bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Electromagnetic Actuator for Impedance Pumping
Authors: Lee Chia Yen , Tai Chang Hsien , Chang Chin Lung , Tsai Chien Hsiung , Wang Yao Nan , Fu Lung Ming
Published: July 2011

This study designs and analyzes an impedance pump utilizing an electromagnetic actuator. The pump is designed to have three major components, namely a lower glass substrate patterned with a copper micro-coil, a microchannel, and an upper glass cover plate attached a magnetic PDMS diaphragm. When a current is passed through the micro-coil, an electromagnetic force is established between the coil and the magnetic diaphragm. The resulting deflection of the PDMS diaphragm creates an acoustic impedance mismatch within the microchannel, which results in a net flow. Overall, the simulated results reveal that a net flow rate of 52.8 μl/min can be obtained using a diaphragm displacement of 31.5 μm induced by a micro-coil input current of 0.5 A. The impedance pump proposed in this study provides a valuable contribution to the ongoing development of Lab-on-Chips (LoCs) systems.
Study on Ultrasonic Fusion Bonding for Polymer Microfluidic Chips
Authors: Luo Yi , He Sheng Qiang , Wang Liang Jiang , Zhang Zong Bo
Published: July 2011

Ultrasonic fusion bonding is a potential method for mass-production of polymer microfluidic chips. However, the micro structures in the chips are easily damaged or even destroyed due to poor controllability and uniformity of the melted energy directors in ultrasonic bonding process. In this paper, a novel micro joint including energy directors and flow blocks is presented. The flow profile of the melted energy directors is controlled by the dimensions of the flow blocks, auxiliary energy-equilibrating structures are also designed to prevent the uneven melt of energy directors. Polymethyl methacrylate (PMMA) microfluidic chips with the new joints were fabricated and ultrasonic bonding experiments were conducted. Micro channels with characteristic dimension of tens of microns were successfully sealed in 0.3 s and free of deformation.
Theoretical Analysis and Experimental Investigation on Designing Method of Micro-Groove Heat Pipe
Authors: Han Tian , Liu Xiao Wei , Cui Ning
Published: July 2011

In this paper, a kind of one-dimensional steady-state model is used to analyze and simulate the capillary motion of the working material in micro heat pipe. The character of this model is that it includes the influence of the interface friction, and the influence of the friction to the micro heat pipe’s performance is also simulated and analyzed. The maximum heat transport capacity and the optimizing size of the grooves are calculated by this model. Some experiments have been carried out to evaluate the simulation results.
A MEMS Fluid Density Sensor Based on Trapezoidal Cantilever
Authors: Zhao Li Bo , Huang En Ze , Zhang Gui Ming , Zhao Yu Long , Wang Xiao Po , Jiang Zhuang De , Liu Zhi Gang
Published: July 2011

A kind of fluid density sensor based on MEMS (Micro-Electro-Mechanical-System) technology is introduced with trapezoidal cantilever structure. The rectangular cantilever and trapezoidal cantilever, based on the same parameters, are analyzed. The simulation results show that the sensitivity of trapezoidal cantilever is higher than that of rectangular cantilever. Four different sizes of trapezoidal cantilever are analyzed by modal and harmonic simulation with ANSYS Software, the optimum solution will be obtained from simulation results.
Lateral RF MEMS Switch Based on Surface Micromachining Process
Authors: Du Guo Ping , Zhu Jian , Yu Yuan Wei , Jia Shi Xing , Jiang Li Li
Published: July 2011

In this paper, a novel RF MEMS switch driven by combs with low insertion loss is presented. The developed SPST RF MEMS switch with a lateral resistive contact and gold structure layer on a silicon substrate has been fabricated by surface micromachining process. The RF performance of the switch indicates an insertion loss below 0.30 dB at 20 GHz, a return loss better than 20 dB and isolation greater than 30 dB. Good RF characteristics have been achieved by the large contact area and a lateral Au-to-Au resistive contact.
Improvement on Mechanical and Piezoresistivity Properties of Cementitious Binder by Using Surface Oxidized Multi-Wall Carbon Nanotubes
Authors: Luo Jian Lin , Duan Zhong Dong , Zhao Tie Jun
Published: July 2011

Two types of the cementitious binders (MWNT/CB, AMNT/CB) filled with 0.5 wt.% multi-wall carbon nanotube (MWNT), and acid-treatment MWNT (AMNT) were prepared. The surfaces of MWNT and AMNT were firstly characterized with TEM micrograph and FT-IR spectrum before and after acid oxidation. The electrical resistivities (ρ) and the longitudinal strains (εl) of two cured nanocomposites under cyclic compressive stress (σ) are real-time collected, in order to investigate their piezoresistivity properties, associated with mechanical behaviors. On one hand, acid treatment can enhance interface bonding between AMNT and cementitious binder decorated with some hydrophilic groups, resulting in some mechanical improvements; on the other hand, it causes better distribution and more network pathway, AMNT/CB has resultantly balanced piezoresistivity property with regular and consistent variation ofρfollowing the σ, or theεl, and fixed stress/strain sensitivity (around 62), compared to that of MWNT/CB.
A Broadband Frequency Piezoelectric Vibration Energy Harvester
Authors: Ma Hua An , Liu Jing Quan , Tang Gang , Yang Chun Sheng , Li Yi Gui , He Dan Nong
Published: July 2011

As the low-power wireless sensor components and the development of micro electromechanical systems, long-term supply of components is a major obstacle of their development. One of solutions to this problem is based on the environmental energy collection of piezoelectric vibration energy harvesting. Currently, frequency band of piezoelectric vibration energy harvester is narrow and the frequency is high, which is not fit for the vibration energy acquisition in the natural environment. A piezoelectric vibration energy harvester with lower working frequency and broader band is designed and a test system to analyze the harvester is presented in this paper. The traditional mass is replaced by a permanent magnet in this paper, While other two permanent magnets are also placed on the upper and above of the piezoelectric cantilever. Experiments showed, under the 0.5g acceleration, compared with the traditional non-magnetic piezoelectric vibration energy harvesting, a piezoelectric cantilever (length 40mm, width 8mm, thickness 0.8mm) has a peak-peak voltage of 32.4V, effectively enlarges working frequency band from 67HZ-105HZ to 63HZ-108HZ.
Molecular Dynamic Simulations of Contact Thermal Resistance between Two Individual Silicon Nanowires
Authors: Wang Jian Giang , Bi Ke Dong , Chen Yun Fei
Published: July 2011

Contact thermal resistance between two individual silicon nanowires is investigated by nonequilibrium molecular dynamic simulations as a function of temperature, overlap, bonding strength and spacing between them. The results indicate that contact thermal resistance per unit area increases with temperature increasing. The increasing overlap leads to the increase of the contact areas, which enhances the per unit area contact thermal resistance. With a weakened interfacial van der Waals bonding strength, the contact thermal resistance per unit area increases significantly. Additionally, a method to verify the effect of the bonding strength is used by changing the interfacial spacing, and a reasonable result is observed.
Analytical Solution of Mixed Electroosmotic and Pressure-Driven Flow in Rectangular Microchannels
Authors: Yang Da Yong
Published: July 2011

Analytical solutions for potential distributions, velocity distributions of the mixed electroosmotic and pressure-driven flow in rectangular microchannels are discussed. To simulate the flow, a mathematical model, which includes the Poisson-Boltzmann equation and the modified Navier-Stokes equations, is presented and solved using the finite element method based on the Matlab software. The results show that the velocity distribution of mixed flow is compound of the “plug-like” and paraboloid at the steady state, and the pure electroosmotic flow is “plug-like”, which is similar with the electric double layer potential profile. The results provide the guidelines for the application of mix driven flow in microfluidic chips.
Low-Cost Fabrication Strategies of Microfluidic Device on Glass Substrate
Authors: Li Dong Ling , Wen Zhi Yu , Shang Zheng Guo , Wang Sheng Qiang
Published: July 2011

This paper presents a simple but reliable fabrication process for microfluidic devices on glass substrate using wet etching technology. Instead of using expensive Pyrex glasses as substrates and depositing expensive metal or polysilicon/amorphous silicon as etch masks in conventional method, glass slide is used as substrate and a single-layer negative photoresist RFJ-220 is used as the etching mask. The etch rates, generation of defects, undercut ratio and surface roughness are studied. In order to achieve high etching depth and smooth surface, buffered oxide etching with hydrochloric acid as additive is proposed. By proper cleaning and long-time hard baking, the undercut ratio can approach to 1. An 110μm depth microchannel with smooth surface is achieved. This fabrication process leads to a considerable reduction of process steps, fabrication time and material consumption. With this technique, we successfully fabricated a microfluidic device, which is used in the capture of hepatoma cells HepG2.
SHS – Synthesis of Ceramic Composite Materials on the Base of Zirconium Compounds
Authors: Mansurov Zulkhair A. , Tantsereva I.V. , Tulepova A. , Karabalin A.N. , Vongai I.M.
Published: July 2011

Chemical processes of the condensed combustion in systems Al – ZrO2 – C and Al – ZrSiO4 – C, systems were studied, dependences of the properties of synthesis products on conditions were determined SHS.
The Effect of Carbon Doping on Electrochemical Properties of LiFePO4/C Powders Prepared by Spray Pyrolysis
Authors: Kodera Takayuki , Bi Dong Ying , Ogawa Daisuke , Ogihara Takashi
Published: July 2011

Spherical LiFePO4/C precursor powders were successfully prepared by spray pyrolysis. Various types of organic compounds such as glycolic acid, malic acid, citric acid, fructose and sucrose were used as carbon sources. X-ray diffraction analysis revealed that the olivine phase was obtained by calcining over 600 °C under an argon (95%)/hydrogen (5%) atmosphere. The particles exhibited a spherical morphology with approximately 1.5 μm. LiFePO4/C cathode derived from sucrose exhibited higher rechargeable capacity and cycle stability. The rechargeable capacity of LiFePO4/C cathode was approximately 154 mAh/g at 1 C. 90% of initial discharge capacity was maintained after 100 cycles.
Synthesis and Electrochemical Properties of Al Doped Lithium Manganate Powders by Spray Pyrolysis Using Carbonate Aqueous Solution
Authors: Hirose Shoji , Kodera Takayuki , Ogihara Takashi
Published: July 2011

Al doped LiMn2O4 powders were prepared by spray pyrolysis using the aqueous solution of manganese carbonate. The aqueous solution, in which manganese carbonate was uniformly dispersed by a surfactant, was used as the starting solution. Al2O3 nanopowders, Al(OH)3 and Al(NO3)3·9H2O were used as the doping agent of Al. A scanning electron microscope photograph showed that Al doped LiMn2O4 powders had spherical morphology with broad particle size distribution. X-ray diffraction revealed that crystal phase of all samples were good agreement with spinel phase. The rechargeable capacity of Al doped LiMn2O4 cathode was about 110 mAh/g at 1 C regardless of doping agent. 75% of initial discharge capacity was maintained after 100 cycles
Preparation and Thermoelectric Properties of TE Module by a Spark Plasma Sintering Method
Authors: Arai Koya , Akimoto Hiroyuki , Kineri Tohru , Iida Tsutomu , Nishio Keishi
Published: July 2011

NaCo2O4and 0.5at%-Sb doped Mg2Si have excellent thermoelectric properties. We tried to fabricate a thermoelectric module composed of these materials and using Ni plates as electrodes. The fine powder of NaCo2O4was prepared by metal-citric acid complex decomposition. 0.5at%-Sb doped Mg2Si bulk was ground to powder and sieved to a powder particle size of 75 micrometers or less. These powders were sintered using spark plasma sintering (SPS) to obtain a body of NaCo2O4and 0.5at%-Sb doped Mg2Si. These thermoelectric materials were connected to the Ni plates by using the SPS method. The whole process took a very short time (less than 2 min) and could be done at low temperature (below 873 K). The open-circuit voltagevalues were 82.7 mV, and the maxima,maximum output currentand maximum output power, for the single module were 212.4 mA and 6.65 mW at ΔT= 470 K.
Dielectric Properties of Nanograined BaTiO3 Ceramics Fabricated by Aerosol Deposition Method
Authors: Furuta Tsutomu , Hatta Saki , Kigoshi Yoichi , Hoshina Takuya , Takeda Hiroaki , Tsurumi Takaaki
Published: July 2011

Freestanding BaTiO3 ceramics films were fabricated using the aerosol deposition (AD) method and the size effect of nanograined BaTiO3 ceramics was demonstrated. Dense BaTiO3 thick film fabricated by the AD method was crystallized and detached from substrate by an annealing treatment at 600 °C, and then the grain size was controlled by a reannealing treatment at various temperatures. As a result, freestanding BaTiO3 thick films with various grain sizes from 24 to 170 nm were successfully obtained. Polarization–electric field (P–E) measurement revealed that BaTiO3 ceramics with grain sizes of more than 58 nm showed ferroelectricity, whereas BaTiO3 ceramics with an average grain size of 24 nm showed paraelectricity at room temperature. Dielectric measurement indicated that the permittivity decreased with decreasing grain size in the range of 170 to 24 nm.
Magnetic Properties of Epitaxial NiFe2O4 Thin Films Prepared Using Dynamic Aurora PLD in a Magnetic Field
Authors: Kubo Takayoshi , Sakamoto Naonori , Shinozaki Kazuo , Suzuki Hisao , Wakiya Naoki
Published: July 2011

This study examined effects of applying a magnetic field (up to 2 kG) on the magnetic properties of epitaxial NiFe2O4(NF) thin films during deposition. The NF films were deposited on Y0.15Zr0.85O1.93 (YSZ) buffered Si (001) substrates using pulsed laser deposition (PLD). Although application of magnetic field during deposition affected neither the crystal structure nor orientation of the NF thin films, it improved magnetic properties. The saturation magnetization (Ms) of NF thin films deposited at 500°C and 600°C without application of a magnetic field was as low as 40 emu/g. However, that of NF deposited under magnetic field of 2 kG got to bulk Ms (50.3 emu/g). The TEM observation results revealed that the anti-phase boundary (APB) density decreased by application of the magnetic field during deposition. Results show that magnetic properties of NF thin films are controllable using the magnetic field during deposition.
Influence of Al2O3 Addition on the Temperature Dependence of Initial Permeability of NiCuZn Ferrites
Authors: Takane Shin , Umeda Hidenobu , Aoki Takuya , Murase Taku
Published: July 2011

The effect of Al2O3 addition on the temperature dependence of the initial permeability and microstructure of NiCuZn ferrites is investigated. The temperature dependence of initial permeability decreases with an increase in Al2O3 addition. EPMA analysis reveals that Al2O3 dissolves in the NiCuZn ferrite grains but is not uniformly dispersed. Separation of the initial permeability into two components, one due to spin rotation and the other due to domain wall motion, reveals that with an increase in the Al2O3 addition, the temperature dependence of the domain wall motion component decreases, while that of the spin rotation component shows no notable change. This indicates that the decrease in the temperature dependence of initial permeability may be attributed to the influence of Al2O3 on the domain wall motion.
Composite Electromagnetic Wave Absorber Made of Ni-Zn Ferrite Particles Dispersed and Isolated in an SiO2 Medium
Authors: Sakai Kenji , Guan Yang , Sato Yuuki , Yoshikado Shinzo
Published: July 2011

In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μr*, the relative complex permittivity εr*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO2. When ferrite particles were dispersed and isolated in an SiO2 medium, the frequency dependence of μr* was different from that for a composite made of SiO2 particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO2 was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO2 particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO2 medium.
Effect of Sb Addition on ZnO Grain Growth and Electrical Characteristics of Bi–Co–Mn–Ba-Added ZnO Varistors
Authors: Fukumori Ai , Watanabe Takayuki , Sato Yuuki , Yoshikado Shinzo
Published: July 2011

With the goal of fabricating varistors with low breakdown voltages (varistor voltages), the effect of adding Sb to Bi-Co-Mn-Ba-added ZnO varistors on the ZnO grain size was investigated. To obtain a uniform ZnO grain size without reducing the grain size, a small amount (e.g., 0.01 mol%) of Sb was added as an additive. This addition suppresses the variation in the ZnO grain size without reducing the grain size. It also improved the resistance to electrical degradation because compounds of Ba and Mn were not formed.
Synthesis of AnataseTiO2 Having High Specific Surface Area from a Gel Precursor
Authors: Fukushi Keiko , Nakajima Sae , Uematsu Kazuyoshi , Ishigaki Tadashi , Toda Kenji , Sato Mineo
Published: July 2011

Anatase TiO2 having high temperature stability and specific surface area was synthesized using a gel precursor in very mild conditions. The precursor gel was obtained by dialysis treatment of Na16Ti10O28–HNO3 solution. The samples were characterized by X-ray diffraction analysis, transmission electron microscopy, Brunner–Emmett–Teller method for specific surface area measurements, and thermogravimetric analysis.
Ferroelectric Domain Structures and Piezoelectric Properties of Pb(Zr,Ti)O3 Ceramics
Authors: Iwaji Naoki , Sakaki Chiharu , Wada Nobuyuki , Takagi Hiroshi , Mori Shigeo
Published: July 2011

We investigated domain structures in Pb(Zr,Ti)O3(PZT) ceramics whose composition lies on the morphotropic phase boundary (MPB) using transmission electron microscopy (TEM) and evaluated the piezoelectric properties of PZT. We found that monoclinic nanosized domains (nanodomains), which form in tetragonal domains, strongly correlated with the piezoelectric properties of PZT. The degree of formation of nanodomains depends on the grain composition. Thus, controlling the homogeneity of grain composition in the ceramics is crucial for optimizing the piezoelectric properties of PZT.
Relaxor Characteristics of BaTiO3-Bi(Mg1/2Ti1/2)O3 Ceramics
Authors: Fujii Ichiro , Yamato Keisuke , Shimada Mikio , Hayashi Jumpei , Yabuta Hisato , Kubota Makoto , Fukui Tetsuro , Nakashima Kouichi , Kumada Nobuhiro , Wada Satoshi
Published: July 2011

Relaxor characteristics of (1-x)BaTiO3-xBi(Mg1/2Ti1/2)O3 (x=0.1–0.7) ceramics were investigated. Microstructural observation showed second phases and no domain structure for the sample with x=0.6. Deviation from the Curie-Weiss behavior was found in temperature dependence of the inverse permittivity for all the samples. The stronger dielectric dispersion was found for x=0.6 and 0.7 and they were described by the Vogel-Fulcher relationship. The temperature dependence of the remanent polarization and coercive field indicated the freezing temperature was 100~150°C for x=0.6. The strong dielectric dispersion of x=0.6 is believed to be induced by the structural disorder due to the second phases.
Preparation and Characterization of Grain-Oriented Barium Titanate Ceramics Using Electrophoresis Deposition Method under a High Magnetic Field
Authors: Kita Tatsuya , Kondo Shuhei , Takei Takahiro , Kumada Nobuhiro , Nakashima Kouichi , Fujii Ichiro , Wada Satoshi , Suzuki Tohru , Uchikoshi Tetsuo , Sakka Yoshio , Miwa Yasunari , Kawada Shinichiro , Kimura Masahiko
Published: July 2011

Grain-oriented Barium titanate (BaTiO3) ceramics were prepared using an electrophoresis deposition (EPD) method under high magnetic field of 12 T and sintering at 1350 °C. It was found that BT03 and BTKK nanoparticles were necessary to synthesize the grain-oriented BT ceramics. The grain orientation was correlated with particles size and c/a ratio of lattice constants. The reason why the grain-oriented BT ceramics using the BT03 and BTKK were prepared was having the large values of the particles size and the c/a ration of lattice constants.
Chemical Compositions and Crystallization Behavior of BaO-TiO2-GeO2 Glass
Authors: Yamazaki Yoshiki , Takahashi Yoshihiro , Ihara Rie , Fujiwara Takumi
Published: July 2011

We prepared glasses in 30BaO-(15+x)TiO2-(55–x)GeO2 composition (x=0, 10, 20, 35) and examined their crystallization behavior. Relation of crystallizing-phase to optical transparency in the resulting crystallized sample was also considered. Although the glass samples with x=0-20, which precipitate fresnoite-type Ba2TiGe2O8 as main phase, lost transparency after crystallization, the glass with x=30, which precipitates BaTi4O9 phase, kept good transparency. Dependence of transparency on the x is also discussed.
The Kelvin Probe Force Microscopy Measurement of Degraded Multilayer Ceramic Capacitors with Ni Inner Electrode
Authors: Okamoto Takafumi , Inoue Noriyuki , Kitagawa Shuji , Niimi Hideaki , Ando Akira , Takagi Hiroshi
Published: July 2011

Electric potential mapping of degraded dielectric layers of multilayer ceramic capacitors (MLCCs) was carried out using Kelvin probe force microscopy in order to clarify their degradation mechanism under conditions of an accelerated lifetime test condition. In the cross sections of the degraded and as-prepared dielectric layers, a significant electric field concentration was found in the vicinity of the anode of the degraded dielectric layer, in contrast to a homogeneous concentration found throughout layers of the samples before the accelerated lifetime test.
Piezoelectric Properties of Perovskite-Type Lead-Free Piezoelectric Ceramics under Large Amplitude Continuous Driving
Authors: Sato Shigeki , Noumura Yoji , Hiruma Yuji , Nagata Hajime , Takenaka Tadashi
Published: July 2011

High-power piezoelectric characteristics of (Bi1/2Na1/2)TiO3(BNT)- and KNbO3(KN)-based ceramics at continuous driving were investigated. The selected compositions of BNT- and KN-based ceramics were 0.88(Bi1/2Na1/2)TiO3-0.04(Bi1/2Li1/2)TiO3-0.08(Bi1/2K1/2)TiO3doped with 0.6 wt% MnCO3[BNLKT4-8Mn0.6] and KNbO3-MnCO30.8 wt% [KN-Mn0.8] ceramics. It was found that the vibration velocityv0-Pof BNLKT4-8Mn0.6 and KN-Mn0.8 ceramics linearly increased up to approximately 0.8 and 0.6 m/s, respectively. The temperature increases of BNLKT4-8Mn0.6 and KN-Mn0.8 ceramics were approximately 5°C under continuous driving at the vibration velocity of 0.6 m/s.
Magnetic Cluster Expansion Study of Chromium Precipitates in Fe-Cr Alloys
Authors: Lavrentiev Mikhail Yu. , Nguyen Manh Duc , Dudarev Sergei L.
Published: July 2011

Magnetic Cluster Expansion method is applied to the investigation of magnetic properties of Fe-Cr alloys treated as a function of Cr content, the spatial distribution of Cr atoms, and temperature. Random Fe-Cr alloys and Cr clusters formed in concentrated alloys are analyzed. We find significant differences between the types of magnetic order characterizing those systems, which are reflected in the characteristic variation of the temperature-dependent magnetic specific heat. Simulations show that in random Fe-Cr alloys and in alloys containing Cr clusters, the interplay between antiferromagnetic interactions characterizing Fe-Cr and Cr-Cr atom pairs gives rise to unusual patterns of finite temperature magnetic ordering.
Surface Segregation Maps Derived from Tight-Binding Ising Model
Authors: Roussel Jean Marc , Tréglia Guy , Legrand Bernard
Published: July 2011

Surface segregation in transition metals can be analysed within a generalised Ising model,derived from Tight-Binding electronic structure calculations, which identiﬁes three driving forces:the difference in surface energy and atomic volume between the two components and their tendencyto order or phase separate in the bulk. Using this ”three effects” rule, we present here general mapswhich predict the tendency of the solute metal element to segregate (or not) at the surface of a metalmatrix, for the 702 solute/matrix systems that can be formed with transition metal elements. Ourpredictions compare fairly well to the existing ab initio calculations and experimental data availableon these systems. The few exceptions, which mainly concern given matrix elements are discussed indetails.
Simulations of Decomposition Kinetics of Fe-Cr Solid Solutions during Thermal Aging
Authors: Martinez Enrique , Fu Chu Chun , Levesque Maximilien , Nastar Maylise , Soisson Frederic
Published: July 2011

The decomposition of Fe-Cr solid solutions during thermal aging is modeled by Atomistic Kinetic Monte Carlo (AKMC) simulations, using a rigid lattice approximation with composition dependant pair interactions that can reproduce the change of sign of the mixing energy with the alloy composition. The interactions are fitted on ab initio mixing energies and on the experimental phase diagram, as well as on the migration barriers in iron and chromium rich phases. Simulated kinetics is compared with 3D atom probe and neutron scattering experiments.
Investigation of Spinodal Decomposition in Fe-Cr Alloys: CALPHAD Modeling and Phase Field Simulation
Authors: Xiong Wei , Grönhagen Klara Asp , Ågren John , Selleby Malin , Odqvist Joakim , Chen Qing
Published: July 2011

This work is dedicated to simulate the spinodal decomposition of Fe-Cr bcc (body centered cubic) alloys using the phase field method coupled with CALPHAD modeling. Thermodynamic descriptions have been revised after a comprehensive review of information on the Fe-Cr system. The present work demonstrates that it is impossible to reconcile the ab initio enthalpy of mixing at the ground state with the experimental one at 1529 K using the state-of-the-art CALPHAD models. While the phase field simulation results show typical microstructure of spinodal decomposition, large differences have been found on kinetics among experimental results and simulations using different thermodynamic inputs. It was found that magnetism plays a key role on the description of Gibbs energy and mobility which are the inputs to phase field simulation. This work calls for an accurate determination of the atomic mobility data at low temperatures.
Phase-Field Modelling of Spinodal Decomposition during Ageing and Heating
Authors: Lecoq Nicolas , Lacaze Jacques , Danoix Frédéric , Patte Renaud
Published: July 2011

Despite the tremendous success of phase-field (PF) modelling in predicting many of the experimentally observed microstructures in solids, additional progress is required in order to apply it to predict microstructure evolution in real alloy systems. One way to achieve this is to couple thermodynamic and kinetic databases with PF model. In this work, we present phase-field simulations of spinodal decomposition in Fe-Cr alloy during thermal ageing and anisothermal heating. In the PF method, the local free energy is directly constructed using the CALPHAD method. During isothermal ageing, the morphology of decomposed phases consisted in an interconnected irregular shape for short ageing times, and a further ageing caused the change to a droplet like shape of the decomposed Cr-rich phase. The influence of heating rate on phase transformations is then simulated and compared with experimental results obtained by differential thermal analysis, carried out with heating rates in the range 0.5 °C.min-1 to 15 °C.min-1. The simulation results show that heating rate strongly influences the microstructure morphology.
Modeling of Growth and Dissolution of Grain Boundary Cementite in Vacuum Carburizing Process
Authors: Ikehata Hideaki , Tanaka Kouji , Takamiya Hiroyuki , Mizuno Hiroyuki
Published: July 2011

In order to predict microstructures during vacuum carburizing, the model which simulates not only the carbon(C) diffusion but also growth/dissolution of cementite(θ) is required. For development of a new model we applied vacuum carburizing to low alloy steels and analyzed the distribution of C and θ by GD-OES and image analysis of microstructures. The C in retained austenite(γ) phase after carburizing was also measured by lattice constants obtained from XRD. We also simulated multi-component diffusion with γ matrix and θ layer to analyze a velocity of the moving interface. The new carburizing model was proposed based on the findings, which suggest that C in γ phase at the carburizing surface is supersaturated and corresponds to C concentration for metastable equilibrium condition to graphite. The growth and dissolution of the θ follow a square root of time with the coefficients controlled by diffusion of Si in γ and Cr in θ respectively. The required parameters such as diffusivity coefficients are obtained by the CALPHAD method. The calculated C distributions and volume fractions of θ represent the experimental results.
A Simple Model of Dissipative Processes in Ferroelastics
Authors: Paidarova Ivana , Paidar Vaclav , Durand Philippe
Published: July 2011

A simple model of dissipative processes originally developed for magnetic materials is extended to ferroelastic materials, in particular to shape memory alloys that display a pseudoelastic behaviour. The model based on non-equilibrium dissipative dynamics leads to kinetic equations. The characteristic feature of the model is a three-level response to the acting force field describing the transition between two opposite states of saturation through the intermediate parent structural state.
Analytical Modeling of Austenite Growth and Phase Evolution during Reverse Transformation from Pearlite in High Carbon Steels
Authors: Li Zhao Dong , Yang Zhi Gang , Pan Tao , Xia Zhi Xin , Zhang Chi
Published: July 2011

Based on an analytical one-dimensional model, austenite growth into pearlite lamella and the corresponding phase evolution during isothermal reverse transformation to austenite at 1000-1183 K in Fe-C fully pearlitic steels containing 0.6-1.0 mass% C (in the austenite single phase field of Fe-C phase diagram) were simulated. It was found that the rate of austenite growth into ferrite increases faster with increasing reversion temperature than into cementite. Three types of phase evolution dependent on reversion temperature and carbon content were classified: 1) cementite rather than ferrite disappears first; 2) ferrite and cementite simultaneously disappear; 3) ferrite rather than cementite disappears first. The type of phase evolution in a hypoeutectoid steel heated above its Ae3 temperature possibly changes in the order of 1), 2) and 3) as the reversion temperature increases. For eutectoid and hypereutectoid steels, the phase evolution during isothermal reversion always obeys the type 3).
In Situ Synchrotron X-Ray Diffraction Investigation of the Fast Recovery of Microstructure during Electropulse Treatment of Heavily Cold Drawn Nanocrystalline Ni-Ti Wires
Authors: Malard Benoît , Pilch Jan , Sittner Petr , Delville Remi , Curfs Caroline
Published: July 2011

Recovery processes responsible for evolution of microstructures in 0.1mm thin cold-drawn Ni-Ti shape memory alloy wire heat treated by DC electric pulse were investigated by combination of in-situ tensile stress - strain, electrical resistance and X-ray diffraction measurements. The X-ray data were used to obtain direct experimental information on the evolution of the phase fractions, internal strain and defects in the microstructure evolving through activation of a sequence of recovery processes during the short time electropulse treatment. It is shown that superelastic functional properties of the treated Ni-Ti wire can be precisely set by controlling the progress of the recovery processes by prescribing the time evolution of temperature T(t) and tensile stress s(t) (displacement control) in the treated wire.
Application of Advanced Experimental Techniques for the Microstructural Characterization of Nanobainitic Steels
Authors: Timokhina Ilana , Beladi Hossein , Xiong Xiang Yuan , Adachi Yoshitaka , Hodgson Peter
Published: July 2011

A 0.79C-1.5Si-1.98Mn-0.98Cr-0.24Mo-1.06Al-1.58Co (wt%) steel was isothermally heat treated at 350°C bainitic transformation temperature for 1 day to form fully bainitic structure with nano-layers of bainitic ferrite and retained austenite, while a 0.26C-1.96Si-2Mn-0.31Mo (wt%) steel was subjected to a successive isothermal heat treatment at 700°C for 300 min followed by 350°C for 120 min to form a hybrid microstructure consisting of ductile ferrite and fine scale bainite. The dislocation density and morphology of bainitic ferrite, and retained austenite characteristics such as size, and volume fraction were studied using Transmission Electron Microscopy. It was found that bainitic ferrite has high dislocation density for both steels. The retained austenite characteristics and bainite morphology were affected by composition of steels. Atom Probe Tomography (APT) has the high spatial resolution required for accurate determination of the carbon content of the bainitic ferrite and retained austenite, the solute distribution between these phases and calculation of the local composition of fine clusters and particles that allows to provide detailed insight into the bainite transformation of the steels. The carbon content of bainitic ferrite in both steels was found to be higher compared to the para-equilibrium level of carbon in ferrite. APT also revealed the presence of fine C-rich clusters and Fe-C carbides in bainitic ferrite of both steels.
Microstructure Characteristics of the Reaction Product Region Formed due to the High Temperature Contact of Molten Aluminium and ZnO Single Crystal
Authors: Wojewoda-Budka Joanna , Sobczak Natalia , Morgiel Jerzy , Nowak Rafal
Published: July 2011

Interface reactions between liquid aluminium and ZnO single crystal substrates of <1-100> orientation (at 1273 K under vacuum) were examined using scanning and transmission electron microscopy techniques. The substrates were subjected to the “pushing drop” tests when liquid is deposited from the capillary on the substrate surface and then, after appropriate contact time, it is pushed away. After short time of interaction with <1-100>ZnO substrate, three phases were detected: α-Al2O3, the alumina of unknown type and ZnAl2O4 spinel formed due to the solid state reaction between Al2O3 and ZnO.
Beta Titanium Alloys with Very High Ductility Induced by Complex Deformation Mechanisms: a New Material Perspective for Coronary Stent Applications
Authors: Sun Fan , Gloriant T. , Vermaut Philippe , Jacques Pascal , Prima Frédéric
Published: July 2011

The increased use of metallic biomaterials in contact with blood e.g. for application as coronary stents is steadily resulting in the development of new biomaterials. Conventional bare-metal stents made by stainless steel were reported on adverse reactions against human body and are gradually replaced by coated stainless steel. The new generation of stent requires fundamental improvements at the materials point of view. Although titanium and classical Ti-alloys display superior biocompatibility compared to other metallic materials (stainless steels, Co-Cr), the major drawback of their relatively low ductility (typically 15%-25% of elongation) seriously limits their applications as cardiovascular stents, where large ductility is basically required during the stent deployment procedure and long-term service. In this paper, new titanium alloys with high ductility, a binary Ti-12Mo (wt%) and a ternary Ti-9Mo-6W (wt%) were designed by using a chemical formulation strategy based on the electronic design method called “the d-electron alloy design method”. Both alloys were synthesized and thermo-mechanically treated into beta-metastable state. In tensile tests, both alloys exhibited outstanding ductility of 43% and 46% in total elongation at room temperature, which is almost two times greater than the normal value shown with classical titanium alloys. Optical microscopy and detailed TEM observations on the deformed specimens revealed a complex deformation mechanism, involving {332}<113> mechanical twinning, stress induced plate shaped omega phase and stress induced martensitic (SIM) transformation β-α’’.
Full Characterization of a Tool Steel Texture and Microstructure by Using Fast Simultaneous EBSD/EDS Measurements
Authors: Goran Daniel
Published: July 2011

The study presents the latest developments in terms of speed and integration of the electron backscatter diffraction (EBSD) and energy dispersive spectroscopy (EDS) techniques. The microstructural features and texture of a commercially available tool steel have been analyzed by simultaneous EBSD/EDS measurements. The EDS data was used for confirming/correcting the EBSD results as well as for detecting the presence of ultrafine carbide precipitates. The results indicate the formation of two different types of carbides inside a ferritic matrix. Most of the matrix was found to be composed of fully recrystallized grains with average diameters around 10 microns. Zones characterized by finer submicron scale grains could also be identified locally as well as grains containing networks of subgrain boundaries. This study demonstrates that the combination of the two techniques, i.e. EBSD and EDS, results in a powerful tool for a fast, reliable and complete characterization of multiphase materials.
Prediction and Exploitation of Transformation Texture
Authors: Bhadeshia Harshad K.D.H.
Published: July 2011

There is now a great deal known about the atomic mechanisms of solid–state phasetransformations, and this knowledge can be exploited to determine the distribution of crystalorientations. It is possible to estimate accurately, the crystallographic texture, transformationstrains and details of the microstructure, particularly in the context of steels. The concepts havenow been applied to design metallic alloys which compensate automatically for the residualstresses which develop in engineering components when they are cooled heterogeneously fromelevated temperatures. Such materials are now in commercial use and represent an innovationresulting directly from phase transformation theory.
Elastic and Dielectric Measurements of the Structural Transformations in the Ferroelectric Perovskite (Na1/2Bi1/2)1-XBaXTiO3
Authors: Cordero Francesco , Trequattrini Francesco , Craciun Floriana , Mercadelli Elisa , Galassi Carmen
Published: July 2011

The perovskite (Na1/2Bi1/2)TiO3 (NBT) undergoes a series of structural and polar transitions starting from the high temperature paraelectric phase: tetragonal paraelectric, tetragonal antiferroelectric, rhombohedral antiferroelectric and finally rhombohedral ferroelectric, according to neutron diffraction and dielectric spectroscopy. In solid solution with BaTiO3 (BT) the ferroelectric phase changes from rhombohedral to tetragonal, at the so-called morphotropic phase boundary, and the phases at higher temperature become ill-defined, also because of the large lattice disorder induced by the coexistence of differently charged cations in the same sublattice. Combined dielectric and anelastic spectroscopy measurements are presented, which clarify some issues related to the phase transitions in NBT-BT. The influence of Ba substitution on the tetragonal antiferroelectric phase is determined for the first time, and the possibility that a monoclinic phase, although with very short coherence length, exists near the morphotropic phase boundary is discussed in view of a large maximum of the elastic compliance.
Influence of Temperature on Phase Transformation and Deformation Mechanisms of Cast CrMnNi-TRIP/TWIP Steel
Authors: Martin Stefan , Wolf Steffen , Martin Ulrich , Krüger Lutz
Published: July 2011

At different temperatures ranging from ‑60°C to 200°C a cast CrMnNi-TRIP steel was deformed by uniaxial tension. The resulting microstructure was investigated using XRD, EBSD and LOM. The correlation of the phase transformation with the deformation temperature was examined. Depending on temperature, a transition in the deformation mechanisms was observed. Starting with the generation of deformation bands, accompanied by martensitic phase transformation, followed by twinning, the deformation mechanism turned to conventional dislocation glide with raising temperature. Between -60°C and 20°C the TRIP (TRansformation Induced Plasticity)-effect is the dominating deformation mechanism, whereas between 20°C and 200°C the TWIP (Twinning induced plasticity) effect is observed. The geometrical arrangement of martensite within the microstructure is considered within this study. The amount of α'-martensite is mainly responsible for the hardening rate and the resulting mechanical properties.
Modelisation of Precipitation in Concentrated Alloys
Authors: Lépinoux Joel , Sigli Christophe
Published: July 2011

The modelling of precipitation is fairly trivial in very dilute binary alloys but remains a challenge in concentrated alloys. By comparing Kinetic Monte Carlo simulations and Cluster Dynamics calculations the difficulties are identified and solutions to link these two techniques are proposed to build an efficient multi-scale procedure.
Tweed and Nanoscale Cubic / Tetragonal Phase Mixtures in Decomposing Alloys: the Pseudospinodal Concept
Authors: Soffa William A. , Cantando Elizabeth D. , Shugart Kathleen N.
Published: July 2011

In this paper the concept of pseudospinodal decomposition introduced by Ni and Khachaturyan [1] as a symmetry-lifting continuous phase separation, which can produce coherent nanoscale morphologies ranging from nanowires to nanolaminates, is reviewed. The term spinodal arises from the continuous change in the compositions of emerging cubic and tetragonal phases resulting in quasi-periodic microstructures stemming from the attendant transformation strain and surface energy anisotropies. It is argued here that important features of the pseudospinodal mechanism can be understood in terms of conventional classical and non-classical nucleation and that the behaviour is more general than the cubic → tetragonal transformation context articulated by its authors. Also, the possible relevance of the pseudospinodal mechanism to studies of decomposition of hypostoichiometric Fe-Pd alloys will be presented.
Phase Transformation and Shape Memory Effect in Ru-Based High Temperature Shape Memory Alloys
Authors: Manzoni Anna , Chastaing Karine , Denquin Anne , Vermaut Philippe , Portier Richard
Published: July 2011

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. For both systems, it is interesting to find a way to control the transformation temperatures while keeping the shape memory effect. One way to change the transformation temperatures is to change the composition in the binary alloys; another is to add a ternary element like Fe. The eight investigated alloys show two different space groups at room temperature. The monoclinic alloys undergo two successive displacive transformations on cooling, starting from the high temperature β phase field: β (B2) à β’ (tetragonal) à β’’ (monoclinic). The tetragonal alloys exhibit a single transition from cubic to tetragonal. A multiple twinned microstructure can be found in all alloys. Transformation temperatures decrease with lower Ru content and with the addition of Fe. The β’ à β transformation seems to be the main responsible for the SME. Compression tests performed in the martensitic phase give a quantitative result of the shape memory effect. In the binary alloys, the SME decreases with decreasing Ru content, which is in accordance with the evolution of the lattice parameters of martensites. A lower SME in the ternary alloys can also be linked to the lattice parameters and seems to be quite reliable to predict the evolution of the shape memory effect.
Pinning of Austenite Grain Boundaries by Mixed AlN and Nb(C,N) Precipitates
Authors: Kundu Amrita , Davis Claire L. , Strangwood Martin
Published: July 2011

The use of Nb(C,N) to pin prior austenite grains during thermomechanical processing can give rise to bimodal structures linked to Nb segregation and subsequent variation in precipitate distribution and stability on reheating and deformation. The segregation tendency of Al is much less compared with Nb so that AlN may provide grain boundary pinning in regions of reduced Nb(C,N) volume fraction and stability. Quantification of precipitate and prior austenite grain size distributions after reheating has confirmed the governing mechanisms of precipitate dissolution / coarsening whilst identifying grain boundary pinning by AlN at temperature below 1125 °C, but controlled by Nb(C,N) at higher temperatures.
Evolution of Twin-Related Variants of α Phase in a Ti-V-Cu Alloy
Authors: Ng Hoi Pang , Bettles Colleen J. , Muddle Barry C.
Published: July 2011

The precipitation of a-phase has been investigated in a concentrated b-alloy of the Ti-V-Cu system. a-precipitates in geometrically coupled forms were developed in the alloy when subject to isothermal ageing at 500°C. High-resolution transmission electron microscopy (HRTEM) revealed that a-phase embryos tend to nucleate in a symmetrical manner directly from an early-stage solute-partitioned diffusional product. The a-precipitates so developed constitute twin-related variants characterized by a twin plane lying on one of the {0111}a planes. The results are discussed with respect to the role of Cu on the formation of heterogeneous nucleation sites for a-phase.
Characterization of Precipitation Sequences in Superaustenitic Stainless Steels
Authors: Koutsoukis T. , Redjaïmia Abdelkrim , Fourlaris G.
Published: July 2011

Superaustenitic stainless steels exhibit excellent corrosion resistance, at a wide variety of exposure temperatures, especially in chloride containing environments, coupled with desirable mechanical properties. Previous studies have shown that these steels are prone to precipitation of secondary phases, such as sigma phase (σ), chi phase (χ), Laves-phase, carbides, nitrides or secondary austenite, when exposed at elevated temperatures, directly affecting their mechanical properties and corrosion behaviour. A detailed study of the effect of isothermal ageing on the microstructure of S32654 (Fe-24Cr-21Ni-7Mo-0.5N-0.013C) and S31254 (Fe-20Cr-18Ni-6Mo-0.2N-0.012C) superaustenitic stainless steels was carried out. Samples were aged within the temperature range of 650 οC to 950 οC for times up to 3000 h. Following ageing, precipitation of secondary phases was clearly observed with precipitates varying in volume fraction, size, shape and spatial distribution. Several secondary phases were identified via transmission electron microscopy (TEM) and electron diffraction (ED). The orientation relationships between the austenitic matrix and the secondary phases were identified. Interaction and also phase transformation among different types of precipitates, such as between precipitates and the austenitic matrix were observed and an attempt of understanding these phase transformations was carried out.