the granulated Si3N4 powder (less than 500 µ m diameter) discontinuously coated with SiC particles (average size: 0.4 µ m). The creep deformation of PCC was reduced to about 60%.of that of the composites with SiC particles randomly dispersed. Electrical and thermal properties were also improved. These results suggest that the formation of three-dimensional network structure by the second phase particles in a composite would considerably improve its mechanical property as well as electrical and thermal properties.
Structure and Formation Kinetics of Mosi2 Composites Formed by Reactive Vapor Infiltration Process
Authors: Hillig W.B. , Ramakrishnan R.M. , Broglio M. , Patibandla N.
Published: April 2011

Reactive Vapor Infiltration is a convenient new process for producing high purity MoSi2 matrix composites by reacting compacted mixed Mo + MoSi2 powders ranging from 0 to 80 wt. % MoSi2 with H2 + SiCl4 vapors at temperatures from 1000 to 1400°C. Consideration must be taken of the volumetric increase that accompanies this conversion. The kinetics of the advance of the MoSi2 growth layer and the gravimetric uptake are given as a function of temperature and the composition. The parabolic growth rate constant was independent of composition at least up to 30% MoSi2 composition, but then showed a strong, linear increase with increasing MoSi2 content. There appeared to be a levelling off of rate above 70% MoSi2. The corresponding gravimetric rate constant was relatively insensitive to the starting MoSi2 content. This behavior is at variance with a simple one-dimensional diffusive growth model. Possible reasons for this variance are offered.
Elevated Temperature Fiber Push-Out Testing
Authors: Eldridge J.I.
Published: April 2011

The potential use of fiber-reinforced composite materials for high temperature applications makes the development of interface test methodology at those high temperatures very desirable. A facility for performing high temperature fiber push-out tests will be described with emphasis on critical issues in experimental procedure. Examples from several composite systems illustrate the temperature dependence and environmental sensitivity of fiber debonding and sliding. Interpretation of the temperature dependence will be made primarily in terms of changes in residual stresses along with additional effects due to changes in matrix ductility and interfacial wear. Examples will show that high temperature fiber push-out testing can often distinguish between chemical and frictional fiber/matrix bonding in cases where room temperature only testing cannot.
Optimization of Bundle Infiltration in the Forced Chemical Vapor Infiltration (FCVI) Process
Authors: Matlin W.M. , Stinton D.P. , Besmann T.M. , Liaw P.K.
Published: April 2011

A two-step forced-flow, thermal-gradient, chemical vapor infiltration process (FCVI) was proposed to reduced processing time while maintaining uniformly high densities. GTCVI, a finite-volume computer code developed specifically for the FCVI process was used to model thermal gradient effects on processing time and density. An optimum thermal gradient was determined and used to process material with uniformly infiltrated bundles.
In-Situ Measurement of Bending Strength of TiC Whiskers in the Scanning Electron Microscope
Authors: Seino Yutaka , Shin Shoichiro , Nagai Satoshi
Published: April 2011

The three–point bending strength of TiC whiskers was measured in a scanning electron microscope. The whisker samples have ∼ 50µm length and 2∼4µm diameter and are commercially available as reinforcements for composite materials. The distribution of the bending strengths of the whiskers showed a double peak around 5.2GPa and 30.4GPa, respectively. The difference in these values is attributed to differences in the cleavage strength of two crystal planes depending on whisker growth direction.
Carbon and Oxide Coatings on Continuous Ceramic Fibers
Authors: Hay R. S. , Petry M. D. , Keller K. A. , Cinibulk M. K. , Welch J. R.
Published: April 2011

Oxide - carbon multilayer coatings were continuously applied to various fibers of nominal SiC composition. A liquid-phase coating system that allows application of the coatings in a controlled atmosphere at relatively rapid rates was employed. Sugar - ammonium hydroxide solutions were used for carbon coatings, and aqueous sols were used for the oxides. Carbon was also deposited simultaneously with alumina by chemical vapor deposition of a hydrocarbon in the coating furnace. The coatings were extensively characterized by optical microscopy and TEM. Problems with embrittlement by oxide coatings and poor adherence of oxide coatings on carbon, and some possible solutions to these problems, are discussed.
Structural Criteria for Amorphization of Network Solids
Authors: Sreeram A. N. , Hobbs L. W.
Published: April 2011

Amorphization, like glass-formation, represents fundamentally a failure to crystallize. The problem is to understand how atoms can rearrange themselves, perhaps within the confines of unaffected surrounding crystal, after a local disordering event. Some ceramics, like alkali halides and oxides with the rocksalt structure, appear almost impossible to amorphize, forming localized aggregate defects (voids, dislocation loops, colloids) and even decomposing (as a response to radiation disorder), rather than structurally reordering (or disordering). Other network solids such as silicas and silicates readily amorphize. In this study, we attempt to establish topology and structural freedom as criteria for amorphization of network solids.
Raman and Cathodoluminescence Study of Electron Irradiated Bssco and Ybco Ceramics
Authors: Torres A. , Jimenezi J. , Gomez P. , Piqueras J.
Published: April 2011

Electron irradiation damage induced in high Tc superconducing ceramics is studied using microRaman and cathodoluminescence. The formation of extended impurity phases is dominant in BSCCO, while oxygen loss and disorder is the main effect observed in YBCO, in this case the local oxygen loss is quantified.
Suppression of Self-Interstitials in Silicon During on Implantation via in-situ Photoexcitation
Authors: Ravi J. , Erokhin Yu. , Christensen K. , Rozgonyi G. A. , Patnaik B. K. , White C. W.
Published: April 2011

The influence of in-situ photoexcitation during low temperature implantation on selfinterstitial agglomeration following annaealing has been investigated using transmission electron microscopy (TEM). A reduction in the level of as-implanted damage determined by RBS and TEM occurs athermally during 150 keV self-ion implantation. The damage reduction following a 300°C anneal suggests that it is mostly divacancy related. Subsequent thermal annealing at 800°C resulted in the formation of 13111 rod like defects or dislocation loops for samples with and without in-situ photoexcitation, respectively. Estimation of the number of self-interstitials bound by these defects in the sample without in-situ photoexcitation corresponds to the implanted dose; whereas for the insitu photoexcitation sample a suppression of ≈2 orders in magnitude is found. The kinetics of the athermal annealing process are discussed within the framework of either a recombination enhanced defect reaction mechanism, or a charge state enhanced defect migration and Coulomb interaction.
Microstructure of Irradiated Silicon
Authors: Williams J. S. , Wong-Leung J. , Goldberg R. D. , Petravic M.
Published: April 2011

This paper provides a brief overview of some issues relating to the microstructure of irradiated silicon which are of importance to the semiconductor industry. The nature of ion-induced disorder and conditions for amorphization are initially treated since the starting microstructure can strongly influence subsequent annealing behaviour, particularly removal of residual defects, dopant diffusion and electrical activation. The use of implantation-induced disorder as a means of removing metallic impurities, so called gettering, is also an issue of major current interest for improved performance of devices. Some new gettering results are discussed.
Void Swelling Resistance in Fe-Cr Alloys at 200 DPA
Authors: Gelles D. S.
Published: April 2011

Microstructural examinations have been performed on a series of binary Fe-Cr alloys irradiated to 200 dpa at 425°C in a fast breeder reactor. The alloy compositions rangedfrom 3% to 18% Cr in 3% Cr increments, and the irradiation temperature corresponded to the peak swelling condition for this alloy class. Density measurements showed swelling levels as high as 7.4%, with the highest swelling found in the Fe-9Cr and Fe-6Cr alloys. Microstructural examinations revealed that the highest swelling conditions contained welldeveloped voids, often as large as 100 nm, and a dislocation network comprised of both a2 <111> and <100> Burgers vectors. Swelling was lower in the other alloys, and the swelling reduction could be correlated with increased precipitation. These results are considered in light of the current theories for low swelling in ferritic alloys, but no theory is available to completely explain the results.
Z-Scan Measurements on Molten Diphenylbutadiene in the Isotropic Liquid State
Authors: Fleitz P. A. , Sutherland R. L. , Bunning T. J.
Published: April 2011

The two-photon absorption cross-section for diphenylbutadiene heated to the isotropic liquid state has been measured using the Z-scan technique. In this experiment, the solid diphenylbutadiene was heated using a temperature controlled hot stage above its melting point. Z-scan measurements using 35ps laser pulses at 532nm were then carried out on molten diphenylbutadiene. The value of the two-photon absorption cross-section at 532nm was measured to be σ2 = (38±8) × 10−50cm4s/photon-molecule. This value corresponds well with the cross-section measured previously for diphenylbutadiene dissolved in chloroform using the degenerate four-wave mixing technique.
Doped Gels for Optical Limiting Applications.
Authors: Brunel Marc , Canva Michael , Brun Alain , Chaput Frédéric , Malier Laurent , Boilot Jean-Pierre
Published: April 2011

Aluminophthalocyanine and fullerene were trapped in solid transparent matrices using the sol-gel process. The covalent bonding to the matrix improved the chemical stability of the fullerene doped sample. Solid state optical limiting at 532 nm, mainly due to reverse saturable absorption processes, was observed with such samples. The non-linear transmission threshold was typically about 10 mJ/cm2 and an induced density of 1.6 was observed with three orders of magnitude greater illumination. Fluorescent decay measurements support the choice of a three energy level absorption model for the process, which allows indirect measurement of the excited-state absorption.
Optically Nonlinear Crystalline Colloidal Self Assembled Submicron Periodic Structures for Optical Limiters
Authors: Asher Sanford A. , Chang Song-Yuan , Tse Albert , Liu Lei , Pan Guisheng , Wu Zhijun , Li Pusheng
Published: April 2011

The development of optical technologies requires the fabrication of reliable optical switching and limiting devices. Optical switches modulate the transmission or reflection of incident light, while optical limiters serve to limit transmission to prevent the transmitted light intensity from exceeding a defined level. A major application of optical limiters is to protect delicate sensors.
Towards Magnetic Liquid Crystals
Authors: Patel M. K. , Huang Jianping , Kaszynski Piotr
Published: April 2011

A series of new sulfur-nitrogen ring systems with a neutral radical center were designed for incorporation into liquid crystal molecules and formation of discotic and calamitic phases. It is expected that these materials will display unusual magnetic properties associated with partially oriented bulk liquid crystal structures. Synthetic progress toward new radicals and the first discogen with nr-delocalized neutral radical is described.
Optical Limiting in Chromophore-Doped Gelatin Thin Films
Authors: Cooper Thomas M. , Campbell Angela L. , Su Weijie , Obermeier Keith , Natarajan Karthik , Crane Robert L. , Adams W. W. , Brant Mark
Published: April 2011

To develop optical power limiting thin films prepared from water-soluble materials, we have prepared chromophore-doped gelatin thin films. Thin films of gelatin were prepared by spin coating followed by annealing. We also prepared thin films doped with the water-soluble chromophore copper phthalocyanine sodium tetrasulfonate. The films were characterized by film profilometry and optical absorption spectroscopy. Optical power limiting measurements of these films, as well as comparisons with aqueous solution and gels were performed.
Fast Deposition of Polycrystalline Silicon Films by Hot-Wire CVD
Authors: Middya A. R. , Lloret A. , Perrin J. , Huc J. , Moncel J. L. , Parey J. Y. , Rose G.
Published: April 2011

Polycrystalline silicon thin films have been deposited at fast growth rates (50 Å/s) by hotwire chemical vapour deposition (HW-CVD) from SiH4/H2 gas mixtures at low substrate temperature (400–500°C). The surface morphology of these films consists of 0.5 – 2.0μm dendritic grains as seen by electron microscopy. The films have a columnar morphology with grains starting from the substrate either on glass or c-Si. Even the 150 nm thick initial layer is polycrystalline. The preferential crystalline orientation of the poly-Si film is apparently not governed by the radiative source but strongly depends on the type and orientation of the substrate. A strong hydrogen dilution (>90%) of silane is essential to obtain poly-Si films with optimal crystalline structure.
Relation Between Defect Density and Local Structures of a-Si:H
Authors: Azuma M. , Nakamura K. , Yokoi T. , Yoshino K. , Shimizu I.
Published: April 2011

High quality a-Si:H thin films with varied optical gaps in the range from 1.55 to 2.1 eV were fabricated by various methods, i.e., the standard RF glow discharge of silane, “Chemical Annealing” and ECR-H-plasma from SiCl2H2 under in situ monitoring with an ellipsome try. Despite marked differences in the local structure, all these films showed low defect density as low as (3–5) × 1015 cm3. In addition, the stability for light soaking was improved markedly for the films made by promoting intensively structural relaxation with atomic hydrogen.