bluuebunny/crossref_metadata_2025 huggingface dataset:
Processing Low and Ultra-Low Carbon Bainitic Steels with Excellent Property Combinations
Authors: Suikkanen P.P. , Kömi Jukka , Karjalainen L. Pentti
Published: March 2009

Six experimental low and ultra-low carbon C-Mn-Mo-Nb-B and one conventional TMCP steel heats have been prepared to study the effects of chemical composition and hot deformation on the microstructure and the strength-toughness properties. In physical simulation tests, it was found that the deformation of austenite below the non-recrystallization temperature enhances the formation of higher-temperature bainitic morphologies and polygonal ferrite. On the other hand, hardness exhibits relatively low sensitivity to the degree of deformation below Tnr, whereas the deformation results in a distinct refinement in the microstructures, as determined by SEM-EBSD measurements, suggesting an improvement in the impact toughness. Simultaneous alloying with Mo-Nb-B seemed to be most efficient to provide high hardness and strength. Hot rolling trials indicated that the yield strength in the range 500-700 MPa with the excellent toughness down to –80 °C can be achieved in low carbon (≈ 0.03%) bainitic grades.
High Performance Bainitic Steels
Authors: Bhadeshia Harshad K.D.H.
Published: March 2009

The choreography of atoms during the course of the bainite transformation has major consequences on the development of structure. In particular, the scale and extent of the structure is dependent directly on the fact that the atoms move in a disciplined fashion. This information can be exploited to develop unconventional alloys - for example, rail steels which do not rely on carbides for their properties, and the hardest ever bainite which can be manufactured in bulk form, without the need for rapid heat treatment or mechanical processing.
Thermodynamic Investigation of Liquid Alloys in Ga-Sb-Bi-Sn System
Authors: Živković Dragana , Katayama Iwao , Živković Živan , Manasijević Dragan
Published: March 2009

The results of thermodynamic investigation of some liquid alloys in Ga-Sb-Bi-Sn system, obtained by calculation according to different thermodynamic predicting methods, are presented in this paper. The research was done based on the known experimentally obtained thermodynamic properties of related binary and ternary subsystems. Calculated data on a Ga-Sb-Bi-Sn system include thermodynamic properties for liquid alloys at temperature of 900K in chosen sections of investigated quarternary system with molar ratios of Sn:Sb:Bi = 6:3:1; 8:1:1 and 6:1:3.
Recycling Mechanism of Discontinuously Reinforced Al Matrix Composites
Authors: Fan Tong Xiang , Yang Guang Jun , Chen Jian Qi , Zhang Di , Shi Zhongliang , Shibayanagi Toshiya , Naka Masaaki
Published: March 2009

In the present work, the effects of reinforcement type, reinforcement surface treatment, alloying additions, remelting time and remelting number upon the chemical and property degradations of discontinuously reinforced Al matrix composites, are investigated by means of Differential Scanning calorimeter (DSC), Transmission Electron Microscopy (TEM) and thermodynamic calculations. The results show that the SiCp/Pure Al and SiCp/wrought Al alloy composites could not be recycled via remelting, nevertheless SiCp/foundry Al alloy and Al2O3p/Al composites could be recycled via remelting. The remelt-recycling mechanism of discontinuously reinforced Al matrix composites is also discussed in detail in the present work.
Effect of Superficial Residual Stresses on Abrasive Wear Resistance of Al2O3 / Al2O3+3Y-TZP Multilayers
Authors: de Portu Goffredo , Micele L. , Prandstraller D. , Palombarini G. , Pezzotti Giuseppe
Published: March 2009

Multilayered composite specimens consisting of Al2O3 / Al2O3+ 3Y-TZP (A/AZ) layers with different compositions and thicknesses were prepared starting from ceramic sheets obtained by tape casting. Residual stresses arisen from mismatch in thermal expansion coefficient during sintering were evaluated using luminescence piezo-spectroscopy. The stress in the superficial A layer was found to be compressive, and its value depended on the ratio between thickness of A and AZ layer. The influence of the superficial compressive stress on the abrasive wear resistance was investigated using microscale ball cratering test; results were correlated with the superficial compressive stress and compared with a specimen of pure unstressed Al2O3 prepared both by lamination and by cold isostatic pressing. Experiments show an improvement of performances in the samples containing compressive residual stress in the surface.
Concurrent Coupling of Electronic-Density-Functional, Molecular Dynamics, and Coarse-Grained Particles Schemes for Multiscale Simulation of Nanostructured Materials
Authors: Ogata Shuji , Igarashi Takahiro
Published: March 2009

Feature sizes of useful electronic devices are becoming smaller and reaching nanometer ranges. There is increasing demand to perform dynamic simulations of such nano-devices with realistic sizes. To date, various kinds of simulation methods have been used for materials and devices including the density-functional theory (DFT) and the molecular dynamics (MD) for atomistic mechanics and the finite element method for continuum mechanics. We review recent progresses in our multiscale, hybrid simulation schemes that combine those methods. The coarse-grained particles (CG) method originally proposed by Rudd and Broughton [Phys. Rev. B58 (1998), p. R5893] has features suitable to such hybridization. We improve the CG method so that it is applicable to realistic nanostructured materials with large deformations. A novel hybridization scheme that couples the DFT method with the MD method is presented, which is applicable to virtually any selection of the DFT region in a wide range of materials. Hybrid DFT-MD simulations of the H2O reaction with nanostructured Si and alumina systems under stresses are performed, to demonstrate significant effects of stress on the chemical reaction.
Fabrication of Lotus-Type Porous Metals, Intermetallic Compounds and Semiconductors
Authors: Nakajima Hideo
Published: March 2009

Lotus-type porous materials, whose long cylindrical pores were aligned along the same direction, were fabricated by unidirectional solidification in a pressurized gas atmosphere. The pores were formed in the solidified materials as a result of precipitation due to supersaturated gas during solidification of the liquid material dissolved with gas atoms. The lotus-type porous materials with homogeneous size and porosity of the evolved pores can be obtained by the mould casting method with constant solidification rate for the materials with high thermal conductivity. On the other hand, the novel continuous floating zone melting method was invented to fabricate the porous materials with low thermal conductivity. Recently we succeeded in fabricating lotus-type porous materials such as various metals and alloys, intermetallic compound Ni3Al and NiTi, and semiconductor silicon. The fabrication conditions comprise a pressure up to 3.0 MPa and the use of a mixture gas of hydrogen (or nitrogen ) and argon (or helium). Such lotus-type porous materials are expected to be employed in various applications such as machine parts, biomedical materials, etc.
Superplastic Deformation of Ultrafine Grained Al Alloy Processed by ECAP and Post-Rolling
Authors: Park Kyung Tae , Lee Chong Soo , Kim Yong Suk , Shin Dong Hyuk
Published: March 2009

Superplastic behavior of an ultrafine grained (UFG) 5154 Al alloy processed by ECAP and cold rolling (ECAP+CR sample) was investigated and compared with that of the alloy processed by only ECAP without rolling (ECAP sample) in the strain rate range of 10-4~5×10-1 s-1 at 723 K. Processing of the ECAP+CR sample consisted of ECAP of 4 passes, which was less than that showing the optimum microstructure for high strain rate superplasticity of UFG Al alloys (i.e. 8 passes), with route Bc and subsequent cold rolling (70% thickness reduction). The superplastic elongation was remarkably enhanced by post-rolling. An analysis of the mechanical data revealed that deformation of the ECAP+CR sample was dominated by grain boundary sliding, but dislocation viscous glide was the main deformation mechanism for the ECAP sample. In addition, cavitation in the ECAP+CR sample was insignificant up to ∼300% elongation.
Evolution of Microstructure and Precipitation in Heat-Treatable Aluminium Alloys during ECA Pressing and Subsequent Heat Treatment
Authors: Gao Nong , Starink Marco J. , Furukawa Minoru , Horita Z. , Xu Cheng , Langdon Terence G.
Published: March 2009

The precipitation and evolution of microstructure in a spray-cast Al-7034 alloy and a commercial wrought Al-2024 alloy were studied after equal-channel angular pressing (ECAP) using transmission electron microscopy and differential scanning calorimetry (DSC). Microstructural examination showed the grain sizes of both alloys were reduced to the range of ~0.3–0.5 μm through ECAP. The DSC analysis identified the occurrence of thermal effects involving the formation, coarsening, dissolution and melting of the precipitate phases and concurrent recrystallization. The heating and ageing response of the alloys processed by ECAP was identified by micro-hardness testing of the samples after interrupted heating and ageing treatments.
On the Grain Refinement Mechanisms in SPD – Applying High Resolution Electron Microscopy and the LEDS Approach
Authors: Werenskiold Jens C. , Roven Hans Jørgen
Published: March 2009

The present work is an attempt to contribute the current understanding of the operating mechanisms responsible for the development of ultrafine grains during severe plastic deformation (SPD) in aluminium. Equal channel angular pressing (ECAP) at room temperature has been applied to a commercial Al-Mg-Si alloy. Route A was used in all pressings and the first two passes were studied in most detail. Advanced characterization methods such as FEG-SEM with a state-of-the-art
microdiffraction unit has been applied when characterizing samples carefully prepared from different positions along certain flow paths in the process shear zone. Intrinsic strain measurements are done in parallel in order to describe the actual strain tensor in each position studied. Detailed information on phenomena involved in the grain break-up mechanisms has been obtained by high resolution EBSD data collected through the deformation zone. The microstructural development seems to be dominated by deformation banding and may be explained in terms of the LEDS theory.
Studies of Severe Plastic Deformation Conditions for Amorphous and Nanocrystalline Structures Formation in Ti-Ni Based Alloys
Authors: Prokoshkin Sergey , Khmelevskaya I. , Dobatkin Sergey V. , Tatyanin E.V. , Trubitsyna I.B.
Published: March 2009

Structure formation in TiNi-based shape memory alloys depending on deformation temperature (-196 °C to 400 °C) and pressure (4 to 8 GPa) under conditions of high-pressure torsion (HPT) was studied using TEM and X-ray diffraction methods. The tendency to form an amorphous structure depends on relative positions of the deformation temperature and Ms temperature. Isothermal martensitic transformation is observed in the Ti – 48.5 % Ni alloy as a result of 10-year keeping at RT after HPT. Increasing of pressure suppresses the tendency to form an amorphous structure. The upper deformation temperature limits for amorphous and nanocrystalline structures formation are determined. The thermomechanical conditions of the equal-channel angular pressing for obtaining actual nanocrystalline structure are recommended.
Effect of Equal Channel Angular Pressing and Repeated Rolling on Structure, Phase Transformations and Properties of TiNi Shape Memory Alloys
Authors: Pushin V.G. , Valiev Ruslan , Zhu Yuntian T. , Prokoshkin Sergey , Gunderov Dmitriy , Yurchenko L.I.
Published: March 2009

The nanostructured TiNi-based shape-memory alloys were synthesized by multi-step SPD deformations – ECAP plus cold rolling or drawing. It is found that the SPD processing changed the morphology of the martensite and temperature of martensite transformation. Also, we found that the mechanical and shape memory properties can be enhanced by forming nanostructures in these alloys. SPD processing renders higher strength, higher yield dislocation strength and in results - higher recovery stress and maximum reverse strain of shape memory.
Deformation Induced Vacancies with Severe Plastic Deformation: Measurements and Modelling
Authors: Zehetbauer Michael J. , Steiner Gerd , Schafler Erhard , Korznikov Alexander V. , Korznikova E.
Published: March 2009

In discussing hardening characteristics in terms of crystalline lattice defects, in most cases the properties and kinetics of dislocations and their arrangement have been considered. However, during plastic deformation also vacancies and/or vacancy type defects are produced in very high densities which are typically close to those of vacancies in thermal equilibrium at the melting point. The effect of high vacancy concentrations on the hardening characteristics is twofold: (i) direct effects by impeding the movement of dislocations (ii) indirect one by inducing climbing and annihilation of edge dislocations leading to softening or even absolute decreases in strength. This paper presents first measurements of deformation induced vacancies in SPD materials which have been achieved by combined evaluation of resistometry, calorimetry and X-ray diffraction. The density of vacancies during and after SPD deformation is found to be markedly higher than in cases of conventional deformation and/or coarse grained material which may be partly attributed to the particular conditions of SPD namely the enhanced hydrostatic pressure as well as the changes in deformation path. It is suggested to make this high vacancy concentration responsible for both dynamic and static recovery and/or recrystallisation processes recently found during and after SPD, being potential reasons for enhanced ductility and superplasticity which only occur with nanomaterials originating from SPD. Recent publications show that in alloys, SPD induced vacancies can also enable the existence of phases which do not appear in the equilibrium diagram.
The Influence of the SPD Temperature on Superplasticity of Aluminium Alloys
Authors: Islamgaliev Rinat K. , Yunusova N.F. , Valiev Ruslan
Published: March 2009

Recent studies have demonstrated that ultrafinе-grainеd (UFG) alloys processed by equal channel angular pressing (ECAP) and high pressure torsion (HPT) can exhibit enhanced supеrplacticity at relatively low temperature and/or high strain rates. At the same time severe plastic deformation (SPD) of aluminium alloys is often carried out at elevated temperatures leading to various grain size and volume fraction of precipitates. The significance of the SPD temperature for commercial 1420 and 1421 aluminium alloys has been evaluated in this paper using in-situ heating of thin foils in the column of a transmission electron microscope. Superplastic characteristics of alloys processed at various ECAP temperatures are discussed.
HPT-Deformation of Copper and Nickel Single Crystals
Authors: Hafok Martin , Vorhauer A. , Keckes Jozef , Pippan Reinhard
Published: March 2009

Copper and nickel single crystals of high purity with a crystallographic orientation, (001) and (111) respectively, were deformed by applying high pressure torsion (HPT) at room temperature. Special interest was devoted to the structural evolution of the material, which was characterized by electron backscatter diffraction (EBSD) and X-ray texture analysis as well. In addition back scatter electron investigations were applied to characterize shape and size of the new formed structure. Furthermore the study is focused on the micro structural and micro textural evolution that lead to the increase of missorientation angle with increasing plastic deformation. We observed an increasing fragmentation of the structure with increasing plastic equivalent strain up to a level where the grain size is saturated. The saturation could be traced back to dynamical recovery and recrystallisation during the deformation process that is depending on the purity of the material.
Nanocrystalline Formation during Mechanical Attrition of Cobalt
Authors: Zhou J. , Sun C. , Wu X. , Tao N.R. , Liu Gang , Meng X. , Hong You Shi
Published: March 2009

The nanocrystalline (nc) formation was studied in cobalt (a mixture of ε (hexagonal close packed) and γ (face-centered cubic) phases) subjected to surface mechanical attrition treatment. Electron microscopy revealed the operation of
{ 10 10 }〈 1120 〉 prismatic and {0001}〈 1120 〉 basal slip in the ε phase, leading to the successive subdivision of grains to nanoscale. In particular, the dislocation splitting into the stacking faults was observed to occur in ultrafine and nc grains. By contrast, the planar dislocation arrays, twins and martensites were evidenced in the γ phase. The strain-induced γ→ε martensitic transformation was found to progress continuously in ultrafine and nc grains as the strain increased. The nc formation in the γ phase was interpreted in terms of the martensitic transformation and twinning.
Features of Texture and Structure Development in Zirconium under Equal Channel Angular Pressing
Authors: Perlovich Yuriy , Isaenkova Margarita , Fesenko Vladimir , Grekhov M. , Yu Seng Ho , Hwang Sun Keun , Shin Dong Hyuk
Published: March 2009

A detailed X-ray study of Zr rods, subjected to ECAP at 350oC by routes C and BC, was conducted by the new X-ray method of Generalized Pole Figures, combining texture measurement with registration of X-ray line profiles. The data analysis is based on conceptions of the texture formation theory, connecting features of grain reorientation with activated deformation mechanisms. A degree of reproduction of the same distinctive texture by successive ECAP passes with antecedent rotation of the rod reflects attendant structure changes in material.
Corrosion and Mechanical Behaviours of Cu-Cr In Situ Composites
Authors: Choi Y. , Song M.S. , Lee K.L. , Hong Sun Ig
Published: March 2009

The Cu-10vol.% Cr in situ composites were fabricated and their mechanical and corrosion properties were determined. For an equivalent amount of deformation, fcc-bcc composites have a much thinner effective fibre thickness and a much larger interfacial area than do fcc-fcc composite. The yield strength and the modulus of the composite decrease with temperature whereas the failure strain increases with temperature. The observed increase in failure strain with an increase in temperature from 22-600°C is as high as 333 %. Corrosion potential and rate in aerated hydro-sulfuric acid solution are -36.6 mVSHE and 3.525x10-3 A/cm2, respectively. Based on the electrochemical behaviors of the copper and chromium and observation of corrode surface, the corrosion mechanism of the copper-10% chromium composites in aerated hydro-sulfuric acid solution includes deallying mechanism in α-phase
and galvanic corrosion at the interface between copper and chromium.
Martensite Transformation of Ultrafine Grained Austenite in Fe-28.5at%Ni Alloy
Authors: Kitahara Hiromoto , Tsuji Nobuhiro , Minamino Yoritoshi
Published: March 2009

Martensite transformation of the ultrafine grained (UFG) austenite fabricated by the accumulative roll bonding (ARB) process was studied. The Fe-28.5at.%Ni alloy sheet was severely deformed in austenite state by the ARB process up to 5 cycles. The ARB processed sheet had the ultrafine lamellar boundary structure. The mean lamellar spacing was 230 nm in the 5 cycles specimen. The sheets ARB processed by various cycles were cooled down to 77 K to cause the martensite transformation. Martensite transformation starting (Ms) temperature decreased with increasing the number of the ARB process. The Ms temperature of the ultrafine lamellar austenite in the 5 cycles specimen was 225 K, which was lower than that (247 K) of the conventionally recrystallized specimen with mean grain size of 22 μm. The martensite having characteristic morphologies appeared from the UFG austenite, although the martensite transformed from the coarse-grained specimen showed typical plate (or lenticular) morphology. The strength of the nano-martensite transformed from the UFG austenite was about 1.5 times higher than that of the UFG austenite, and it reached to 970 MPa.
Effect of Severe Plastic Deformation on the Structure and Properties of the Age-Hardenable Mg-Sm Alloys
Authors: Rokhlin L.L. , Dobatkin Sergey V. , Dobatkina Tatiana V. , Nikitina N.I. , Popov Mikhail V.
Published: March 2009

In this work severe plastic deformation (SPD) was applied to magnesium base alloys of the Mg-Sm system (2.8-5.5 mass %Sm). These alloys are characterized by high strength at elevated temperatures and high strengthening effect during aging. SPD was performed by torsion under pressure of 4 GPa at 20 and 200°C to ε ∼ 6. SPD results in significant strengthening of the Mg-Sm alloys due to the formation of submicrocrystalline structure. In all cases SPD accelerates the solid solution decomposition upon subsequent aging. The highest strengthening can be obtained if the solution treated alloy is aged at 200°C after SPD at room temperature. The state of high strength can be also reached if the following sequence of the operations is used: solution treatment + aging at 200 °C up to maximum hardness + SPD at 20°C + aging at 200°C accompanied by Sm –rich phase precipitation in the submicrocrystalline matrix.
Texture Formation during ECAP of Aluminum Alloy AA 5109
Authors: Skrotzki Werner , Scheerbaum N. , Oertel C.G. , Brokmeier Heinz Günter , Suwas Satyam , Tóth László S.
Published: March 2009

The technical aluminum alloy AA 5109 with a strong cube rolling texture has been deformed at room temperature by equal channel angular pressing (ECAP) using three passes of route A. Samples for ECAP have been cut parallel and at 45° with respect to the rolling direction yielding different starting textures. The local texture after ECAP has been investigated by highenergy synchrotron radiation. It is characterized by typical shear components of face-centred cubic (fcc) metals which deviate from their ideal positions. The texture with respect to intensity and deviation from ideal positions of the components depends on the distance from the top of the extruded billet and changes from pass to pass. It is also strongly influenced by the starting texture. The texture gradient has been discussed in the light of Tóth’s flow line model. The texture results have also been compared with those of other fcc metals with different stacking fault energy.
Study of Hole-Machining on Pyrex Wafer by Electrochemical Discharge Machining (ECDM)
Authors: Liao Yunn Shiuan , Peng Wen Yang
Published: March 2009

The gap control problem in hole-machining of Pyrex® wafer by electrochemical discharge machining (ECDM) to obtain a smooth quality and acceptable material removal rate is studied. Analysis of the pulse signals shows that the average current pulse interval is constant, and it is mainly related to the ion translation conditions, such as the electrolyte concentration and the flushing strategy. The most steady and intense average current density can be obtained if the voltage on-time is
around 3 times the average current pulse interval and the voltage off-time is 1/4 of the on-time for bubble film dissipation. The utmost allowable feed rate at each depth is recorded as the reference of the feed rate in real continuous machining to avoid the damage to the wafer. By applying 80% of the extreme allowable feed rate, 99.9% quality-proved holes can be acquired. The diametric error at the entrance or exit is within 6%. Besides, there is no crater-like problem around the hole that facilitates
the succeeding bonding process. This study contributes to the successful production of reusable optical biological chips with integrated micro fluidic channels.
Chemical-Assisted Mechanical Polishing of Diamond Film on Wafer
Authors: Cheng Hong Ho , Chen C.C.
Published: March 2009

Diamond has been well recognized a strategic engineering material. It possesses excellent physical and chemical properties including the highest hardness and thermal conductivity, and good resistance to chemical erosion. Although CVD diamond film has good potential outstanding properties, its industrial applications have been limited by the non-uniform thickness and rough surface. In the current study, the CVD diamond film is polished by the chemical-assisted mechanical
method with different slurries. These slurries contain strong oxidation chemical and diamond powder. During the process, the diamond film was held against the rotational ceramic plate with transverse oscillation at 90 °Cor lower. The profilometer, atomic force microscope and scanning electron microscope were used to evaluate the surface integrity of the diamond films before and after
polishing. Based on the experimental results, the slurry containing potassium persulfate (K2S2O8) produces the highest material removal rate while potassium permanganate (KMnO4) develops the best local surface roughness. The strategy of using potassium persulfate for coarse polishing followed
by potassium permanganate for fine polishing yields the diamond films of the best global surface roughness. The average surface roughness of the diamond film produced by the proposed technique is below 10 nm after 5 hours.
A Fundamental Modeling Approach for Nano-Grinding of Silicon Wafers
Authors: Young Hong Tsu , Huang Hung Yi , Yang Ying Jay
Published: March 2009

The advantages of ductile regime grinding of silicon wafer such as smooth surface roughness (Ra < 10 nm) and minimum subsurface damage layer (< 10μm) have great impact on the production process of wafer. With ductile regime grinding, the subsequent processes such as etching and rough polishing processes can be minimized. To achieve ductile regime grinding, a fundamental concept is the application of grain depth of cut being less than the critical cut depth, dc, of the silicon wafer. However, dc is dependent on material properties, cutting conditions, and crystallographic orientation [1].The objective of this paper is to derive, and to investigate by experiment, the dc value for silicon wafer grinding. Following these key steps, the effects of dc on various major grinding parameters are studied.
Transducing Mechanical Forces Using a Polymer Optical Grating Sensor
Authors: Chuang Wei Ching , Ho Chi Ting , Lian Yi Ru , Chao Ching Kong , Shyu Ruey Fang , Wang Wei Chih
Published: March 2009

A new means of transducing mechanical force using a diffractive Bragg grating based polymeric sensor is presented. The diffraction gratings are successfully fabricated on a polydimethylsiloxane (PDMS) polymer using the holographic interference and micromolding technique. The micro MTS tensile test incorporated with the Raman experiment showed that a relationship between the load and the observed diffraction pattern shift could be obtained. The results show an excellent correlation between the optical measurements and load with a sensitivity of 0.05N.
Solidification and Melting – Asymmetries and Consequences
Authors: Rettenmayr Markus , Buchmann Martin
Published: March 2009

Solidification and melting are phase transitions from the liquid to solid state or vice versa and are thus often assumed to be similar processes with only opposite direction. However, they can be fundamentally different, i.e. asymmetric, in aspects of both thermodynamics and kinetics. It is known that superheat in the solid is difficult to obtain, unlike supercooling in the liquid. This is often attributed to the fact that nucleation in the liquid can occur (homogeneously or heterogeneously) in the bulk, in the solid it will occur at outer or inner surfaces of the crystal. A
further asymmetry is evident as the growing phase is a phase with fast diffusion kinetics in the case of melting, with slow diffusion kinetics in the case of solidification. Two types of experiments (solutal melting and melting/resolidification in a temperature gradient) are presented that allow an evaluation and quantification of the consequences of these asymmetries.
Marangoni Convection and Fragmentation in LASER Treatment
Authors: Drezet Jean Marie , Mokadem Sélim
Published: March 2009

Epitaxial Laser Metal Forming (E-LMF) consists in impinging a jet of metallic powder onto a molten pool formed by controlled laser heating and thereby, generating epitaxially a single crystal deposit onto a single crystal substrate. It is a near net-shape process for rapid prototyping or repair engineering of single crystal high pressure/high temperature gas turbines blades. Single crystal repair using E-LMF requires controlled solidification conditions in order to prevent the nucleation and growth of crystals ahead of the columnar dendritic front, i.e., to ensure epitaxial growth and to avoid the columnar to equiaxed transition. A major limitation to the process lies in the formation of stray grains which can originate either from heterogeneous nucleation ahead of the solidification front or from remelting of dendrite arms due to local solute enriched liquid flow, .i.e fragmentation. To study this last aspect, heat and fluid flow modelling is required to establish the relationship between process parameters such as laser power, beam diameter and scanning speed, and the local solidification conditions plus the fluid flow in the vicinity of the mushy zone. Surface tension driven convection known as the Marangoni effect needs to be included in the model owing to its large influence on the development of eddies and on the shape of the liquid pool. The 3D model implemented in the FE software calcosoft® is used to compute the fluid convection within the liquid pool and to assess the risk of fragmentation using a criterion based on the local velocity field and thermal gradient. The computed results are compared with EBSD maps of laser traces carried out at EPF-Lausanne in re-melting experiments.
A Brief History of the Science of Dendritic and Eutectic Growth until 1980
Authors: Kurz Wilfried
Published: March 2009

The evolution of our understanding of dendritic and eutectic growth is presented. The control of both phenomena is essential in solidification processing. In this article, the development of the most important concepts which evolved over essentially one century will be described. Some of the original contributions which came from solid state transformation theory will also be included. This paper traces the history of the experimental and theoretical (analytical) work but leaves the numerical approach of the last 25 years for future papers.
X-Ray Monitoring of Solidification Phenomena in Al-Cu Alloys
Authors: Mathiesen Ragnvald H. , Arnberg Lars
Published: March 2009

In-situ synchrotron X-ray radiography has been used to study columnar and equiaxed dendritic growth in directional solidification of Al-Cu alloys employing a Bridgman furnace. Nominal spatial and temporal resolutions of 1.5 µm and 150 ms, respectively, were obtained with a 1.3 %1.3 mm2 field of view, and a signal-to-noise above 99.5 %. Dedicated processing software has been developed to allow for quantitative extraction of data such as solid-liquid interface morphology, local propagation velocities and constitutional gradients from the images. The data
collected also contain unprecedented in-situ observations on dendrite fragmentation. The limited field of view together with a slight sample position dependency in the heat transfer coefficients made it necessary to impose thermal gradients, G > 10 K/mm, to have reproducible solidification processes. Non-vanishing horizontal G-components contributed to convection that at some occasions resulted in observable effects on growing crystals or on liquid segregates.
Micro Groove Forming on AlN/hBN Composites Using Powder Blasting Process
Authors: Cho Won Seung , Cho Myeong Woo , Park Dong Sam
Published: March 2009

In this study, powder blasting techniques are applied for micro groove forming on the
developed AlN/hBN composites. First, material properties of the composites are evaluated according to the variation of h-BN contents. And, a series of required experimental works are performed to determine optimum powder blasting conditions for micro groove forming. The experiments are performed for the prepared samples with masked patterns. As the results, it can be observed that the machiniability of the developed AlN/hBN composites increases as h-BN contents in the composites. Also, from the experimental results, it is possible to determine the optimum
blasting conditions for micro groove forming on the developed AlN/hBN composites.
Electrical Properties of (Ba,Sr)TiO3 Thin Films with Self-Seed Layer Deposited by R.F. Magnetron Sputtering
Authors: Park Chul Ho , Son Young Gook
Published: March 2009

Barium strontium titanate (Ba0.66Sr0.34TiO3) thin films and seed-layers were deposited on the Pt/Ti/SiO2/Si substrate by R.F. magnetron sputtering method. Effects of the substrate temperature on electrical properties of BST thin films were studied. The effect of seed-layer was also studied. From the XRD results, we could confirm that the seeding layer of BST thin film plays a key role in lowering
the crystallization temperature of BST thin films. When seed-layer was inserted between BST and Pt, the crystallization of the BST thin films was considerably improved and the processing temperature was lowered. Compared to the pure BST thin films, dielectric constant, dielectric loss, and leakage current of BST thin films deposited on the seed-layer were considerably improved. It could be
revealed that electrical properties are influenced by the substrate temperatures of BST thin films and are enhanced by the seed-layer.
Fabrication and Thermoelectric Properties of p-Type Bi1Sb4Te7.5 Alloy Doped with Fe3O4
Authors: Min Wang Kee , Lee Chang Ho , Park Yong Ho , Park Ik Min
Published: March 2009

We investigated the effects of Fe3O4 (0~0.1 wt.%) on the thermoelectric properties of Bi1Sb4Te7.5 alloy prepared by mechanical alloying process. The Seebeck coefficient increased with Fe3O4 content, but the power factor decreased with Fe3O4 content because of the decreased electrical conductivity. The thermal conductivity decreased with Fe3O4. The carrier concentration measured
by the Hall effect measurement decreased with Fe3O4. The thermal conductivity of 0.1 wt.% Fe3O4 alloy was 0.814 W/Km, 20%lower than that of Fe3O4 free alloy. As a result, the small addition of Fe3O4 improved the Z value owing to the decreased thermal conductivity by adding Fe3O4. The Z value of 0.01 wt.% Bi1Sb4Te7.5 alloy was 3.1×10-3 /K, the highest value among the prepared alloys.
Characterization of a Piezoresistive Microcantilever as a Sensor for Detecting the Bio-Molecules
Authors: Yoo Kyung-Ah , Na Kwang Ho , Joung Seung-Ryong , Jeon D. , Choi Y.J. , Kim Yong Sang , Kang C.J.
Published: March 2009

We propose an electrical detection method for detecting the various bio-molecules
effectively with microcantilevers. The piezoresistive microcantilevers were fabricated employing surface micromachining technique that has attractive advantages in terms of cost efficiency, simplicity, and ability of fabricating in array. The fluid cell system for injection of bio-molecular solution is fabricated using polydimethylsiloxane (PDMS) and a fused silica glass. The microcantilever is deflected with respect to the difference of the surface stress caused by the
formation of self-assembled bio-molecules on the gold coated side of the microcantilever. We confirmed that the deflections occurred by the bio-molecule adsorption and microcantilever can be widely used to a &-TAS and a lab-on-a-chip as a sensor for the potential detection of various biomolecules.
Characterization of Li1-xNi1+xO2 Prepared by Using Tartaric Acid as a Complexing Agent
Authors: Thongtem Titipun , Thongtem Somchai
Published: March 2009

Li1-xNi1+xO2 powder was prepared by using tartaric acid as a complexing agent. A 1 : 1 : 2 mole ratio of Li : Ni : tartaric acid was used to form carboxylate precursors which were calcined at 650–800 oC for 14–48 h. TGA of the precursors showed that formation of Li1-xNi1+xO2 initiates at 600 oC and above. By using XRD, Li1-xNi1+xO2 with 650–800 oC calcination was detected. Calculated intensity ratios of I(003)/I(104) and I(006+102)/I(101) showed that the best condition is at 750 oC for 34 h. The crystallite size was estimated using the Scherrer equation. AAS and titration techniques showed that Ni3+/(Ni3+ + Ni2+) and mean oxidation state of nickel are 66.50 wt% and 2.67 respectively. EDX showed that the powder was comprised by Ni and O. The faceted particles are shown by SEM. TEM and electron diffraction showed the results that are in accordance with the
above.
Evaluating the Electrochemical Properties in the Protection Potential of Material for Use in Al Vessels in Seawater
Authors: Kim Seong Jong
Published: March 2009

FRP (fiber-reinforced polymer) ships used with small boats for fishing pose numerous problems related to both the environment and recycling. From this perspective, aluminum offers an environmentally friendly substitute for FRP that is easy to recycle and imparts a high added value to fishing boats, with a reduction in fuel demands. The current density of 7075 Al alloy increases linearly with an increase in potential during anodic polarization, which implies that no passivation
of this alloy occurs. With 1050 and 5456 alloys, passive films form during anodic polarization but are destroyed by the Cl in seawater, only to regrow as a result of the self-healing capacity of aluminum. A shift to more anodic or cathodic conditions in the potential range of –1.5 ~ –0.68 V resulted in a sudden increase in current density. Current densities in the high-strength 7075 Al alloy showed the greatest values. In contrast, the current densities of 5456 alloy, known to have excellent
corrosion resistance in seawater, were the lowest in the range of –0.70 ~ –1.3 V, and we conclude that this potential range offers optimal protection.
In-Situ Joining of Combustion Synthesized Ni-Al Alloys with Al Casting Alloy
Authors: Cho Gue Serb , Lee Kang Rae , Choe Kyeong Hwan , Lee Kyong Whoan , Ikenaga Akira
Published: March 2009

We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic
compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and
x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental
powders. The reaction layer of about 25m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.
Nanocrystalline Structure of Organic Photoconducting Materials Derived by Microwave Recrystallization Method
Authors: Park Ji Hwan , Hwang Chae Ho , Son Dae Hee , Hong Seong Soo , Park Hong Chae , Park Seong Soo
Published: March 2009

We investigated the feasibility of preparing nanocrystalline oxotitanium phthalocyanine (TiOPc) from crude TiOPc using liquid-phase direct recrystallization under the microwave irradiation. Different crystal structures and morphologies of TiOPc were obtained through acidtreatment and recrystallization method. The nanocrystalline TiOPcs prepared in various conditions were characterized by the means of an X-ray diffractometry (XRD), a transmission
electron microscopy (TEM) and a photoconductivity measuring device.
Effect of Processing Parameters on the Fabrication of Al2O3p/Al Composites by In-Situ Reaction Process of Molten Al
Authors: Kim Hyung Jin , Kim Jae Dong , Kim M.H. , Koh Sung Wi , Kim Yeong Sik , Ryu J.I. , Um Yong Su
Published: March 2009

The effects of processing parameters such as addition type and Mg content on the
fabrication of Al2O3p/Al composites by in-situ reaction process of molten Al were investigated in terms of infiltration behavior of molten Al and the variation of the microstructure and hardness of the composites. It was ascertained that additional Mg content is the most important parameter for the infiltration of molten Al. Furthermore, increase in additional Mg content and processing temperature
resulted in a high infiltration ratio of molten Al and a high hardness value of the composites. However, these caused a greater scatter of the hardness value of the composites due to the nonuniform dispersion of the reinforcement phase, which arose from an excessive reaction of Mg.
Modification of Mg2Si Morphology in As-Cast Mg-Al-Si Alloys with Strontium and Antimony
Authors: Nam K.Y. , Song Dae Hyun , Lee C.W. , Lee S.W. , Park Yong Ho , Cho Kyung Mok , Park Ik Min
Published: March 2009

The effects of antimony (Sb) and strontium (Sr) additions on the microstructure of Mg-Al-Si alloys were studied. The results show that the additions of Sb and Sr can modify the Mg2Si particles from Chinese script shape to refined polygonal shape. Tensile strength and creep resistance are improved, and tensile elongation is also increased in the modified alloy. Sr modification is more effective than Sb modification of AS52 alloy for refining the microstructure and thus improving its
properties.
Development of Manufacturing Process Using Cold Incremental Forming Technique for Micro-Alloyed Non-Heat-Treated Material
Authors: Lee Hyoung Wook , Lee Geun An , Yoon Duk Jae , Choi Seo Gou , Lee Nak Kyu , Lee Hye Jin , Bae Sung Min
Published: March 2009

A micro-alloyed non-heat-treated material does not need post heat treatment processes such as quenching and tempering after the forming process in production stages. This material can be called a green material since it can reduce industrial costs and harmful pollutants generated from post heat treatments. In this paper, near-net-shape forming processes were studied in order to make an automotive part using a micro-alloyed material. The cold forging technique using a former was utilized for the main shaping, and the cold incremental forming technique using a cross wedge rolling machine was adopted for the enhancement of strength and the final shaping of the part. In order to get more adequate process, the cross wedge rolling process is compared to the swaging process for the micro-alloyed steel and general carbon steels through experiments.
Al-La-Ni-Fe Amorphous Alloys and Amorphous-Crystalline Composites Produced by Mechanical Alloying
Authors: Choi Pyuck Pa , Kim Ji Soon , Nguyen O.T.H. , Kwon Dae Hwan , Kwon Young Soon
Published: March 2009

Al-La-Ni-Fe alloys of three different compositions (Al82La10Ni4Fe4, Al85La9Ni3Fe3 and Al88La6Ni3Fe3) were prepared high-energy milling in a planetary ball-mill (AGO-2). Complete amorphization was observed for the Al82La10Ni4Fe4 alloy after milling for 350 h at a rotational speed of 300 rpm. In contrast, the Al85La9Ni3Fe3 and Al88La6Ni3Fe3 powders contained the FCC Al
phase even for prolonged milling. The amorphization tendency was found to increase in the order of Al88La6Ni3Fe3 < Al85La9Ni3Fe3 < Al82La10Ni4Fe4, which may well be ascribed to the increasing atomic size mismatch of the constituent elements on La addition. DSC analyses of amorphous samples revealed two-stage crystallization processes for all three alloys, however, with strong variations in the thermal stability upon compositional changes. As observed by SEM, amorphous
powders consisted of particles with nearly spherical shape and diameters ranging from 5 to 20 µm.
Improved Heat and Corrosion Resistance of Mg-Al-Zn Alloys by Additions of Minor Alloying Elements
Authors: Kim Jeong Min , Park Bong Koo , Jun Joong Hwan , Kim Ki Tae , Jung Woon Jae
Published: March 2009

Small amounts of minor alloying elements such as RE and Sr were added to Mg-
8wt%Al-5wt%Zn (AZ91D+4%Zn), and their effects on the microstructure, mechanical properties and corrosion resistance were investigated. The microstucture of the investigated alloys could be characterized by dendritic Mg, Mg17Al12, a quasi-crystalline Zn-rich phase, and Al4RE (if RE is
added). Although the tensile strength of alloys was not improved, the creep strength was significantly enhanced by the additions of minor alloying elements. No apparent influence of the additions could be found on the corrosion resistance.
Impact Evaluation to Human Body Skin of Titania Photocatalyst Fine Particles
Authors: Watanabe Eiji , Fukaya Mitsuharu , Taoda Hiroshi
Published: March 2009

The establishment of evaluation test method of the titania photocatalyst fine particle
impact to human body skin was attempted. In this method, the amount of emergence of carbon dioxide, which was expected one of the generation products from the artificial skin according to the titania photocatalyst fine particles activity, was identified and measured by the gas analyzer. It was found that the amount of the carbon dioxide evolution from the artificial skin was different according to the difference of the particle size of the titania photocatalyst fine particle.
Evaluation of Oxidation Behavior of the C-B4C-SiC Composite through Continuous Measurement of Mass Change and Gas Concentration
Authors: Uchiyama Yasuo , Abe Yusuke , Zheng Guo Bin , Sano Hideaki
Published: March 2009

Change in mass and gas concentration during oxidation of carbon matrix composite added with B4C and SiC particles as an inhibiter for oxidation were measured continuously and accurately using a thermogravimetric analyzer, a couple of zirconia type oxygen sensors and infrared CO-CO2 gas
analyzer. Total amount of oxygen consumed, the amount of oxygen consumed for matrix carbon oxidation, the amount of oxygen incorporated in CO and CO2 gases, total oxygen consumption rate during oxidation of the composite were obtained. The amount of glass phase formed from the inhibiter and the amount of matrix carbon oxidized could be estimated from calculation of a mole balance between the total oxygen consumption and the amount of oxygen incorporated in CO and CO2 gases.
Oxidation behavior and oxidation mechanism of the C-B4C-SiC composites were clarified.
Fabrication of Nano-Sized Gold Dot Array Using Bi-Layer Nano Imprint Lithography
Authors: Yang Ki Yeon , Hong Sung Hoon , Lee Heon , Choi Jeong Woo
Published: March 2009

UV nano imprint lithography (UV NIL) that uses a monomer based UV curable
monomer resin is proposed as a method of imprinting at low temperature and pressure. The fabrication of high fidelity patterns on a topographical substrate is a formidable challenge. To accomplish this, the use of bi-layer nano imprint lithography, which involves the use of an easily removable under-layer and an imprinted pattern, is proposed. We hypothesized that by etching the under layer by oxygen RIE, we might be able to build the bi-layer patterns for easy lift-off and fabricate nano-sized metal patterns through this lift-off process.