bluuebunny/crossref_metadata_2025 huggingface dataset:
Slip Casting of α-Sialon/AlN/BN Powder Carbothermally Prepared by Boron-Rich Slag-Based Mixture
Authors: Wu Jun Bin , Xue Xiang Xin , Jiang Tao , Zhang Qing
Published: July 2011

With boron-rich slag, silica fume, bauxite chalmette and carbon black as starting materials, α-sialon/AlN/BN powder was prepared by carbothermal reduction-nitridation. The powder was attrition milled to submicron size and suspended in water. The effects of yttrium oxide as a sintering aid, pH, and addition of deflocculant on the suspensions were studied. Optimum slip casting properties, i.e. lowest viscosity values, the highest absolute zeta potential values, the smallest floc size and sediment volume were found at pH=10 for the powder. The suspensions were used to slip cast discs which were sintered in a high purity nitrogen atmosphere at 1700 °C for 2 h. The strength was about 230 MPa, the toughness 3.6 MPa•m1/2 and the hardness about 13.8 GPa.
Microstructure and Mechanical Properties of Joints in Sintered SiC Fiber-Bonded Ceramics
Authors: Matsunaga Tadashi , Singh Mrityunjay , Asthana Rajiv , Lin Hua Tay , Kajii Shinji , Ishikawa Toshihiro
Published: July 2011

Active metal brazing of a new high thermal conductivity SiC-polycrystalline fiber-bonded ceramic (SA-Tyrannohex™) has been conducted using a Ti-containing Ag-Cu active braze alloy (Ticusil®). The brazed joints were characterized using SEM-EDS and Knoop hardness scans across the interfaces. The effects of fiber orientation in the composite on the microstructure, elemental composition, and microhardness are presented. Results show that this material can be successfully joined using judiciously selected off-the shelf active braze alloys to yield metallurgically sound joints possessing high integrity.
Lithium Intercalation Properties of Lithium Tetratitanate Obtained by Nanosheets Process
Authors: Suzuki Shinya , Miyayama Masaru
Published: July 2011

Lithium intercalation properties of lithium tetratitanate obtained by nanosheets process (NS-LT4) was examined and compared with those of conventional lithium tetratitanate. NS-LT4 was prepared by restacking of tetratitanate nanosheets with LiOH aqueous solution. NS-LT4 exhibited a reversible capacity of approximately 140 mAh g-1, which corresponds to approximately two Li insertions per formula unit. Two Li insertions per formula unit mean that half of the Ti atoms were reduced from a tetravalent state to a trivalent state. The quasi open-circuit voltage of NS-LT4 was comparable with that of conventional lithium tetratitanate, and the voltage change of NS-LT4 as the change in lithium composition was greater than that of conventional lithium tetratitanate. This potential behavior would be caused by the unique stacking structure with stacking fault and random rotation in nanosheet-plane generated during the restacking of nanosheets.
Ferroelectricity of SrTiO3 Thin Films Prepared by Dynamic-Aurora Pulsed Laser Deposition
Authors: Yamashita Kiyotaka , Sakamaki Yoshihiro , Sakamoto Naonori , Shinozaki Kazuo , Suzuki Hisao , Wakiya Naoki
Published: July 2011

The effect ofin-situmagnetic field during deposition (dynamic aurora PLD) was examined for SrTiO3thin film deposited on (La0.5Sr0.5)CoO3/CeO2buffered YSZ(001) substrates. It was found that both in-plane and out-of-plane lattice parameters were changed by thein-situmagnetic field. Reciprocal space map measurement revealed that the in-plane and out-of-plane lattice parameters are 0.3817 and 0.3953 nm without magnetic field, meanwhile those are 0.3906 and 0.3974 nm with magnetic fields of 2 kG. This indicates that biaxial strain induced by the magnetic field. The effect of magnetic fields on the ferroelectric properties was examined.
Synthesis and Electrochemical Properties of Hollandite-Type KXTiO2
Authors: Sakao Mitsumasa , Kijima Norihito , Kataoka Kunimitsu , Akimoto Junji , Okutani Takeshi
Published: July 2011

Single phase specimen of K0.12TiO2 with hollandite-type structure was successfully synthesized by the solid-state reaction under Ar/H2 atomosphere. K+ ions were partially extracted from the parent K0.12TiO2 specimen by the HCl treatment. The K+-extracted K0.08TiO2 specimen worked as a rechargeable electrode material. An initial capacity of 92 mAh/g (cut-off voltage: 1.0 V) could be achieved, which approximately correspond to the composition Li0.28TiO2. A reversible capacity after 50 cycles was about 50 mAh/g.
Microwave Synthesis of Nano-Sized SnO2 for Lithium-Ion Batteries
Authors: Yoshinaga Masashi , Kijima Norihito , Wakahara Sonoko , Akimoto Junji
Published: July 2011

SnO2nanoparticles were successfully synthesized by the microwave heating. The crystallite size of the SnO2nanoparticles was estimated to be about 3 nm from the Scherre’s equation. The initial lithium insertion capacity of the SnO2nanoparticles was 2110 mAh/g which is larger than that of the micro-sized commercial SnO2product. The rechargeable capacity at 10 cycles was 1060 mAh/g, and the capacity retention over the tenth cycles was about 50 %.
Quasi-Solid-State Dye-Sensitized Solar Cells Using ZnO Photoelectrodes Fabricated by a Liquid Process
Authors: Hosokawa Morio , Fujihara Shinobu
Published: July 2011

Nanostructured ZnO films for use in dye-sensitized solar cells were fabricated by utilizing a chemical bath deposition process and a newly developed liquid–liquid process. Layered zinc hydroxides were first deposited on fluorine-doped tin oxide (FTO)-coated substrates and then heated at 450 °C in air to obtain ZnO. Cells were constructed by employing a quasi-solid-state polymer gel electrolyte. The performance of the cells with the ZnO films from the different deposition processes was compared and discussed in terms of the microstructure. Light-to-electricity conversion efficiency reached 2% in all the cells under full sunlight. The cells were kept for 500 h at room temperature, revealing that they maintained 90% of their initial performance.
Evaluation of TiO2 Nanoparticle Thin Films Prepared by Electrophoresis Deposition
Authors: Kawakami Ryo , Ito Kazuatsu , Sato Yuuki , Mori Yasushige , Adachi Motonari , Yoshikado Shinzo
Published: July 2011

The absence of cracks and a high optical transparency are critical factors for obtaining high performance when TiO2 thin films are used as photocatalysts and as the cathode material in dye-sensitized solar cells. Synthesized TiO2 nanoparticles were deposited by constant-current electrophoresis in ethanol. TiO2 nanoparticle thin films deposited at a low current density had no apparent cracks and a high optical transparency. Small TiO2 nanoparticles deposited are thought to be transported at low current densities. This enables TiO2 nanoparticle chains to form by the oriented attachment mechanism and thereby increases the electron diffusion length.
Development of Electric Power Measurement for Energy Harvesting Using Unimorph-Type Piezoceramics
Authors: Shimura Yoshikazu , Pulpan Petr , Fujii Ichiro , Nakashima Kouichi , Wada Satoshi
Published: July 2011

In this study, a new electric power generation measurement system was developed for piezoelectric energy harvesting using unimorph-type piezoceramics. Relationships between electric power and material constants such as d33, d31, g31, k31, e33T/e0, s11E, Qe and Qm were investigated using various lead zirconium titanate (Pb(Zr,Ti)O3, PZT) ceramics with different material constants. Using the equipment, pulse-type stress was applied to unimorph-type piezoceramics. Then, optimum measurement conditions were determined. Under these conditions, the electric power for piezoelectric energy harvesting was measured as a function of the material constants. Finally, it was clarified that for piezoelectric energy harvesting using a unimorph-type device, the figure of merit was combination of the 3 kinds of material constants such as large d31, small e33T/e0, and large s11E.
Growth of Orientation-Controlled Epitaxial KNbO3 Thin Film by Hydrothermal Method
Authors: Einishi Hiro , Ishikawa Mutsuo , Nakajima Mitsumasa , Yasui Sintaro , Yamada Tomoaki , Kurosawa Minoru , Funakubo Hiroshi
Published: July 2011

KNbO3 thin films were deposited at 240 oC on various kinds of single crystal substrates by hydrothermal method using aqueous solutions containing Nb2O5 and KOH. The deposition amount of the films was found not to be much dependent on the orientation and the surface roughness of the substrates, but on the electrical conductivity of the substrate. Epitaxial {100}, {110} and {111}-oriented KNbO3 films with ferroelectricity were grown on (100)c, (110)c, and (111)c -oriented SrRuO3//(100)SrTiO3 substrates, respectively.
Influence of Schottky Interfaces on Dielectric Properties in Perovskite-Type Oxide Thin-Film Capacitors
Authors: Horiuchi Naohiro , Hoshina Takuya , Takeda Hiroaki , Tsurumi Takaaki
Published: July 2011

An estimation method of the influence of interfaces on properties in perovskite-type oxide thin-film capacitors is presented. We proposed a modified Schottky model that can be employed to explain the electric properties of metal/perovskite-type oxide junctions. The modified model considers the electric field dependence of permittivity and the flow of electrons from metal to defect states located in the band gap of the perovskite oxide. The simulation based on this model could successfully describe the results of capacitance-voltage measurements of junctions between metals (Pt, Au, and Ag) and Nb-doped SrTiO3, which were not explained by the conventional Schottky model. Additionally, a simulation for a thin-film capacitor with hysteretic behavior could depict an asymmetric capacitance-voltage curve.
Alkaline-Earth and Rare-Earth Elements and Oxygen Vacancy in BaTiO3: Analyses by First-Principles Calculations and EXAFS
Authors: Honda Atsushi , Higai Shin'ichi , Okamoto Takafumi , Inoue Noriyuki , Motoyoshi Yasuhiro , Wada Nobuyuki , Takagi Hiroshi
Published: July 2011

We performed first-principles calculations to examine the interaction among rare-earth (RE), alkaline-earth (AE) elements and oxygen vacancy (VO) in BaTiO3, in order to clarify the combined effects of VO trapping by two different elements. It was found that there is a synergistic effect of VO trapping by RE at Ba site and AE at Ti site, so that the co-doping is effective to improve insulating reliability of BaTiO3. We also verified that the local atomic structures around dopants obtained by calculations well agree with that obtained experimentally by extended X-ray absorption fine structure (EXAFS) analyses. The present work is the first one to clarify the structural environment around dopants including VO by both theoretical and experimental approaches.
Cathodoluminescence of ZnO Crystals Prepared via Electric Current Heating Method Using Zn Wire
Authors: Hagizawa Takumi , Kuroki Yuichiro , Okamoto Tomoichiro , Takata Masasuke
Published: July 2011

Zn wire was used as starting material in the fabrication of ZnO crystals in which a glass substrate was placed above the wire to grow ZnO crystals. The wire was heated by electric current in air. When the wire broke because of Joule heating, smoke arose from the wire and ZnO crystals were observed on the broken point, in the vicinity of the broken point, and on the glass substrate. The morphology and cathodoluminescence of the crystals were investigated. The crystals on the wire were 0.2–5 μm in size. The peak intensity ratio of ultraviolet (UV) emission to green emission increased with decreasing crystal size. The crystals on the substrate were tetrapod-like; the length and diameter of the tetrapod legs were 100–500 nm and 10–30 nm, respectively. The tetrapod-like nanocrystals produced only UV emissions.
Investigation of Electrical Hydrogen Detection Properties of Pt/WO3 Thin Films Prepared by Sol-Gel Method
Authors: Yamaguchi Yuki , Kineri Tohru , Fujimoto Masakatsu , Mae Hideo , Yasumori Atsuo , Nishio Keishi
Published: July 2011

Platinum (Pt)nanoparticle-dispersed tungsten trioxide (WO3) thin film is a gasochromic material that changes color from transparent to blue in an H2 gas atmosphere. The electrical conductivity of Pt-nanoparticle-dispersed WO3 is dependent on inserted protons and electrons, though the material is insulator in air, because these electrons and protons work as electrical carriers in WO3. In this study, Pt-nanoparticle-dispersed WO3 thin films were prepared using the sol-gel process, and the optical and electrical properties were evaluated in an atmosphere with or without H2 gas. Pt/WO3 thin films prepared at 400°C showed the largest change in electrical conductivity when exposed to 1% H2 gas compared with thin films prepared at other temperatures. The electrical conductivity of the film was dependent on an H2 gas concentration in the range from 100 ppm to 1%. Pt/WO3 thin films prepared by the sol-gel process are expected to be used for H2 gas sensor devices due to the linear relationship between the electrical conductivity and H2 gas concentration.
Solvothermal Synthesis of WO3 Photocatalysts and their Enhanced Activity
Authors: Kondo Yuji , Fujihara Shinobu
Published: July 2011

Tungsten trioxide (WO3) is known as a visible light responsive photocatalyst, but its photocatalytic activity is relatively low, as compared to that of anatase titanium dioxide (TiO2). To enhance the activity, high specific surface areas are necessary. In this study, WO3particles with a hierarchical architecture, which was assemblies of spherical particles 20 – 30 nm in diameter, were synthesized by the solvothermal method. The hierarchical WO3particles had high specific surface areas and their photocatalytic activity was found to be 2.5 times higher than that of the commercial WO3.
Electrical Properties and Polarization Reversal in (Li,Na)NbO3 Lead-Free Piezoelectric Ceramics
Authors: Ohashi Takayuki , Aoyagi Rintaro , Maeda Masaki , Iwata Makoto
Published: July 2011

In this study, the relationships between the electrical properties and polarization switching of lead-free (Li0.06Na0.94)NbO3 (LNN6) ceramics were investigated. The electrical properties of stoichiometric LNN6 did not change with polarization switching. On the other hand, the frequency dependence of the impedance of Na-deficient LNN decreased with polarization switching, and the coupling factor kp, the piezoelecric constant d33 and the dielectric constant ε33T/ε0 decreased with polarization switching. Moreover, the dielectric curve of Na-deficient LNN6 after 10 switchings showed peaks at approximately 330, 400 and 500 °C
Modelling of Reaction of Metallic Nanospheres with Gas
Authors: Fischer Franz Dieter , Svoboda Jiří
Published: July 2011

The stoichiometric MpXq hollow nanospheres are produced by reaction of metallic M nanospheres with the gaseous X phase. In the first stage a sufficiently thick MpXq nanoshell on the metallic core of phase M is formed. During this stage high supersaturation of vacancies in the M core or very high hydrostatic stress in the M core, due to the misfit between the core and the nanoshell, are developed and provide favourable conditions for the hollow nucleation. The misfit is caused by the Kirkendall effect. Based on the application of the thermodynamic extremal principle a kinetic model of MpXq nanoshell formation is derived. The kinetics is driven by the change of the chemical energy due to reaction of M and X components, of the interface and surface energies, and of the elastic strain energy due to misfit strain of the whole system. The model is used for simulation of the Cu2O shell growth kinetics due to oxidation of a Cu nanosphere, and the results of simulations are discussed.
Phase Field Modelling of Austenite Formation in Low Carbon Steels
Authors: Matthias Militzer , Azizi-Alizamini Hamid
Published: July 2011

There is renewed interest in the investigation of austenite formation due to the development and increased use of advanced high strength steels for automotive applications. Intercritical annealing is an essential processing step for cold rolled and coated steel products with multi-phase microstructures. During intercritical annealing the initial ferrite-pearlite microstructure transforms partially to austenite. Models for the austenite formation are critical to predict the austenite fraction as a function of the thermal cycle thereby facilitating the design and control of robust processing paths. Modelling the austenite formation is challenging because of the morphological complexity of this transformation. Phase field models are a powerful tool to describe the evolution of microstructures with complex morphologies, e.g. formation of finger-type features during austenite formation. The present paper gives an overview of model approaches for the austenite formation. Phase field simulations are presented for two scenarios: (i) austenite formation from a fully pearlitic structure with a lamellar arrangement of carbide aggregates and (ii) austenite formation from ferrite-pearlite microstructures. Simulation results are compared with experimental observations for pearlitic steels. The challenges are delineated for the development of austenite formation models with predictive capabilities.
Spin Models for Ferroelastics: towards a Spin Glass Description of Strain Glass
Authors: Vasseur Romain , Lookman Turab
Published: July 2011

We review the description of ferroelastic transitions in terms of spin models. We show how one can systematically obtain a pseudo-spin Hamiltonian from the Landau energy describing the first order transition between Austenite/Martensite phases. It is shown that a Local Mean-field approximation predicts the same microstructure as the continuous Landau model in terms of strain variables. This method can be applied to a wide range of two and three dimensional transitions. We then demonstrate how quenched disorder in such pseudo-spin models yields the existence of a glass phase, characterized by the Edwards-Anderson order parameter. Our approach uses Mean-field approximation and Monte-Carlo simulations (using Zero Field Cooling/Field Cooling experiments) to study the influence of the long-range interactions. Although our model captures the salient features of a ferroelastic material in the presence of disorder, the influence of the disorder on the high symmetry austenite phase is not quite consistent with expected behavior. We examine different means of introducing disorder that can improve upon the results.
Phase-field Model for Diffusional Phase Transformations in Elastically Inhomogeneous Polycrystals
Authors: Heo Tae Wook , Bhattacharyya Saswata , Chen Long Qing
Published: July 2011

A phase-field model is described for predicting the diffusional phase transformation process in elastically inhomogeneous polycrystals. The elastic interactions are incorporated by solving the mechanical equilibrium equation using the Fourier-spectral iterative-perturbation scheme taking into account elastic modulus inhomogeneity. A number of examples are presented, including grain boundary segregation, precipitation of second-phase particles in a polycrystal, and interaction between segregation at a grain boundary and coherent precipitates inside grains. It is shown that the local pressure distribution due to coherent precipitates leads to highly inhomogeneous solute distribution along grain boundaries.
Theoretical Investigation of Alloy Phase Equilibria by Continuous Displacement Cluster Variation Method
Authors: Mohri Tetsuo
Published: July 2011

Continuous Displacement Cluster Variation Method is employed to study binary phase equilibria on the two dimensional square lattice with Lennard-Jones type pair potentials. It is confirmed that the transition temperature decreases significantly as compared with the one obtained by conventional Cluster Variation Method. This is ascribed to the distribution of atomic pairs in a wide range of atomic distance, which enables the system to attain the lower free energy. The spatial distribution of atomic species around a Bravais lattice point is visualized. Although the average position of an atom is centred at the Bravais lattice point, the maximum pair probability is not necessarily attained for the pairs located at the neighboring Bravais lattice points. In addition to the real space information, k-space information are calculated in the present study. Among them, the diffuse intensity spectra due to short range ordering and atomic displacement are discussed.
Lengthening Kinetics of Pro-Eutectoid Ferrite Ledge in Fe-C Alloy under Interface-Diffusion Mixed Control Mode
Authors: Yang Zhi Gang , Li Zhao Dong , Liu Zhi Yuan , Liu Zhen Qing , Xia Zhi Xin , Zhang Chi
Published: July 2011

A mixed control mode is developed to model the ledge growth of pro-eutectoid ferrite, considering coupled effects of migration of austenite/ferrite interface and carbon diffusion in austenite. Carbon concentration of austenite at the austenite/ferrite interface increases from the bulk carbon concentration to a steady level, which is lower than that in local equilibrium, during the ferrite growth process. Correspondingly, ferrite grows rapidly at the beginning since all the driving force of ferrite transformation is dissipated on the interface migration. In the later stage of isothermal transformation, the growth rate of ferrite decreases towards a steady level since a part of driving force is dissipated on carbon diffusion in austenite. The effect of interface migration on ferrite growth rate by changing the interface mobility is emphatically discussed. In the case of the low interface mobility, the growth rate of ferrite is very small while the growth is dominated by the carbon diffusion ability in the case of large interface mobility. When a medium interface mobility is obtained, the growth rate of ferrite may reach a maximum value, which exceed the limitation of diffusion control and interface control modes. After comparing the modeled growth rate of ferrite with the experimental data of 0.11-0.49 wt% C alloy at 973-1113 K, the pre-expontential factor (M0) of interface mobility is estimated within the range of 0.1-1 mol m J-1 s-1, around the value 0.5 mol m J-1 s-1 theoretically estimated.
3D Cellular Automata Modelling of Solid–state Transformations Relevant in Low–alloy Steel Production
Authors: Mecozzi Maria Giuseppina , Bos C. , Sietsma Jilt
Published: July 2011

A three-dimensional cellular automata (CA) model is developed for the kinetic and microstructural modelling of the relevant metallurgical mechanisms occurring in the annealing stage of low–alloy steels: recrystallisation, pearlite–to–austenite transformation and ferrite–to–austenite transformation on heating and austenite–to–ferrite transformation on cooling. In this model the austenite–to–ferrite transformation is described by a mixed–mode approach, which implies that the transformation kinetics is controlled by both the interface mobility and the diffusivity of the partitioning elements. This approach also allows incorporation of the ferrite nucleation occurring on structural defects. The developed CA algorithm, in which the transformation rules for the grain boundary and interface cells are controlled by the growth kinetics of the forming phase, allows three-dimensional systems to be treated within relatively short simulation times. The simulated microstructure reproduces quite well the microstructure observed in experimental samples. A good agreement is obtained between the experimental and simulated ferrite recrystallisation and ferrite and austenite transformation kinetics. The present approach also models the development of the carbon concentration profile in the austenite, which is, for instance, essential for subsequent martensite formation.
Diffusion under a Stress in Metals and Interstitial Alloys
Authors: Nazarov Andrei V. , Mikheev Alexander , Valikova Irina , Zaluzhnyi Alexander
Published: July 2011

Elastic fields, generating by precipitates, cracks, dislocations and other defects of the structure, influence the diffusion processes. It leads to the alteration of the phase transformation kinetic, segregation formation and changes of the alloy properties. However, understanding the effects of strain on diffusion in solids is now limited. One of the chief aims of our approach is to obtain the general equations for the diffusion fluxes under strain that give the possibility of using these equations at low temperatures, as in this case, the strain influence on the diffusion fluxes is manifested in maximal degree. Recently some important generalization of our approach was done and equations for the vacancy fluxes in cubic metals were obtained. Now we have made the next step in the development of approach: general equations for the fluxes in interstitial alloys are obtained for different kinds of jumps in bcc and fcc structures. We are going to discuss the main features of the theory of diffusion under stress, to compare the equations for the fluxes and to present results of theory applications that are obtained with the help of computer simulations.
Critical Assessment of Bainite Models for Advanced High Strength Steels
Authors: Fazeli Fateh , Jia Tao , Militzer Matthias
Published: July 2011

Bainite is an essential constituent in the microstructure of many advanced high strength steels, e.g. ferrite-bainite dual-phase, transformation induced-plasticity (TRIP) and complex phase (CP) steels. A complex thermo-mechanical processing is employed in industry such that following ferrite formation a desired fraction of bainite can be obtained during austenite decomposition. In order to evaluate robust processing routes it would be very useful to have a bainite transformation model with predictive capabilities. In this work a transformation start criterion for bainite is proposed by defining a critical driving pressure concept. Subsequent bainite formation kinetics from a mixture of ferrite-austenite is described using phenomenological modelling methodologies. In particular, the predictive capabilities of two approaches will be critically discussed, i.e. (i) the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model in conjunction with Rios treatment of the additivity rule and (ii) a nucleation-growth based model that describes simultaneous formation of bainitic ferrite and carbides. Using experimental transformation data for TRIP and CP steels, status and limitations of these models will be delineated.
Kinetics of the Austenite-Ferrite Transformation with and without Applied Stress
Authors: Liu Yong Chang , Sommer F. , Mittemeijer Eric Jan
Published: July 2011

The formation of ferrite (α) from austenite (γ) and vice versa, upon thermo-mechanical processing of steels, are phase transformations of great technological importance. Often these transformations occur in the presence of externally or internally imposed stress. This paper provides an overview of recent research on the quantitative analysis of the transformation kinetics of the γ®a and a®g transformations subjected to uniaxial compressive stress below the yield stress of g and a, based on the application of the high-resolution differential dilatometry and the modular model of transformation kinetics. The application of uniaxially compressive stresses leads to antagonistic effects on the transformation kinetics: the stress applied upon the γ®a transformation prompts the transformation, while it obstructs the a®g transformation. These results can be quantitatively discussed in terms of chemical driving forces and transformation-induced deformation energies.
A Convex Hull Algorithm for Minimization of Gibbs Energy in Two-Phase Multicomponent Alloys
Authors: Perevoshchikova Nataliya , Appolaire Benoît , Teixeira Julien , Denis Sabine
Published: July 2011

We have adapted the Quickhull algorithm with the general dimension Beneath-Beyondalgorithm [6] for computing the convex hull of the Gibbs energy hypersurface of multicomponenttwo-phase alloys. We illustrate the salient features of our method with calculations of isothermalferrite-austenite equilibria in Fe-C-Cr. Finally, successive equilibrium calculations in a Fe-C-Cr-Mosteel over a large temperature range show the beneﬁt of computing the convex hull before performingthe conventional Newton-Raphson search.
Simulation of Atomic Structure and Diffusion Characteristics of Point Defects in BCC and FCC Metals
Authors: Valikova Irina , Nazarov Andrei V.
Published: July 2011

Our recent model has been used to evaluate the point defect characteristics including those determining the effect of pressure on the concentration of vacancies, di-vacancies, interstitials and their diffusion mobility in set of BCC and FCC metals. Our model has been developed to calculate temperature dependences of mentioned features. In contrast to other studies, the vacancy migration volumes have been found for all the metals studied.
In Situ Study of Microstructural Development during Phase Transformation in Welding Process
Authors: Terasaki Hidenori , Komizo Yu Ichi
Published: July 2011

The applications of laser scanning confocal microscopy (LSCM) system were introduced to the track the phase transformation of steel. For the low and high carbon steel, the microstructural change along various thermal cycles was directly observed with LSCM system. The nature of non-themoelastic martensite was directly observed. Furthermore, direct checking of the nucleation site of ferrite phase was carried out for aluminum killed weld metal and titanium killed-steel. It was carried out concerning to acicular ferrite formation in high strength and low alloy steel. The assessment of the pinning effect of alumiunu nitride on the austenite phase at high temperature was also carried out by using LSCM system.
Plastic Flow Localization Viewed as an Auto-Wave Process Generated in Deforming Metals
Authors: Zuev Lev , Barannikova Svetlana A.
Published: July 2011

The localized plastic flow auto-waves observed for the stages of easy glide and linear work hardening in a number of metals are considered. The propagation rates were determined experimentally for the auto-waves in question with the aid of focused-image holography. The dispersion relation of quadratic form derived for localized plastic flow auto-waves and the dependencies of phase and group rates on wave number are discussed. A detailed comparison of the quantitative characteristics of phase and group waves has revealed that the two types of wave observed for the stages of easy glide and linear work hardening are closely related. An invariant is introduced for localized plastic flow phenomena occurring on the micro- and macro-scale levels in the deforming solid.
FIB/SEM Applied to Quantitative 3D Analysis of Precipitates in Ni-Ti
Authors: Cao Shan Shan , Nishida Minoru , Schryvers Dominique
Published: July 2011

Ni4Ti3 precipitates with a heterogeneous distribution growing in a polycrystalline Ni50.8Ti49.2 alloy have been investigated in a Dual-Beam FIB/SEM system. The volume ratio, mean volume, central plane diameter, thickness, aspect ratio and sphericity of the precipitates in the grain interior as well as near to the grain boundary were measured or calculated. The morphology of the precipitates was classified according to the Zingg scheme. The multistage martensitic transformation occurring in these kinds of samples is interpreted in view of the data of this heterogeneous microstructure of matrix and precipitates.
Neutron Diffraction Study on Magnetic Structure in Layered Manganite La2-2xSr1+2xMn2O7 (x=0.307)
Authors: Sonomura Hirosuke , Terai Tomoyuki , Kakeshita Tomoyuki , Osakabe Toyotaka , Kakurai Kazuhisa , Kuroiwa Yoshihiro , Moriyoshi Chikako , Okubo Toshinori , Kato Kenichi , Kim Jungeun , Takata Masaki
Published: July 2011

Magnetic structure in a layered perovskite manganite, La2-2xSr1+2xMn2O7 (x = 0.307) has been investigated by neutron diffraction measurements. We found that the ground state (at 4 K) has a ferromagnetic structure with magnetic moment of Mn ions being aligned in a direction inclined by 10 degree from the c-axis. The magnetic structure changes to a canted antiferromagnetic one (CAFM-I) at about 20 K and then to another canted antiferromagnetic one (CAFM-II) at about 80 K. Here the magnetic moment lies in the ab-plane in CAFM-II but not in CAFM-I. The magnetic structure then changes to an antiferromagnetic one with magnetic moment lies in the ab-plane at about 90 K, and then to a paramagnetic one at about 100 K.
Heteroepitaxy Crystallography in Low Dimensional Nanostructures
Authors: Qiu Dong , Zhang Ming Xing , Kelly Patrick
Published: July 2011

Low dimensional nanostructures, e.g. nanowires, self-assembled through heteroepitaxy, present a variety of crystallographic features that do not always follow conventional V-W or S-K growth mode. Applying Δg parallelism rules and edge-to-edge matching (E2EM) model in β-DySi2/Si and CoSi2/Si systems provides a better understanding of the natural preference of the interface orientation and the orientation relationship (OR) during heteroepitaxial growth. This may help improving the quality of nanowires through optimizing the substrate orientation.
Acoustic Emission Avalanches in Martensitic Transitions: New Perspectives for the Problem of Source Location
Authors: Vives Eduard , Soto Parra Daniel Enrique , Planes Antoni , Mañosa Lluís , Romero Ricardo , Edwards Rachel S. , Dixon Steve
Published: July 2011

Different experimental procedures for the location of sources of Acoustic Emission (AE) avalanches during Martensitic Transformations are discussed. A first example corresponds to the 1D location of AE events during stress-induced martensitic transitions in a Cu-Zn-Al shape memory alloy (3.5 cm length). The obtained data allows monitoring of the interface advancement with a spatial resolution of less than 1 mm. Secondly, we discuss two different ideas that have significant potential for improving this resolution in the case of thermally induced transitions in small single crystalline samples (~1 cm): the use of elastodynamic simulations based on finite element methods and the simultaneous detection of AE and Barkhausen noise in ferromagnetic samples.
Microstructural Control of the Austenite Stability in Low-Alloyed TRIP Steels
Authors: Blondé Romain , Jimenez-Melero Enrique , van Dijk Niels H. , Brück Ekkes , Zhao Lie , Sietsma Jilt , van der Zwaag Sybrand
Published: July 2011

We have performed in-situ magnetization and high-energy X-ray diffraction measurements on two aluminum-based TRIP steels from room temperature down to 100 K in order to evaluate amount and stability of the retained austenite for different heat treatment conditions. We have found that the bainitic holding temperature affects the initial fraction of retained austenite at room temperature but does not to influence significantly the rate of transformation upon cooling.
Acceleration of Bainitic Transformation in Nanostructured, Low Temperature Bainitic Steels by Using of Thermodynamic Model
Authors: Yoozbashi Mir Nariman , Yazdania Sasan
Published: July 2011

Nanostructured, low temperature bainitic steels with remarkable combination of ultimate tensile strength of about 2.5 GPa and high uniform elongation have been developed in the recent decade. To accelerate the bainitic transformation in theses steels, new chemical composition was designed by MUCG83 thermodynamic model which was developed in Cambridge University by Bhadeshia. The samples, prepared from the hot rolled ingots, were transformed isothermally at the temperature range of 200 to 300°C for different times. The microstructure and mechanical properties of the samples were evaluated by XRD, SEM, hardness and tensile tests. The results showed a unique microstructure and good mechanical properties like other bainitic steels, while the needed time for the completion of transformation is shorter compared to that of others.
Advanced TEM and SEM Methods Applied to 3D Nano- and Microstructural Investigations of Ni4Ti3 Precipitates in Ni-Ti (SMA)
Authors: Schryvers Dominique , Tirry Wim , Cao Shan Shan
Published: July 2011

Two different kinds of experimental approaches yielding three-dimensional structural information on metastable semi-coherent precipitates are demonstrated. By combining high-resolution images from two independent viewing directions a full description of the strain field surrounding a nano-sized Ni4Ti3 precipitate in Ni-Ti can be obtained. The principal axes and strains correlate well with the transformation strain of the observed R-phase transformation close to the precipitate. Using a slice-and-view procedure in a FIB/SEM dual-beam instrument, a three-dimensional voxel dataset is produced from which morphological and distributional information on the same precipitates can be obtained yielding new insight into the particular transformation paths of these alloys, relevant for their functional behaviour.
Substitution Effect of the Third Element X on the Morphology of A1/L12/D022 Three-Phase Microstructure in Ni-V-X (X=Si, Al) Alloy
Authors: Kozakai Takao , Sakurai Daisuke , Doi Minoru
Published: July 2011

Morphology of phase-separated microstructure consisting of cubic disordered A1 and ordered L12 phases and tetragonal ordered D022 phase in Ni-V-X (X=Al, Si) alloys has been investigated by transmission electron microscopy. Ternary Ni-V-Al alloy showed the lamellar structure of D022 phase with spherical L12 particles, while Ni-V-Si ternary alloy indicated the anisotropic microstructure consisting of plate- or diamond-shaped D022 and plate-shaped L12 phases. When a part of element Al is substituted by Si, the morphology of three-phase microstructure (A1/L12/D022) varied depending on the amount of element substitution. When Ni-16.1V-4.0Al-2.8Si (at.%) alloy was aged at 1173K for long time, D022 plate-like particle aligned along <110> direction and L12 particles formed between them in the shape of sphere. In the case of Ni-16.6V-2.8Al-4.0Si (at%) alloy more substituted for Al by Si, cuboidal L12 phases were first formed aligning along <100> direction and then plate-shaped D022 phases precipitated along the <100> direction in the channel of cuboidal L12 particles. Such morphological changes with the substitution of the third elements X by Al or Si were able to be explained based on lattice mismatch.
The Interface between γ and γ’ in Ni-Al Alloys by HREM
Authors: Calderon Hector A. , Calzado Lopez Lorenzo , Mori Tsutomu
Published: July 2011

Ni Base superalloys owe their excellent mechanical properties to the presence of particles of γ’ phase (Ni3Al with an L12 struc­ture) in a g matrix (Ni–Al solid solution with an fcc structure). Besides Al, other elements are used to im­part either a higher strengthening or improved corrosion properties at high temperature. The interface between γ and γ’ becomes of absolute importance for the resulting mechanical properties and technological application. Especially by considering the consequences that diffusion driven coarsening brings about to the parti­cle distribution either with or without the influence of an applied stress or strain. In this work the interface between γ and γ’ phases is characterized by means of measurements on phase images obtained from high resolution transmission electron microscopy images (HRTEM). Phase images represent the sample structure much more accurately than typical HREM experimental images and allow correction of spherical aberration and other residual aberrations. The investigation is performed by using a binary Ni-Al alloy as well as technical Ni base superalloys (MC2 and MCNG). While a sharp interface is developed during stress free coarsening in Ni-Al alloys, a wider volume needs to be considered when alloying elements are introduced. Measurements of lattice spacings on phase images and chemical composition from energy dispersive spectroscopy are used to show the interface characteristics in the alloys under consideration. The interface in the binary Ni-Al alloy can be described by micro­mechanics as a typical misfitting inclusion. In the technical alloys, the presence of concentration gradients changes the expected lattice strains in a given volume around the particles.
Exchange Coupling Nanophase Fe-Pd Ferromagnets Through Solid State Transformation
Authors: Shugart Kathleen N. , Ludtka Gerard M. , Mackiewicz-Ludtka Gail , Soffa William A.
Published: July 2011

This study continues previous work on off-stoichiometric Fe-Pd alloys using a combined reaction strategy during thermomechanical processing [1,2]. Severe plastic deformation of the initial disordered fcc gamma phase (γ) of compostion Fe-35at.%Pd, followed by heat treatment in the two phase field produces a nano-composite ferromagnet comprised of soft alpha phase/ferrite (α) in a high-anisotropy L10 FePd matrix. The length scale and morphology of the transformation products have been characterized using x-ray diffraction, and scanning electron microscopy. The transformed microstructures exhibit strong texture retention similar to the stoichiometric alloy suggesting a massive ordering mode. The alloy has shown a proclivity to exchange couple at a length scale not in agreement with proposed theories of exchange coupling [3,4]. The magnetic properties were measured using standard vibrating sample magnetometry (VSM). This research has been supported by the National Science Foundation (NSF-DMR).
The Role of Dispersions in Modeling the Kinetics of Phase Transformations
Authors: Gouné Mohamed , Maugis Philippe
Published: July 2011

In classical models of microstructural evolution, the natural dispersion existing in the samples is often neglected. In this paper, we propose a general model that takes into account the dispersion. This model is applied to two cases of phase transformations in steels: the first one concerns the bainitic transformation and the second is dedicated to austenite to ferrite transformation. Through these examples, we show that not taking account the effects of dispersion in the model can lead to (i) incorrect prediction of the overall kinetics or (ii) an incorrect parameter fitting of the experimental data.
Atomic Scale Investigation of Cr Precipitation in Cu and Related Mechanical Properties.
Authors: Chbihi Abdelahad , Sauvage Xavier , Blavette Didier
Published: July 2011

The early stages of precipitation of Cr rich precipitates were investigated by Atom Probe Tomography (APT) in a Cu-1Cr-0.1Zr (wt.%). This way, quantitative data were obtained about their size, 3D shape, density, composition and volume fraction. Surprisingly, in the early stage of precipitation, nanoscaled precipitates exhibit various shapes (spherical, plates and ellipsoid) and contain a large amount of Cu (up to 50%), in contradiction with the equilibrium Cu-Cr phase diagram. APT data also show that some impurities (Fe) segregate along Cu/Cr interfaces. A precipitation sequence is proposed and the relationship between mechanical properties and microstructure is discussed.
Transformation and Twinning Pseudoelasticities in Fe3Ga Single Crystals
Authors: Yasuda Hiroyuki Y. , Oda Yasuhiro , Kishimoto Takuya , Umakoshi Yukichi
Published: July 2011

In Fe3Ga single crystals with the D03 structure, three types of pseudoelasticities based on dislocation motion, martensitic transformation and twinning take place depending on the heat treatment, the loading axis and the stress sense. In this paper, we report the detail of the transformation and twinning pseudoelasticities in the crystals focusing on the crystallography and the temperature dependence. In particular, the driving force for the twinning pseudoelasticity was discussed, focusing on the atomic arrangement. In Fe3Ga single crystals homogenized or solutionized in the α disordered region, the martensites with the 14M structure, containing numerous stacking faults were stress-induced during loading, while they disappeared during unloading by the reverse transformation, resulting in the transformation pseudoelasticity with small stress-strain hysteresis. In contrast, twinning pseudoelasticity caused by twinning and untwinning of 2.2T-type pseudo-twins appeared in the well-ordered D03 crystals, accompanied by a serrated flow in the stress-strain curve. The contribution of the twinning pseudoelasticity to strain recovery became significant at low temperatures at which the dislocation motion was difficult. It should be noted that the formation of the pseudo-twins could be regarded as a certain displacive phase transformation since the crystal structure of the twins became orthorhombic due to the twin shear without atomic shuffling. The free energy difference between the D03 matrix and the pseudo-twins resulted in the twinning pseudoelasticity. Moreover, the pseudo-twins were transformed into the perfect twins by annealing at 300 °C where the atomic shuffling could occur. The perfect twins remained even after complete unloading due to their low driving force for the pseudoelasticity.
Beyond the Cahn-Hilliard Equation: a Vacancy-Based Kinetic Theory
Authors: Nastar Maylise
Published: July 2011

A Self-Consistent Mean Field (SCMF) kinetic theory including an explicit description ofthe vacancy diffusion mechanism is developed. The present theory goes beyond the usual local equi-librium hypothesis. It is applied to the study of the early time spinodal decomposition in alloys. Theresulting analytical expression of the structure function highlights the contribution of the vacancydiffusion mechanism. Instead of the single amplification rate of the Cahn-Hillard linear theory, thelinearized SCMF kinetic equations involve three constant rates, first one describing the vacancy re-laxation kinetics, second one related to the kinetic coupling between local concentrations and paircorrelations and the third one representing the spinodal amplification rate. Starting from the same va-cancy diffusion model, we perform kineticMonte Carlo simulations of a Body Centered Cubic (BCC)demixting alloy. The resulting spherically averaged structure function is compared to the SCMF pre-dictions. Both qualitative and quantitative agreements are satisfying.
Thermal Embrittlement of a Lean Grade of Duplex Stainless Steel: Alloy 2003
Authors: Tucker Julie D. , Young Jr. George A. , Eno Daniel R.
Published: July 2011

Duplex stainless steels are desirable for use in power generation systems due to their attractive combination of strength, corrosion resistance, and cost. However, thermal embrittlement at intermediate temperatures (~475°C) via α-α' phase separation limits upper service temperatures for many applications. The development of low Cr and Ni equivalent lean grade alloys potentially increases the upper service temperature of these alloys by delaying the onset of α-α' phase separation. The present work assesses the thermal stability of a relatively new lean grade of duplex stainless steel, alloy 2003. In this paper, alloy 2003 has been compared to the most widely used duplex alloy, 2205, through a series of isothermal agings between 260°C and 538°C for times between 1 and 10,000 hours. The thermal stability of these alloys was primarily characterized by changes in microhardness. The microhardness data were fit to a JMA-type equation to quantify embrittlement rates and predict microstructural changes out to 50 years. Additionally, as-received specimens were characterized with the scanning electron microprobe to quantify the chemistry within the ferrite grains relative to the bulk material. Alloy 2003 was shown to be much more resistant to thermal embrittlement than alloy 2205. For 50 years of service at 288°C, it is predicted that alloy 2003 components will have a change in microhardness of about 25 HK where alloy 2205 components would increase approximately 175 HK, which indicates significant embrittlement. These findings show that lean grade alloys will have a greater service temperature range than standard grades. However, additional data, characterization, and modeling are needed to better predict embrittlement kinetics over component lifetimes.