bluuebunny/crossref_metadata_2025 huggingface dataset:
Spark Plasma Sintering Nd2Fe14B/α-Fe Bulk Exchange-Spring Magnets
Authors: Yue Ming , Tian Meng , Liu Wei Qiang , Zhang Jiu Xing
Published: March 2009

The Nd2Fe14B/α-Fe bulk exchange-spring magnets have been prepared by spark plasma sintering melt spun Nd9.8Dy0. 4Fe78.4Co5.6B5.8 flakes under different temperatures and pressures. It was found that higher sintering temperature improved the densification of the magnets, while deteriorated their magnetic properties simultaneously. An increased compressive pressure can restrain the grain growth remarkably and then leads to better magnetic properties and higher density for the magnet at same sintering temperature. XRD analysis showed that with the increase of sintering pressure, some peaks indicating c-axis texture such as (006) and (105) became dominant. As a result, the bulk magnet exhibited higher remanence and maximum energy product than starting powders.
Influence of Cooling Rate on Microstructure of NdFeB Strip Casting Flakes
Authors: Guo Bing Lin , Li Bo , Wang Dongling , Yu Xiaojun , Hu Ji Fan
Published: March 2009

In this paper, flakes of NdFeB cast alloys were prepared by using the strip casting
technique. Microstructure and composition of phases in NdFeB SC flakes were studied by SEM and energy spectra. Especially, the influences of cooling rate on the microstructure of SC flakes were discussed, helping us to master strip casting technology. The results show that the cooling rate plays an important role in obtaining the perfect microstructure of SC flakes, which thickness is supposed not less than 0.32mm in these studies.
Magnetic Properties of Ni-Zn Ferrite Ceramics Prepared from the Blend of Powders
Authors: Zhong Haisheng , Li Qiang , Zhong Zhifeng , Cheng Ming
Published: March 2009

Ni-Zn ferrite ceramics were prepared from the blend of nano-sized powders and
ultra-fine particles at the relative low sintering temperature (≤1200°C). The microstructure of the as-sintered samples characterized by SEM indicated that this process obstructed abnormal grain growth which often appeared in the Ni-Zn ferrite ceramics sintered from the nano-sized powders. The result of VSM measurements showed that the ratio of nano-sized powders to ultra-fine particles effected the initial permeability (μi) of the as-sintered samples. Optimum initial permeability can be obtained by adjusting the ratio as 1:1.
Magnetoresistive Switch Effect and Its Application to Magnetic Field Sensors
Authors: Sun Zhi-gang , Mizuguchi Masaki , Akinaga Hiroyuki
Published: March 2009

Magnetoresistive switch effect (MRS effect) devices containing two gold (Au) electrodes with a gap less than 2 µm were successfully fabricated on semi-insulting GaAs substrates by wet etching method. Huge MRS effect was observed. Magnetoresistance (MR) ratio reached 1,000,000% under the magnetic filed of 1.5 T when the devices were operated just above the threshold voltage. The magnetic field sensitivity at small magnetic fields was significantly improved. MR ratio of more than 1000% was achieved at 0.03 T. A relative high MR ratio of 100,000% under the magnetic filed of 1.5 T was also achieved when the devices operating before the threshold voltage.
Martensitic Transition and Magnetic Field-Induced Strains in Melt-Spun Ni-Mn-Ga Ribbons
Authors: Zhao W.R. , Li Jian Liang , Qi Yan , Wang Xin Lin
Published: March 2009

The characteristics of microstructures, martensitic transition, and magnetic field- induced strains of melt-spun ribbons are reviewed. The preferential alignment of crystal grains in the spun ribbons depends not only on the composition, but also on the spinning velocity. The increase of spinning velocity decreases the temperature of martensitic transition and decreases the enthalpy change. The anisotropies and retardance of field-induced strains was discussed, especially for the influence of the texture and annealing of the ribbons.
Chemical Synthesis of Magnetic Fe3O4 Nanoparticles
Authors: Yang Rui Feng , Lv Yu Zhen , Zhang Yahui , Liu Chen Min , Guo Lin
Published: March 2009

Fe3O4 nanoparticles were simply prepared by a wet chemical solution method. In this method, poly (N-vinyl-2-pyrrolidone) (PVP) was used as surface modified reagent to control the shape of the product. Transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) were used to characterize the asprepared Fe3O4 nanoparticles. Furthermore, the magnetic properties of the sample were investigated by a VSM (vibrating sample magnetometer) technique.
Effect of Nitrogen on Mechanical Properties of Porous Titanium Compacts Prepared by Powder Sintering
Authors: Nomura Naoyuki , Oh Ik Hyun , Hanada Shuji , Kanehira Masafumi , Sasaki Keiichi , Chiba Akihiko
Published: March 2009

Nitrogen-doped and -undoped Ti powders were obtained by Plasma Rotating Electrode Process (PREP) in an Ar atmosphere using Ar-2 vol.%N2 and pure Ar, respectively, for plasma flame. Auger electron spectroscopy (AES) revealed that nitrogen is enriched at the surface of nitrogen-doped Ti powder and decreases along with the depth direction. Microstructure of a compact prepared by hot pressing the nitrogen-doped Ti powder shows a shell structure. The outer area is considered to form by the diffusion of nitrogen. This microstructure disappears after annealing at 1373 K for 3.6 ks. It is found that the compressive yield strength of porous Ti compacts can be improved by introducing nitrogen in Ti powder and is superior to that of human cortical bone.
Study on Adhesion and Biocompatibility of Copolymer of MMA-BMA-MAA for Coronary Stents Coatings
Authors: Tan Lili , Yang Ke , Zhang Bing Chun , Liang Yong
Published: March 2009

Implantation of drug releasing coronary stents has been developed as an useful method for prevention of the restenosis in blood vessels. Copolymers of methyl methacrylate (MMA), butyl methacrylate (BMA) and methacrylic acid (MAA) were prepared as the coating polymer for drug releasing stent. The adhesion of the polymer with metal substrate and the biocompatibility were studied. Effect of the polymer composition on the adhesion between polymer coatings and metal substrate, as well as the effect of the polymer purification method on biocompatibility of the polymer, was studied. The results showed that the copolymer coating has good dry and wet adhesion properties, which can be improved by control of the polymer compositions. Biocompatibility of the prepared copolymer comes within the permission limit.
Study on the Subsonic Thermal Sprayed Ti/Bioglass Composite Coatings on Titanium Alloy
Authors: Li Mu Qin , Shang Da Shan , Ma Chen , Yang Shi Qin
Published: March 2009

Ti/bioglass composite coatings on titanium alloy were prepared by a subsonic thermal spraying technology. Mixtures of titanium and bioglass powders with different proportions were used as feedstock. The effect of soaking of bioglass on the bond strength of between coatings and substrate was discussed. The bond strength and residual stress were investigated. The morphology was observed using scanning electron microscopy (SEM). The results showed that TiO2, CaTi4(PO4)6, CaTiO3, NaTi2(PO4)3 formed during thermal spraying process and the residual stress in the coatings was in compressive state. After the coatings were heat-treated, soaking of bioglass made some particles achieve metallurgical bond. Furthermore, new bioglass was formed and the compressive stress was increased. The phenomenon of bioglass healing up the cracks in the heat-treated coatings was observed through SEM, which reduced the porosity of the interface layer resulting in the significant increase of the bond strength.
Metal-Complex Hydrides for Hydrogen-Storage Application
Authors: Gou Xing Long , Xu Li Na , Li Wei Yang , Chen Jun , Xu Qiang
Published: March 2009

Metal-complex hydrides Li3AlH6 and V-doped Li3AlH6 nanoparticles were synthesized by solid reactions of LiH and LiAlH4 in the absence and in the presence of VCl3, respectively. X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer- Emmett-Teller sorption, thermogravimetry and differential thermal analysis have been used to investigate the phase composition, microstructure and surface properties. Not only the nanocrystalline Li3AlH6, but also the coexisting catalyst with “valence-transfer” state can influence the dehydrogenation kinetics. The extension of the catalytic mechanism is attractive for reversible hydrogen storage of the alanate system.
Synthesis of Composite Metal Hydride Alloy of A2B and AB2 Type by Mechanical Alloying and Spark Plasma Sintering
Authors: Suk Nam Young , Lee Kyung Sub
Published: March 2009

The effects of Ca addition on the microstructure and mechanical properties of AZ91
magnesium alloy have been investigated. The main changes in microstructure caused by Ca addition were the grain refinement in the as-cast alloys and the formation of new Al2Ca phase along the grain boundaries. The tensile strength and elongation of the AZ91 magnesium alloy were improved by small addition of Ca due to grain refinement and replacement of Mg17Al12 phase with new Al2Ca compound. However, when above 0.7wt.% Ca was added, mechanical properties of AZ91 magnesium alloy were decreased.
Crystallization of Spherical Single Crystal of Silicon from Undercooled Droplet under Containerless Processing
Authors: Jian Zeng Yun , Kuribayashi Kazuhiko , Jie Wan Qi
Published: March 2009

The images of the growing crystal in the growth process of the undercooled droplets of silicon were lively recorded by using a high-speed camera. The number of crystal that nucleated spontaneously from the undercooled liquid was found to decrease to 1 when the undercooling was higher than 5K. The morphology of the growing single crystal of silicon was a thin plate. A model for predicting the critical undercooling of growing single crystal of silicon from undercooled liquid has been developed. The theoretically predicted value of the undercooling from present model for silicon is in agreement with the experimentally measured result.
Microstructure Evolution of a Zn-4wt.% Cu Hyperperitectic Alloy under Laser Surface Remelting
Authors: Huang Wei Dong , Su Yun Peng , Wang Meng , Lin Xin
Published: March 2009

Laser surface remelting experiments on Zn-4.0wt.%Cu hyperperitectic alloy have been performed on a 5kW CW CO2 laser with the scanning velocities between 6 and 1207mm/s. Microstructures in both longitudinal and transverse section of the molten pools have been analyzed by optical microscope and SEM technique, and the average composition in the molten pools has been measured by Electron Probe Microanalysis(EPMA). With the increasing of growth rate, the microstructures of Zn-4.0 wt.%Cu alloy change from planar interface to lamellar structures and then
cellular structures, and finally to absolute stability planar interface at a growth rate of 562mm/s, which shows reasonable agreement with that predicted by M-S theory.
Enhanced Growth Kinetics of Intermetallic Compounds between Bi-Containing Sn-3.5Ag Solders and Cu Substrate during Aging
Authors: Kim Soon Tae , Huh Joo Youl
Published: March 2009

The effect of adding Bi to a eutectic Sn-3.5Ag solder alloy on the growth kinetics of the intermetallic compounds (IMCs) in solder/Cu joints was examined at the aging temperatures of 130°C, 150°C and 180°C. At 150°C and 180°C, the growth rate of the Cu6Sn5 layer was significantly enhanced, but that of the Cu3Sn layer was rather reduced with increasing Bi content up to 12 wt.%. At 130°C, however, both the η and ε layers appeared to grow faster as the Bi content in the solder was increased to 12 wt.%. These results suggest that the accumulation of Bi ahead of the Cu6Sn5 layers can affect not only the interfacial reaction barrier but also the local thermodynamics at the interface between the Cu6Sn5 layer and the solder.
Investigation on the Electromagnetic Contactless Shaping and Directional Solidification of Plates of Stainless Steel and Supperalloy under Vacuum
Authors: Shen Jun , Yu Jian Wei , Lu Bai Ping , Liu Lin , Fu Heng Zhi
Published: March 2009

In this study, the distribution of electromagnetic pressure and the coupling between
shaping force and temperature field are investigated in electromagnetic contactless shaping process for plates of stainless steel and superalloy. The distributions of electromagnetic pressure on outlines of melt cross sections are very different along sides than at corners. Under the vacuum, the cooling ability is not strong enough, and therefore the position of melt in inductor is too low, which causes an unbalance between electromagnetic pressure and static pressure. Experiments show the insert of a screen shell from the bottom of inductor can change the distribution of magnetic field very much and make a good and stable coupling between shaping force and temperature field.
An Investigation of a Nitrogen Enhanced Steel Processed by Explosive Powder Compaction
Authors: Zhou Can Dong , Fan Jun Fei , Le Hai Rong , Jiang Guo Chang , Zhang Jing Guo
Published: March 2009

A structural steel, 35CrMoV steel, has been attempted firstly by explosive powder
compaction followed by sintering (EPC-sintering). The nitrogen content of the steel was 0.15wt%, which was accordant with the definition of high nitrogen steel (HNS). The final density of the EPC-sintering steel was only about 6.9g/cm3, which indicated that the processing parameters must be modulated further. In the sample of this steel, some radial cracks were found around the center of the
cross-section of the steel, resulting in no mechanical tests carrying out. Observing the majority of the rim region of the sample of this steel, the microstructures were very tight, suggesting that it was possible and successful to manufacture HNS through EPC-sintering. The characteristics of the EPC-sintering high nitrogen 35CrMoV steel were that the cementites in the pearlites were found to be extremely fine. There were many (Cr,Mo)23(C,N)6 carbonitrides precipitates in the matrix. Some precipitates were round and others were needle-like. Some were distributing orderly in matrix and crossing over the dislocations. The dislocation density in the EPC-sintering steel remained high.
Numerical Analysis of Deformation and Damage in Copper Alloy Sheet
Authors: Dong Qi Ming , Liu Ping , Su Juan Hua , Li He Jun , Tian Bao Hong
Published: March 2009

By using the finite element method and large strain two-dimension plane strain model,
the flaking damage of Cu-Fe-P lead frame sheet is investigated. The characterization of microstructure under surface flaking is the larger Fe particles embedded in the copper matrix. The numerical analysis reveals that at the interface of Cu and Fe there are greater strain mutation and intense stress concentration that is increased with particle diameter and the extent of deformation. This strain and stress concentration makes the interface initiate crack and develop crack easily. The micro-crack around the Fe particle is also attributed to surface flaking damage under the finish rolling deformation. The larger Fe particles should be avoided in the production of Cu-Fe-P alloy.
Effects of Casting Conditions on the Mold Filling Characteristics of Mg Alloy in the EPC Process
Authors: Choe Kyeong Hwan , Cho Gue Serb , Lee Kyong Whoan , Ikenaga Akira
Published: March 2009

Mold filling characteristics in the Mg Expendable Pattern Casting(EPC) process were investigated in terms of casting conditions such as reduced pressure, pouring temperature and casting modulus including foam materials. With increasing pouring temperature up to 775oC the filling velocity increased. However, the filling velocity decreased at temperatures above 775oC. This is likely due to the increase of back pressure. Concerning the effect of reduced pressure on filling velocity, it increased sharply at lower reduced pressure while became stable at higher reduced pressure. In thick pattern, high reduced pressure would be needed to obtain high filling velocity. In expanded polystyrene(EPS) patterns, mold filling was found to be faster in the thick pattern than thin pattern at temperatures below 750oC. This propensity was observed to be reverse at pouring temperatures above 750oC. In polymethyl methacrylate(PMMA) patterns, the filling velocity almost leveled off without showing a dependence of pouring temperature. This result is attributed to the difference in gas pressure between EPS and PMMA patterns during the EPC
process.
Numerical Heat Transfer Modelling in Spray Formed IN718 Billets
Authors: Shi Z. , Mi Jia Wei , Grant Patrick S.
Published: March 2009

A numerical finite difference model has been developed to describe the transient heat
flow inside Ni superalloy IN718 billets manufactured by spray forming. This model described the progressive build-up and solidification of the billets, and accounted for the latent heat of solidification, convective and radiation heat loss, and heat removal through the substrate, coupled with transient heat transfer in the substrate. The model has been used to predict critical values of important process parameters: average droplet arrival temperature, deposition rate, and billet surface convective heat transfer coefficient, in terms of key microstructural features by correlation
of quantitative predictions with qualitative microstructural investigations of the as-sprayed billets. On a micro scale, repeated re-heating/remelting of deposited layers because of subsequent deposition was predicted and has been suggested to be beneficial in reducing porosity and microsegregation, as well as in playing an important role in the formation of the characteristic equiaxed spray formed microstructure.
Geometry and Heat Transfer Considerations in Rapid Manufacturing
Authors: Kahlen Franz-Josef , Kar Aravinda
Published: March 2009

The authors review a laser-assisted rapid manufacturing process which allows to
manufacture components from the original powderized material, overcoming
functionality test limitations of conventional rapid prototyping processes. In a
comprehensive experimental and analytical investigation, a set of rules which predicts the heat transfer and the geometrical properties of the fabricated parts was derived and verified. Further, the resulting set of equations was connected to a second model which predicts the mechanical properties of the fabricated parts. The results agree very well with measured mechanical properties, showing that, depending on the operating parameters laser power, scanning speed and powder delivery rate, the mechanical strength is anisotropic.
Deformation Behavior of Ti-6Al-4V and Ti-6.85Al-1.6V Alloy with a Globular Microstructure
Authors: Kim Jeoung Han , Semiatin S. Lee , Lee Chong Soo
Published: March 2009

The high temperature deformation mechanisms of two phase a+b alloy and a near-a alloy were investigated, and compared within the framework of inelastic-deformation theory. For this purpose, load-relaxation tests were conducted on the two alloys at temperatures of 750~900°C. The flow stress-vs.-strain rate curves for both alloys were well fit with inelastic deformation equations describing dislocation glide and grain boundary sliding. The amount of grain boundary sliding resistance was higher in the near-a alloy rather than the two phase a+b alloy due to difficulty in stress
relaxation at triple junction region.
On the Low Strain Rate Regime of Structural Superplasticity - an Internal Variable Approach
Authors: Bang Won Kyu , Park J.E. , Kwon Yong Nam , Lee Chong Soo , Chang Young Won
Published: March 2009

The superplastic deformation behavior of a fine-grained 7075 Al has been investigated to clarify the issue of threshold stress. A series of mechanical tests has been conducted at various temperatures for the specimens with various grain sizes. The quantitative constitutive parameters have been determined from load relaxation test by applying the internal variable theory of structural superplaticity (SSP) proposed by Chang et al. The GBS flow could be formulated as a viscosity-type equation, characterized by the Newtonian exponent of 1.0. The unresolved issue of threshold stress is clarified and identified as a critical stress required for the GBS. The micro-mechanical roll of grain size refinement has also been manifested in terms of proposed constitutive parameters.
Application of Superplastic Flow to Manufacturing of Microcellular Aluminum Foams
Authors: Kamimura Shinya , Kitazono Koichi , Sato Eiichi , Kuribayashi Kazuhiko
Published: March 2009

A new application of superplasticity was proposed in the manufacturing process of metal foams. Preform sheets were manufactured using superplastic 5083 aluminum alloy sheets through accumulative roll-bonding (ARB) process. Microcellular aluminum foam plates with 50% porosity were produced through solid-state foaming under the superplastic condition. The cell shape was oblate spheroid, which is effective to reduce the thermal conductivity. The present aluminum foam plates have a potential as an excellent heat insulator.
Superplastic Deformation and Microstructure Evolution of Friction Stir Weld of 1420 Al-Li Alloy
Authors: Guo He Ping , Han Xiu Quan , Wu Wei , Li Zhi Qiang
Published: March 2009

Friction stir welding is a novel welding technique which has been successfully applied in structure manufacturing of aluminium alloys (including 2XXX and 7XXX). Friction stirring in aluminium alloy welds produces a combination of very fine grain size. This paper deals with the SPF response in 1420 Al-Li alloy welds. The results showed that the friction stir weld could achieve good superplasticity performance. The lateral elongation in the weld could reach 120% and the grain size still remain the same size with little change. And the drawback in the friction weld is the obstacle to fufill the good SPF ability. During the friction stir welding, some oxides or contaminates were stired into the weld in the form of black line. When the weld was experienced superplastic deformation, the crack initiated from the line and finally reach the surface and bottom of the plate. The oxide was formed mainly in the nugget of the friction weld. So the parameters and preparation before welding must be optimized so that the weld can achieve maximum superplasticity performance.
Towards the First-Principles Investigation of Ordering Dynamics
Authors: Mohri Tetsuo , Ohno Munekazu , Chen Ying
Published: March 2009

Phase Field Method (PFM) is hybridized with Cluster Variation Method (CVM) to investigate the ordering dynamics of L10-disorder transition at atomistic and microstructural scales simultaneously. For this, coarse graining operation is attempted on the inhomogeneous free energy functional of CVM. The resultant gradient energy coefficient is found out to be dependent on temperature and order parameters, which is in marked contrast to a conventional PFM formalism.
Electronic structure total energy calculations for Fe-Pd system are incorporated to the hybridized scheme and the first principles calculation of microstructural evolution process is attempted.
Point Defects and Re in L12 Ni3Al: Atomic Studies
Authors: Shu Xiao Lin , Wang Yu Hu , Deng Hui Qiu , Zhang Ying , Deng Sheng Hua , Wang Chong Yu , Zhang Bang Wei
Published: March 2009

The point defect properties of L12 Ni3Al are determined by MD with a simple modified
analytic EAM model with the basic physical properties of pure constituents Ni and Al. On the basis of the calculated lattice constants, the formation energies of vacancy and antisite are calculated and the defect types are also discussed. The energies of alloying element Re replacing Ni site and Al site in Ni3Al are estimated. The occupational site of Re is found in Al site. The present calculations are
in agreement with the experimental value and the theoretical results obtained from other authors.
Theoretical and Experimental Ti-K NEXAFS of Various Ti-Oxides
Authors: Mizoguchi Teruyasu , Sakurai Masaki , Nakamura Atsutomo , Sasaki Takeo , Sato Yukio , Matsunaga Katsuyuki , Yamamoto Takahisa , Ikuhara Yuichi
Published: March 2009

Near-edge structure of X-ray absorption spectrum (NEXAFS) of various Ti-oxides were investigated by combined with first principles orthogonalized linear combinations of atomic orbitals (OLCAO) method. From experimental and theoretical studies on the NEXAFS of the tetravalent and trivalent Ti-oxides, including rutile, anatase, brookite, columbite, and Ti2O3, it was found that
the valence state of Ti can be identified by regarding the positions of the spectral onset and the shoulder in the main-peak of Ti-K NEXAFS.
Bainitic Transformation Model in Low Alloy Carbon Steels Considering the Effect of Reaction Constant in JMA Equation
Authors: Uhm Sang Ho , Moon Joo Noh , Lee Chang Hee , Yoon Ji Hyun , Lee Bong Sang
Published: March 2009

As a part of a study on modeling the microstructural evolution during the welding process, a prediction model of TTT diagram for bainite transformation was studied. This model consisted of a thermodynamic model for the bainite-start(Bs) temperature and a kinetic model for the bainite transformation. A kinetic model was empirically established for low alloy carbon steels, based on Johnson-Mehl-Avrami(JMA) equation. Reaction constants seemed not to have noticeable tendencies
for temperatures and were averaged for each alloy. It was, however, found that the mean reaction constant significantly affected the reproducibility for the isothermal kinetics. Therefore, a calibration method to the kinetic parameter was proposed. From calibrations, rate constants were formulated as a function of alloying element and temperature. And TTT diagrams were calculated and compared with experiments.
An Eulerian Finite Element Analysis for the Steady State Rolling Process
Authors: Lee Yong Shin
Published: March 2009

An Eulerian finite element analysis for the steady state rolling process is addressed. This analysis combines the crystal plasticity theory for texture development as well as the continuum damage mechanics for growth of micro voids. Although an Eulerian analysis for steady state rolling has many advantages, it needs an initial assumption about the shape of control volume. However, the assumed control volume does not match the final shapes. To effectively predict the correct shape in an assumed control volume, a free surface correction algorithm and a streamline technique are
introduced. Applications to plate rolling, clad rolling, and shape rolling will be given and the results will be discussed in detail.
A Numerical Analysis of Powdered Metal Compaction Processes for Two-Level Flanged Solid Cylindrical Components
Authors: Lim Joong Yeon , Seo Jung Min , Hwang Beong Bok
Published: March 2009

A finite element method for the compaction process of metallic powder is introduced in the present work. Basic equations for the finite element formulation are summarized. A yield criterion, which is modified by describing asymmetric behavior of powder metal compacts, is introduced and applied to a certain class of powdered metal compaction processes. Two-level flanged solid cylindrical components are analyzed in three different compacting methods with three different compact geometries. The simulation results are summarized in terms of relative density distribution within compacts, pressure distributions along the die-wall interfaces, load-stroke relationships of each punch, average densities as functions of height and radius of the compact, respectively, and average densities of pin and head. For each compact from different compacting method, the best pressing method is chosen for uniform density distributions within the compact.
A Design of Manufacturing Processes for Valve-Spring Retainer Component
Authors: Ko B.D. , Choi Hyoung Jin , Hwang Beong Bok , Kim S.H. , Hwang Sun Keun
Published: March 2009

New manufacturing processes for a valve-spring retainer (VSR) are proposed by replacing the initial solid billet for commercially available thick-walled pipes. The rigid-plastic FEM has been applied to simulate the conventional five-stage manufacturing process for VSR component. The existing process includes mainly backward extrusion and heading operations. A process design methodology is proposed and applied for the analysis. The process design criteria are the maximum force requirement within the available press limit, and the material saving by reducing the wastes from the process. As a result, several simulations of one-step process from selected stocks to the final product shape are performed for a possibly better process than the conventional one. Statistics among different processes are summarized and compared each other in terms of number of required operations for final product, forging load, material waste, number of individual die, process time, and even the possibility of fracture during service. Experiment also has been conducted to ensure that the proposed one-step process is safe operation without geometrical defects.
Molecular Dynamics Simulation of Compressive Mechanical Behavior of Nanocrystalline Fe
Authors: Xiao Shi Fang , Wang Yu Hu
Published: March 2009

The uniaxial compressive mechanical properties of nanocrystalline Fe are simulated with a molecular dynamics technique and the analytical embedded-atom method. An asymmetrical mechanical phenomenon between tensile and compressive process is found, and the yield stress and flow stress in compression are higher than those in tension simulations. The compressive deformation process can be described as three characteristic regions: quasi-elastic deformation, plastic flowing deformation, and strain strengthening. During the plastic flowing deformation region, the material shows very good compressive ductibility. The plastic deformation is mainly dominated by the grain boundary atom slide.
The Effects of the Heating Conditions on the Hydro-Formability of the Aluminum Alloys at High Temperatures
Authors: Kim B.J. , Son S.M. , Park K.S. , Moon Young Hoon
Published: March 2009

Modern automobiles are built with a steadily increasing variety of materials and
semifinished products. The traditional composition of steel sheet and cast iron is being replaced with other materials such as aluminum and magnesium. But low formability of these materials has prevented the application of the automotive components. The formability can be enhanced by conducting the warm hydroforming using induction heating device which can raise the temperature
of the specimen very quickly. The specimen applied to the test is AA6061 extruded tubes which belong to the age-hardenable aluminum alloys. But in the case of AA6061 age hardening occurs at room temperature or at elevated temperatures before and after the forming process. In this study the effects of the heating condition such as heating time, preset temperature, holding time during die
closing and forming time on the hydroformability are analyzed to evaluate the phenomena such as dynamic strain hardening and ageing hardening at high temperatures after the hydroforming process.
Bounds of the Thermal Conductivity in Discontinuously Reinforced Metal-Matrix Composites
Authors: Alhama F. , Alcaraz Diego , Gómez-Lopera S.
Published: March 2009

A simple model based on the network simulation method is proposed to estimate
numerically the thermal conductivity of particulate reinforced metal-matrix composites. The estimation is carried out running the model in the standard Pspice code, the computing time being negligible. The 3-D solid is discretized in 1000 cubic volume elements which represent an acceptable approximation of the shape of the particles. For each reinforcement percentage and each combination of matrix and reinforcement more than 200 tests were carried out, so that the results may be
considered close to the exact values. The limit values are scarcely influenced by the effect of the 3-D geometry and basically depend on the amount of the reinforcement. Applications to aluminum and titanium matrix composites reinforced with different types of particles are presented covering a wide range of reinforcement percentages.
Nano Atom Clusters and Their Long-Range Quasiperiodic Arrangements in Al-Ni-Ru Decagonal Quasicrystal
Authors: Sun Wei , Zhang Ze , Hirage Kenji
Published: March 2009

The structural features of nano-sized atom clusters and their long-rang arrangement in the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity have been studied and compared with those in the Al-Pd-Mn decagonal quasicrystal on the basis of electron microscopy. From the perpendicular-space analysis of the tiling obtained in a wide region, we conclude that long-range arrangement of atom clusters in the Al-Ni-Ru decagonal quasicrystal with 1.6 nm periodicity can
form a Penrose-tiling-like quasiperiodic structure which is almost free of linear phase strain. In contrast, the tiling structure of the Al-Pd-Mn decagonal quasicrystal contains heavy phason strain. Our results clearly show that atom clusters formed in the Al-Ni-Ru decagonal quasicrystals and their linkage manner are completely different from those in the Al-Pd-Mn decagonal quasicrystal.
MOCVD Growth and Annealing of Gallium Oxide Thin Film and Its Structural Characterization
Authors: Kim Hyoun Woo , Kim Nam Ho
Published: March 2009

We have demonstrated the production of gallium oxide thin films on various substrates such as Si(111), SiO2, and sapphire by metalorganic chemical vapor deposition using the trimethylgallium (TMGa) as a precursor in the presence of oxygen. The XRD data revealed that the as-deposited gallium oxide films were fully amorphous but very small crystallites with monoclinic structures were found with the thermal annealing at a sufficiently high temperature, regardless of substrate materials. The AFM analysis indicated that the surface roughness increased by the thermal annealing.
Crystallization Kinetics of Zr65Ni25Ti10 Metallic Glass Alloy
Authors: Liu Xiongjun , Hui Xidong , Chen Guo Liang
Published: March 2009

The crystallization reaction of Zr65Ni25Ti10 (at. %) metallic glass was studied by using differential scanning calorimetry (DSC) at constant heating rate. Two distinct exothermic peaks were observed from the continuous heating DSC curves, implying the crystallization process undergoes two different stages. The crystallization kinetic parameters, including activation energy (E), Avrami
exponent (n) and frequency factor (K0), were determined with non-isothermal analysis method based on the DSC data. The values of E are 267.353 KJ/mol and 224.293 KJ/mol, n 4.0±0.1 and 6.8±0.1, K0 4.4±0.05E+20 and 2.0±0.08E+15, for the first and second crystallization stage, respectively. The results suggest that the crystallization mechanism is governed dominantly by interface controlled
growth with constant nucleation rate for the first crystallization stage and with increasing nucleation rate for the second stage.
Enhancement of Plasticity in Ti-Based Bulk Metallic Glass
Authors: Chang H.J. , Kim Won Tae , Kim Do Hyang
Published: March 2009

The effects of structural relaxation and partial crystallization on the mechanical property of the Ti40Zr29Cu9Ni8Be14 bulk metallic glass (BMG) have been investigated. The atomic structure of the as-cast Ti40Zr29Cu9Ni8Be14 metallic glass transforms into a more relaxed state at the temperature region of 452 –585 K, below the crystallization onset temperature of 631 K. Stable icosahedral phase
forms in the amorphous matrix by growth of the pre-existing nuclei in the amorphous matrix during first crystallization step. The compressive plastic strain of the as-cast Ti40Zr29Cu9Ni8Be14 BMG is 6.7 %, and decreases when the structural relaxation occurs. However, the plastic strain increases when a few nanometer size icosahedral phase particles form in the amorphous matrix by the partial crystallization treatment.
Hole Punching onto the Zr65Al10Ni10Cu15 BMG Sheet Fabricated by Squeeze Casting
Authors: Jeong Ha Guk , Kim Woo Jin , Bae Jung Chan , Yoon Duk Jae , Choi Seo Gou , Na Kyoung Hoan
Published: March 2009

Bulk metallic glass Zr65Al10Ni10Cu15 was fabricated in a sheet form with thickness 1.5 mm by a squeeze casting method. The structure of the as-cast Zr65Al10Ni10Cu15 sheet was confirmed to be fully amorphous. The sheet was punched into a blank under high hydrostatic pressure at room temperature. A round hole was created with a possible evidence for plastic-like deformation along
the edge of rim. No visible cracks were observed around the hole. This result indicates that bulk metallic glasses, which are known to be very brittle at room temperature, can be deformed in a ductile mode under hydrostatic pressure condition. Hydrostatic pressure may suppress the formation
and development of micro defects leading to ductile fracture
Ti-Based Bulk Metallic Glass with High Cold Workability at Room Temperature
Authors: Park J.M. , Park J.S. , Kim J.H. , Lee Myung Hyun , Kim Won Tae , Kim Do Hyang
Published: March 2009

The cold workability of Ti-based bulk metallic glasses (BMGs) have been investigated. Ti45Zr16Be20Cu10Ni9 BMG with a large compressive plastic strain of 4.7 % shows a high cold workability, i.e. total reduction ratio of 50 % by cold rolling at room temperature. The multiple shear bands formed during rolling are effective in enhancing the plasticity. The cold rolled Ti45Zr16Be20Cu10Ni9 BMG (reduction ratio: 30 %) exhibits a large plastic strain of ~14 %.
Development of Ni-Zr-Nb-Al-M(=Ta,Ti,Y) Metallic Glass
Authors: Na J.H. , Han K.H. , Kim Won Tae , Kim Do Hyang
Published: March 2009

The effects of Ta, Ti and Y addition substituting Zr in the Ni-Zr-Nb-Al metallic glass alloys have been investigated by using thermal analysis, X-ray diffractometry and transmission electron microscopy. Partial replacements of Zr with M(=Ta, Ti, Y) in Ni61Zr28Nb7Al4 alloy significantly enhance the glass forming ability and enlarge the undercooled liquid region during continuous heating of glassy ribbons. Fully glassy rods with the diameter of up to 2 mm can be fabricated by a copper
mold casting method.
Wear Properties of Bulk Amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 Alloys for Crystallization
Authors: Lee B.J. , Song Dae Hyun , Cho Kyung Mok , Park Ik Min , Kim K.H. , Yoon S.Y. , Cho Young Rae
Published: March 2009

The influence of annealing conditions on the crystallization and wear properties of bulk amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 (BAZ) alloys was investigated. Nanocrystalline phases were precipitated from the bulk amorphous alloy matrix after an annealing treatment at both 670 K and at 780 K. The Vickers hardness (Hv) increased with the volume fraction (Vf) of the nanocrystalline phases with increasing annealing temperature. The friction coefficient and the wear loss showed a somewhat different trend with the volume fraction of the nanocrystalline phases. The friction coefficient had a minimum value of 0.46 at 670 K and a maximum value of 0.96 at 780 K. The wear loss of the BAZ showed a very similar trend of friction coefficient. The improved wear and hardness properties can be attributed to the formation of nanocrystalline precipitates in the Zr-based amorphous matrix.
Cu-Zr-Ti Bulk Metallic Glass Composites Produced by Mechanical Alloying and Vacuum Hot-Pressing
Authors: Wang C.C. , Lin Chung Kwei , Lin Y.L. , Chen J.S. , Jen R.R. , Lee Pee Yew
Published: March 2009

In the present study, WC/Cu60Zr30Ti10 metallic glass composite powders were
prepared by mechanical alloying of pure Cu, Zr, Ti, and WC powder mixtures. Cu60Zr30Ti10 metallic glass composite powders were obtained after 5 h of milling as confirmed by X-ray diffraction and differential scanning calorimetry. The metallic glass composites powders were found to exhibit a supercooled liquid region before crystallization. Bulk metallic glass (BMG) composites were synthesized by vacuum hot pressing the as-milled Cu60Zr30Ti10 metallic glass composite powders at 723 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense anocrystalline/amorphous matrix was successfully prepared under applied pressure of 1.20 GPa. It was found that the pressure could enhance the thermal stability and promotes nocrystallization of WC/Cu60Zr30Ti10 BMG composites.
Femtosecond Laser Driven Shock Quenching of the Nanocrystalline High-Pressure Phase of Iron
Authors: Sano Tomokazu , Mori Hiroaki , Sakata Osamu , Ohmura Etsuji , Miyamoto Isamu , Hirose Akio , Kobayashi Kojiro F.
Published: March 2009

Quenching of the nanocrystalline high-pressure e phase of iron, which has not been
observed under a conventional shock compression, was attained using a femtosecond laser. A small quantity of the g phase of iron also existed. We found that the e phase was induced by the shock itself but not the g phase. The g phase was suggested to be induced as an intermediate structure between the a-e transition. The femtosecond laser driven shock may have the potential to quench
high-pressure phases which has not been attained using conventional methods.
Low Temperature Synthesis of PbTiO3 Nanoparticles
Authors: Sun Yu Jing , Tian Shi , Li Xiao Bing
Published: March 2009

PbTiO3 nano-sized powders were synthesized at 150oC by a new hydrothermal [denoted as sol-hydrothermal] method by using modified titanium tetra-n-butoxide and lead acetate as the precursors. Furthermore, tetragonal PbTi0.8O2.6 nano-sized powders were obtained by this method at 80oC. Compared with hydrothermal synthesis, the effect of temperature on the formation of products prepared by sol-hydrothermal was investigated. The characteristics of products were studied by XRD, TEM and SAXS. The results show sol-hydrothermal method choosing
acetylacetonate-modified titanium tetra-n-butoxide and lead acetate to form a sol could obtain PbTiO3 in 120nm size and PbTi0.8O2.6 powders with average diameter of 30nm, and both of them are pure tetragonal phase. In addition, PbTi0.8O2.6 could be converted into PbTiO3 gradually after annealed at giving condition.
Synthesis and Characterization of ZnO Nanowires Using a Simple PVD Approach without Catalysts
Authors: Wang Long Shan , Zhang X. , Zeng Fan Hao
Published: March 2009

Two kinds of ZnO nanowires with different morphologies and characters were produced on Si (100) using a new PVD approach by heating and oxidizing Zn powders directly without any catalysts. The nanowires have an average diameter of 80nm (deposited at the evaporation source) and 30nm (deposited downstream of the evaporation source) respectively, and are evenly distributed over
an area of > 20mm2. The two nanowires have complete different photoluminescence properties. One has a strong green emission (510nm) with a weak UV emission (380nm). The other has a strong and sharp UV emission (385nm), showing the capability for UV laser emitters.
Cu Oxide Nanoparticle Formation: Effects of Curing Time
Authors: Song Mun Seop , Yoon Chong Seung , Kim Young Ho
Published: March 2009

Cu oxide nanoparticles were formed by reacting with Polyamic acid (PAA) with Cu during imidization. In this paper, we investigated the effect of holding time during curing on the Cu oxide nanoparticle formation. Cu thin films were deposited on SiO2/Si substrates by thermal evaporation. Polyamic acid was then spin-coated on the Cu thin film. The polyamic acid films were soft-baked at 135°C for 30 minutes and thermally cured at 350°C with various holding time in a nitrogen atmosphere. The size of the Cu2O nanoparticles formed in the polyimide (PI) matrix increased as the holding time increased. The size and distribution of Cu oxide particles were characterized using Transmission Electron Microscope (TEM). The degree of imidization of PI also increased proportional to the increase in holding time. The degree of PI imidization was analyzed by Infrared (IR) spectroscopy. Very uniform Cu2O particles less than 5 nm in size with particle density greater
than 2×1012/cm2 were fabricated by controlling the holding time during curing.
Synthesis of Bamboo-Shaped Gallium Nitride Nanorods
Authors: Dong Zhi Zhong , Gao Haiyong , Xue Cheng Shan , Dong Zhi Hua , He Jian Ting
Published: March 2009

Heagonal GaN nanorods have been synthesized through ammoniating ZnO/Ga2O3 films deposited by radio frequency(rf) magnetron sputtering on Si(111) substrates.X-ray diffraction(XRD), Fourier transform infrared spectrophotometer (FTIR), transimission electron microscopy(TEM), high-resolution transmission electron microscopy(HRTEM) and selected-area electron diffraction
(SAED) are used to analyze the structure,composition and morphology of the synthesized GaN nanorods. TEM result shows that GaN nanorods own bamboo-shaped morphalogy and have a single-crystal hexagonal wurtzite structure.The average length and dimeter of the nanorods are 3μm and 50 nm espectively.Ga2O3 and NH3 reactived directly and synthesized GaN nanorods without any
catalyzer and the process of space-confined reactions.
Preparation and Field Emission Characteristics of CNx Nanotubes Thin Film
Authors: Zhang Lan , Ma Hui Zhong , Li Xue Xiang , Yao Ning , Zhang Bing Lin
Published: March 2009

Carbon nitride nanotubes (CN-NT) thin films were prepared on Ni-Cr coated glass substrate by microwave plasma enhanced chemical vapor deposition at a relatively low temperature of 600～650 °C. The morphology of the films were observed by scanning electron microscopy. The microstructure of the film were analyzed by x-ray photoelectron spectroscopy, x-ray diffraction, and
Raman spectroscopy. The characteristics of field emission of CN-NT thin films were measured. Experimental results indicate that the film structure and properties of the field electron emission are related to flow ratio of N2 to CH4. When the flow ratio of N2 to CH4 was 3.3, the obtained film had a better field electron emission characteristics. The turn-on field of the film was 3.7 V/µm . The
current density was 413.3 µA/cm2 at an electric field of 8 V/µm.
Study of Precipitation Sequence in Al-Mg-Si Alloys by HRTEM
Authors: Matsuda Kenji , Ikeno Susumu
Published: March 2009

The precipitation sequence of Al-Mg-Si alloys has been studied by high-resolution
transmission electron microscopy (HRTEM). G.P. zone is a fine-plate having dimensions of a mono- layer in thickness, 2.5nm in width, and less than 30nm in length. Its elongated direction is parallel to the <100>m direction. Several types of metastable phases were observed in the excess Si alloy and they were classified with the b ’-phase in the balanced alloy. Especially, the b ”-phase was the typical phase in the excess Si alloy aged at low temperature or at the early stage during aging.
Influence of Film Thickness on Intrinsic Growth Stress and Raman Evaluation of Tetrahedral Amorphous Carbon Films
Authors: Zhu Jia Qi , Han Jie Cai , Meng Song He , He Xiao Dong , Tan Manlin , Gao Wei
Published: March 2009

To investigate the effects of film thickness on Raman characterization and intrinsic stress of tetrahedral amorphous carbon and ascertain the correlations between stress and Raman spectra, the ta-C films with different film thickness were deposited on the polished P-type (100) c-silicon substrate with the same conditions by the filtered cathodic vacuum arc technology. The film thickness
was measured by the surface profiler and the atomic force microscope; stress was calculated according to the curvature of the stress samples examined by the surface profiler; the microstructure of the films was characterized by the Ramanscope. It has been shown that the stress drops down continuously and the dropping rate turns mild with the increase of film thickness. When the film
thickness surpasses 30 nm, the compressive stress is kept at less than 5 GPa. The intensity of the first and second order peak of the c-Si substrate in the visible Raman spectra gradually depresses with the increase of thickness. However, the FWHM is minimal and the maximal intensity is highest from 50 nm to 80 nm, accordingly the clearest Raman signals can be acquired in this scale. Additionally, the position of the asymmetric broad peak gradually shifts towards the lower wavenumber with the increase of thickness and the decease of intrinsic stress.