bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoscale Dynamics at Reactive Wetting Front on SiC
Authors: Tanaka Shun Ichiro , Iwamoto Chihiro
Published: March 2009

Nanoscale singularity at the reactive wetting front on SiC (0006) was studied using video recorded in situ to clarify the dynamic atomistic behaviours of the brazing and the molten tip spreading on a high-temperature stage of a high-resolution transmission electron microscope. An atomistic process controls the wetting at the front of the spreading film where the classical macroscopic phenomenon never holds true and the singularities are observed in a precursor film. A 0.5-nm-thick precursor film spreading ahead of the main molten alloy on SiC (0006) at 1073 K and continuous spreading of the molten alloy were clearly observed on the SiC (0006) surface with a less than 1-nm-thick amorphous layer. Molten Ti and TiC nanolayers preceded the Ti5Si3 nanolayer at the tip and they traveled continuously at a velocity of 14 nm/sec on the plane perpendicular to SiC (0006). Since Ti atoms in the molten alloy diffuse sufficiently rapidly on the SiC surface to the tip, the formation of these layers may be the rate-determining step of spreading. Discontinuous spreading of the precursor tip on SiC (0006) with a thick amorphous film was observed in contrast to the continuous spreading on SiC with a thin film. This suggests that the spreading of the Ti molten alloy on SiC is also controlled by the dissolution of the amorphous layer.
First-Principles Calculations of Metal/Oxide Interfaces: Effects of Interface Stoichiometry
Authors: Kohyama Masanori , Tanaka Shingo , Okazaki Kazuyuki , Yang Rui , Morikawa Yoshitada
Published: March 2009

Ab initio pseudopotential calculations of Cu/Al2O3 and Au/TiO2 interfaces have revealed strong effects of interface stoichiometry. About the Cu/Al2O3 system used for coatings and electronic devices, the interfacial bond of the O-terminated (O-rich) Cu/Al2O3(0001) interface is very strong with ionic and covalent Cu-O interactions, although that of the Al-terminated (stoichiometric) one is rather weak with electrostatic and Cu-Al hybridization interactions. About the Au/TiO2 system with unique catalytic activity, the adhesive energy between non-stoichiometric (Ti-rich or O-rich) TiO2(110) surface and a Au layer is very large, and there occur substantial charge transfer and orbital hybridization, which should have close relations to the catalytic activity.
Laser Weldability of Aluminum Alloy and Steel
Authors: Katayama Seiji , Joo Sung Min , Mizutani Masami , Bang Han Sur
Published: March 2009

With the intention of improving butt or lap joint of dissimilar materials, specially devised weld beads together with lap and butt-joints were produced between A5052 and SPCC, where A5052 butt-joint was melted by heat-conduction of SPCC weld bead in addition to the formation of a limited weld fusion zone at the lap part in A5052 alloy. The thickness of intermetallic compounds at the butt-joint interface was approximately 2 μm and free of cracks. It was also revealed that crack-free lap weld metals were formed between aluminum alloy and steel when the penetration was controlled to be of less than 0.3 mm in depth at small heat input. It was moreover found that the majority of a laser weld fusion zone solidified as alpha(bcc)-iron phase containing small amount of aluminum, and cracks were absent in the case of hard intermetallic (AlxFey type) layer of less than 10μm zone. It was confirmed that a weld with lap and butt joints possessed high strength (leading to the load 3500 N to 4,380 N for 40 mm width specimen). In addition, SPCC and A1100 or A5052 were subjected to lap welding with a cw YAG laser, where one to three passes were performed to produce wider bonded areas. Dissimilar steel and aluminum joints with good mechanical properties were obtained, since the fracture occurred in the aluminum alloy base metal in the tensile test. It is concluded that welded joints of high strength can be produced between aluminum alloy and steel with proper devices.
Improvement of Solution Type Plasma Spraying Process
Authors: Futamata Masami , Gai Xiaohui , Mizumoto Toyokazu , Nakanishi Kimio
Published: March 2009

To fabricate thermal spraying coatings with good reproducibility, it is necessary to improve the process of the equalization of both thermal history and impacting behavior of the particles. In this study, the characteristics of the solution type plasma spraying using the hollow-cathode type torch are investigated. The physical and mechanical properties that are different from usual thermal spraying coatings are described. By using solutions including metal ingredients in a state of ion, colloid or sol, thinner coating that cannot be made by conventional plasma spraying methods is formed on various substrates. The coatings are uniform in appearance.
Cluster, Surface and Bulk Properties of ZnCd Binary Alloys: Molecular-Dynamics Simulations
Authors: Erkoc Sakir
Published: March 2009

The structural and electronic properties of isolated neutral ZnmCdn clusters for m+n £ 3 have been investigated by performing density functional theory calculations at B3LYP level. The optimum geometries, vibrational frequencies, electronic structures, and the possible dissosiation channels of the clusters considered have been obtained. An empirical many-body potential energy function (PEF), which comprices two- and three-body atomic interactions, has been developed to investigate the structural features and energetics of ZnmCdn (m+n=3,4) microclusters. The most stable structures were found to be triangular for the three-atom clusters and tetrahedral for the four-atom clusters. On the other hand, the structural features and energetics of Znn-mCdm (n=7,8) microclusters, and Zn50, Cd50, Zn25Cd25, Zn12Cd38, and Zn38Cd12 nanoparticles have been investigated by performing molecular-dynamics computer simulations using the developed PEF. The most stable structures were found to be compact and three-dimensional for all elemental and mixed clusters. An interesting structural feature of the mixed clusters is that Zn and Cd atoms do not mix in mixed clusters, they come together almost without mixing. Surface and bulk properties of Zn, Cd, and ZnCd systems have been investigated too by performing molecular-dynamics simulations using the developed PEF. Surface reconstruction and multilayer relaxation on clean surfaces, adatom on surface, substitutional atom on surface and bulk materials, and vacancy on surface and bulk materials have been studied extensively.
Subgrain Size-Distributions, Dislocation Structures, Stacking- and Twin Faults and Vacancy Concentrations in SPD Materials Determined by X-Ray Line Profile Analysis
Authors: Ungár Tamás
Published: March 2009

The fundamentals of X-ray line profile analysis are summarised in terms of subgrain size and size-distribution, dislocation density and dislocation types, especially edge and screw dislocations, intrinsic and extrinsic stacking faults and twin boundaries and vacancies produced during plastic deformation. It is shown that deformation induced vacancy concentrations in the grain boundaries of compressed copper polycrystals are close to the equilibrium values at the melting temperature. The discrepancy between X-ray and TEM size values is discussed in terms subgrain- and grain size. It is shown that this apparent discrepancy might be used to determine the status of fragmentation by severe plastic deformation.
Outlook for Manufacturing Materials by Severe Plastic Deformation
Authors: Lowe Terry C.
Published: March 2009

Six years have passed since the international workshop “Investigations and Applications of Severe Plastic Deformation” held 2-8 August 1999 in Moscow, Russia. This workshop focused on severe plastic deformation (SPD) processing to produce bulk nanostructured metals and alloys. Since 1999 the field has expanded from 200 to over 2000 publications that have addressed the microstructures and properties that can be produced by a growing number of SPD techniques. In view of this expansion, the outlook for ongoing development of severely deformed materials is updated. Special attention is given to factors influencing the manufacturing and commercialization of SPD-processed metals, including barriers to their widespread application. Recommendations are made for future SPD research that will facilitate more rapid commercialization of SPD-processed metals and enhance the competitiveness of SPD processing with respect to alternative technologies for producing bulk nanostructured metals.
Hydriding Properties of the Mechanically Deformed Mg-Ni Alloys
Authors: Ikeda Kazutaka , Nakamori Yuko , Orimo Shinichi
Published: March 2009

Mechanical deformations with/without elemental substitutions have been carried out on Mg-Ni-based alloys to improve their hydriding properties. The alloys Mg-x at.%Ni (x = 33, 38, 43 and 50) with different nanometer-scale structures were successively synthesized by mechanical milling of Mg2Ni mixed with various amounts of additional Ni, and the relations between their structural and hydriding properties were investigated in detail. By milling only Mg2Ni, nanostructured Mg2Ni composed of the intra- and inter-grain regions was obtained (x = 33). Amorphous MgNi (a-MgNi) as a third region was dispersed around the nanostructured Mg2Ni by milling of Mg2Ni mixed with additional Ni (x = 38 and 43), and the pure amorphous MgNi was homogeneously synthesized in equivalent composition (x = 50). The coordination numbers and interatomic distances of the Mg-D and Ni-D correlations in the amorphous MgNi-D show that deuterium occupies the interstitial tetrahedral site composed of nearly [2Mg2Ni]. According to the specific structural properties, there is obvious miscibility gap (plateau) pressure higher than 1 × 10-4
MPa at room temperature even in the amorphous phase, and the total hydrogen content reached up to 2.2 mass%. Further studies on an amorphous MgNi-based system were carried out to clarify the effect of the short-range ordering on the structural and hydriding properties due to substitution of Mg- and Ni-sites by various elements.
Microstructure and Mechanical Properties of Pure Nickel Processed by Severe Plastic Deformation
Authors: Nurislamova G.V. , Islamgaliev Rinat K. , Valiev Ruslan
Published: March 2009

Microstructure and mechanical properties of pure nickel processed by high pressure torsion (HPT) and equal channel angular pressing (ECAP) have been investigated in the present paper. The uniformity of microstructure and misorientation angles in the SPD samples were studied using transmission electron microscopy and electron back scattering diffraction. Microstructural requirements for achivement of high strength and ductility in SPD metals are discussed.
The Influence of the ECAP Temperature on Microstructure and Mechanical Properties of a Magnesium Alloy
Authors: Kulyasova Olya B. , Islamgaliev Rinat K. , Krasilnikov Nikolay A.
Published: March 2009

The influence of the equal channel angular pressing (ECAP) temperature (150-350oC) on microstructure of the AM60 magnesium alloy has been investigated using transmission electron microscopy. It was demonstrated that application of various ECAP regimes leads to significant difference in a grain size and volume fraction of precipitates in investigated material. Thermal stability of precipitates and correlation between microstructure and tensile strength are discussed.
Formation of Nanocrystalline Structure by Shot Peening
Authors: Todaka Yoshikazu , Umemoto Minoru , Watanabe Yukinori , Tsuchiya Koichi
Published: March 2009

The effects of the shot peening (SP) condition and the initial hardness of specimens on the formation and thickness of nanocrystalline (NC) layer were investigated. The NC structure is found to be independent of the SP techniques, air blast, impeller and ultrasonic SP. In the SP condition, the increase in the kinetic energy per one shot is effective to increase the thickness of NC layer. It is also found that there is a certain critical initial hardness of specimens to produce the NC structure by SP. The NC structure forms when the specimen hardness is lower than the shot hardness.
Effects of the Number of ECAP Passes and ECAP Route on the Heterogeneity in Mechanical Properties across the Sample from Titanium VT1-0
Authors: Korshunov Alexander , Vedernikova Irina , Polyakov Lev , Kravchenko Tamara , Smolyakov A.A. , Solovyev V.P.
Published: March 2009

Titanium VT1-0 was processed by four passes of equal-channel angular pressing (ECAP) using two routes, BC and C. Pressed samples had a square section with a side length of 8 mm. Mechanical properties at tension (tensile strength, conventional yield strength and elongation) were determined at 9 points across the sample using small-size specimens, 1.5 mm in diameter, cut out along the pressing direction. Heterogeneity in the mechanical properties across the sample was determined based on the value of the variation coefficient. One can observe that heterogeneity in the mechanical properties generally tends to decrease with the number of ECAP passes.
Microstructural Features and Mechanical Properties of the Ti-6Al-4V ELI Alloy Processed by Severe Plastic Deformation
Authors: Semenova Irina P. , Saitova Lilia R. , Raab Georgy I. , Korshunov Alexander , Zhu Yuntian T. , Lowe Terry C. , Valiev Ruslan
Published: March 2009

This paper investigates microstructures and mechanical properties of the TI-6AL-4V ELI alloy processed by ECAP and extrusion with various morphology of α and β-phase. Preliminary thermal treatment consisted of quenching and further high-temperature ageing. The present work reveals that the decrease of volume fraction of α-phase globular component in the initial billet results in a more homogeneous structure refinement during SPD, lower internal stress, enhancement of microstructure stability and mechanical properties. An ultimate strength of UTS ≥1350 MPa was obtained in the Ti-6Al-4V ELI alloy while maintaining a ductility of δ≥11%.
The Microstructures and Mechanical Properties of Hot-Processed Magnesium Casting Alloys
Authors: Yamaguchi Takeshi , Tsukeda Tadayoshi , Saito Ken , Kawamura Yoshihito
Published: March 2009

In order to make the effect of processing clear, AM50A magnesium casting alloys were extruded at various extrusion conditions such as extrusion temperature and extrusion ratio. The mechanical properties of AM50A alloy increased with decreasing extrusion temperature. Tensile yield strength and tensile strength of extruded AM50A alloy were 389MPa and 420MPa respectively when the extrusion temperature was 348K. The microstructure of the extruded magnesium alloy showed large grains stretched to the extrusion direction and fine recrystallized grains. Decreased extrusion temperature resulted in improved strength and decreased elongation with increasing of the degree of work hardens and extrusion force. When the extrusion ratio is high, improvement of strength is prevented by rycrystallization and it was observed as crystal orientation by XRD. The elongation of the extrusion increased with the recrystallization of grains. Every magnesium alloy extruded at low temperature has high strength.
Fracture and Fatigue Resistance of Ultrafine Grain CuCrZr Alloy Produced ECAP
Authors: Vinogradov Alexei , Kitagawa Kazuo , Kopylov V.I.
Published: March 2009

Anisotropy of mechanical properties, fatigue and fracture resistance of precipitation hardened CuCrZr alloy ultrafine (UFG) grained by equal-channel angular pressing (ECAP) is in focus of the present communication. Fracture toughness was estimated in terms of J-integral and the fatigue crack growth rate was quantified. It was found that although the estimated JIC-value appeared lower than that reported in the literature for a reference alloy, the ductility, fracture and crack growth resistance remained satisfactory after ECAP while the tensile strength and fatigue limit improved considerably. The stable crack growth rate did not differ very much for ECAP and reference conventional CuCrZr and no remarkable anisotropy in the stable crack growth was noticed.
Fabrication of Copper-Graphite Multifilamentary Composite Wire by Severe Plastic Deformation Microstructures and Electrical Properties
Authors: Guillet Alain , Yama Nzoma E. , Pareige Philippe
Published: March 2009

Copper-carbon composites (where carbon can be graphite, carbon-fibers, fullerenes and carbon nanotubes) are used and under investigations for various applications. The reported manufacturing methods are diverse, but, to our best knowledge, no process is available to fabricate a multifilamentary Copper-Graphite wire with a large number of graphite filaments. We describe a new processing route, which allows the fabrication of such composite by severe plastic deformation. The resulting microstructures and electrical properties are presented and discussed.
Grain Refinement of Commercial Al-Mg Alloy Using Severe Torsion Straining Process
Authors: Neishi Koji , Higashino Akihiko , Miyahara Yuichi , Nakamura Katsuaki , Kaneko Kenji , Nakagaki Michihiko , Horita Z.
Published: March 2009

Severe plastic deformation (SPD) makes it possible to refine grain size in many metallic materials. Recently, we have developed a new SPD process designated the severe torsion straining process (STSP). This process requires no die but one side of a rod is rotated with respect to the other while producing a local heated zone in the rod and cooling both sides of the heated zone. Torsion strain is then introduced in the local heated zone. The STSP can be a continuous process because the rod is moved in the longitudinal direction while introducing torsion strain through the rotation. For grain refinement using the STSP, various factors may affect, which are the rotation speed, moving speed, straining temperature, cooling rate and diameter of the rod. In this study, the STSP is applied to grain refinement of an A5056 Al-Mg commercial alloy and the factors affecting the grain refinement are optimized. STSP was conducted at a temperature in the range from 573K to 723K. Microstructure was observed by optical microscopy, scanning electron microscopy with an orientation imaging system, and transmission electron microscopy. Microscopy observations revealed that the grain size was reduced to ~0.9 μm, when STSP was conducted at 573K with a rotation speed of 10 rpm and moving speed of 50 mm/min. There is a critical ratio of rotation speed to moving speed above which the rod breaks. The grain size tends to be finer as the straining temperature is lower, the cooling rate is faster and the ratio of rotation speed to moving speed is closer to the critical value.
Grain Refinement by High Temperature Plane-Strain Compression of Fe-2%Si Steel
Authors: Rodriguez-Calvillo Pablo , Reis Ana Carmen C. , Kestens Leo A.I. , Houbaert Yvan
Published: March 2009

An Fe-2%Si alloy, which was designed for electromagnetic applications was submitted to a series of plane strain compression (PSC) tests with reductions of 25, 35 and 75% at temperatures varying from 800 to 1,100°C and at a constant engineering strain rate corresponding to a constant cross velocity of 20 mm/s. The initial structure of the material displayed nearly equi-axed grains with an average size of 80 μm. The as-received texture was characterised by a nearly random cube fibre (<100>//ND) with a relatively weak maximum on the rotated cube component ({001}<110>). After deformation the samples were water quenched in order to avoid post-process static recrystallization events. The microstructures were analysed by orientation imaging microscopy (OIM) revealing that the zone of PSC was restricted to the central layers of the sample but minimally covering 50% of the sample thickness. After deformation at 800°C the conventional lamellar deformation structures were observed on the sections perpendicular to the transverse direction of PSC. At higher deformation temperatures the structure was of a bimodal nature consisting of lamellar deformation bands and equi-axed small grains. The volume fraction of these small equi-axed grains increased from 19.9% after 75%reduction at 800°C to 67.8% after 75% reduction at 1.100°C. After 75% reduction the equi-axed grains exhibited an average size of 10 μm which represents a strong grain refinement with respect to the initial size of 80 μm prior to PSC. Ferrite Silicon steels undergo extensive dynamic recovery during hot working. Dynamic recrystallization (DRX), though, has not yet been reported for these alloys although the present data suggest that a DRX mechanism might be responsible for the remarkable grain refinement after relatively low amounts of strain applied at high temperatures.
Auto-Tuning Digital Control Based on Parameters Identification and Disturbance Observer
Authors: Chen Chin Sheng , Lee Yu Reng
Published: March 2009

This paper presented a digital servo driver that realizes an auto-tuning feedback and
feedforward controller design using on-line parameters identification. Firstly, the variant inertia constant, damping constant and the disturbed load torque of the servo motor are estimated by the recursive least square (RLS) estimator, which is composed of an RLS estimator and a disturbance torque compensator. Furthermore, the auto-tuning algorithm of feedback and feedforward controller
is realized according to the estimated parameters to match the tracking specification. The proposed auto-tuning digital servo controllers are evaluated and compared experimentally with a traditional controller on a microcomputer-controlled servo motor positioning system. The experimental results show that this auto-tuning digital servo system remarkably reduces the tracking error.
Experimental Research on Grind-Hardening of 65Mn Steel
Authors: Liu Ju Dong , Wang Gui Cheng , Wang Zhi , Fan Shu Tian
Published: March 2009

Grind-hardening was done on 65Mn steel with a conventional surface grinder and a
corundum-grinding wheel. Research was conducted to probe into microstructures and properties of the hardened layer under varied depth of cut and cooling conditions. Results show that the hardened layer does not change noticeably in their martensitic structures and micro-hardness, which is ranged between 810-870HV. When the depth of cut increases or the dry grinding technique is adopted, the hardened layer becomes thicker accordingly. Under the condition of dry grinding with the depth of cut 1.0mm, the hardened layer depth reaches 2.0mm. It can find applications in grinding and metal surface modification field.
Three-Dimensional Single Crystal Morphologies of Diffusion Limited Growth in Experiments and Phase Field Simulations
Authors: Singer H.M. , Bilgram J.H.
Published: March 2009

In growth experiments for 3D xenon crystals we have observed three different
morphologies: dendrites, doublons and seaweed. The 3D shape of dendrites and doublons is reconstructed by means of refractive reconstruction. Our measurements on the fin thickness of dendrites support the validity of analytical predictions by Brener. We have found that the fins of the
doublon morphology can be fitted with the fin predictions for dendrites. Measurements of the doublon gap as a function of the supercooling show that the gap decreases hyperbolically with increasing supercooling. Phase field simulations of 3D doublons reveal that the channel shows an inner structure in the presence of anisotropy of surface tension. A combination of reconstructions and phase field simulations leads to a geometrical description of doublon cross sections.
Experimental Observation of Convection during Equiaxed Solidification of Transparent Alloys
Authors: Eck Sven , Mogeritsch J.P. , Ludwig Andreas
Published: March 2009

3D samples of NH4Cl-H2O solutions were solidified under defined experimental
conditions. The occurring melt convection was investigated by Particle Image Velocimetry (PIV). The occurrence of NH4Cl crystals was observed optically and first attempts were made to quantitatively measure its number density, size distribution and sedimentation rate by PIV and Particle Tracking (PT). In order to prove the reproducibility of the results several experimental runs
with equal and slightly modified conditions were analyzed.
The Effect of Melt Flow on the Dendrite Morphology
Authors: Póliska Csaba , Gácsi Zoltán , Barkóczy Péter
Published: March 2009

The anisotropy of dendritic structure is characterized in this paper. The direction of move of liquid/solid interface influence the velocity of the melt flow. In the course of the experiments the liquid/solid interface was moved in three different directions: i) at right angles to the direction of gravity vector, ii) in the direction identical with it and iii) in the direction opposite to it. Our purpose was to investigate the shape of solidifying dendrites as a function of the angle included by the gravity vector and solidification [6]. The measurements were done in real images fixed by us. The
following parameters were chosen for characterizeing the anisotropy of dendrites: intersection number of the test lines and dendrite interface (P), orientation factor (), dendritic surface in volume (SV). The material was solidified by using an equipment developed by the authors. The solidification rate is a constant value: 0.001 mm/s and 0.003 mm/s, the composition of material used for modelling purposes is: SCN (succinonitrile) -2.5-3 mass% of acetone. 100 images were processed
in each direction. It was necessary to rotate the images in order to count the number of intersections. A program developed by the authors was used for this purpose; the number of intersections was given by the program as a function of the angle of rotation, and the perimeter and area of the dendrites.
Microstructure Formation in AlSi7 Alloys Directionally Solidified with Forced Melt Flow
Authors: Zimmermann Gerhard , Weiß A.
Published: March 2009

AlSi7Mg0.6 alloys are directionally solidified with forced melt flow induced by a rotating magnet ring. By increasing the rotational frequency of the permanent magnet the columnar dendritic microstructure in the centre part of the samples changes completely towards a structure of small equiaxed grains with different crystallographic orientations, accompanied by an increased amount
of eutectic and Mg2Si phases.
On the Temperature Gradient Induced Interfacial Gradient Force, Acting on Precipitated Liquid Droplets in Monotectic Liquid Alloys
Authors: Kaptay György
Published: March 2009

The final morphology of liquid metallic emulsions, produced in a temperature gradient, depends on the interfacial gradient force acting on small metallic droplets. This force is proportional to the temperature coefficient of the interfacial energy between the two immiscible liquid phases. In the present paper first a widely used equation of Young, Goldstein and Block for the steady-state velocity of liquid droplets under the influence of the temperature gradient is discussed. Then a new equation is proposed for the temperature dependence of the interfacial energy.
Liquid-Metal Foams – Feasible In Situ Experiments under Low Gravity
Authors: Babcsán N. , Garcia-Moreno F. , Leitlmeier D. , Banhart John
Published: March 2009

Metal foams are quite a challenge to materials scientists due to their difficult manufacturing. In all processes the foam develops in the liquid or semiliquid state. Liquid-metal foams are complex fluids which contain liquid metals, solid particles and gas bubbles at the same time. An X-ray transparent furnace was developed to monitor liquid metal foam evolution. Aluminium foams - similar to the commercial Metcomb foams - were produced by feeding argon or air gas bubbles into an aluminium composite melt. The foam evolution was observed in-situ by X-ray radioscopy under normal gravity. Drainage and rupture were evaluated during the 5 min foam decay and 2 min solidification. Argon blown foams showed significant drainage and cell wall rupture during the first 20 s of foam decay. Air blown foams were stable and neither drainage nor rupture occurred. We demonstrated the feasibility of experiments during parabolic flight or drop tower campaigns. However, the development of a foam generator for low gravity is needed.
Modeling Microsegregation in Metal Alloys
Authors: Voller Vaughan R.
Published: March 2009

Direct simulations of solidification processes that account for all space and time scales are often beyond the reach of current computational power. To overcome this limitation micromacro approaches that incorporate the effects of small-scale phenomena into large-scale process models have been developed. An important small-scale solidification phenomenon is microsegregation —the redistribution of rejected solute components at the scale of the solid crystal morphology. This paper outlines a general microsegregation model that not only accounts for many of the critical small-scale phenomena in alloy solidification but also well suited as the micro component of a micro-macro model of metal casting. In the development of this microsegregation model, particular emphasis and testing is placed on alternative treatments of modeling the microscale solute diffusion in the solid phase—the so-called “back-diffusion.”
Microstructure Evolution in Rapidly Solidified Immiscible Alloys
Authors: Reuß Michael , Ratke Lorenz , Zhao Jiu Zhou
Published: March 2009

We prepared Al-Bi alloys with our new aerogel counter gravity casting facility and Al-Pb alloys by simple mould casting with variable cooling rates. By counter gravity casting, it is possible to have directional solidification with flat isotherms and without forced melt flow during the casting process. Both methods allow studying the nucleation rate in liquid-liquid decomposition. The most important result is that a separation between monotectic and hypermonotectic particles is possible
by using suitable cooling rates. The difference of the frequency maxima is a function, depending on cooling rate and starting composition. By casting experiments with variable cooling rates, we found that the average particle diameter is a function of the cooling rate, according to the theory of Ratke and Zhao, but the nucleation rate is higher than assumed in their theory.
Effects of Liquid Core Reduction during Solidification of Pb2.5wt%Sb Thin Slabs
Authors: Peralta J.L. , Santos R.G.
Published: March 2009

The influence of thickness reduction during solidification of Pb2.5wt%Sb thin slabs in
the microstructure was experimentally analyzed using a physical simulator consisted of a water cooled mould with a moveable sidewall, driven by a hydraulic piston, to squeeze the liquid core during the solidification. Experiments were carried out in order to obtain slabs without thickness reduction and with thickness reduction of about 20% and 40%. The microstructures are revealed in order to analyze the influence of the thickness reduction applied in the formation of central equiaxial structure and in the secondary dendrite arm spacing. From the results it was observed that increasing the thickness reduction increases the extension of the equiaxial structure.
Investigations on Columnar-to-Equiaxed Transition in Binary Al Alloys with and without Grain Refiners
Authors: Sturz Laszlo , Zimmermann Gerhard
Published: March 2009

We have investigated the columnar to equiaxed transition experimentally in directionally solidified hypoeutectic binary AlSi alloys with and without grain refinement particles and for different processing parameters in the framework of the ESA-MAP CETSOL (Columnar-to-equiaxed transition in solidification processing). A power-down technique was used in a Bridgman-Stockbarger type gradient-furnace to simultaneously increase the solidification rate and decrease the temperature gradient in the cylindrical sample during directional solidification vertically upwards. The position of the CET was determined from the cut and polished samples and correlated to the applied cooling rate for different experiments. Critical parameters for the temperature gradient and the solidification rate at the transition were determined from cooling curves measured within the sample and from a time-of-flight analysis of ultrasonic pulses propagated in the solid part of the sample and being reflected at the solid-liquid interface. The critical values found are compared to the deterministic models of Hunt and of Martorano et al. The objective of this contribution is the presentation of preliminary results for the different alloys and processing parameters of ground-based experiments. These results will be used for the testing of different models describing the CET within the framework of the ESA-MAP CETSOL and for the preparation of comparative microgravity experiments.
The Effect of Superheat on Micro- and Macrosegregation and Crack Formation in the Continuous Casting of Low-Alloyed Copper
Authors: Mäkinen Mika , Uoti Markku
Published: March 2009

In continuous casting, the severity of centerline macrosegregation and internal crack formation is linked to the cast structure, which can be minimized by increasing the equiaxed zone. Thus all the factors which favour an equiaxed structure are useful to quality. These are: low superheat, electro magnetic stirring (EMS) in the mould, large section size and especially in the case of internal cracks, uniform heat transfer between the strand and the mould. Microsegregation, which is the primary reason for macrosegregation, is due to the distribution coefficient and the growth rate of the solidification front. It is known that superheat has an influence on the solidification structure on both the micro- and macro- levels. Research has confirmed that superheat also affects crack formation in the solidifying front. These observations are usually reported on steels but little has been reported on low-alloyed coppers. In our experimental studies we examined the effects of superheat and uneven heat transfer on segregation behavior of phosphorus and iron in round, deoxidized, high phosphorus (DHP) copper billets. Furthermore crack formation and the solidification structure on both the micro- and macro- levels were studied. Results were verified by optical emission spectrometry (OES) and scanning electron microscopy (SEM).
Properties of AlN-Based Magnesium-Matrix Composites Produced by Pressureless Infiltration
Authors: León C.A. , Arroyo Y. , Bedolla E. , Aguilar E.A. , Drew Robin A.L.
Published: March 2009

A novel ceramic-metal composite with continuous interconnected ceramic and metal phases has been fabricated from sintered porous particulate AlN preforms infiltrated with magnesium. The 48 vol. % AlN composites are fabricated by pressureless infiltration in argon in the temperature range of 870 °C to 960 °C. An increase in the infiltration rate is observed as the temperature increases. Results on the mechanical characterization of the composites indicate an elastic modulus of 90 to 110 GPa and hardness of 70 to 80 HRB. The tensile strength calculated by the shear punch test method ranges from 260 to 390 MPa. As a general rule, it is observed that the lower the infiltration temperature, the higher the tensile strength. The linear coefficient of thermal expansion of the infiltrated composites in the temperature range of 215 to 315 °C is 7.65 x 10-6 °C-1. This value is lower than those found for similar Al/AlN composites reported in the literature.
High Temperature Chemical Interaction Between SiO2 Substrates and Ag-Cu Based Liquid Alloys in Vacuo
Authors: López-Cuevas Jorge , Gutiérrez Carlos A. , Pech-Canul Martin I. , Castro-Román M. , Rendón-Angeles Juan Carlos
Published: March 2009

The interfaces formed between vitreous or thermally devitrified fused quartz substrates and silver alloys after 90 min at 850 °C in vacuum have been characterized. Three silver alloys have been used: Cusil (Ag–28 wt % Cu), Cusil-ABA (Ag–35 wt % Cu–1.5 wt % Ti), and Incusil-ABA (Ag–27 wt % Cu–12 wt % In–2 wt % Ti). A non wetting condition is found for the Cusil alloy in both substrates. In contrast, the formation of Ti5Si3, Cu3Ti3O and Ti2O3, following the sequence SiO2 → Ti2O3 → Ti5Si3 → Cu3Ti3O, is observed at the metal/ceramic interface for the two titaniumcontaining alloys on both substrates. Ti2O3 is commonly found as small particles dispersed in a silver-rich matrix. During the experiments, the reaction product layers detach from the ceramic surface and float away from the ceramic/metal interface due to their relatively low density with respect to the liquid alloy. The formation of the phases detected at the ceramic/metal interface can be explained in terms of their relative thermodynamic stability.
Microstructural and Mechanical Characterization of Nitinol GTAW and FB Welds of Titanium
Authors: Kabatskaia Ivanovna Alla , López-Hirata Victor M. , Oliva López Eduardo , Rodríguez Figueroa Ricardo , Rodríguez Miramontes Jorge
Published: March 2009

Microstructural and mechanical characterization of Nitinol gas tungsten arc weld
(GTAW) and furnace brazing (FB) welds for grade 1 titanium plates are carried out in order to study the microstructure developed after welding and its effect on the mechanical properties of welds. The GTAW process yields the highest hardness weld. The constituents for this weld consist of a dendritic structure of NiTi and NiTi2 intermetallic phases. The FB process promotes a change
of the welds chemical composition due to atomic diffusion of Ti. The weld microconstituents consist of a mixture of a Ti-rich and NiTi2 eutectic and a proeutectic Ti-rich phase.
Macro-Micro Modeling and Simulation of Solidification Kinetics of Pb-Sn Alloys
Authors: López L. , Cruz H. , Campillo B. , González-Rivera Carlos
Published: March 2009

The purpose of this work is to explore the effect of the presence of two different primary phases on the microstructure and solidification kinetics of Pb-Sn alloys. The experimental results have been compared with predictions obtained from the Newton Thermal Analysis of cooling curves generated by a conventional heat transfer-solidification kinetics model. Three Pb-Sn alloys have been considered in this work in order to explore the solidification characteristics of the eutectic in hypoeutectic, hypereutectic and eutectic compositions. Experimental results indicate that
the Pb-Sn eutectic morphology and the solidification rate depend on the nature of the pre-existent primary phase during eutectic solidification. From the observed discrepancies between experimental and simulated results it is concluded that further improvements are needed to simulate the solidification kinetics of eutectic microconstituents in the presence of pre-existing primary phases.
Biomimetic Process in Metals
Authors: Lopez-Heredia Marco A. , Cortés-Hernández Dora A. , Escobedo-Bocardo José C. , Medina Ramírez A.
Published: March 2009

A titanium base alloy and a cobalt base alloy have been subjected to a biomimetic process. Samples of titanium and cobalt alloys have been immersed in 10M and 5M NaOH solutions, respectively, then the samples have been heat treated and finally, immersed in either a simulated body fluid (SBF) with ionic concentration close to human blood plasma or in a simulated body fluid with an ionic concentration 1.5 times that of the SBF (1.5SBF) for a period of 21 days. An apatite layer has been observed after the immersion of the samples in SBF for both Ti and Co base alloys. The apatite layer observed on the Ti alloy samples is more homogeneous and thicker than that observed on the Co alloy samples. However, the apatite layer on both samples is not continuous and homogeneous along the surface. The layer of apatite formed is thicker on samples immersed in 1.5SBF. This is attributed to the higher ion concentrations, mainly of calcium and phosphorus. The Ca/P ratios measured in the apatite layers are close to that of bone.
Characterization of Global and Local Textures in Hot Rolled CGO Fe3%Si
Authors: Cruz-Gandarilla Francisco , Baudin Thierry , Mathon Marie Helene , Penelle Richard , Mendoza León Hector , Cabañas-Moreno J. Gerardo
Published: March 2009

The present work is an attempt to understand the recrystallisation mechanisms in Fe-3% Si alloys used in transformer cores. After secondary recrystallisation silicon steels exhibit a Goss texture with a more or less important spread depending on the details of the processing route, namely, Conventional Grain Orientation CGO or High Permeability Hi-B. The mechanisms of Goss grain formation during hot rolling and primary recrystallisation, as well as those controlling the first steps of abnormal growth, are not yet well understood. The present work mainly deals with texture characterization of the hot rolled state. Surface, quarter and half thickness samples are prepared from hot-rolled sheet. Global and local textures are characterized by neutron diffraction and electron backscattered diffraction, respectively. The Orientation Distribution Functions and the volume fraction of the different texture components are calculated. The components from global texture measurements are (001)[1-10], (112)[1-10] (α fiber ), (011)[100] (Goss) and (111)[1-21] (111) [1-10](γ fiber). EBSD measurements have shown large variations of texture from the surface to the half thickness of the sheet. These local measurements are related to the global results by rotation about the transverse direction. Moreover, the grain size appears to be inhomogeneous.
Dislocation Mechanisms and Plasticity of Quasicrystals: TEM Observations in Icosahedral AlPdMn
Authors: Caillard Daniel
Published: March 2009

Quasicrystals can deform Plastically at high temperatures by the movement of
dislocations like in crystals. Little is known, however, on the mechanisms that control dislocation movements in these structures. In a first part, the crystallography of quasicrystals is introduced as the projection, in the physical space, of a periodic structure in a hyperspace with more than three dimensions (6 in the case of icosahedral structures). The main properties of dislocations are defined
in the physical space and in the six-dimensional space. New results are then presented, showing that dislocation movements may have a large component of climb, in contrast with all existing models that are based on glide processes only. Dislocation movements in two-fold and five-fold planes are
compared and discussed in connection with macroscopic mechanical properties.
Joining of Silicon Nitride to Metal (Mo and Ti) Using a Cu-Foil Interlayer
Authors: Flores José G. , Cervantes José , Lemus-Ruiz José
Published: March 2009

This work focuses on various aspects of diffusion bonding silicon nitride to Mo and Ti
using a Cu-foil interlayer. Si3N4/Cu/Ti/Cu/Si3N4 and Si3N4/Cu/Mo/Cu/Si3N4 combinations have been diffusion joined at temperatures ranging from 950 to 1150 °C using different holding times in Ar. The results show that Si3N4 could not be bonded to Mo at temperature lower than 1100 °C even for holding times of 60 minutes, however, successful joining is achieved at 1150 °C. On the other
hand, successful joining is accomplished at 1050 and 1100 °C for a Si3N4/Cu/Ti/Cu/Si3N4 sample. In the Si3N4/Cu/Ti system, joining occurs by the formation of a reactive interface with several reaction products on the metal side of the joint. All the silicon nitride samples have joined to titanium with
no several interfacial cracking and porosity at the interface. The results corresponding to the Si3N4/Cu/Mo system show that a higher temperature is required to join the materials compared with the Si3N4/Cu/Ti system, since the formation of liquid produced by the interaction of Cu with Ti and
Si promotes bonding and the high affinity of Ti for Si results in rapid interface formation.
Electrochemical Characteristics of Nano-Silicon/Graphite Composite for the Anode Material of Lithium Secondary Batteries
Authors: Lee Joong Kee , Park Tae Jin
Published: March 2009

Silicon coated graphite particles prepared by gas suspension spray method were used as a raw material for the battery anode, which showed high specific capacity and good cycle performance. The improvement of electrochemical performance seems to be due to the formation of amorphous silicon-carbon black composite layer on the surface of the graphite particles. It has a stable structure under repeated volume expansion and contraction.
Fabrication and Characterization of Porous Ceramic Panel Using Recycled Glass Powder
Authors: Lim Tae Yeoung , Park Y.M. , Hwang Jong Hee , Kim Chang Yeoul , Kim Cheol Y.
Published: March 2009

The porous ceramic panel using glass powder as a main raw material can be applied for the thermal insulator in architecture and industry since it is noncombustible and chemically stable as well as eco-friendly unlike the organic thermal insulators. For the study of fabrication and characterization of this material, we used grinded glass powder with grain size smaller than 150, and Calcium carbonate(CaCO3) and Calcium phosphate(Ca3(PO4)2, CaHPO4·2H2O) as foaming agent. The shape and size of pore cell in porous glass structure with the change of additives and sintering temperature were studied. The physical properties as like density, thermal conductivity and compressive strength of materials are also studied. It was possible to make a porous ceramic panel with multi-layered which has the form of sandwich with layer of low density and high density in one body by adjusting the foaming characteristics.
Hydrothermal Syntheses of Nickel Nanosheets and Their Morphology
Authors: Jun Seong Yup , Ryou Kyeong Doo , Hong Seong Soo , Lee Gun Dae , Park Hoy Yul , Kang Dong Pil , Park Seong Soo
Published: March 2009

Nanocrystalline nickel powders were prepared by chemical reduction of nickel chloride hydrate with different surfactant at moderate temperature in a pressurized vessel. Nickel nanosheets were generated successfully through reducing the nickel ion complexes, formed by sodium tartrate, at alkaline condition by hydrazine hydrate. The nanosheets and nanowires were characterized by the means of an X-ray diffractomer (XRD), a field emission scanning electron microscopy (FESEM), an energy dispersive X-ray spectrometer (EDS) and a high sensitive
magnetometer (HSM).
Characterization and Synthesis of Functional TiO2 Sol-Gel Coatings on the Glass
Authors: Shin Dae Yong , So Myung Gi , Han Sang Mok
Published: March 2009

Thin film photocatalysts of TiO2 coated on the glass were prepared to self-clean and
eliminate air pollutants by spin coating process with Ti(OC3H7 i)4, including PEG. The surface structure of TiO2 films changed according to the molecular size of PEG. It was found that NOx was efficiently eliminated by the TiO2 film photocatalyst. The contact angle of water drop on the TiO2 films decreased to less than 10°. It revealed the hydrophilic property of TiO2 films. The morphology
and the crystal structure of TiO2 films were affected most.
Application of Numerical Simulation Considering the Effect of Phase Transformation to the Estimation of Hardness Distribution in Welds
Authors: Mikami Yoshiki , Mochizuki Masahito , Nakamura Terumi , Hiraoka Kazuo , Toyoda Masao
Published: March 2009

This study investigated a method for estimating hardness distribution in welds, considering the effect of phase transformation and weld thermal cycles. Hardness distribution in welds was estimated from fractions and hardness of each microstructure by using rule of mixture. Finite element heat conduction analysis was performed to calculate weld thermal cycles. Microstructures formed
corresponding to the thermal cycle were also calculated based on the continuous cooling transformation (CCT) diagram. The method mentioned above was applied to welds of Ultra-Narrow Gap welding process, which was developed for welding of ultrafine-grained steels. The calculated thermal cycles in the welds corresponded with measured results. Moreover, the estimated hardness distribution in the welds, which were estimated by using calculated thermal cycles and the phase
fraction of each microstructure, was also in good agreement with measured values.
Donor-Acceptor Substituted Thienylpyrrole Azo Dyes: Synthesis, Solvatochromic and Electrochemical Properties
Authors: Raposo M. Manuela M. , Sousa Ana M. R. C. , Fonseca António Maurício C. , Kirsch Gilbert
Published: March 2009

The synthesis of thienyl- substituted pyrrole azo dyes and their UV-visible,
solvatochromic and electrochemical properties are described. In agreement with the solvatochromic data and also with the electrochemical study the new donor-acceptor systems synthesized could have applications in NLO.