bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Characterization of GaN Epilayers Grown on Patterned Sapphire Substrates
Authors: Kim Chang-Soo , Moon Ji-Hyun , Lee Sang-Jun , Noh Sam-Kyu , Kim Je Won , Lee Kyuhan , Choi Yong Dae , Song Jay P.
Published: June 2019

The structural properties of GaN epitaxial layers grown on patterned sapphire substrates by MOCVD have been investigated using HRXRD(high-resolution X-ray diffraction), GIXRD(grazing incidence X-ray diffraction) and PL(photoluminescence). For X-ray characterizations rocking curves for GaN (10·5), (00·2), (11·4) and (11·0) reflections for which incidence angles of X-rays are 32.0°, 17.3°, 11.0° and 0.34°, respectively, were measured. For (10·5), (00·2) and (11·4) reflections FWHMs of the rocking curves for a patterned substrate were broader than those for a unpatterned substrate, for (11·0) reflection, however, FWHM for a patterned substrate was much narrower than that for a unpatterned substrate. The normalized FWHM for all reflections decreases as the incidence angle of X-ray decreases. The results indicate that the crystalline quality in the surface region of the epilayer on a patterned substrate was especially improved because the penetration depth of X-ray depends on the incidence angle. The intensity of PL peak of the epilayer for a patterned substrate increased compared to that for a unpatterned substrate, and the increase in PL intensity is attributed to the reduction in dislocation density at the surface region revealed the by X-ray results.
Effect of Ohmic Contacts on Polysilicon Memory Effect
Authors: Herner S.B. , Jahn C. , Kidwell D.
Published: June 2019

Polysilicon memory switching is demonstrated in vertical n-i-p diodes with TiN contacts and feature size 150 nm. An increase of more than three orders of magnitude forward current at +2 V is achieved after the application of a +8 V programming pulse. The programming pulse electro thermally melts the polysilicon through Joule heating, and the quenched diodes have higher forward current. By changing one of the contacts from TiN to TiSi2, polysilicon memory switching is eliminated, with high forward current in the diode before and after a programming pulse. The TiSi2 contact seeds the crystallization of polysilicon with fewer defects during fabrication, compared to crystallization with TiN-only contacts, as shown by transmission electron microscopy. The mechanisms for increased forward current induced by either programming the TiN-only contacted diodes or making one contact TiSi2 are discussed.
Contact Free Defect Investigation in as grown Fe-doped SI-InP
Authors: Hahn Sabrina , Dornich Kay , Hahn Torsten , Gründig-Wendrock Bianca , Niklas Jürgen R. , Schwesig Peter , Müller Georg
Published: June 2019

The methods of microwave-detected photo-induced current transient spectroscopy (MD-PICTS) and microwave-detected photoconductivity (MDP), which proved themselves as very successful for defect investigations in GaAs wafers, were applied to Fe-doped SI-InP samples. It was possible to observe characteristic defect levels. One important defect center showed a similar behavior as the well known EL2 defect in GaAs. This defect exhibits positive and negative PICTS signals depending on the Fe concentration. The associated activation energies show that these signals can be interpreted as an interaction of the Fe2+/3+ level in InP with both, the valence and the conduction band.

Beside this major defect we discovered a wide range of shallow defects which may be important for material properties.

This result and successful microwave detected photoconductivity mappings of InP wafers show that the new non-destructive investigation methods provide valuable information on defect distribution and characteristics.
Thermal Growth of He-cavities in Si Studied by Cascade Implantation
Authors: Ntsoenzok E. , Bouayadi R. El , Regula G. , Pichaud B. , Ashok S.
Published: June 2019

Float Zone (FZ) silicon samples have been cascade-implanted with helium ions at energies decreasing from 1.9 MeV to 0.8 MeV in steps of 0.1 MeV, with flux maintained between 5 × 1012 and 1 × 1013 He cm-2-1s. The dose was 5×1016 He cm-2 for all the energies except 0.8 MeV where a lower dose of 3×1016 He cm-2 was used. After thermal annealing, the sample was studied by cross section transmission electron microscopy (XTEM) using a Field Emission Gun Microscope (Jeol 2010F). Our results clearly demonstrate that these cavities mainly grow by the Ostwald ripening mechanism. This means a growth by exchange of He and vacancies from smaller to bigger cavities. Further this study provides essential data for resolving the controversy on the growth mechanism governing He-cavities.
Multistep Resonant Excitation of Erbium Ions in Thin Silicon Oxide Layers
Authors: Fleischman Z. , Sandmann Chr. , Dierolf V. , White M. , Zhao Y. , Michel J. , Stolfi M.A. , Negro L. Dal
Published: June 2019

Using the site-selective technique of combined excitation emission spectroscopy, we have studied a variety of Er doped silicon oxide layers with and without silicon nanocrystals. This technique allows clear distinction of cluster defect sites that are created during thermal annealing and become dominant for higher Er ion concentration and are suppressed by the presence of nanocrystals. In several samples, we were able to observe fluorescence line narrowing under resonant excitation allowing defect-selective excitation.
The Adhesion of Pad Particles on Wafer Surfaces during Cu CMP
Authors: Song Jae-Hoon , Han Ja-Hyung , Hong Yi-Koan , Kang Young-Jae , Park Jin-Goo , Maeng Ju-Ho , Won Young-Man
Published: June 2019

The adhesion force of pad and alumina were experimentally and theoretically investigated in slurry solutions of different pHs. The isoelectric point (IEP) of pad particles was measured to be around pH 3. The wafer surfaces showed negative zeta potentials in the investigated pH ranges with exception of FSG and Ta. Cu and Ta showed higher interaction forces than dielectric materials. The lowest adhesion force was measured between pad particle and wafer surfaces in a slurry solution of pH 11. The magnitude of adhesion force of pad particles was lower than alumina particles.
Development of Multi-plume and Multi-turn (MPT) PLD for YBCO Coated Conductor
Authors: Watanabe Tomonori , Kuriki Reiji , Muroga Takemi , Miyata Seiki , Ibi Akira , Yamada Yutaka , Shiohara Yuh , Kato Takeharu , Hirayama Tsukasa
Published: June 2019

Our multi-plume and multi-turn (MPT) pulsed-laser deposition (PLD) has been improved to accelerate reliable and fast deposition technique of high Ic (critical current) YBCO (YBa2Cu3O7-x) layer for a long coated conductor fabrication, for we increased the number of multi-turn, from three to four, in our multi-plume and multi-turn (MPT) PLD system. This increase of the number of depositing turns achieved high deposition rate corresponded to 75 mm3/h (=1 μm-thick × 10 mm-wide × 7.5 m/h, throughout all 4 turns) for YBCO layer. This four turn (4t)-MPT-PLD also indicated a capability to combine high deposition rate and high Ic. We attained the highest Ic's of 321 A at the tape speed of 3 m/h and 340 A at tape speed of 2 m/h by 4t-MPT-PLD in 10 mm-wide and 10 cm-long samples.

Based on these results, we successfully deposited a 100 m long YBCO layer by 4t-MPT-PLD. This coated conductor had high Ic as high as 159 A, therefore, the multiplication of Ic and length exhibited high value of 15.9 kA·m.
Chemical synthesis of nanoparticles for artificial pinning centers in YBCO coated conductors
Authors: Sathyamurthy Srivatsan , Leonard Keith J. , Paranthaman M. Parans
Published: June 2019

Ceria nanoparticles were prepared using a solution based approach using cerium (III) acetate as a starting material and cetyltrimethylammonium hydroxide (CTAOH) as a precipitating agent and surfactant. The presence of the surfactant CTAOH helps prevent agglomeration of the nanoparticles. Using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), the particle size was determined to be 3.5 – 4 nm. The structure and properties of these CeO2 nanoparticles have been analyzed.
Comparative Study of Structural Properties of YBa2Cu3O7 Thin Films on SrTiO3 Single Crystal and Bicrystal Substrates by X- ray Diffraction
Authors: Navacerrada M.A. , Mehta A. , Sahibudeen H.S. , Acrivos J.V.
Published: June 2019

We present a comparative study in terms of structural properties deduced from X - ray diffraction diagrams between YBa2Cu3O7 (YBCO) thin films fabricated on SrTiO3 (STO) single crystal substrates and bicrystallines substrates with a symmetrical tilt angle of 24 degrees. Periodic Lattice Distortions (PLD) have been observed around different Bragg peaks in YBCO thin films deposited on STO bicrystals while only diffraction peaks have been measured in the diagrams corresponding to the YBCO thin films deposited on STO single crystal substrates. Only in regions situated a 3.5 mm at both sides of the grain boundary the PDL have been investigated. Scans along different (h, k, l) directions allow us to conclude that the qPLD vector associated to the distortion is along the (h,-k,0) direction. However, we found that the amplitude of the components of the qPLD vector depend on the Bragg peak chosen. We believe such a result indicates that we have not a PDL with a simple qPLD vector. In this line, other (h, k, l) directions must be investigated to deduce the exact origin of the qPLD vector. Nevertheless, independently on the qPLD vector associated to the PLD, we believe that such a distortion in the lattice is a consequence of the stress field induced by the grain boundary in the YBCO thin film deposited on the bricrystal.
Low-damage patterning of pentacene using a SiNx/PVA-photoresistmulti-layermask
Authors: Hirai Nobukazu , Yoneya Nobuhide , Kawashima Noriyuki , Noda Makoto , Nomoto Kazumasa , Wada Masaru , Kasahara Jiro
Published: June 2019

We have developed a photolithographic technique of patterning a pentacene layer with low damage using a SiNx/poly(vinyl alcohol) (PVA) photoresist multi-layer mask. We used a hexavalent chromium-free PVAphotoresist. By inserting a SiNx buffer layer between the pentacene layer and the PVAphotoresist layer, we could suppress an increase in off current caused by interaction between pentacene and the photosensitive functional group in the PVA photoresist. In the patterning process, we found that carriers generated by O2-plasma doped into the pentacene layer and the off current of the pentacene thin-film transistor (TFT) increased.We also found that successive annealing caused de-doping of the pentacene layer and reduced off current of the pentacene TFT.We investigated the density of doped carriers using a simplemodel of a planer pentacene diode aswell as a pentaceneTFT.
Novel 3-D MEMS Approach to Digitally Printing Organic Semiconductors
Authors: Schoeppler Martin W.
Published: June 2019

Ink jet printheads are now widely used in manufacturing processes that require precise dispensing of materials. In response to requirements for dispensing novel electronic fluids, we are developing next generation jetting technology based on our silicon MEMS technology with a three-dimensional silicon technology and a piezo-based pumping chamber integrated into the chip structure. Examples of opportunities and applications in electronics packaging for MEMSbased ink jet technology will be presented.
High-Speed Photography of Human Trabecular Bone during Compression
Authors: Thurner Philipp J. , Erikson Blake , Schriock Zachary , Langan John , Scott Jeff , Zhao Maria , Fantner Georg E. , Turner Patricia , Kindt Johannes H. , Schitter Georg , Hansma Paul K.
Published: June 2019

The mechanical properties of healthy and diseased bone tissue are extensively studied in mechanical tests. Most of this research is motivated by the immense costs of health care and social impacts due to osteoporosis in post-menopausal women and the aged. Osteoporosis results in bone loss and change of trabecular architecture, causing a decrease in bone strength. To address the problem of assessing local failure behavior of bone, we combined mechanical compression testing of trabecular bone samples with high-speed photography. In this exploratory study, we investigated healthy, osteoarthritic, and osteoporotic human vertebral trabecular bone compressed at high strain rates simulating conditions experienced in individuals during falls. Apparent strains were found to translate to a broad range of local strains. Moreover, strained trabeculae were seen to whiten with increasing strain. We hypothesize that the effect seen is due to microcrack formation in these areas, similar to stress whitening seen in synthetic polymers. From the results of a motion energy filter applied to the recorded movies, we saw that the whitened areas are, presumably, also of high deformation. We believe that this method will allow further insights into bone failure mechanisms, and help toward a better understanding of the processes involved in bone failure.
Mechanisms Governing the Inelastic Deformation of Cortical Bone
Authors: Mercer C. , Wang R. , Evans A. G.
Published: June 2019

To understand the inelastic response of bone, a two-part investigation has been conducted. In the first, a flexural test protocol has been designed and implemented that monitors the axial and transverse strains on both the tensile and compressive surfaces of cortical bone. The results are used to assess the relative contributions of dilatation and shear to the inelastic deformation. Unload/reload tests have characterized the hysteresis and provided insight about the mechanisms causing the strain. These tests reveal strain healing attributed to sacrificial bonds. The second part devises a model for the stress/strain response, based on a recent assessment of the nano-scale organization of the collagen fibrils and mineral platelets. The model rationalizes the inelastic deformation in tension, as well as the permanent strain and hysteresis.
On the Origin of Stiffening in Biopolymers
Authors: Giessen Erik Van der , Koeman Teun , Dillen Teun Van , Onck Patrick
Published: June 2019

Strain stiffening of protein networks is explored by means of a finite strain analysis of a two-dimensional network model of cross-linked semiflexible filaments. The results show that stiffening is caused by non-affine network rearrangements that govern a transition from a bending dominated response at small strains to a stretching dominated response at large strains. Thermally-induced filament undulations only have a minor effect; they merely postpone the transition.
A new technique for imaging Mineralized Fibrils on Bovine Trabecular Bone Fracture Surfaces by Atomic Force Microscopy
Authors: Kindt Johannes H. , Fantner Georg E. , Thurner Philipp J. , Schitter Georg , Hansma Paul K.
Published: June 2019

High resolution atomic force microscopy (AFM) images of bovine trabecular bone fracture surfaces reveal individual fibrils coated with extrafibrillar mineral particles. The mineral particles are distinctly different in different regions. In some regions the particles have average dimensions of (70 ± 35) nm along the fibrils and about half that across the fibrils. In other regions they are smaller and rounder, of order (53 ± 14) nm both along and across the fibrils. In other regions they are smaller and rounder, of order (25 ± 15) nm both along and across the fibrils, with more rounded top surfaces.

Significantly, we rarely observed bare collagen fibrils. If the observed particles can be verified to be native extrafibrillar mineral, this could imply that the fractures which created the observed areas propagated within the mineralized extrafibrillar matrix.
Collagen Content and Organization Relate to Bone Nanomechanical Properties
Authors: Donnelly Eve , Williams Rebecca M. , Baker Shefford P. , Meulen Marjolein C. H. van der
Published: June 2019

Cancellous bone plays an important load-bearing role in the skeleton, yet relatively little is known about the microstructure-mechanical property relationships of the tissue at the sub-10 [.proportional]m level. Cancellous tissue is characterized by a layered microstructure with variable proportions of collagen and mineral. The lamellar material is substantially stiffer than the interlamellar material at the nanomechanical level. However, the microstructural origin of the observed differences in mechanical properties of these structures has not been investigated. In this study, second harmonic generation microscopy was used to examine collagen in human vertebral cancellous bone. At the same location in the tissue, nanoindentation was used to assess the indentation modulus of lamellar and interlamellar bone. The stiff lamellae corresponded to areas of highly ordered, collagen-rich material, while the compliant interlamellar regions corresponded to areas of unoriented or collagen-poor material. The lamellar bone was approximately 30% stiffer and contained approximately 50% more oriented collagen than the interlamellar bone. These observed differences in the mechanical properties and collagen content and organization of lamellar and interlamellar tissue are consistent with previous scanning electron microscopy studies showing greater mineral and collagen content and organization in lamellar bone. Given the well-known coupling between collagen and mineral in bone tissue, the mineral distribution may mirror that of the aligned collagen. However, similar measurements of local variations in mineral content are needed to confirm this hypothesis and may provide additional insights into the tissue nanomechanical behavior.
A Two-Dimensional Free Energy Model for Single Crystalline Ferroelectrics
Authors: Kim Sang-Joo , Seelecke Stefan , Ball Brian L. , Smith Ralph C. , Lee Chang-Hoan
Published: June 2019

The one-dimensional free energy model for ferroelectric materials developed in [1-3] is general-ized to two dimensions. The proposed two-dimensional energy potential consists of four energy wells corresponding to four variants of the material, four saddle points representing the barriers for 900 switching processes, and a local energy maximum across which 1800-switching processes take place. The free energy potential is combined with the evolution equations based on the theory of thermally activated processes. The prediction of the model is compared with the recent measurements on a Ba- TiO3 single crystalline ferroelectric in [4]. The responses of the model at various loading frequencies are calculated and the kinetics of 900 and 1800 switching processes are discussed.
Modeling the Behavior of Heterogeneous Materials with Non Linear Couplings using “Translated Fields”
Authors: Berbenni S. , Favier V. , Berveiller M.
Published: June 2019

The determination of the behavior of heterogeneous materials with complex physical and mechanical couplings constitutes a challenge in the design of new materials and the modeling of their effective properties. In real inhomogeneous materials, the simultaneous presence of elastic mechanisms and non linear inelastic ones (viscoplastic, magnetic, ferroelectric, shape memory effect etc.) leads to a complex non linear coupling between the mechanical fields which is tricky to represent in a simple and efficient way. Hence, for many situations the effective global behavior does not follow the same structure than the local constitutive one. Regarding space-time couplings for instance, a heterogeneous material composed of phases described by Maxwell elements can not be considered as a Maxwellian solid at the macro scale.

In this paper, we introduce a new micro-macro approach based on translated fields in its generalized form to be applied to different coupled phenomena. The local total strain (rate) is composed additively of an elastic strain (rate) and an inelastic one which is no more limited to be “stress free” as considered originally by Kröner. An extended (non conventional) self-consistent model is then proposed starting from the integral equation for a translated strain (rate) field and using the projection operators algebra introduced by Kunin. The chosen translated field is the compatible inelastic strain (rate) of the fictitious inelastic heterogeneous medium submitted to a uniform unknown boundary condition. The self-consistency condition amounts to define analytically these boundary conditions so that a relative simple and compact strain (rate) concentration equation is obtained.

In order to illustrate the method, the case of a non linear elastic-viscoplastic coupling is developed and applied to different classes of composites and polycrystals.
Finite Element Formulation of a Piezoelectric Continuum and Performance Studies of Laminar PZT-Patch-Modules
Authors: Gall Monika , Thielicke Bärbel , Poizat Christophe , Klinkel Sven
Published: June 2019

Efficient application of piezoelectric sensors and actuators requires extensive investigations of their loading limits, failure-behavior and life-span under service conditions. Here the performance of laminar PZT-patch-modules is studied, applying a combined approach of experimental and numerical tests. Four-point bending tests are used to evaluate the sensor performance. Linear electro-mechanical coupling is implemented in an 8-node brick user element of the research finite element code FEAP to develop a flexible FE-tool for piezoelectric problems. Comparative FE-analyses of the bending test are carried out in order to assess the capability of the implemented FEAP user element versus the commercially available FE-code ABAQUS. FE-results show good agreement with the experimental tests, different element types yield slight deviations which are discussed.
Effect of Crosslinking on the Elastic Properties of the Cytoskeleton: A 3D Discrete Modeling Approach
Authors: Dalmas Florent , Mohrdieck Camilla
Published: June 2019

In living eukaryotic cells a crosslinked network of polymer fibers, the cytoskeleton, endows the cells with structural integrity and mechanical stability and flexibility. To understand the mechanisms that are at the base of these functions, it is important to know in what way the microstructure and the mechanical behavior of the cytoskeleton change as a function of the type and the density of crosslinking molecules. To address this issue, we have developed a new modeling approach based on the discretization of polymeric fibers that are modeled as homogeneous straight beams in a constant volume. Crosslinks between adjacent fibers are taken into account by creating additional beams between the fibers if their spacing is smaller than a meaningful upper bound. By varying their geometrical and mechanical properties, the influence of the crosslinks on the shear modulus of the network can be studied systematically. Our simulations predict interesting new scaling behaviors that depend on the degree of crosslinking.
Investigating the Interfacial Interactions Between Organic and Inorganic Phases and Their Influence on the Mechanics of Organic Phase in Natural Bone
Authors: Bhowmik Rahul , Katti Kalpana S , Katti Dinesh R
Published: June 2019

Bone is a highly ordered nanocomposite system consisting primarily of organic (collagen) and inorganic (hydroxyapatite(HAP)) phases. The nanocrystals of hydroxyapatite (HAP) mineralize at specific locations in bone. The collagen molecule in bone has C and N terminals which are known as C and N telopeptides. We have performed Molecular Dynamics (MD) and Steered MD (SMD) simulations to study the interface between HAP (mineral) and collagen with N-terminal telopeptides. The force field parameters for HAP were taken from our previous study and the force field parameters for collagen with telopeptides were taken from CHARMm force field. We have investigated the detailed conformation of telopeptides interacting with specific surfaces of mineral and the interface between HAP and collagen. The load-deformation behavior of collagen is obtained with SMD simulations. It has been found that the load deformation behavior of collagen is different when in close proximity of and interacting with HAP.
Micromechanical Measurements on Chemomechanical Protein Aggregates
Authors: Schwan Stefan , Fritzsche Markus , Cismak Andreas , Noll Gundula , Prüfer Dirk , Spohn Uwe , Heilmann Andreas
Published: June 2019

Chemo-mechanical protein aggregates in plants, e.g. the forisomes of legumes, transform the chemical free energy of their reaction with calcium ions into mechanical energy. Light and scanning electron microscopy analyses demonstrated that the spindle-shaped bodies with lengths between 25 and 40 μm consist of fiber bundle units which change their length and diameter during a reversible switching reaction induced by either calcium, barium, strontium ions or by changes of the pH value. For the determination of forces generated during the switching reaction a force measurement in vitro system based on the bending of thin glass fiber was developed. By using this set-up, dynamical forces of forisomes, in the presence of different alkaline ions, in the range up to 180 nN were measured.
Failure Investigation of Polymer Mechanical Micromponents
Authors: Zhao Yi , Zhang Xin
Published: June 2019

This paper reports typical failure modes of polymer microstructures. Polydimethylsiloxane (PDMS) microstructures were fabricated using replication-based methods. The mechanical collapses of these structures were observed using scanning electron microscopy. In this work, we classified the mechanical collapses based on their individual geometries and discussed the mechanism of each failure mode. We also worked on solutions to recover these failed PDMS structures. This work helps to better understand the collapsing mechanism and to facilitate the development of control strategies to enhance the mechanical reliability of polymer microdevices.
Microstructure, Nanostructure and Properties of the Wasp Petiole
Authors: Reed Emily J. , Dunlap Michael R. , Jasinski Jacek , Viney Christopher
Published: June 2019

The wasp petiole (waist) is a self-assembled, multifunctional, hierarchically structured tube, which in some species has a simple, near-cylindrical shape that simplifies mechanical property characterization. We describe studies performed by scanning electron microscopy and transmission electron microscopy that reveal several details about the hierarchical structure of mud dauber wasp petiole, including: the number and thickness of the concentric layers of cuticle comprising the wall; the similarity (and differences) between the wall structure and the structure of multi-layer corrugated cardboard; and the different anisotropies of the dorsal and ventral internal surfaces. We also describe a simple experiment in which a petiole is used as a cantilever to determine its stiffness in bending; the result (1.5 GPa) demonstrates a material efficiency in bending similar to that of GFRP and aluminum.
Poroelastic Indentation Analysis for Hydrated Biological Tissues
Authors: Oyen Michelle L. , Bembey Amanpreet K. , Bushby Andrew J.
Published: June 2019

Indentation techniques are employed for the measurement of mechanical properties of a wide range of materials. In particular, techniques focused at small length-scales, such as nanoindentation and AFM indentation, allow for local characterization of material properties in heterogeneous materials including natural tissues and biomimetic materials. Typical elastic analysis for spherical indentation is applicable in the absence of time-dependent deformation, but is inappropriate for materials with time-dependent responses. Recent analyses for the viscoelastic indentation problem, based on elastic-viscoelastic correspondence, have begun to address the issue of time-dependent deformation during an indentation test. The viscoelastic analysis has been shown to fit experimental indentation data well, and has been demonstrated as useful for characterization of viscoelasticity in polymeric materials and in hydrated mineralized tissues. However, a viscoelastic analysis is not necessarily sufficient for multi-phase materials with fluid flow. In the current work, a poroelastic analysis—based on fluid motion through a porous elastic network—is used to examine spherical indentation creep responses of hydrated biological materials. Both analytical and finite element approaches are considered for the poroelastic Hertzian indentation problem. Modeling results are compared with experimental data from nanoindentation of hydrated bone immersed in water and polar solvents (ethanol, methanol, acetone). Baseline (water-immersed) bone responses are characterized using the poroelastic model and numerical results are compared with altered hydration states due to polar solvents.
Biopolymer Polyelectrolyte Complex – Hydroxyapatite Composites for Bone Tissue Engineering
Authors: Verma Devendra , Katti Kalpana S , Mohanty Bedabibhas , Katti Dinesh R
Published: June 2019

The excellent biocompatibility, biofunctionality, and non-antigenic property make chitosan an ideal material for tissue regeneration. In addition to that its hydrophilic surface promotes cell adhesion, proliferation, and differentiation, and evokes a minimal foreign body reaction on implantation. In spite of these favorable properties, the inadequate mechanical strength and loosening of structural integrity under wet conditions, limit its application for bone tissue engineering. To improve the suitability of chitosan for bone tissue engineering, we have biomimetically synthesized composites of chitosan, polygalacturonic acid and hydroxyapatite. Polygalacturonic acid (PgA) is biocompatible, biodegradable and electrostatically complementary to chitosan. The strong interactions between negatively charged carboxylate groups of PgA and positively charged amino groups of chitosan lead to complex formation. This biopolymer complex provides improved mechanical strength and better structural integrity under wet condition. In this study, we have investigated the applicability of chitosan-PgA-hydroxyapatite composites for bone tissue engineering.
Microstructural Behavior and Failure of FCC Crystalline Aggregates
Authors: Rezvanian O. , Zikry M. A. , Rajendran A. M.
Published: June 2019

A unified dislocation density-based microstructural representation of f.c.c. crystalline materials, has been developed such that the microstructural behavior can be accurately predicted at different physical scales. This microstructural framework is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs), and grain boundary dislocations (GBDs). This interrelated dislocation-density formulation is then used with specialized finite-element modeling techniques to predict the evolving heterogeneous microstructure and the localized phenomena that can contribute to failure initiation as a function of inelastic deformation.
Predicting the Benefits of Adding Ternary Elements to Al-Sc Alloys
Authors: Simonovic Darko , Sluiter Marcel H. F.
Published: June 2019

We seek to explain 1) the effectiveness of substituting Sc with Dy, Er, Y and 2) the loss of properties when Sc is replaced with Yb, Gd and Sm [1]. For a preliminary insight into the stability of structures we utilize the concept of Atomic Environment Type (AET) as pertaining to trialuminides. Electronic density functional total energy calculations at zero temperature are performed to obtain the enthalpy of mixing of quasi-binary Al-Sc-X structures. Estimates of the entropy are used to compute the stability regions of Al3Sc1-αXα L12 phase. We show that Sc is completely miscible with X=Dy, Er, Y and that there is a miscibility gap for X=Yb, Gd and Sm at temperatures near the aging temperature of Al-Sc alloys.
Modifications of Surface Microstructure and Properties Induced by High Current Pulsed Electron Beam (HCPEB) Treatments of Intermetallics
Authors: Grosdidier Thierry , Zou Jianxin , Ji Gang , Zhang Kemin , Zhang Xiangdong , Hao Shengzhi , Dong Chuang
Published: June 2019

High current pulsed electron beam (HCPEB) is a fairly new technique for surface modifications. The present contribution reviews some recent insights on the microstructure modifications encountered at the top surface of HCPEB treated (NiTi and FeAl) intermetallics. In particular, the potential of the technique for structure modifications associated with the use of the pulsed electron beam under “heating” and “melting” conditions is highlighted. The interesting surface modifications include the creation of an homogeneous protective layer under the melting mode while thermal stresses under the heating mode can induce surface hardening and stress enhanced rapid solid state alloying.
Internal Structure of B19 Martensite in AuTi Shape Memory Alloy
Authors: Inamura Tomonari , Tachi Ryosuke , Wakashima Kenji , Hosoda Hideki
Published: June 2019

Internal twin of B19 martensite in equiatomic AuTi binary alloy was examined by conventional transmission electron microscopy observation and the phenomenological theory of martensite crystallography (PTMC). The crystal structure of martensite was B19 (orthorhombic) with the lattice parameters of 0.2944nm, 0.4900nm and 0.4633nm. Most of martensite plates were internally twinned by {111}typeI twin. <211>typeII twin was occasionally observed and {011}compound-twin relationship was observed at boundaries between adjacent martensite plates. However, no martensite plate entirely twinned by the <211>typeII twinning or the {011}compound twinning was observed. PTMC analysis showed that the invariant plane is formed only by the introduction of the internal twin of {111}typeI or <211>typeII twin in the present geometry of the transformation. Geometry of a typical martensite plate with internal twin of {111}typeI twin was in good agreement with that required for the formation of habit plane with the invariant plane character. The observed {111}typeI twin is, therefore, considered to be the lattice invariant shear to minimize the elastic strain energy due to the transformation.
Change in Creep Deformation of PST Crystals with Different Stress Axes
Authors: Min Xiaohua , Sakurada Eisaku , Takeyama Masao , Matsuo Takashi
Published: June 2019

Based on our analysis of a lot of creep rate-strain curves of PST crystals with the different angles between the lamellar plate and the stress axis, designated as ø, it was confirmed that the creep rate and the creep deformation manner strongly depend on the ø. It was supposed that the predominant creep deformation using γ plate during the transient stage is derived by the fully suppression of the operation of another slip systems not parallel to γ plate through α2 plate. It was also confirmed that the initial stress axes of the PST crystals within the standard stereographic triangle move for the [001]-[111] line, and then turn their directions for [111] pole during the transient stage. This moving manner of the stress axis indicated that the first slip system of [101](111) continues to the area near the [001]-[111] line in the standard stereographic triangle, and then, the second slip system of [110](111) operates. By comparing this moving manner to the creep rate-strain curve, it is suggested that the first slip system of [101](111) operates during the Stage I where the light decrease in the creep rate remains, after that, the second slip system of [110](111) appears and leads to steep decrease in the creep rate. This stage was designated as the Stage II. According to this conception, it is supposed that the strain at the end of the Stage I is directly correlated with the angle from the initial stress axis to the [001]-[111] line in the standard stereographic triangle. In this study, this supposition was confirmed by conducting the creep tests at 1148 K/68.6 MPa using two PST crystals with ø of 31° and 34°. The initial stress axis of the PST crystal with ø of 31° locates nearer to the [001]-[-111] line than that of the PST crystal with ø of 34°. The strain at the end of the Stage I of the PST crystal with ø of 31° is half that of the PST crystal with ø of 34°. By analyzing the inverse pole figures of the creep interrupted PST crystals, it was confirmed that the angle from the initial stress axis to the [001]-[111] line is correlated with the strain of the transient stage.
High Temperature Sulfidation Resistance of DO3 - Ordered FeAl Tested in H2S-rich Gases
Authors: Thery Pierre-Yvan , Fraczkiewicz Anna , Genevois Cecile , Longaygue Xavier , Ropital Francois
Published: June 2019

The sulfidation behaviour at 973 K in a 30 vol.% H2S-H2-H2O-N2 gas mixture of Fe-25 % at. Al, DO3-ordered alloys, binary or alloyed with niobium, was investigated. Binary alloys presented a quite good sulfidation resistance in comparison with 321 stainless steel, even if a large amount of iron sulfides FeS grew over the alumina layer on corroded samples. The sulfidation resistance of DO3 alloys could be significantly improved by an oxidation treatment prior to corrosion test. The Nb in iron aluminides was supposed to preferably react with S and therefore, to enhance sulfidation resistance through preventing the nucleation and growth of harmful FeS. Unfortunately, the scales of Nb-allloyed FeAl contained only a small amount of Nb3S4 which did not prevent efficiently the formation of iron aluminides FeS. Adding Nb to Fe-25Al even resulted in a severe deterioration of the microstructure during sulfidation due to intense diffusion of S inward the sample.
Synthesis of Magnetic Nanoparticles by Sputtering
Authors: Miyata Mai , Kishida Kyosuke , Tanaka Katsushi , Inui Haruyuki
Published: June 2019

The influence of experimental condition on morphology of FePt and Sm-Co nanoparticles synthesized by sputtering in a relatively high gas pressure has been studied. The sputtering apparatus is equipped with an annealing furnace that enables pre-deposition annealing of the nanoparticles. The effect of the annealing temperature on the ordering to the L10 FePt nanoparticles was also investigated. The morphology of the particles depends on a gas pressure and gas flow rate, but the sensitivity to experimental condition differs between FePt and Sm-Co. The morphology and domain structure of FePt nanoparticle are relatively the same in a wide range of experimental condition, whereas those of Sm-Co nanoparticle are significantly changed by variation of a gas pressure. FePt nanoparticles annealed in the annealing furnace prior to their deposition onto the substrate have the ordered L10 phase, which has an advantage for producing a magnetic recording media.
Anisotropic Microstructure and Hydrogen Permeability of Nb-Ti-Ni Duplex Phase Alloy Prepared by Hot Forging-Rolling Technique
Authors: Tokui Sho , Ishikawa Kazuhiro , Aoki Kiyoshi
Published: June 2019

It has been demonstrated that the as-cast Nb40Ti30Ni30 duplex phase alloy, which consists of the primary (Nb, Ti) solid solution and the fine lamellar type eutectic {TiNi+(Nb, Ti)} phase, shows higher hydrogen permeability ¶ than that of pure Pd without the hydrogen embrittlement at 673K. In this alloy, the eutectic phase contributes to the suppression of the hydrogen embrittlement, while the primary one does mainly to the hydrogen permeation. It is important to note that even if the eutectic microstructure disappears and is replaced by the small spherical (Nb, Ti) phase embedded in the TiNi matrix by rolling and subsequent annealing, its high hydrogen permeability and large resistance to the hydrogen embrittlement are sustained. Furthermore, the present authors have observed that the primary (Nb, Ti) phase is largely elongated along the rolling direction. Consequently, it is expected that rolled and annealed Nb-Ti-Ni alloys show the large anisotropy of the microstructure and the hydrogen permeability. In the present work, the microstructure and hydrogen permeability ¶nof the Nb40Ti30Ni30 alloy after rolling and annealing treatments are examined in order to develop highly hydrogen permeable alloys utilizing the anisotropic microstructure.

The primary (Nb, Ti) phase and the very fine eutectic {TiNi+(Nb, Ti)} phase are observed in the as-cast Nb40Ti30Ni30 alloy by scanning electron microscopy (SEM). The X-ray diffractometry (XRD) indicates that this alloy consists of the B2-TiNi intermetallic compounds and the bcc- (Nb, Ti) solid solution. The primary (Nb, Ti) phase is largely elongated along the rolling direction by forging and subsequent rolling at 1173 K. On the other hand, the eutectic microstructure becomes unclear with increasing the rolling reduction. The composite alloys in which the (Nb, Ti) phase is elongated along to the rolling direction are obtained by 69 % rolling reduction. ¶n of this sample is four times higher than that of as-cast one. On the other hand, ¶ for the sample vertical to the rolling direction is reduced to about one third of that of as-cast one. Thus, the hydrogen permeability of the Nb40Ti30Ni30 alloy varies about ten times or more depending on the direction of the primary¡]Nb, Ti¡^ phase. We conclude that it is possible to produce highly hydrogen permeable Nb-Ti-Ni alloys using the anisotropy of the microstructure prepared by hot forging and rolling.
Crack Growth Behavior in a Two-Phase Mo-Si-B Alloy
Authors: Kumar Sharvan , Alur Amruthavalli Pallavi
Published: June 2019

Mo-rich Mo-Si-B multiphase alloys are currently being explored for their potential as high-temperature structural materials for components in hot sections in aircraft engines. In this paper, we present crack growth behavior in one such two-phase alloy consisting of a Mo solid solution matrix in which is dispersed approximately 40 volume percent of the Mo5SiB2 (T2) phase. Crack growth under monotonic and cyclic loading is considered over a temperature range spanning 20°C to 1400°C. The effects of loading rate (in monotonic loading) and dwell times at maximum stress (in cyclic loading) at high temperatures on crack growth were examined to understand the contribution from creep. Results confirm a gradual increase in fracture toughness upto 1000°C, beyond which the increase is more substantial with temperature; fatigue susceptibility was also observed in excess of 900°C and crack-tip-stresses-driven microstructural instability is evident at 1400°C. At this temperature, slow loading rates or dwell times at maximum stress lead to crack-tip recrystallization and creep cavitation that together degrade the material's properties.
High Temperature Deformation Behavior of a Mechanically Alloyed Mo Silicide Alloy
Authors: Heilmaier Martin , Saage Holger , Jéhanno Pascal , Böning Mike , Freudenberger Jens
Published: June 2019

A 3-phase Mo-Si-B alloy consisting of Mo solid solution and the intermetallic phases Mo3Si and Mo5SiB2 (T2) was manufactured employing mechanical alloying (MA) as the crucial processing step. After consolidation via cold compaction, sintering in hydrogen atmosphere and final hot isostatic pressing (HIP) at 1500°C, one obtains an ultra-fine microstructure with a nearly continuous Mo(ss) matrix and the sizes of all phases being in the 1 micron range. Tensile tests were carried out in vacuum at initial strain rates ranging from 10-4 to 10-2 s-1 and the temperature varied between n1200 an 1400 °C. With a stress exponent of about 2 and the activation energy being close to that of Mo-self diffusion the material exhibits superplasticity at temperatures as low as 1300°C and tensile strain to failures up to 400%, thus, making sound wrought processing on industrial-scale facilities at temperatures typical for refractory metals and alloys feasible. To enhance creep resistance at high temperatures the alloys were annealed at 1700°C for 10h for a coarsening of the microstructure. While, still, the average sizes of all phases were below 10 microns, a considerable reduction in minimum creep rate was noted. This finding also demonstrates the extraordinary high thermal stability of this 3-phase Mo-silicide alloy.
Role of Thermal Expansion and Redistribution of Components on the Temperature Dependence of the Lattice Misfit in γ/γ' Superalloys
Authors: Kontsevoi Oleg , Gornostyrev Yuri N. , Freeman Arthur J.
Published: June 2019

The relative role of thermal expansion and redistribution of alloy components in the temperature dependence of the lattice misfit in γ/γ' alloys is investigated on the basis of ab initio calculations. We show that in a wide temperature region up to approximately 0.6·Tmelt, the lattice misfit is determined by the difference in thermal expansion of γ and γ' phases and shows only a slight variation. For higher temperatures the redistribution of the major alloy components between the phases becomes a leading contribution to the lattice misfit.
First Principles Calculations of Helium Solution Energies in BCC Transition Metals
Authors: Willaime François , FU Chu Chun
Published: June 2019

Density functional theory calculations of the solution energies of helium in substitutional, tetrahedral and octahedral sites have been performed for all BCC transition metals: V, Nb, Ta, Cr, Mo, W and Fe. The effects of exchange correlation functional and of pseudopotential have been investigated in Fe; they are relatively small. The solution energies are found to be weakly dependent on the element for the substitutional site whereas for the interstitial sites they are much smaller in group V than in group VI and they decrease from 3d to 4d and 5d metals. As a result an inversion is observed from V, Nb and Ta - which tend to favor the interstitial site - to Mo and W, which favor the substitutional one, with an intermediate behavior for Cr and Fe. Finally, the results indicate that the tetrahedral site is always energetically more favorable than the octahedral one by 0.2 to 0.3 eV.
Atomistic Simulations of Displacement Cascades in Fused Silica: It is Compared with Different Concentration of H in the Bulk
Authors: Mota Fernando , Caturla Maria Jose , Perlado Jose Manuel , Ibarra Angel , Molla Joaquin
Published: June 2019

Amorphous Silica is one of candidate materials for both final focusing optics of lasers for NIF and future inertial fusion reactors and diagnostics of the Safety and Control Systems of the ITER machine as well as DEMO magnetic fusion reactors. In operation, these materials will be exposed to high neutron irradiation fluxes and it can result in point defect and vary the optical absorption, that is, degradation of the optical properties. In this paper we present molecular dynamic simulation of displacement cascade due to energetic recoils in amorphous silica without hydrogen atoms and with 1% of hydrogen atoms trying to identify defects formation. We have made a statistics of the different kind of defects at different energy of primary knock-on atoms (PKA). The range of studied PKA energies are from 400 eV to 3.5 keV and it is made to both component of this material Silicon and Oxygen.
Comparative Study of Structural Damage Under Irradiation in SiC Nanostructured and Conventional Ceramics
Authors: Leconte Yann , Monnet Isabelle , levalois Marc , Morales Magali , Portier Xavier , Thomé Lionel , Herlin-Boime Nathalie , Reynaud Cecile
Published: June 2019

In the context of research on new materials for next generation nuclear reactors, it becomes more and more interesting to know what can be the advantages of nanostructured materials for such applications. In this study, we performed irradiation experiments on microstructured and nanostructured â-SiC samples, with 95 MeV Xe and 4 MeV Au ions. The structure of the samples was characterized before and after irradiation by grazing incidence X ray diffraction and Raman spectroscopy. The results showed the occurrence of a synergy between electronic and nuclear energy loss in both samples with 95 MeV Xe ions, while the nanostructured pellet was found to have a better resistance to the irradiation with 4 MeV Au ions.