bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of Homogeneous Nb-Al Intermetallic Compound Sheet by Multi-Layered Rolling and Subsequent Heat Treatment
Authors: Nishimoto Akio , Akamatsu Katsuya
Published: January 2010

The intermetallic compound Nb3Al is widely investigated because of its high temperature strength, superior superconductivity and relatively small density. As Nb3Al has an extremely high melting point and lack of deformability, it is impossible to prepare it by using the conventional metallurgy. In this study, a Nb-Al intermetallic compound was prepared by multi-layered roll-bonding of elemental Nb and Al foils. The process consisted of the accumulative roll-bonding (ARB) for making a laminated Nb/Al sheet and the subsequent heat treatment promoting a solid-phase reaction in the laminated Nb/Al sheet. Accumulated foils were roll-bonded at 573 K. The rolling reduction at 1 pass was ~50%, and the final rolling reduction at 4 passes was ~94%. A pulsed electric current sintering (PECS) process was used for the subsequent heat treatment. The microstructures produced at each processing stage were characterized by X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). A homogeneous intermetallic compound of Nb3Al could be obtained after the subsequent heat treatment for 1.8 ks at 873 K and for 0.9 ks at 1673 K.
Microstructure Formation in Cast β-Solidifying γ-Titanium Aluminide Alloys
Authors: Oehring Michael , Appel Fritz , Paul Jonathan H.D. , Imayev Renat M. , Imayev V.M. , Lorenz Uwe
Published: January 2010

In view of the development of improved TiAl cast alloys the potential of the  transformation and its dependence on the addition of several alloying elements has been investigated. It was found that microstructural refinement in  solidifying alloys can be attributed to the alloying effect on the kinetics of the  transformation. This also holds for grain refinement through Borides which apparently serve as nucleation sites for the  phase in the solid-state transformation.
Crystal Growth and Characterization of FeAs-Based Superconductors
Authors: Takeya Hiroyuki , Kasahara Shigeru , Hirata Kazuto
Published: January 2010

FeAs-based single crystals of Ba1-xKxFe2As2 and Sr1-xKxFe2As2 were grown in a Mo capsule at the temperatures from 1200oC down to 850oC by a FeAs-self-flux method. Most of their sizes were approximately 0.2-0.5 mm. A larger single crystal of Sr Fe2As2 about 7mm in diameter was obtained by the same procedure, as appeared in a round-shape. Most of the time, potassium-doped crystals tends to be smaller than undoped ones. An example of Tc for a Ba1-xKxFe2As2 single crystal measured with a SQUID magnetometer, which indicates Tc at 38 K. Tc s are sometimes lower dependent on the potassium composition. The substitution reaction between SrFe2As2 and potassium was examined. An undoped crystal absorbed potassium at around 600oC and showed superconductivity by the reaction.
Study of Refined Microstructures after Two-Step Heat Treatments by Means of EBSD Technique on γ-TiAl Alloys
Authors: Pérez-Bravo Maria , Baudin Thierry , Boivin Denis , Thomas Marc , Madariaga Inaki , Ostolaza K. , Tello M.
Published: January 2010

In this work, significant modification of the microstructure of a rolled Ti-45Al-5Nb (at.%) alloy has been achieved by a two-step heat treatment. A combination of high cooling rates for the first step of the treatments with a subsequent annealing at high temperatures, results in refined microstructures where substantial discontinuous coarsening seems to play an important role for the grain refinement. In order to fully understand the transformation mechanisms responsible for such a refinement, Electron Back Scattered Diffraction (EBSD) technique has been extensively used. In particular, a study of orientation relationships between the phases which are present in the transformed microstructures, was performed by this technique. Besides discontinuous coarsening process, the obtained results also suggest that a modified discontinuous coarsening mechanism is operative, in order to justify the formation of novel microstructures, whose development could not be explained by the classical discontinuous coarsening.
An Investigation of Fracture Origins in Heat-Treated Ti49Al47Cr2Nb2 Powder Compacts
Authors: Berteaux Olivier , Valle Roger , Raffestin Monique , Thomas Marc , Henaff G.
Published: January 2010

The fatigue behaviour of a powder-metallurgy (PM) + heat-treated Ti49Al47Cr2Nb2 alloy is investigated using detailed SEM characterization. Based on the results of comparative static and cyclic loadings at RT, the fracture origins for the different test specimens is investigated. Conventional fractographic analyses revealed that internal structural defects inherent to powder metallurgy such as compaction defects, porosities and non-metallic inclusions can promote crack initiation. However, the fracture surface of test specimens is markedly affected by the microstructure, which is indicative of the microstructure dependence on crack initiation and propagation. In sub-transus heat treatment conditions, the detrimental effect of structural defects is illustrated by clear crack initiation sites onto the fracture surfaces. In super-transus conditions, crack propagation from defects can be blunted due to crack deflection, branching through lamellar interfaces, thus leading to lower defect sensitivity. Correlation of the results of these microfractographic examinations with the stress-strain curves corresponding to the various specimens allows identifying the role of such structural defects on the static and cyclic deformation behaviours. Finally, implications of such dependencies will be assessed relative to the requirements for aerospace gas turbine applications.
Growth of Crystals and Formation of C40/C11b Lamellar Structure in (Mo0.85Nb0.15)Si2
Authors: Zhang Lan Ting , Zhu Ou , Jiang Yan , Shan Ai Dang , Wu Jian Sheng
Published: January 2010

In this paper, high-quality single crystals of (Mo0.85Nb0.15)Si2, around 8 mm in diameter and 90 mm in length, have been grown by optical heating floating zone method. Effects of chemical composition and growth rate on forming C40 structured single crystal were studied. Aligned C40/C11b lamellar structured can be formed in the as-grown crystals after post annealing at temperatures between 1473 and 1873 K. Chemical composition as well as annealing temperature are found to be two important factors to form C11b lamellae in the C40 matrix. Fully C40/C11b lamellar structure was formed after annealing at 1873 K in the present work. The aligned C40 and C11b lamellae follow a crystallographic orientation relationship of (0001)C40//(110)C11b. Dislocations were observed in some coarse C11b lamellae but never in C40 lamellae of the duplex structure. This is probably due to accumulation of misfit strain during formation of C40/C11b lamellae.
Creation of Fine Structure in Magnesium Alloys by Electromagnetic Vibration Process
Authors: Miwa Kenji , Li Ming Jun , Tamura Takuya
Published: January 2010

We have developed the refinement process of the microstructure of metallic materials by imposition of electromagnetic vibration force during solidification. This process is effective for both wrought magnesium alloys and cast ones. By simultaneous imposition of a static magnetic field of 10 Tesla under an alternative electric current of 60A, the average grain sizes of the AZ31B wrought alloy and the AZ91D cast alloy were obtained about 50 micron in both alloys. The grain size was affected by electric current frequency and had the minimum value at the special electric current frequncy of 500 to 2000 Hz and 900 Hz for wrought alloy and cast alloy, respectively. From experimental results, we suggested the mechanism of refinement of microstructure during solidification by imposition of electromagnetic vibration force. The cavitation phenomenon in liquid phase during electromagnetic vibration was effective to break down th esolid phase. And also the difference of electric conductivity between the solid phase and the liquid one brought vigorous vibration of the solid phase. Then the solid phase was suppressed its growth.
Effect of Cooling Rate on Morphology and Crystallography of Lath Martensite in Fe-Ni Alloys
Authors: Morito Shigekazu , Igarashi Ryota , Kamiya Keiichiro , Ohba Takuya , Maki Tadashi
Published: January 2010

The development of blocks and subblocks in the lath martensite was observed with SEM/EBSD and TEM/Kikuchi diffraction patterns analyses. Morphology of lath martensite formed below Ms temperature was observed using step quenching method in 18 mass% Ni maraging steel. The development of lath martensite structure can be described as follow; lath groups with single K-S variant start to form at the austenite grain boundary. Next, other sub-blocks appear adjacent to the lath groups formed first and these lath groups form macroscopic blocks observed in optical microscopy. The morphologies of the lath martensite in Fe -23 mass% Ni alloy cooled at different cooling rates after austenitization were also observed. The packet size and block thickness decreases with increasing cooling rate, although the sub-block thickness do not change. A packet locally contains small packets with different relationship of close packed planes, and the amount of small packets increases with increasing the cooling rate.
Optimization of Heat Treatment Conditions of Magnesium Cast Alloys
Authors: Dobrzański Leszek Adam , Tański Tomasz , Trzaska Jacek
Published: January 2010

In this paper there are presented results of the optimization of heat treatment conditions, which are temperature and heating time during solution heat treatment or ageing as well the cooling rate after solution treatment for MCMgAl12Zn1, MCMgAl9Zn1, MCMgAl6Zn1, MCMgAl3Zn1 cast magnesium alloys. A casting cycle of alloys has been carried out in an induction crucible furnace using a protective salt bath Flux 12 equipped with two ceramic filters at the melting temperature of 750±10°C, suitable for the manufactured material. The heat treatment involve the solution heat treatment and cooling in different cooling mediums as well water, air and furnace. The improvement of the manufacturing technique and chemical composition as well as of heat treatment and cooling methods leads to the development of a material designing process for the optimal physical and mechanical properties of a new developed alloy.
Modeling Environment of Friction Stir Joining for AA2017T351 Plates in Butt Joint
Authors: Tcherniaeff Serge , Girot Franck , Iordanoff Ivan
Published: January 2010

The understanding of the weld formation process in FSW is difficult due to: (1) the complexities resulting from coupled physical phenomenon’s (thermo mechanical and metallic process); (2) the difficulties characterizing exactly the interactions between the tool and the materials (friction, 3D material flow, …); (3) the collecting of complete and relevant information during the generation of the weld.
Technological studies prove that FSW process is easy to realise. In addition to that, the welds may have good mechanical behaviours, in comparison with those resulting from traditional fusion welding as GMAW. The challenge is to relate the main and relevant parameters of the process (geometry of the tool, topologies of the assembly, others parameters such as axial force, torque, tool positioning, the nature of materials to be assembled,..) to the mechanical properties expected for that weld
The study proposes an analogical simulation in a modeling clay (plasticine) workpieces environment. The goal is to obtain a better understanding of the joining creation in the case of butt join of homogeneous assembly of two flat plates made of aluminium alloy AA2017T351. By varying different parameters such as geometrical conditions of assembly, geometry of the tool, other kinematics parameters, we can measure the consequences on the dimensional morphology of the weld. The latter is then characterized by geometrical parameters such as penetration, area of the join, geometrical offset between tool axis and weld interface, and chromatic parameters… . A comparison between the assembly of two aluminium alloys sheets and the equivalent in plasticine workpieces will be discussed, so as to outline differences and analogies between them.
Friction Stir Welding of SiCp/Al Composite and 2024 Al Alloy
Authors: Xiao B.L. , Wang Dong , Bi J. , Zhang Z. , Ma Z.Y.
Published: January 2010

6 mm thick SiCp/2009Al composite and 2024Al-T351 alloy plates were successfully joined by friction stir welding (FSW) with and without the tool pin offsetting to the 2024Al side (denoted as NOS and OS samples, respectively), producing defect-free joints. The SiC particles from the composite were distributed along a ring structure in the nugget and the volume fraction of the SiC particles decreased as the tool pin offset to the 2024Al side. The Al-clad layer on the 2024Al plate was aggregated on the retreating side of the nugget after FSW. For the OS sample, the Al formed a layer along the nugget boundary. The strength of the NOS sample reached up to 85% of the 2024Al alloy with the joint failing in the heat affected zone on the 2024Al side. The strength of the OS samples was 47% of the 2024Al alloy due to the aggregated Al layer on the retreating side of the nugget which decreased the strength of the joint.
Impact Properties of TIG Welded AZ31 Magnesium Alloy Joints
Authors: Asahina Toshikatsu , Katoh Kazuyoshi , Tokisue Hiroshi
Published: January 2010

Magnesium and its alloys are the lightest among the metallic materials which are in common use, having a high strength-to-weight ratio along with an excellent machinability and a high damping capacity.　Because of these characteristics, nowadays they are applied to various structural parts such as aircraft, automobiles, optical and electronic instruments, industrial robot components. 　TIG welded joints of AZ31 magnesium alloy has high joint efficiency which can be obtained by the selection of optimum welding conditions. If the welded joints of magnesium alloy are applied to the structure materials, it is very important not only the strength of under static load but also the strength of under dynamic load. However, there is only few report about impact properties of welded AZ31 magnesium alloy joints.
In this research, AZ31 magnesium alloy plates 6 mm in thickness were welded on butt welding of square groove without root gap and filler wire using TIG welding process. AZ31 magnesium alloy was carried out at various welding conditions. The effects of welding conditions and notch location on impact properties were studied.
Impact values of welded joints were nearly equal to those of the base metal, regardless of welding current. In case of the notched specimens of welded joints, crack initiation energy showed slightly lower than crack propagation energy, regardless of notch location. But, unnotched specimens of welded joints, crack initiation energy showed remarkably high value than crack propagation energy. This means, crack initiation energy spent the large amount of total absorbed energy.
Effect of Annealing Treatments on Strain Rate Sensitivity and Anisotropy in a Magnesium Alloy Processed by Severe Rolling
Authors: del Valle J.A. , Ruano Oscar
Published: January 2010

The effect of annealing treatments on the evolution of the strain rate sensitivity with strain of AZ61 magnesium alloy processed by severe rolling was investigated and related to previous results on normal plastic anisotropy (r-value). The various annealing treatments produce two effects on the microstructure: grain coarsening and slight weakening of the texture. In addition, these treatments produce a noticeable decrease in strain rate sensitivity and an increase of work hardening rate that is related to the decrease of the anisotropy. It is concluded that these effects are related to an enhanced contribution of basal slip as a consequence of the microstructural changes induced by the annealing treatments.
Extrusion of AZ31 Magnesium Sheet
Authors: Gall Sven , Müller Sören , Reimers Walter
Published: January 2010

Due to the increasing demand of deep drawing applications for magnesium alloys in the future magnesium sheets with good mechanical and forming properties are required. These properties depend on the processing route of the sheet material. The deformation behavior of magnesium alloys is strongly influenced by the texture. Extruded magnesium sheets exhibit a different texture than rolled magnesium sheets. Therefore, the forming properties of the extruded magnesium sheets are supposed to be different compared to rolled sheets. Thin extrusion of the magnesium alloy AZ31 with a thickness of 1.5 and 2 mm were performed. Adjacent the extruded sheets were tested for their microstructure, texture and mechanical properties. The texture stability and evolution after the rolling of extruded magnesium sheets were investigated. Thus some of the 1.5 mm sheets were rolled to 1.0 mm and analyzed by OIM, X-Ray and mechanical testing. Concluding the results were compared to the properties of the just extruded 1.5 mm sheet and conventionally rolled sheet of 1 mm thickness.
Mechanical Properties of Large-Scale Extruded Mg-Zn-Y Alloys
Authors: Ienaga Yuichi
Published: January 2010

In order to realize large-scale Mg-Zn-Y alloys with high strength and high heat resistance, we have developed a unique casting process to produce a large homogeneous ingot investigating the mechanical properties of the extruded alloys. First homogeneous ingots (335 mm x 850 mm) were prepared by a unique stir casting process. Then large-scale extruded alloys (100 mm) were prepared at 648 K with the extrusion ratio of 10. The Mg-Zn-Y alloys have exhibited higher yield and fatigue strengths than those of aluminum alloys. The yield strengths of the aluminum alloys have decreased drastically above 473 K, whereas those of the Mg-Zn-Y alloys have not. It is noteworthy that the yield strength (200 MPa) and the fatigue strength (75 MPa) of the Mg-Zn-Y alloys at 523 K are about twice and 1.2-1.4 times as high as those of the aluminum alloys respectively. Moreover, the creep strengths have been equivalent or higher than those of aluminum alloys. From the above results, we have verified that even being made by the large-scale extrusion, the Mg-Zn-Y alloys possess higher strength than those of heat resistant aluminum alloys.
Creep Behaviour of AE42 Magnesium Alloy and its Composites Using Impression Creep Technique
Authors: Mondal A.K. , Kumar Subodh
Published: January 2010

The creep behaviour of a creep-resistant AE42 magnesium alloy has been examined in the temperature range of 150 to 240°C at the stress levels ranging from 40 to 120 MPa using impression creep technique. A normal creep behaviour, i.e., strain rate decreasing with strain and then reaching a steady state, is observed at all the temperatures and stresses employed. The stress exponent varies from 5.1 to 5.7 and the apparent activation energy varies from 130 to 140 kJ/mol, which suggests the high temperature climb of dislocation controlled by lattice self-diffusion being the dominant creep mechanism in the stress and temperature range employed. The creep behaviour of the AE42 alloy has also been compared with its composites reinforced with Saffil short fibres and SiC particles in four combinations. All the composites exhibited a lower creep rate than the monolithic AE42 alloy tested at the same temperature and stress levels and the decrease in creep rate was greater in the longitudinal direction than in the transverse direction, as expected. All the hybrid composites, i.e., the composites reinforced with a combination of Saffil short fibres and SiC particles, exhibited creep rates comparable to the composite reinforced with 20% Saffil short fibres alone at all the temperature and stress levels employed, which is beneficial from the commercial point of view.
Effect of Rare Earth Element on Microstructure and Mechanical Properties of Mg-Sn-Ca Alloys
Authors: Kim Dae Guen , Lee Jae Seol , Park Seul Ki , Kim Young Mo , Son Hyeon Taek , Huh Moo Young
Published: January 2010

In the present work, the effect of Nd addition on microstructure change, precipitation behaviours and mechanical properties, of Mg-5Sn-3Ca based alloys were investigated. With increasing of Nd addition, size of the Mg-Sn-Ca ternary phases with fine needle shape (A-type) was decreased and volume fraction of these phase were increased. As Nd was increase from 0.5, 1.0 and 3.0 wt.%, size and volume fraction of Mg2Sn with coarse needle shape phase (B-type) was decreased. However, in 3.0 wt.% Nd containing alloy, size of these Mg2Sn phase was smaller than that of 0.5 and 1.0 wt% Nd addition alloy and volume fraction of these phase was decreased.
Inhomogeneous Deformation Observed Using High-Precision Markers Drawn by Electron Beam Lithography in a Magnesium Alloy with LPSO Phase
Authors: Morikawa Tatsuya , Mitani Yuuki , Higashida Kenji
Published: January 2010

Inhomogeneous deformation in a magnesium alloy with long-period stacking order
(LPSO) phase has been investigated using high-precision markers drawn by electron beam
lithography. Mg alloys containing Zn and rare earth elements such as Y have a characteristic
microstructure including the LPSO phase and the usual hcp matrix phase. The mechanical
performance of this alloy is remarkably enhanced by warm-extrusion. The microstructure developed
by such extrusion consists of elongated grains with fine-lamellae of LPSO phase and fine-grained
matrix of hcp phase. In order to clarify the details of inhomogeneous deformation which should
relate with the superior mechanical properties in this alloy, high-precision marking method using
electron beam lithography has been employed. By using the method, local displacement due to
tensile deformation in the Mg alloy was directly measured.
Cross-Sectional Geometry and the Intermetallics Structure in a High Pressure Die Cast Mg-Al Alloy
Authors: Nagasekhar A.V. , Cáceres Carlos H. , Easton Mark
Published: January 2010

Specimens of rectangular and circular cross section of a Mg-9Al binary alloy have been tensile tested and the cross section of undeformed specimens examined using scanning electron microscopy. The rectangular cross sections showed three scales in the cellular intermetallics network: coarse at the core, fine at the surface and very fine at the corners, whereas the circular ones showed only two, coarse at the core and fine at the surface. The specimens of rectangular cross section exhibited higher yield strength in comparison to the circular ones. Possible reasons for the observed increased strength of the rectangular sections are discussed.
Effects of Stacking Faults on High Temperature Creep Behavior in Mg-Y-Zn Based Alloys
Authors: Suzuki Mayumi , Maruyama Kouichi
Published: January 2010

Compressive creep behavior of hot-rolled (40%) Mg-Y and Mg-Y-Zn alloys are investigated at 480 ~ 650 K. Creep strength is substantially improved by the simultaneous addition of yttrium and zinc. The minimum creep rate of Mg-0.9mol%Y-0.04mol%Zn (WZ301) alloy decreases to 1/10 lower than that of Mg-1.1mol%Y (W4) alloy at 650 K. Activation energy for creep in W4 and WZ301 alloys are more than 200 kJ/mol at the temperature range of 480 ~ 550 K. These values are higher than the activation energy for self-diffusion coefficient in magnesium (135 kJ/mol). Many stacking faults (planar defects, PDs) are only observed on the basal planes of the matrix in Mg-Y-Zn ternary alloys. Stacking fault energy is considered to decrease by the multiple-addition of yttrium and zinc. The size and density of these planar defects depend on solute content, aging condition. TEM observation has been revealed that the decreasing of the stacking fault energy affects the distribution of dislocations during creep. Many a-dislocations on basal planes are extended significantly. Dislocation motion is restricted significantly by both of these two types of stacking faults (planar type and extended dislocations).
Microstructure and Mechanical Properties of High Aluminum Content Magnesium Alloys Fabricated by Twin-Roll Casting Process
Authors: Watari Hisaki , Nishio Yoshimasa , Nakamura Ryoji , Davey Keith , Koga Nobuhio
Published: January 2010

This paper describes the twin roll casting technology of magnesium alloys that contains relatively high weight ratio of aluminum, such as AM60, AZ91 and AZ121. The cast magnesium alloy sheets were hot-rolled in an elevated temperature to investigate the appropriate hot-rolling conditions for producing high-quality strip using a purpose-built strip-casting mill. The influences of such process parameters as materials of roll, casting temperature, and roll speed are ascertained. A simple method of predicting the convection heat transfer coefficient between casting rolls and molten metal is introduced. The microstructure of the manufactured wrought alloy sheets was observed to investigate the effects of the hot-rolling and heat-treatment conditions on crystal growth in the cast products. It is found that manufacturing thin magnesium alloy sheet was possible at a roll speed of 110m/min by a vertical type roll caster. The grain size of the manufactured wrought magnesium alloys sheet was less than 30 micrometers due to rapid solidification in the proposed process.
Viscosity of Metallic Glass Forming Liquids: Analysis Based on Bond Strength-Coordination Number Fluctuations
Authors: Aniya Masaru , Ikeda Masahiro
Published: January 2010

A model that describes the viscous behavior in terms of the mean values of the bond strength, the coordination number, and their fluctuations of the structural units that form the melt has been proposed by one of the authors. In the present study, the viscous behavior of several metallic glass forming systems are analyzed by using the model. From the analysis, microscopic information such as the number of bonds that must be broken to observe the viscous flow is obtained. It is also shown that when the magnitudes of energy and coordination number fluctuations are equal, the behavior of the viscosity described by our model corresponds perfectly to the behavior described by the Vogel-Fulcher-Tammann (VFT) equation.
Thermal and Mechanical Properties of the (Cu36Zr48Al8Ag8)100-xSix (x = 0–1) Amorphous Alloys
Authors: Wu N.Y. , Hsieh C.J. , Jang Jason S.C. , Jian S.R. , Chen Y.T.
Published: January 2010

In this study, (Cu36Zr48Al8Ag8)100-xSix (x = 0–1) amorphous alloy rod with (2~4) mm diameter were prepared by arc melting. The thermal properties and microstructure development during the annealing of amorphous alloys have been investigated by the combination of differential scanning calorimetry (DSC),, X-ray diffractometry (XRD) and Vickers indentation. The XRD result reveals that all these as-quenched, (Cu36Zr48Al8Ag8)100-xSix alloys exhibit the broad diffraction patterns of amorphous phase. A clear Tg (glass transition temperature) and supercooled region (about 102 K) were revealed for all of those amorphous alloy rods. The crystallization temperature (Tx), (ΔTx) , and micro-hardness of (Cu36Zr48Al8Ag8)100-xSix amorphous alloys is increased as the Si content.
Inhomogeneous Amorphous Structure of Bulk Metallic Glasses Examined from Structural Relaxation Kinetics
Authors: Haruyama Osami , Wada R. , Kohda M. , Yokoyama Yoshihiko , Nishiyama Nobuyuki , Egami Takeshi
Published: January 2010

The kinetics of structural relaxation in fragile glass former, Pd46Cu35.5P18.5 BMG, and strong glass former, Zr50Cu40Al10 BMG, was investigated by volume relaxation. The former exhibited a relaxation phenomenon that is well understood by the local topological instability model, while the latter showed monotonous relaxation behavior over a wide range down to Tg-60 K. The discrepancy may be closely related to the difference in the fragility of both glasses.
The Prediction of Glass-Forming Compositions in Metallic Systems - The Development of New Bulk Metallic Glasses
Authors: Laws Kevin J. , Shamlaye K.F. , Gun B. , Wong K. , Ferry Michael
Published: January 2010

A novel methodology of predicting specific compositions for glass forming alloys based on elemental cluster selection, liquidus lines, atomic packing efficiency and ab initio calculations is presented and discussed. The proposed composition selection model has lead to the discovery of a number of novel, soon to be reported Mg, Cu, Zn and Ag-based bulk metallic glasses. The proposed model may also be used to explain high glass forming ability and physical properties of known BMG compositions and to pin-point new or superior BMG compositions in existing glass forming systems. Further, the aforementioned model shows strong correlations between proposed elemental clusters, glass forming ability and BMG ductility. This model has also shown applicable adaptation to known ceramic oxide glass forming systems.
High Plastic Ti66Nb13Cu8Ni6.8Al6.2 Composites with In Situ β-Ti Phase Synthesized by Spark Plasma Sintering of Mechanically Alloyed Glassy Powders
Authors: Li Yuan Yuan , Yang Chao , Chen Wei Ping , Li Xiaoqiang , Qu Sheng Guan
Published: January 2010

High plastic Ti66Nb13Cu8Ni6.8Al6.2 composites with in situ precipitated ductile -Ti phase were firstly synthesized by mechanical alloying and subsequent consolidation by spark plasma sintering with crystallization. Microstructure analysis indicated that all composites contain soft (Cu, Ni)-Ti2 regions and hard -Ti regions, but the two regions have different scale and distribution. The synthesized composites exhibit high fracture strength of 2415 MPa and large plasticity as high as ~31.8%. The large plastic deformability was well explained based on the distinctive microstructure by a developed “hard-soft model”.
Molecular Dynamics Study on Structural Relaxation of Metallic Glasses
Authors: Shimono Masato , Onodera Hidehiro
Published: January 2010

Structural relaxation process in the Zr-Cu metallic glasses is investigated by using molecular dynamics simulations. The enthalpy change in isothermal annealing of the glassy state cannot be fitted by a simple exponential function but obeys a stretched exponential function, which indicates that the relaxation in glassy phase is not a single Debye type process. A close examination of individual atomic motion reveals that the enthalpy relaxation is related to a string-like cooperative motion of atoms. The analysis of the local symmetry around each atom shows that a network of the icosahedral clusters grows in the glassy phases during annealing and it closely relates to the free-volume annihilation in the structural relaxation.
Analysis of Optical Properties of GaN/AlGaN Quantum Well Ultra-Violet Laser Diode Using 6X6 Hamiltonian
Authors: Patil Dnyaneshwar S. , Samuel E.P.
Published: January 2010

The Quantum well structures have exhibited significant utility in the fabrication of advanced laser devices. The Gallium nitride semiconductor and its alloy particularly AlGaN based quantum structures are having important applications in optical data storage systems and the visible displays. Due to tailoring of wide band gap energy the spectrum obtained is from visible to ultraviolet wavelength range. We had thoroughly investigated the influence of Aluminum mole fraction variation in AlxGa1-xN under a biased condition for GaN/AlGaN based quantum heterostructure optical properties. Here, we had used 6X6 Hamiltonian to realize these properties. The 6X6 Hamiltonian has been chosen to include the many body effect in the calculation and to enhance the accuracy of the optimized results. The paper is focused to reveal the Aluminum mole fraction dependence of near and far filed intensities, peak optical gain, carrier concentration, and optical confinement factor. The effective index method has been used in determination of the optical field intensity in the near and far regimes. The variation in Aluminum mole fraction produces disparity in carrier concentration; hence, we have obtained the spontaneous emission and optical gain as a function of photon energy for different carrier density. The piezoelectric effect on GaN quantum well due to AlGaN barriers has been included through Poisson equation. This Poisson equation has been solved in a self-consistent manner along with Schrödinger and subsequently carrier concentrations have been deduced with a high accuracy using our simulation tools developed in MATLAB.
Fatigue Crack Initiation and Propagation at a Sharp Notch in Zr-Based Bulk Metallic Glass
Authors: Nakai Yoshikazu , Fujihara Kohei , Sei Naoki , Kim Bok Key
Published: January 2010

Fatigue strength of notched specimen and smooth specimen of Zr-based bulk metallic glass, Zr55Cu30Ni5Al10, were conducted under either plane-bending or axial-loading. Fatigue notch factor, Kf, for axial-loading was almost equal to the elastic stress concentration factor, Kt, and the value of Kf for plane-bending was 5% lower than the value of Kt. It indicates that the effect of stress gradient around notch root is negligible, and the fatigue limit of notched specimen is determined by the stress at the notch root. On the contrary, the fatigue strength and the fatigue limit were lower for axial-loading than plane-bending either for notched or smooth specimen. It is considered that the fatigue strength of BMG depends on the cooling rate in the casting process of the material, which is different along the thickness direction, and the fatigue strength of plane-bending reflects the strength at the specimen surface while that of axial-loading is determined by the weakest strength in the thickness direction.
Glass Formation and Structural Study of Ti50Cu50 Alloy by Molecular Dynamics
Authors: Pang Jian Jun , Tan Ming Jen , Jarfors Anders W.E. , Chuang P.D.
Published: January 2010

Ti-based metallic glasses (MGs) due to their relative low densities exhibit ultrahigh specific characteristics. In this article the glass-forming behavior and atomic structure of Ti50Cu50 MG were investigated through molecular dynamics simulation (MDS) using the general embedded-atom method (GEAM) potential. As observed experimentally, simulated Ti50Cu50 alloy undergoes three states on quenching: (i) equilibrium liquid; (ii) supercooled liquid and (iii) glassy solid. The atomic configuration of the glass was analysed based on the radial distribution function (RDF) and Voronoi tessellation (VT). It was found that there exist a variety of polyhedral units in Ti50Cu50 MG, where distorted icosohedral and bcc clusters are dominant.
The Role of Casting Temperature in Preparation of Bulk Metallic Glasses
Authors: Wang Hao
Published: January 2010

In the past research on bulk metallic glasses (BMGs) has been concentrated on searching for alloy composition to obtain high glass forming ability. Very few studies are on the effect of processing condition on glass forming ability of BMGs. In this study, we have prepared CuZr-based BMGs at different casting temperatures. Increasing casting temperature increases glass forming ability and decreases the amount of the crystalline phase during BMG solidification. At a high casting temperature 1723 K, fully amorphous sample is obtained at a size of 2 mm in diameter. While under the lower casting temperatures (1523 K and 1323 K), crystalline CuZr phases exist. The formation of the crystalline phase is attributed to the initial crystals or cluster survived in the BMG melt during ingot remelting. The study indicates that casting temperature can be used as the controlling parameter to produce purely amorphous materials or crystalline CuZr-phase reinforced BMG composites, and the mechanical properties and thermal stability of the BMG composites can be tailored by the amount of the crystalline phase existed in the materials.
Roles of Hydrogen Atmospheres in Growth of Ultrananocrystalline Diamond by Pulsed Laser Deposition
Authors: Hanada Kenji , Nishiyama Takashi , Yoshitake Tsuyoshi , Nagayama Kunihito
Published: January 2010

The growth of ultrananocrystalline diamond (UNCD) by pulsed laser deposition necessitates hydrogen atmospheres during the deposition. Optical emission spectroscopy was used to study the roles of the hydrogen atmosphere on the UNCD growth. Time-resolved images of a plume that expanded from a laser-irradiation spot toward a substrate were taken using a high-speed ICCD camera equipped with narrow-bandpass filters. While the plume disappeared at the longest within 1 s in vacuum, the emission from C+ lasted above the substrate surface for approximately 7 microseconds at a hydrogen pressure of 53.3 Pa. Since emission lifetimes of species are approximately 10 nanoseconds, this implies that C+ ions collided actively for such a long time. The hydrogen atmosphere has a role of forming a high number density of C+ ions. In addition, we believe that atomic hydrogen that might be generated by the collisions with carbon species contributes to the UNCD crystallite formation by their terminating the dangling bonds of carbon clusters as theoretically predicted in previous reports.
Nanograined Size Pure Iron Elaborated by Means of Spark Plasma Sintering
Authors: Fabrègue Damien , Piallat Julien , Maire Éric , Jorand Yves , Massardier-Jourdan Véronique
Published: January 2010

In this study, Spark Plasma Sintering has been used to sinter pure iron with an initial crystallite size around 100 nm. The process parameters for sintering pure iron have been optimized in order to obtain fully dense materials and avoid excessive grain growth. Archimede's method has been used to calculate the relative density of the sintered samples. It appears that almost fully dense materials can be obtained (95%). X Ray diffraction applied to the sintered samples shows the presence of iron and of the wustite oxide FeO (around 6% wt) formed during the sintering process. Peak enlargement measurements show that the grain size after sintering is around 200nm. This is confirmed by TEM observations showing a dual distribution of grain size. Finally, mechanical characterization has been carried out. The sintered compact exhibits a very high hardness of about 400 Hv. Compression test reveals a very high maximal stress of about 1.2 GPa and that the ductility in compression is non negligible. Using the Hall and Petch law, the calculated grain size should be around 450 nm which is in accordance with direct observations.
Carbon-Based Magnetic Nanocomposite Prepared by Arc-Evaporation of Sm/Co/C System
Authors: Grushko Y.S. , Bänitz M. , Lebedev V.T. , Lüders K.
Published: January 2010

Magnetic nanocomposite of Sm/Co/C-system is prepared and characterized. It reveals chemical and thermal stability. SQUID magnetometry is applied to study hysteresis behaviour of the material. Modified Langevin formalism is used to distinguish between ferromagnetic and paramagnetic contribution to magnetization. It is shown that 80 % of low temperature remanence is stable at 350 K and coercive field at this temperature is 140 Oe.
Principles of Fabrication of Bulk Ultrafine-Grained and Nanostructured Materials by Multiple Isothermal Forging
Authors: Imayev Renat M. , Nazarov Ayrat A. , Mulyukov Radik R.
Published: January 2010

On the basis of generalization of research results obtained at the Institute for Metals Superplasticity Problems, principles of fabrication of bulk ultrafine-grained and nanostructured materials by multiple isothermal forging are formulated. Multiple isothermal forging is shown to be a universal high-performance deformation technique for the grain refinement in metals and alloys maximally exploiting the potential of dynamic recrystallization.
Fabrication of Metallized Electrospun Copper Nanofiber Webs
Authors: Kim Ick Soo , Wei Kai , Ohta Tomohiro , Kim Byoung Suhk , Watanabe Yoshimi
Published: January 2010

The conductive metallic nanofibers were prepared by using a combined technology of electrospinning and metallization. The electrospun polyurethane and poly(vinyl alcohol) (PVA) nanofibers are metallized with different thicknesses of metal (Cu, Ni) layer via a metallization. The thickness of the metallic layer, which is ranging from 50 nm to 200 nm, was controlled. The resultant metallized nanofibers are characterized using field emission scanning electron microscopy (FE-SEM), wide angle X-ray diffraction (WAXD), and thermogravimetric analysis (TGA). FE-SEM micrographs demonstrate that the nano-scaled metallic layers are well deposited onto the nanofibers. TGA result indicates that thermal stability of the metallized nanofibers was enhanced due to the barrier effects of the metallic thin layer. WAXD data also confirm that the metallic layers are well deposited onto the nanofibers. Remarkably, the fibrous morphologies were satisfactorily conserved after removal of the nanofiber template by heat treatment at ca. 400 oC for 24 hr., suggesting the successful deposition of metal layer onto the nanofiber template, and thereby resulted in the formation of metallic nanofibers and nanotubes depending on the diameter of electrospun nanofibers and the thickness of the deposited metallic layers in the conductive metallic nanofibers. In addition, it was observed that the metallized nanofibers exhibit higher conductive properties depending on the thickness of the deposited metallic layers.
Grain Boundary Nanostructure and High Temperature Plastic Flow in Polycrystalline Oxide Ceramics
Authors: Yoshida Hidehiro , Morita Koji , Kim Byung Nam , Hiraga Keijiro
Published: January 2010

High temperature creep and superplastic flow in high-purity, polycrystalline oxide ceramics is very sensitive to a small amount of doping by various oxides. The doping effect is attributed to change in grain boundary diffusivity owing to grain boundary segregation of the doped cations. The doping effect on the grain boundary diffusivity is caused mainly by change of chemical bonding state in the vicinity of the grain boundary segregated with the doped cations. In other words, controlling of grain boundary nanostructure based on the doping process will be a useful way to develop new high-performance functional ceramics in the near future.
Magnetic Properties, Nanostructure, and Ordering Kinetics of Nb Additive FePtCu Films
Authors: Chen G.J. , Shih Y.H. , Jang Jason S.C. , Jian S.R. , Tsai P.H. , Chen H.W.
Published: January 2010

In this study,the (FePt)94-xCu6Nbx (x=0, 2.87, 4.52, 5.67) alloy films were prepared by co-sputtering. The effects of Nb addition content and heat treatment on the microstructure and magnetic properties of the polycrystalline FePtCu films are reported. Our previous experiments showed that the ordering temperature of the (FePt)94Cu6 films reduced to 320 °C, which is much lower than that of the FePt alloy. However, the grain growth after heat treatment limited the practical application in recording media.
By adding the Nb content in the (FePt)94Cu6 film, the grain sizes of the films can be adjusted from 50 to 18nm, even for the films annealed at temperature as high as 600°C. DSC traces of as-deposited disorder films at different heating rates, to evaluate the crystallization of the order phase, revealed that the addition of Nb enhanced the activation energy of ordering from 87 kJ/mol to 288 kJ/mol for the (FePt)94-xCu6Nbx (x=0 and 2.87, respectively) films. The reduction of the grain size and the corresponding increase in the activation energy of the Fe-Pt-Cu-Nb films might result from the precipitation of the Nb atoms around the ordering FePt phase. The (FePt)94-xCu6Nbx (x=2.87) film showed a coercive force of 13.4 kOe and the magnetization of 687 emu/cc.
Study on the Nanostructure and Magnetic Properties of NdFeNbB Permanent Magnets
Authors: Wang X.F. , Chen X.Y. , Jiang Z.L. , Chen Y. , Chen H.M.
Published: January 2010

Nd2Fe14B/-Fe nanocomposite permanent magnet contains the hard and soft magnetic phases, Nd2Fe14B and -Fe respectively. An exchange coupling effect exists between the two magnetic phases.
The effect of alloying element Nb on its nanostructure and properties have been studied.
Adding Nb to the alloy is effective to refine grains, a relatively small grain size causes a high intrinsic coercivity, remanence and therefore a high maximum energy product, (BH)max.
MFM (Magnetic Force Microscope) was used to observe the magnetic micro-domain structure in the nanophase alloys. The length of the magnetic contrast shows a significant dependence on the microstructure and phase constitution, and the longer length is correspond with the larger exchange coupling effect between the soft and hard magnetic phases.
Dispersion of Nano-Materials into Polymeric System for Enhanced Properties
Authors: Sharma S.C. , Murthy H.N. Narasimha , Nagaraj Shanmukha
Published: January 2010

This paper highlights a systematic investigation (related to percentage addition of solvents) of finding the appropriate solvent to reduce the viscosity of the structural grade of resin (AV138M) within castable range to effectively disperse the nanofillers (Carbon Nano Powder - CNP and Multi Walled Carbon Nano Tubes - MWCNT). AV138M + HY998/CNP and AV138 + HY998/MWCNT were cast within-process degassing using a vacuum pump of capacity 4 torr. High energy sonic waves (27kHz) were used for dispersion. Morphological studies were undertaken to analyze the uniformity in dispersion of nano fillers. The cured specimens were subjected to: Resistivity measurements using a Resistivity Meter, Glass Transition Temperature (Tg) using a Differential Scanning Calorimetry (DSC) and Tensile properties using UTM. The properties have been determined for the nanocomposites with different wt % of the fillers. It has been found that for 0.6 wt % of filler (CNP / MWCNT), there is an increase in UTS of 10 times for MWCNT compared to CNP; for 1.0 wt % of the fillers, the Tg improved by 10 °C for MWCNT and by 4 °C for CNP when compared with neat resin. Both CNP and MWCNT showed drop in electrical resistivity of the neat resin; a drop to the extent of 10 3 has been achieved with 1 wt % MWCNT and the same was 2 wt % in case of CNP.
Effects of Nano / Meso Harmonic Microstructure on Mechanical Properties in Austenitic Stainless Steel Produced by MM / HRS Process
Authors: Hiroshi Fujiwara , Tanaka Hideyuki , Nakatani Masashi , Ameyama Kei
Published: January 2010

Mechanically milled austenitic stainless steel powder is applied to hot roll sintering (HRS) process. Microstructure and mechanical properties of the HRS material are investigated in detail. The mechanically milled powder has a bimodal structure with a severely deformed powder surface domain which is named as “Shell”, and an inner domain which is named as “Core”. The shell and core microstructure in the milled powder can be maintained even after sintering. As the result, microstructure of the HRS materials consists of a shell and core bimodal microstructure. Because severe plastic deformation mainly concentrates to the shell domain, a nano grain structure forms in the shell, while a coarse (meso) grain structure forms in the core. Such a nano / meso harmonic structured material demonstrates not only superior strength but also a large elongation. The mechanical properties of the HRS materials are strongly influenced by the nano / meso harmonic microstructure, such as grain size of the shell / core and the shell volume fraction. The shell has role of strength and the core has role of ductility. Thus, the nano / meso harmonic microstructure has been proved to be very effective to improve mechanical properties of structure materials.
A Study on the Optimization of Reduction-Diffusion Process for Synthesis of Sm2Fe17Nx Nanopowder
Authors: Yun J.C. , Jung S.S. , Lee Jung Goo , Choi C.J. , Lee Jai Sung
Published: January 2010

The present investigation attempted to optimize the R-D (reduction-diffusion) process for fabricating Sm2Fe17 nanoscale powder from ball-milled powders of samarium oxide and iron oxide using a solid reducing agent of calcium hydrides (CaH2). It was found that the target alloy phase of Sm2Fe17 can be produced by controlling the gas atmosphere in the process of powder preparation to R-D reaction. Powder handling of CaH2 in a protective atmosphere is essential to avoid the formation of Ca(OH)2 which suppresses calcium formation. A switching gas atmosphere of H2 to Ar-H2 during the R-D process at 350oC resulted in a reduction of Fe2O3 and alloying of Sm-Fe, consequently forming nanocrystalline Sm2Fe17.