bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of a W-25%Cu Nanocomposite by High Pressure Torsion
Authors: Sabirov I. , Schöberl Thomas , Pippan Reinhard
Published: March 2009

A coarse-grained W-25%Cu composite with a tungsten particle size between 2 and 10 μm is subjected to high pressure torsion (HPT) at room temperature to different strains. The evolution of microstructure with increasing strain is studied. At low strains (εeq ≤ 16), an inhomogeneous deformation of the material is found. This inhomogeneity is studied in detail by nanoindentation experiments. At larger strains (εeq ≥ 16), a fragmentation of tungsten particles is observed. The specimen deformed to a strain of 256 exhibits a homogeneous microstructure with a tungsten particle size between 10 and 20 nm. A further increase of strain does not cause a further significant tungsten particle refinement. A possibility of industrial application of HPT to produce nanocomposite materials is discussed.
Structural Analysis and Properties of Bi2-xSbxTe3-ySey Prepared by Angular Extrusion
Authors: Hayashi Takahiro , Sekine Msasayoshi , Suzuki Junya , Horio Yuuma
Published: March 2009

The purpose of this work is producing bismuth telluride based alloys with both well-orientated texture and fine grains to improve thermoelectric properties. The angular extrusion process was applied to Bi1.9Sb0.1Te2.7Se0.3 foils which were prepared by a liquid quenching method [1]. The extrusion temperatures examined ranged from 380 to 540 °C. The microstructures of the specimens were characterized with an optical microscope and OIM. Recrystallized grains sizes ranging from 3.61 to 10.01 μm were obtained at these temperatures. The textures of the specimens show the basal plane preferably aligns along to the extruded direction. A maximum power factor of 4.18 × 10-3 W / mK2 was obtained in this work. These results indicate that the angular extrusion process is effective to improve the thermoelectric properties of bismuth telluride based alloy.
Substructure and Nanocrystalline Structure Effects in Thermomechanically Treated Ti-Ni Alloys
Authors: Inaekyan K.E. , Prokoshkin Sergey , Brailovski Vladimir , Khmelevskaya I. , Demers Vincent , Dobatkin Sergey V. , Tatyanin E.V. , Bastarache E.
Published: March 2009

Substructure and structure formation as well as functional properties of thermomechanically treated Ti-Ni wire have been studied using differential scanning calorimetry, X-ray diffraction, transmission electron microscopy and mechanical. The low- temperature themomechanical treatment (LTMT) was carried out by rolling at room temperature in a true strain range e = 0.3 to 1.9. It was shown that severe plastic deformation (e=1.9) of Ti-50.0at.%Ni alloy results in partial amorphization and formation of nanocrystalline austenite structure during post-deformation annealings up to 400 °C. As a result, the fully recoverable strain and recovery stress become much higher than the values reachable after traditional LTMT (e=0.3 to 0.88) with post-deformation annealing which creates a poligonized dislocation substructure.
Three-Dimensional Imaging of Shear Band Produced by ECAP Process in Al-Ag Alloy
Authors: Inoke Koji , Kaneko Kenji , Horita Z.
Published: March 2009

A significant change in microstructure occurs during the application of severe plastic deformation (SPD) such as by equal-channel angular pressing (ECAP). In this study, intense plastic strain was imposed on an Al-10.8wt%Ag alloy by the ECAP process. The amount of strain was controlled by the numbers of passes. After 1 pass of ECAP, shear bands became visible within the matrix. With increasing numbers of ECAP passes, the fraction of shear bands was increased. In this study, the change in microstructures was examined by three-dimensional electron tomography (3D-ET) in transmission electron microscopy (TEM) or scanning transmission electron microscopy (STEM). With this 3D-ET method, it was possible to conduct a precise analysis of the sizes, widths and distributions of the shear bands produced by the ECAP process. It is demonstrated that the 3D-ET method is promising to understand mechanisms of microstructural refinement using the ECAP process.
Microstructural Evolution in Pure Copper Severely Deformed by the ARB Process
Authors: Li Bo Long , Shigeiri N. , Tsuji Nobuhiro , Minamino Yoritoshi
Published: March 2009

An oxygen free high conductivity (OFHC) copper (99.99%) was intensely deformed by the accumulative roll-bonding (ARB) process up to equivalent strain of 4.8 at ambient temperature. The microstructure evolution during the ARB process was explained by grain subdivision. The deformed specimens revealed dislocation cell structures at low strain and elongated ultra fine grains separated by high angle boundaries at high strain. The spacing of the high angle lamellar boundary exponentially decreased as a function of strain. The fractions of high angle boundaries (HAB) and the low angle boundaries (LAB) were nearly equal even at strain of 3.2, which was significantly different from the ARB processed Al alloys and ferritic steel where the HAB fraction was above 70% at the same strain. TEM observations indicated a mixed microstructure of dislocation boundaries and cell walls with dislocation tangle at low strain of 1.6, and small recrystallized grains partly appeared above strain of 3.2. As a result, the LAB fraction due to partial recrystallization was high even at strain of 4.8. The occurrence of recrystallization is attributed to high purity of the OFHC copper, the accumulated dislocation density, and the adiabatic heating during the ARB process of one-pass large reduction without lubrication.
Limit of Dislocation Density and Dislocation Strengthening in Iron
Authors: Nakashima Koichi , Suzuki M. , Futamura Y. , Tsuchiyama Toshihiro , Takaki Setsuo
Published: March 2009

The limit of dislocation density was investigated by means of mechanical milling (MM) treatment of an iron powder. Mechanical milling enabled an ultimate severe deformation of iron powder particles and dislocation density in the MM iron powder showed the clear saturation at around the value of 1016m-2. On the other hand, the relation between hardness and dislocation density was examined in cold-rolled iron sheets, and the linear Bailey-Hirsch relationship; HV[GPa]=0.7+3×10-8ρ1/2 was obtained in the dislocation density region up to 3×1015m-2. Extrapolation of the Bailey-Hirsch relationship indicated that the dislocation strengthening should be limited to about 3.7GPa in Vickers hardness which corresponds to about 1.1GPa in 0.2% proof stress.
Enhanced Ductility due to Grain Refinement by Equal Channel Angular Extrusion in Automotive Aluminium Alloy 6016
Authors: McKenzie P.W.J. , Lapovok Rimma , Thomson Peter F.
Published: March 2009

Equal Channel Angular Extrusion (ECAE) with varying levels of applied backpressure was used to refine the microstructure of commercial automotive aluminium alloy 6016 at room temperature using route BC and a 90° die. Before processing, the alloy was solution heat treated at 560°C for 1 hour to produce an initial average grain size of ~190μm (in the furnace cooled condition) and ~200μm (in the water quenched condition). Two needle-like secondary phase precipitates were observed predominantly at grain boundaries and identified as α-Fe Al12Fe3Si2 and β-Fe Al5FeSi. The ability of Al 6016 to accumulate strain by simple shear was found to be dependent upon both the heat treatment condition and level of applied backpressure. The furnace cooled (FC) condition was found to accumulate higher strains than the cold water quenched (WQ) condition (under the same applied backpressure) with higher levels of backpressure allowing both conditions to accumulate greater equivalent plastic strains. A series of static annealing experiments were performed on as-processed material to investigate the grain stability of the ultrafine grained structure obtained after ECAE. Grain growth was observed to occur at 250°C in the FC condition of Al 6016 after 12 passes of ECAE where the average grain size approached 1μm. The engineering strain to failure in elevated temperature tensile testing was found to be dependent upon the number of passes of ECAE, test temperature, strain rate and level of applied backpressure. Increasing the number of passes and level of applied backpressure during ECAE and decreasing the strain rate during testing was found to produce the greatest tensile ductilities at 200°C (FC condition) and 300°C (WQ condition).
Microstructure, Texture and Property Changes of High Purity Aluminium during Accumulative Roll Bonding and Conventional Rolling
Authors: Slámová Margarita , Homola Petr , Sláma P. , Čížek Jakub , Procházka Ivan , Cieslar Miroslav
Published: March 2009

It is known that the severe plastic deformation (SPD) induced by Accumulative Roll Bonding (ARB) results in more important grain refinement as compared to conventional rolling. Since ARB enables production of large amounts of ultra-fine grained (UFG) materials, its adoption into industrial practice is favoured. The paper presents the results of a study of high purity aluminium processed by ARB and cold rolling. Microstructure changes induced by both methods were studied by light and transmission electron microscopy. Dislocation density and arrangement were assessed by positron annihilation spectroscopy. Strength evolution was estimated by hardness measurements. Texture measurements were performed by X-ray diffraction. ARB processing results in over twofold increase in hardness. Hardness increases significantly after two ARB cycles and it raises only a little or decreases during subsequent cycles. The increase in hardness induced by conventional rolling is smaller. Positron lifetime measurements reveal a substantial increase of dislocation density at the first ARB cycle and a moderate increase or even a decrease at further cycles. The high fraction of positrons trapped at grain-boundary dislocations gives evidence for substantial grain refinement confirmed by TEM examinations. Grain size of 1.2 m in the rolling plane and as small as of 90 nm in the normal direction is obtained. The rolled samples have a typical rolling texture (-fibre). The - fibre of the sample ARB processed to strain of 2.4 is weaker as compared to its rolled counterpart and it presents through thickness variations. The surface layers do not have any -fibre orientations but they have ND-rotated cube texture formed by the shear strains induced by lubricant-free rolling.
Mechanical Spectroscopy of High Pressure Torsion Deformed Fe-Based Alloys and Ti
Authors: Golovin Igor S. , Pavlova Tatiana S. , Grusewski C. , Ivanisenko Julia , Gunderov Dmitriy
Published: March 2009

Low temperature dislocation- and point defect-related anelasticity in high pressure torsion (HPT) deformed metallic materials bcc Fe-26Al, fcc Fe-36Ni, hcp Ti is studied by mechanical spectroscopy. Internal friction (IF) peaks, which correspond to these phenomena, have different stability against heating. Up to five IF peaks are recorded, at least some of these peaks can be classify as Hasiguti peaks. Mechanical spectroscopy gives a useful tool to study early stages of severely plastic deformed alloys study.
Strain Rate Sensitivity of Ultrafine Grained FCC- and BCC-Type Metals
Authors: May Johannes , Höppel Heinz Werner , Göken Matthias
Published: March 2009

The dependence of the strain rate sensitivity (SRS) of α-Fe and Al 99.5, as typical representatives of fcc- and bcc-type metals, on the testing temperature and with respect to the microstructure is investigated. In particular, the differences between conventional grain size (CG) and ultrafine grain size (UFG) are pointed out. UFG Al 99.5 generally shows an elevated SRS compared to CG Al 99.5. In case of α-Fe the SRS of the UFG state is decreased at room temperature, but increased at 200 °C, compared to the CG state. It is shown that the SRS also influences the ductility of UFG-metals in tensile tests.
The Effect of the Initial Orientation on Microstructure Development of Copper Single Crystals Subjected to Equal-Channel Angular Pressing
Authors: Miyamoto Hiroyuki , Fushimi J. , Mimaki Takura , Vinogradov Alexei , Hashimoto Satoshi
Published: March 2009

Copper single crystals were subjected to equal-channel angular pressing (ECAP) via the so-called route A and Bc, in order to examine the influence of initial crystallographic orientation and processing route on microstructure development and grain fragmentation. Microstructural changes were examined by transmission electron microscopy (TEM). The pressing via the route Bc resulted in finer microstructure for all orientations in terms of grain size, equiaxiality and orientation scattering after four passes. Effect of initial crystallographic orientation on the grain refinement was also recognized, and it might be attributed to heterogeneous deformation such as shear bands, whose formation is strongly orientation dependent. After eight passes, however, the effect of processing route and initial orientation cannot be recognized.
Improving the Mechanical Properties of AZ31 Mg Alloy by High Ratio Extrusion
Authors: Chen Yongjun , Wang Qu Dong , Peng Jianguo , Zhai Chun Quan
Published: March 2009

Experiments were conducted both to evaluate the potential for grain refinement, the subsequent mechanical properties at room temperature in samples of AZ31 Mg alloy and also to investigate the relationship between one-step and two-step high ratio extrusion (HRE). The one-step HRE was undertaken using a high extrusion ratio of 70:1 at 250, 300 and 350°C. And the two-step HRE was conducted with an extrusion ratio of 7 for the first step at 250, 300 and 350°C, followed by a second-step extrusion with an extrusion ratio of 10 at 250, 300 and 350°C. The initial grain size in the AZ31 ingot was 100μm and that after one-step HRE became similar to 5μm, after two-step HRE at 250, 300 and 350°C were 2, 4, 7μm, respectively, resulting in superior mechanical properties at ambient temperature. The microstructure of two-step HRE was finer and uniformer than that of one-step HRE and the strength of one-step and two-step HRE were similar, moreover, the elongation of one-step HRE was improved markedly than that of two-step HRE. Dynamic recrystallization and adjacent grain broking during HRE is introduced to explain the effects of one-step and two-step HRE on the microstructure and mechanical properties of AZ31 Mg alloy. The current results imply that the simple HRE method might be a feasible processing method for industry applications, and the multiply steps extrusion are effective to fabricate high strength of fine grained hcp metals.
An EBSD Study of Texture and Grain Boundary Evolution in a Strongly Textured Aluminium Alloy during ECA Pressing
Authors: Starink Marco J. , Wang Shun Cai , Gao Nong , Singh Ubhi H. , Xu Cheng , Langdon Terence G.
Published: March 2009

The texture and grain boundary evolution during equal channel angular pressing (ECAP) of a spray-cast Al-7034 (Al-Zn-Mg-Cu) alloy containing intermetallic particles with a range of sizes was studied through electron backscatter diffraction (EBSD). Up to 8 passes of ECAP using route Bc were employed. The initial ECAP pass leads to the development of low angle grain boundaries and subsequent passes lead to a relatively rapid increase in the fraction of high angle grain boundaries. Before ECAP, the material possessed a strong <111> and <100> fibre texture. On ECAP, the <111> fibre texture component is mostly retained but the <100> fibre develops to a Cube texture after the first ECAP pass. Goss textures form from about 4 passes of ECAP.
The Effect of Equal-Channel Angular Pressing on Structure-Phase Changes and Superplastic Properties of Al-Mg-Li Alloy
Authors: Naydenkin Evgeny V. , Dudarev E.F. , Kolobov Yu.R. , Bakach G.P. , Langdon Terence G.
Published: March 2009

The effect of equal-channel angular pressing (ECAP) on the structure-phase state and superplasticity development was investigated using the 1421 Al-Mg-Li alloy. The physical reasons for the displacement of the temperature range of superplasticity to lower temperatures after ECAP by comparison with the initial state are considered. Possible reasons are discussed for the decrease in the activation energy of true grain boundary sliding in the alloy produced using ECAP by comparison with the initial condition.
Developing a Moving-Coil Actuator for Nano-Imprint Lithography System
Authors: Renn Jyh Chyang , Yang Yi An , Chan Cherng Shyong
Published: March 2009

Nano-imprint lithography (NIL) is one of the most promising technologies for the massproduction of nano-meter patterns. A commercial hydraulic press and a pair of hot plates were used as the NIL system reported so far. It is, however, large and heavy. In this paper, therefore, a new moving-coil actuator is proposed and is intended to be used as the driving power for a compact NIL system. Compared to the commercial hydraulic NIL system, two advantages of the new NIL system using the moving-coil actuator are the ease of precise control as well as the compact dimensions. Thus, it is suitable for the fabrication and replication of small-sized nano-meter patterns. To develop such a new moving-coil actuator, the electromagnetic finite element method (FEM) is utilized. In addition, a simple but effective state-space model is also established to describe the dynamic behavior of the moving-coil actuator. Finally, a series of simulations and experiments are carried out and the results show that the positioning accuracy of the developed moving-coil actuator is 1µm.
Preparation and Characterization of the Modified Carbon Nanotubes Enhanced Epoxy Resin Composites
Authors: Lee Kuang Chyi , Yu Hsin Her , Hwang Shug June , Li Ye Shiu , Cheng Min Hsun , Lin Chien Chang
Published: March 2009

In this study, the surfaces of the multi-walled carbon nanotubes (MWNTs) were treated by acrylic acid. The acid-treated MWNTs were functionalized and were characterized by Infrared spectroscopy. The MWNTs were opened at their ends by ultrasonic treating and UV irradiating. Different adding amounts of the opened MWNTs were filled to the epoxy resin, and their mechanical properties and thermal properties were measured by Instron, impact and differential scanning
calorimeter (DSC), etc. The optimum adding amount of MWNTs to the epoxy resin is 2.0%, which is according to the parameters obtained from mechanical testing and Tg. The activation energy of the epoxy resin during curing can be calculated from infrared spectra according to the change of the epoxide band. The electrical conductivity of the MWNTs-filled composites was increased with proper (12.87%) amount of MWNTs adding, this is due to the networks constructed between
MWNTs completely.
Experimental and Numerical Investigation into Mixing Efficiency of Micromixers with Different Geometric Barriers
Authors: Lee Chia Yen , Lin Chiufeng , Hung M.F. , Ma R.H. , Tsai Chien Hsiung , Lin Che Hsin , Fu Lung Ming
Published: March 2009

This paper proposes a numerical and experimental investigation of mixing behaviors of two liquid samples in microchannels that are shaped into different geometric barriers. The micro-mixers utilized in this study are fabricated on low-cost glass slides using a simple and reliable fabrication process. Samples are driven by a hydrodynamic pump to lead them into the mixing section of the microchannels. The effects of mixing performance of various kinds of barrier shape are
discussed in this study. The numerical and experimental results show that a better mixing efficiency can be obtained in the microchannels while using the elliptic-shape barriers in compare with the leaking side-channels. In this study, the simulated and experimental results are in good agreement. The investigation of mixing efficiency in microchannels with different geometric barriers could be crucial for microfluidic systems.
Precision Positioning of Piezo-Actuated Stages Based on Feedback Control with GA Modeling
Authors: Lin Chih Jer , Chen Shu Yin
Published: March 2009

The piezo-actuated stages are composed of the piezo-electric actuator and the positioning mechanism. The positioning accuracy of the piezo-actuated stage is limited due to hysteretic nonlinearity of the PEA and friction behavior of the positioning mechanism. To compensate this nonlinearity of piezoelectric actuator, a PI feedback control associated with feedforward compensating based on the hysteresis observer is proposed in this paper. Identifying its parameters is very important; so the genetic algorithm is studied to find the optimal parameters. To verify the feasibility of the proposed method, it is implemented on the precision positioning task of the piezo-actuated stage in the real-time control architecture.
Thermal Contact Residual Stress Analysis of Elastic-Plastic Bilayer Micro-Cantilevers with Platinum Electrodes
Authors: Chen Li Wen , Lee Chia Yen , Tsai Chien Hsiung , Chen Yung Chuan
Published: March 2009

This paper studies the residual stress distributions and tip deflections of microfabricated bilayer cantilevers of varying beam thickness and platinum electrode length. The bilayer cantilevers discussed here are composed of low-stress silicon nitride films deposited on silicon beams. Platinum electrodes are deposited and patterned on the low-stress silicon nitride layers. A thermal elastic-plastic finite element model is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the cantilever tip deflection following heat treatment. A contact model is introduced to simulate the influence of contact on the residual stress distribution. The influences of the beam thickness and the platinum electrode length on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a smaller beam thickness leads to a larger compressive residual stress within the platinum electrode and delivers a larger tip deflection. The results also indicate that a larger platinum electrode length delivers a smaller tip deflection.
Simulation of ESA's msl Furnace Inserts and Sample-Cartridge Assemblies Using the Thermal Modeling Tool Crysvun
Authors: Hainke Marc , Dagner Johannes , Friedrich Jochen , Müller Georg
Published: March 2009

has commissioned the Crystal Growth Laboratory in the framework of the Materials
Science Laboratory (MSL) User Support Program to develop the MSL furnace inserts and samplecartridge assemblies Thermal Modeling Tool (TMT). The TMT assists the definition, preparation and analysis of the experiments onboard the International Space Station (ISS). The tool is based on the CrysVUn software, which was especially designed for global simulation of heat and mass transport processes during crystal growth and alloy solidification in high tem perature furnaces with complex (axi-symmetric) geometries. The main features of CrysVUn are briefly presented in this paper. The preliminary thermal model of the Low Gradient Furnace is illustrated and the model optimization strategy using genetic algorithms is briefly explained. Initial correlation results show
that good agreement between simulated and measured axial temperature distributions is obtained. Direct modeling of the radiative heat transfer through the heater Multi-Layer Insulation (MLI) using view factors appears to be necessary for an accurate predict on of the resulting heater power. An example for the application of the TMT is presented.
Embedding of Ceramic Particles in Metals Using Different Techniques for Undercooling of Metallic Melts
Authors: Lierfeld Thomas , Kolbe Matthias , Herlach Dieter M. , Eggeler Gunther F.
Published: March 2009

Metal Matrix Composites (MMCs) have great technical potential as they combine the ductility of metals with the hardness of ceramics: the reinforced material has improved mechanical properties. MMCs are interesting for the use in automotive or aerospace applications, e.g. in rolling bearings or turbine components. Recent manufacture is done by expensive methods like powder metallurgy to disperse the ceramic particles homogeneously in the metal matrix. In this contribution, we report on an approach to understand the basic mechanisms governing direct casting of MMCs. The basic problem is the particle-solid/liquid-interface interaction during dendritic solidification of metallic melts containing ceramic particles. The experimental idea is to deeply undercool the melt below its melting point. This results in a fast propagating solidification front when the solidification occurs. Due to the rapid solidification, the microstructure is frozen instantaneously and can be investigated post-mortem. It is expected that particles are incorporated in the material in the case of rapid solidification. Experimental techniques are electromagnetic levitation under terrestrial conditions and low gravity conditions during parabolic flight. With the electromagnetic levitation technique, samples were undercooled up to 150 K under its melting points despite the presence of particles. The experiments under low gravity show the importance of the reduction of melt convection on particle distribution within the rapidly solidified sample.
Effects of the Interface Curvature and Dendrite Orientation in Directional Solidification of Bulk Transparent Alloys
Authors: Weiss Cedric , Bergeon Nathalie , Mangelinck-Noël Nathalie , Billia Bernard
Published: March 2009

The properties of structural materials are to a large extent determined by the solid microstructure so that the understanding of the fundamental physics of microstructure formation is critical in the field of materials engineering. A directional solidification facility dedicated to the characterization of solid-liquid interface morphology by means of optical methods has been developed by CNES in the frame of the DECLIC project. This device enables in situ and real time studies on bulk transparent materials. The aim of the project is to perform experiments in microgravity to eliminate the complex couplings between solidification and convection and to get reliable benchmark data to validate and calibrate theoretical modeling and numerical simulations. Presently, ground experiments are performed to finalize the design and the experimental procedures and to guarantee the accuracy of the measurements. These experiments also provide reference data for the study of solidification microstructure dynamics in the presence of buoyancy-driven natural convection. Recent progress is presented concerning the control of the interface shape (critical for pattern analysis), the selection of single crystal of defined orientation (critical for dendritic growth) and the analysis of the dendrite shape.
From Solidification Simulation to Virtual Product Development
Authors: Bähr R. , Honsel Christoph , Weiß K. , Todte M.
Published: March 2009

Although the use of the Finite Elements Method (FEM) has more and more become a natural course of action for the creation of component parts, not yet the whole potential of numerical simulation is used. The absences of interfaces between the different calculations, missing or inaccurate physical data as well as the lack of theoretical background in certain areas prevent a complete virtual product development. Design, solidification simulation, calculation of mechanical properties, stress calculations, and the prediction of the operating life of a component are at present almost exclusively regarded as separate solutions. Necessary however is a meshed computation loop, where the solutions of previous steps are moved on to the following ones. Due to improvements in the area of solidification simulation and with the help of new theoretical concepts for the prediction of mechanical properties of casted aluminum parts, it is now possible to do all the technical analysis with just one software package. This solves the interface problem and especially the error-prone change between different numerical calculation processes.
Chemical Diffusion Experiments in AlNiCe-Melts
Authors: Griesche Axel , Garcia-Moreno F. , Macht M.P. , Frohberg Günter
Published: March 2009

The long-capillary method was used to measure chemical diffusion in molten AlNiCe alloys. The interdiffusion coefficients were determined for a mean concentration of Al87Ni10Ce3 at 1273 K and for a mean concentration of Al77Ni20Ce3 at 1373 K. The absence of major convection disturbances and of macro-segregation was demonstrated by time-dependent diffusion measurements. An in-situ x-ray monitoring technique for real-time concentration profile determination is presented.
Thermo-Mechanical Analysis of Directional Crystallisation of Multi-Crystalline Silicon Ingots
Authors: M'Hamdi Mohammed , Meese Ernst A. , Laux Harald , Øvrelid Eivind J.
Published: March 2009

Multi-crystalline silicon ingot casting using directional crystallisation is the most costeffective technique for the production of Si for the photovoltaic industry. Non-uniform cooling conditions and a non-planarity of the solidification front result, however, in the build-up of stresses and viscoplastic deformation. Known defects, such as dislocations and residual stresses, can then occur and reduce the quality of the produced material. Numerical simulation, combined with experimental investigation, is therefore a key tool for understanding the crystallisation process, and optimizing it. The purpose of the present work is to present an experimental furnace for directional crystallisation of silicon, and its analysis by means of numerical simulation. The complete casting procedure, i.e., including both the crystallisation phase and the subsequent ingot cooling, is simulated. The thermal field has been computed by a CFD tool, taking into account important phenomena such as radiation and convection in the melt. The transient thermal field is used as input for a thermo-elasto-viscoplastic model for the analysis of stress build-up and viscoplastic deformation during the process. Numerical analysis is employed to identify process phases where further optimisation is needed in order to reduce generated defects.
Metastable Phase Formation in Undercooled Nd-Fe-B Alloys Investigated by In Situ Diffraction Using Synchrotron Radiation
Authors: Strohmenger Joern , Volkmann Thomas , Gao J.R. , Herlach Dieter M.
Published: March 2009

Diffraction experiments on electromagnetically levitated Nd-Fe-B alloys during solidification of the undercooled melt have been performed at the European Synchrotron Radiation Facility (ESRF). By using high intensity synchrotron radiation complete diffraction spectra could be detected within a short period of some seconds thus enabling the observation of metastable solidification products that exhibits a limited lifetime. A metastable phase that crystallizes in wide composition range and that initiates the solidification of the stable Nd2Fe14B1-phase (φ-phase) have been observed.
High Temperature Oxidation of Cr-ZrO2-Al2O3 Composite Fabricated by Mechanical Alloying and Spark Plasma Sintering
Authors: Arce-Colunga U. , Reyes-Valdes F.A. , Martínez-Villafañe A. , Orozco-Carmona Victor M. , Almeraya-Calderón F. , Saucedo-Acuña R.A. , De la Torre S.D.
Published: March 2009

The high temperature oxidation resistance of Cr-ZrO2-Al2O3 composites fabricated by mechanical alloying and spark plasma sintering (SPS) has been evaluated. Composite powders were prepared by ball milling Cr-5vol%ZrO2-50vol%Al2O3 powder mixtures. Powders were compacted by SPS in less than 5 min, so that a particular metal-ceramic interpenetrating network is obtained. High temperature oxidation tests (900-1100 0C) in air have revealed good oxidation resistance (1.8, 2.6 and 15.3 mg/cm2 at 900, 1000 and 1100 °C, respectively) due to a protective Cr2O3 layer. EDX analysis revealed that Cr diffusion takes place at 1100 oC from the bulk towards the composite surface leading to Cr depletion at near-surface zones. Chromium contained in the bulk tends to oxidize through oxygen diffusion apparently occurring along the grain boundaries.
The Transformation of Co-Rich Alloys Produced by Mechanical Alloying
Authors: Cruz-Gandarilla Francisco , Gayosso-Armenta R. , Cabañas-Moreno J. Gerardo , Balmori-Ramírez Heberto
Published: March 2009

Elemental powder mixtures of Co and Ti were subjected to high-energy ball milling in order to produce mechanically alloyed powders with nominal compositions Co64Ti36, Co67Ti33, Co70Ti30, Co73Ti27, Co76Ti24 and Co85Ti15. The mechanically alloyed powders were treated during 30 minutes in inert atmosphere at temperatures in the range 300 – 700 °C. Both the as-milled powders as well as those subjected to heat treatments have been characterized by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectrometry and differential thermal analysis. As-milled products consist mostly of agglomerated powders with a size between 10 and 80 µm which give an amorphous-like diffraction pattern, except for the Co85Ti15 sample whose pattern presents the characteristic peaks of the Co3Ti intermetallic phase. The transformation of the asmilled powders occurs at temperatures in the range of about 530 – 670 °C with clearly observed exothermic events. The Co3Ti phase is found in all heat treated samples, together with fcc-Co (in Co76Ti24 and Co85Ti15) or the hexagonal Co2Ti intermetallic phase (in Co64Ti36, Co67Ti33 and Co70Ti30); the Co73Ti27 sample was essentially single-phase Co3Ti after heating to 700 °C. Our results suggest the occurrence of crystallization of an amorphous phase in two overlapping stages during heating of the mechanically alloyed powders.
Microstructure and Self-Affine Fracture Surface Parameters in Steel
Authors: Niño J. , Hinojosa M. , González V.
Published: March 2009

The fracture surfaces of SAE-1018 steel tension and impact test specimens with different grain sizes are analyzed in order to explore the possible relations between the microstructure and the self-affine fracture surface parameters such as the roughness exponent, ζ, and the correlation length, ξ. The topography of the fracture surfaces was observed and quantified by means of scanning electron microscopy, atomic force microscopy, optical microscopy and optical digitizer. It is confirmed that the fracture surfaces exhibit a self-affine behavior extending over six decades of length scale, from nanometers up to a few millimeters. The roughness exponent exhibits a value of ζ∼0.82 for all the cases regardless of the microstructural condition.
Strain-Resistivity Behavior of a Ti-45Ni-5Cu Shape Memory Alloy during Superelastic and SATWME Cycling
Authors: López Cuellar E. , Guénin Gérard , Morin Michel
Published: March 2009

The strain-resistivity behavior of Ti-45.0Ni-%.0Cu wires has been measured during
superelastic cycling. The results are in good agreement with previous results, showing that the main changes of resistivity during superelastic cycling are due to Austenite ↔ Martensite phase changes and anisotropic variant orientation. The true plastic strain (dislocations) does not seem to play an important role for this alloy.
Synthesis and Structural Investigation of Nano-Sized BaTiO3 Powders
Authors: Moon S.M. , Cho Nam Hee
Published: March 2009

~100 nm-sized BaTiO3 powders were prepared by hydro-thermal techniques, and the structural features of the powders were investigated as a function of synthesis temperature and time. The spectral features of (200) XRD peaks and FT-Raman peaks at frequencies of 305 and 710 cm-1, which are sensitive to the presence of tetragonal BaTiO3, indicate that the nano-sized BaTiO3 powders are dominantly of a cubic phase, but the tetragonal phase is also exhibited at room temperature. The tetragonal and cubic phases exist in the core and shell regions in the powder, respectively; the difference in lattice spacing between the core and the shell regions is 0.061 Å, and the thickness of the cubic-phased shell region of the powders prepared at 180°C for 24 hrs is 3 nm.
Fabrication of Nanoscale SiC-Based Ceramic Patterns with Near-Zero Residual Layers by Using Imprinting Technique and Reactive Ion Etching
Authors: Park Kyoung Hoon , Park Jun Hong , Kim Dong Pyo
Published: March 2009

Nano-scale SiC-based ceramic patterns on Si substrates were fabricated via imprint lithography technique by using viscous polyvinylsilane as a ceramic precursor and economic nano-scale master such as CD, followed by pyrolysis at 800oC under nitrogen atmosphere. The thickness of residual layers was controlled by varying the spin-coating conditions (solution concentration, spinning speed) and the patterning conditions (molding pressure). In addition, for the effective removal of the remaining residual layer, the etching kinetics of both polymeric and ceramic patterns was also comparatively studied by Ar or reactive ion etching process.
Environmentally Conscious Gas Mixtures for Magnesium Melt Protection
Authors: Ha Won , Youn Jeong Il , Kim Young Jig
Published: March 2009

The candidate gases for the replacement of SF6 in magnesium melt protection were reviewed from the viewpoint of environmental effects, melt protection properties, and chemical properties. The surface films formed under fluorine bearing gases were analyzed by using XPS. The XPS results revealed that the surface films consist of MgO and MgF2. The fluorine content of the surface film increases with increasing gas concentration and exposure time. The Pilling- Bedworth ratio (PBR) of MgO was 0.73, and the porous magnesium oxide could not cover the whole melt surface. PBR of MgF2 was 1.29, and the surface film which contains MgF2 could cover a lager area of the melt surface. This higher PBR of composite surface film prevented further oxidation and evaporation of magnesium.
Antibacterial Effect and Security Evaluation on Nano-Hydroxyapatite Bearing Cu2+ and Zn2+
Authors: Li Ji Dong , Li Yu Bao , Zuo Yi , Lv Guo Yu , Yang Wei Hu , Tian Zhi Yue
Published: March 2009

Nano-hydroxyapatite (n-HA) slurry was synthesized at normal pressure, and (Cu2+, Zn2+)-bearing nano-hydroxyapatite (Cu-Zn-HA) was prepared by ion exchange reaction in water medium. The properties of n-HA and Cu-Zn-HA were characterized by AAS, TEM, XRD and FTIR. The results of XRD analysis indicate that Cu2+ and Zn2+ can occupy Ca2+ sites and enter the crystal lattice of hydroxyapatite. Through the antibacterial experiments, it was found that Cu-Zn-HA had better antibacterial ability on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). After heat treatment at 400°C for an hour, the materials still had good antibacterial effect. The accelerated aging method was employed to test antibacterial durability of the material and the results indicated that the durability was good. The results of the security assessment, including skin stimulation test
of rabbit, acute toxicity test by stomach filling and the micronucleus test in bone marrow polychromatic erythrocytes of mice, showed that the security of the material was excellent.
Surface Properties of Ag-Cu-Zr Liquid Alloys in Relation to the Wettability of Boride Ceramics
Authors: Novakovic R. , Muolo Maria Luigia , Ricci E. , Ferrera E. , Giuranno D. , Gnecco F. , Passerone Alberto
Published: March 2009

The wetting phenomena and adhesion between Ag-Cu-Zr molten alloys (where Zr is an active brazing element) and ZrB2-ceramic substrate have been investigated from theoretical and experimental point of view. The wetting phenomena of molten alloy/ceramic substrate depend on the bonding characteristics of liquid alloys and ceramics as well as the magnitude of interactive forces at the interface. Accordingly, the first step of this investigation is to determine the surface properties of Ag-Cu, Ag-Zr and Cu-Zr liquid alloys. The energetics of the bulk and the surface of
liquid alloys have been analysed in the framework of statistical mechanical theory in conjunction with Quasi-Lattice Theory (QLT), through the study of the concentration dependence of various properties such as surface tension, surface composition, concentration fluctuations in the long wavelength limit and Warren-Cowley chemical short-range order parameter. Combining the Young and the Dupré equations, the obtained values of surface tension together with contact angle data
have been used to calculate the work of adhesion.
Convection in Weld Pool under Microgravity and Terrestrial Conditions
Authors: Fujii Hidetoshi , Sogabe Nobuyoshi , Nogi Kiyoshi
Published: March 2009

Electron beam (EB) welding and tungsten inert gas (TIG) welding were performed under both microgravity and terrestrial conditions in order to investigate the effects of gravity and surface tension on the convection in a molten pool. The microgravity conditions were achieved using the drop-shaft at the Japan Microgravity Center (JAMIC). A small-sized EB or TIG welding system was
loaded into the drop capsule, and then the capsule was dropped 710m below ground level. The system attains a microgravity level of 10-5 G for a duration of 10 seconds. Pure iron and an iron-tungsten alloy (SKD4) were used for the iron samples, while pure aluminum and an aluminum-copper alloy (A2219) were used for the aluminum samples. The cross sections of the specimens were analyzed by EPMA after the welding to investigate the distribution of the minor elements. During the EB welding,
the surface tension and the buoyancy determine the convection. Under microgravity, only the surface tension causes the convection because the buoyancy is considered to be negligible. As a result, it was found that the convection due to the surface tension is dominant for the iron alloys, but it is very weak
for the aluminum alloys.
Comparison of Shot Peening and Nitriding Surface Treatments under Complex Fretting Loadings
Authors: Kubiak Krzysztof , Fouvry Siegfried , Wendler Bogdan
Published: March 2009

Considered as a plague for numerous industrial assemblies, fretting associated with small oscillatory displacements is encountered in all quasi-static contacts submitted to vibrations. According to the sliding conditions, fretting cracks and/or fretting wear can be observed in the contact area. On the other hand an important development has been achieved in the domain of surface engineering during the past three decades and numerous new surface treatments and coatings are now available. Therefore there is a critical challenge to evaluate the usefulness of these
new treatments and/or coatings against fretting damage. To achieve this objective, a fast fretting methodology has been developed. It consists in quantifying the palliative friction, cracking and wear responses through a very small number of fretting tests. With use of defined quantitative variables, a normalized polar fretting damage chart approach is introduced. Finally, to evaluate the performance of the assemblies after these protective surface treatments under complex fretting loadings, an original sequence of partial slip and gross slip sliding procedure has been applied. It
has been demonstrated that performing of a very short sequence of gross slip fretting cycles can critically decrease the resistance of the treated surfaces against cracking failures activated under subsequent partial slip loadings.
Change of Micromechanical Properties of Polyethylene Induced by a Tribological Process in Polymer/Metal System
Authors: Maszybrocka J. , Cybo Jerzy , Frąckowiak J.E. , Krzemień K.
Published: March 2009

The influence of a tribological process in the polymer/metal system on changes in
microhardness (H) and Young’s modulus (E) of the surface under friction and UHMWPE volume has been studied. Twelve samples of polyethylene characterized by a different degree of initial plastic deformation and different electron irradiation dose were analyzed. For four of the samples a decrease by 5÷10 times in polyethylene degradation has been found. This result is promising in that a prolonged durability can be expected in case of application for endoprostheses
acetabular cups. It has been found also that a polyethylene material irradiated after initial prestraining only once shows enhanced micromechanical properties after friction. It has been found that this result was due to reorientation of lamellas on the friction surface taking place during deformation which accompanies the tribological process. It has been proved that the increase of H and E values in the layers situated at a depth of 1.5 mm÷7.5 mm is due to a decrease of the free
volume centers in the UHMWPE polyethylene and to an increase of the degree of spatial arrangement of the structure (absorption in crystallinity band of FTIR spectrum).
Extensibility of the Inter-Lamellar Amorphous Layer and the Mechanical Behaviour of Polyethylene
Authors: Viana Julio , Cunha Ermelinda M.
Published: March 2009

The mechanical behaviour of semicrystalline polymers is dependent upon the property of both the amorphous and crystalline phases and their eventual interactions. In this context, heat shrinkable films have been evidenced as an interesting material model to investigate the influence of the amorphous phase on the mechanical behaviour of semicrystalline polymers, as upon heating these materials only show changes on the extensibility of the amorphous phase (macromolecular
conformational state). The effect of the amorphous phase on the mechanical behaviour can therefore be studied independently. In this work are investigated the mechanical properties of a heat shrinkable polyethylene films as processed and after annealing at 60 °C (for 15 min). The morphology of the film before and after the annealing treatment was characterised by 2D-SAXS patterns. The tensile tests were performed at 50 mm/min and room temperature (23 °C) in different directions respectively to the longitudinal film direction, LD (0, 30, 45, 60 and 90º). The results show that the conformational state of the amorphous phase affects the tensile modulus and the deformation capabilities of the films, namely in the transverse machine direction. No influence on the sustained stress level was observed. Furthermore, the essential work of fracture is determined at large extent by the conformational state of the amorphous phase. This study suggests the high
importance of the amorphous network on the initial strain levels and on deformation capabilities of the lamellar structure loaded transversely to the crystalline phase orientation.
Influence of PCA Content on Mechanical Properties of Sintered MA Aluminium
Authors: Cintas Físico Jesus , Martos Juan Manuel Montes , Cuevas Francicso Gomez , Gallardo José M.
Published: March 2009

Aluminium powder has been mechanically milled using different amounts of process control agent (PCA). Mechanically alloyed aluminium powder (MA Al) was prepared by attrition milling in the presence of 1.5 and 3wt.% of an EBS wax. Milling was carried out in vacuum during 10 h. Milled powders were consolidated by a press-and-sintering method. This consolidation method is not usually employed with MA Al powders. The amount of dispersed carbides formed in the Al powder increases with the percentage of PCA. These carbides restrain Al grain growth during sintering, resulting in consolidated compacts with a grain size of about 550 nm. Thus, these PM materials can be considered ultrafine grained materials. Due to grain refinement and dispersion strengthening, the tensile strength of MA Al specimens is increased remarkably.