bluuebunny/crossref_metadata_2025 huggingface dataset:
The Analysis of Space Charge Behavior in Nylon 11
Authors: Neagu Eugen R. , Marat-Mendes José N. , Neagu Rodica M.
Published: March 2009

A combined isothermal and non-isothermal measurement technique is described for analyzing space charge behavior in dielectric materials. The experimental conditions are chosen so that the dipolar effects are insignificant and the measured current is mainly due to space charge detrapping. For polyamide 11 four peaks have been identified above the poling temperature. As the difference between the peak temperature and the poling temperature increases, the apparent activation energies decrease suggesting that only the faster modes participate to the charging process. The charge associated to the apparent peak and the peak at 96 °C scales linearly with the polarization field. The injected space charge at 35 °C is very stable at 150 °C, an important fact with respect to technological applications of polyamide 11 as an electroactive material.
Detection Properties of CdZnTe Semiconductor for Diagnostic X-Ray Spectroscopic Applications
Authors: Freitas M.B. , Medeiros F.H.M. , Yoshimura Elisabeth M.
Published: March 2009

Currently, many semiconductor compounds, particularly Cd1-xZnxTe, have attracted attention for applications in detection of radiation, due to the very good resolution without cryogenic cooling (a 1.3 keV-FWHM at the 122 keV line from 57Co is reported for some detectors). In this study the properties of a zinc doped cadmium telluride detector mounted on a thermoelectric cooler (Amptek Inc., model XR-100T-CZT) were studied. The detection system is based on a Cd0.9Zn0.1Te crystal of 3x3x2 mm, which operates at approximately -21°C and uses a rise time
discrimination (RTD) circuit to improve the energy resolution. Although the quantum efficiency of this compound is very high, the small dimensions of the crystal limit its use to low energy photons (some hundreds of keV). Because of the carrier trapping characteristics of CZT, the experimental determination of the response function is essential. In this work it was measured in the range of
energies from 10 to 400 keV, employing gamma rays and fluorescence x-rays from different sources (57Co, 133Ba, 152Eu and 241Am). In spite of the experimental difficulties, the x-ray escape fraction was also evaluated, making it possible the correction of the distortion it causes in the measured spectra. Measurements of x-ray spectra produced by a tungsten tube operating at small currents were carried out, and the stripping procedure was performed, taking into account the two
contributions (efficiency and escape fraction). Results obtained point to the feasibility of use of this detector for in-situ diagnostic x-ray spectroscopy, provided that low intensity beams are available.
Fracture Behaviour of Brittle (Glass) Matrix Composites
Authors: Dlouhý Ivo , Chlup Zdeněk , Boccaccini Aldo Roberto
Published: March 2009

A number of examples exist that indicate the potential for increasing the toughness of brittle matrices by dispersing different reinforcements. For further development of these advanced materials the actual material response during mechanical loading under presence of flaws appears to be important. Theoretical and experimental knowledge acquired on different kinds of brittle matrix composites is summarised in the paper. These include glass matrix composites with metallic particles, alumina platelets, continuous SiC (Nicalon®) fibres, and both chopped fibres and ZrO2particles (hybrid composites). The composites were tested in as-received state but also after different forms of thermomechanical loading, e.g. thermal shock, thermal cycling in air, which were investigated according to the envisaged composites application. Chevron notch technique was mainly used for fracture toughness evaluation. Microstructural damage is explained based on identified fracture micromechanisms.
Breakdown of the Schmid Law in BCC Molybdenum Related to the Effect of Shear Stress Perpendicular to the Slip Direction
Authors: Gröger R. , Vitek V.
Published: March 2009

The breakdown of the Schmid law in bcc metals has been known for a long time. The
asymmetry of shearing in the slip direction 〈111〉 in the positive and negative sense, respectively, commonly identified with the twinning-antitwinning asymmetry, is undoubtedly one of the reasons. However, effect of stress components other than the shear stress in the slip direction may be important. In this paper we investigate by atomistic modeling the effect of shear stresses perpendicular to the Burgers vector on the glide of a/2〈111〉 screw dislocations. We show that these shear stresses can significantly elevate or reduce the critical resolved shear stress (CRSS) in the direction of the Burgers vector needed for the dislocation motion, i.e. the Peierls stress. This occurs owing to the changes of the core induced by these stresses. This effect may be the reason why slip systems with smaller Schmid factors may be preferred over that with the largest Schmid factor.
Near-Field Study of Carrier Dynamics in InAs/GaAs Quantum Dots Grown on InGaAs Layers
Authors: Tománek Pavel , Dobis Pavel , Benešová Markéta , Grmela Lubomír
Published: March 2009

InAs/GaAs quantum dots (QDs) with ordered structure, due to their peculiar properties, open new way to design novel semiconductor devices such as single-electron transistors or highly parallel computing architectures. The lateral quantum dot alignment achieved during the selfassembly process is not well understood heretofore. The reason is, that quantum structures areusually small and studied at low temperatures. Conversely, the Scanning near-field optical microscopy (SNOM) allows study nanometer details in the non-offensive manner, in the room
temperature with high spatial and temporal resolution. The first results of near-field optical study on aligned QDs are presented.
The Migration of Solute Atoms in the Stress Field of a Slowly Moving Crack
Authors: Streitenberger Peter
Published: March 2009

The stress-driven diffusion of solute atoms to a slowly moving brittle crack is studied
under the condition of pure drift. The first-order drift-diffusion equation for a slowly moving crack at uniform velocity is solved yielding the flow lines and the impurity segregation rate in terms of the crack growth rate. The flow line patterns reveal important insights with respect to the solute migration kinetics near a steadily advancing subcritical crack at stage I and stage II crack growth.
Interaction of a Crack in the Plasma-Sprayed Ceramic Coating with the Metal Substrate
Authors: Náhlík Luboš , Knésl Zdeněk , Kroupa F.
Published: March 2009

Plasma-sprayed ceramic coatings contain a high density of intrasplat microcracks which are responsible for small Young’s moduli and low fracture toughness. The extension of an initial surface crack in the direction to the interface, where the crack is repelled by the metal substrate with higher Young’s modulus, is studied using the methods of fracture mechanics. It is shown that high tensile stresses induced by the crack in the interface can lead to a local decohesion along the interface so that the crack can deviate into the interface.
Critical Strain Energy Density along the Curved Front of the Growing Fatigue Crack
Authors: Denk Tomáš , Oliva Vladislav , Materna Aleš
Published: March 2009

A two-parameter constraint-based fracture mechanics approach is used to explain the effect of the constraint on the apparently anomalous behavior of short fatigue cracks. The different levels of stress constraint are quantified by the T-stress, and microstructurally as well as mechanically short cracks are discussed. Short cracks generally behave more sensitively to the constraint than the long ones. It is shown that in most cases, the existence of short cracks goes hand in hand with an intrinsic loss of the constraint, which contributes to a decrease of their fatigue
threshold values and accelerates their growth. In this paper, the above effect is quantified and conclusions concerning the applicability of the fracture mechanics parameters and approaches to the estimation of the residual fatigue life of structures are discussed.
On the Crack Tip Shielding in Particle Reinforced Composites
Authors: Horníková Jana , Šandera Pavel , Pokluda Jaroslav
Published: March 2009

The paper is focused on crack-tip shielding effects caused by crack deflection (tilting) processes in particle reinforced composites. A numerical analysis by means of the ANSYS code was employed in order to assess these effects caused by rigid particles and holes in the matrix. As the first step, the effective stress intensity factor Keff was calculated for many crack tip positions in front, and in
between, two particles of the same kind. In spite of a significant crack tip tilting, the spherical holes induce a slight increase in the Keff factor (anti-shielding). On the other hand, the rigid particles cause a significant decrease in the Keff-value (shielding), while leaving the crack practically unaffected. In the second step, the effect of particles in the wake of the crack tip will be analyzed in order to obtain a complex picture of shielding.
Influence of Inclusions on Fatigue Characteristics of Non-Combustible Mg Alloy
Authors: Kitahara Y. , Shimazaki H. , Yabu T. , Noguchi Hiroshi , Sakamoto Michiru , Ueno Hideto
Published: March 2009

It is common knowledge that Mg is very light and high specific strength material. But there is a problem that Mg alloy easily burns during its machining, because the ignition point of Mg is 700K.[1] The ignition point of new Mg alloy to which Ca is added is about 1000K. This new Mg alloy is called non-combustible Mg alloy. As a result, many inclusions exist in Mg alloy. Then, fatigue test was carried out and gave evidence that inclusions have an effect on the fatigue strength. Then
relationships between size of inclusions and fatigue limit were drawn. Therefore, the fatigue limit can be predicted by estimating the maximum inclusion size. The method of estimating the maximum
inclusion size is “Estimation for particle size distribution in materials“[2] .
Mechanical Response of Semi-Brittle Nano Particles under an Imposed Cyclic Field
Authors: Katz Y. , Mook W. , Mukherjee R. , Gidwani A. , Deneen J. , Gerberich William W.
Published: March 2009

In elastic plastic solids, approaching the sub micron scale, critical experiments indicated significant differences in the mechanical response. Thus, mainly in small volume behavior a length scale issue is introduced with implications on the basic understanding of deformation and fracture processes. The current study is centered on the mechanical response of silicon particles in the range of 20-50 nm on sapphire substrate. Monotonic and cyclic mechanical tests have been performed by contact mechanics methodology at ambient temperature. Mechanical information and visualization assisted by scanning probe microscope-based nano indentation alluded to a model founded on dislocation dynamic effects. This facilitated developments regarding the length scale subject in the light of fatigue concepts and structural integrity aspects.
Mechanical Behavior of Nanostructured Aluminum Alloys Containing Quasicrystalline Phase
Authors: Milman Yu.V.
Published: March 2009

Aluminum-based alloys containing quasicrystalline particles of 50 – 600 nm in diameter as a reinforcing phase were produced in the form of powder or ribbons by water atomization or melt spinning techniques, respectively. Rods were compacted from powders and some ribbons by severe plastic deformation without sintering. Structure and mechanical behavior of alloys are discussed.
Vibration and Impact Noise Damping Properties of Wood/Polymer Composites
Authors: Lee Hyun Jong , Lee Beom Goo , Shin Dae Yong
Published: March 2009

This study investigates the influence of viscoelastic properties of a series of ethylene-vinyl acetate copolymer on impact noise and vibration damping of wood/polymer/wood sandwich composites. It was found that the impact noise and vibration damping of composites are very sensitive to the state of molecular motion of polymer. The noise and vibration damping of composites was better when the polymer was in the glass transition state (vinyl acetate 55~75%) at the
test-temperature, and it was worse when the polymer was in rubbery state (vinyl acetate 47~20%) or in glassy state (vinyl acetate100~87%). The impact noise decreased by about 6-12dB when the glass transition state of polymer was sandwiched between wood panels.
Effect of Rare-Earth Elements Y and Ce on the Microstructure and Mechanical Properties of ZK60 Alloy
Authors: Yi Dan Qing , Wang Bin , Fang Xiya , Yao Su Juan , Zhou Ling Ling , Luo Wen Hai
Published: March 2009

The Mg-Zn-Zr alloy ZK60 with added trace rare-earth elements Y(0.9wt%) and
Ce(0.9wt%) were prepared. After hot extrusion and aging treatment, the tensile mechanical properties of the alloys were tested at room temperature. Microstructures of the alloys were investigated by optical microscope (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The existing form, affecting mechanisms of trace Y and Ce in alloys and the effects on the microstructures and mechanical properties of ZK60 alloy were discussed. The results showed that: trace rare-earth elements Y and Ce both had remarkable grain-refining effects on the alloys, while the grain-refining effect of Y was more significant than that of Ce. RE elements Y and Ce improved the mechanical properties of the ZK60 alloy, but the strengthening effect of Y was more remarkable. It was found that σb of Mg-Zn-Zr-Y alloy was improved by 12.6％. Addition of Ce to the ZK60 alloy led to an increase in ductility of the alloy from 15% to 17%.
Microstructures and Tensile Properties of Hot-Rolled AZ31-xCa Sheets
Authors: Chang Dong Yim , You Bong Sun , Lee Jin Su , Kim Wan Chul
Published: March 2009

In this study the effects of Ca addition on the rollability, microstructures and tensile
properties of AZ31 alloy were evaluated. In Ca containing alloys, reduction ratio and preheating temperature are the most important variables to make good sheet without any crack. The number and length of side crack increased with increasing Ca content. With increasing the reduction ratio per pass and decreasing the preheating temperature, crack initiates easily at the side. The dendritic grains were changed to fine equiaxed grains through hot rolling by dynamic recrystallization. The Al2Ca
precipitates which were segregated to grain boundaries during solidification were rearranged parallel to the rolling direction. The tensile properties of hot-rolled AZ31-xCa sheets were decreased slightly by addition of Ca.
Microstructure and Mechanical Properties of a Mg-Zn-Y-Zr Alloy Processed by Thermo-Mechanical Treatment
Authors: Zhang Ya , Zeng Xiao Qin , Lu Chen , Ding Wen Jiang , Zhu Yan Ping
Published: March 2009

Mg92Zn6Y1.5Zr0.5 alloy was extruded at 300, 350, 400 ı. Then, the alloy was aged at 180 ı. The microstructure and mechanical properties of the extruded alloy and aged alloy were investigated. The precipitation behavior of aging process was investigated. The increase of yield strength at room temperature and ultimate strength at elevated temperature after the aging process has been ascribed to the strengthening effect of these precipitates.
Microstructure and Properties of Mg-Al Based Casting Alloys Modified with Minor Alloying Elements
Authors: Kim Jeong Min , Park Bong Koo , Jun Joong Hwan , Kim Ki Tae , Jung Woon Jae
Published: March 2009

Minor alloying elements such as RE, Sb, and Si were added to Mg-Al based commercial alloys and their effects on the mechanical properties, corrosion resistance, and castability were investigated.The result show that small amount of cerium-rich misch metal (RE) addition with antimony enhances the heat resistance of AZ91 alloy effectively without deteriorating other good properties. The addition of Si with RE was also found to improve the heat resistance and casting
capabilities (fluidity and hot cracking resistance) of AM50 alloy.
Effect of Heat Treatment on Microstructure and Mechanical Properties of MA2-1 Alloy Sheet
Authors: Zheng Weichao , Sun Xiao Li , Li Peijie , Zeng Daben , Ber L.B.
Published: March 2009

Effect of heat treatment on the microstructure and mechanical properties of high purity MA2-1(Mg-5wt.%Al-1wt.%Zn-0.4wt.%Mn) alloy sheet were investigated. X-ray diffraction analysis indicated that the microstructure of high purity MA2-1 alloy sheet annealed consisted of α-Mg solid solution, β (Mg17Al12) phase and Al-Mn phases such as Al6Mn and Al10Mn3. β phase dissolved into α-Mg solid solution during the solution treatment and formed supersaturated α-Mg solid solution. After aging at the temperatures of 423 K, 473 K and 523 K for 12 hours, β phase precipitated from the supersaturated α-Mg solid solution. Optical microscope observation found that the grain size of the MA2-1 alloy sheet became larger after heat treatment. As a result, the mechanical properties of the MA2-1 alloy sheet such as the tensile strength and yield strength declined after the heat treatment.
Effects of Silicon and AlP on Microstructure and Properties of Mg-8Zn-4Al-0.3Mn Alloy
Authors: Zhang Chun Xiang , Guan Shaokang , Zhao Hong Liang
Published: March 2009

The effects of silicon and AlP on microstructure and properties of Mg-8Zn-4Al-0.3Mn
alloy were studied. When 0.96%Si was added in the base alloy, Chinese script Mg2Si formed, the precipitation of τphase was restrained while the precipitation of φ phase was facilitated for decreasing of the concentration of solute in the residual liquid phase, at the same time, the fluidity was remarkably improved. To modify Chinese script type Mg2Si, a new green modificator--Al-AlP master alloy was added in Mg-8Zn-4Al-0.3Mn-1Si alloy. It showed that AlP addition promoted the formation of fine polygonal type Mg2Si particles by providing the nucleation sites, refined the
grains, facilitated the precipitation of τphase while inhibited the precipitation of φ phase by changing the concentration of solute in the residual liquid phase and shortening the diffusion distance of the atoms. The improved microstructure of the modified alloy resulted in the large improvement in tensile properties at both ambient temperature and 150 as compared to the base alloy.
Effect of Antimony and Ce-Rich Mischmetal Additions on As-Cast Microstructure and Mechanical Properties of AZ91 Alloy
Authors: Yang Zhong , Li Jian Ping , Li Gao Hong , Yang Jueming
Published: March 2009

Various amounts of antimony and mischmetal (Ce-rich) were added into AZ91 cast
magnesium alloy and the microstructural characteristics of the cast magnesium alloys were studied by optical microscopy, electronic microscopy and X- ray diffraction techniques. Both antimony and mischmetal had grain refinement effect to AZ91 alloy. When they were added together, a further refinement was observed. SEM-EDX and XRD analysis indicated that a plate-shaped phase, Al11RE3,
formed at the boundaries of dendritic α-Mg grain. A rod-like Mg3Sb2 compound distributed both within α -Mg dendrites and along grain boundaries. A new spherical particle, ReSb, formed in the magnesium alloy when 0.8wt%RE and 0.4wt%Sb were join added. The individual additions of antimony or mischmetal to AZ91 alloy did not result in a noticeable improvement to its room temperature tensile properties, but when 0.8wt%RE and 0.4wt%Sb were added together, the as-cast tensile properties of the alloy were increased dramatically.
Effects of Technological Factors on the Mold Filling Velocity of Magnesium Alloys in the Expendable Pattern Casting (EPC) Process
Authors: Yang Ming Bo , Pan Fu Sheng , Tang Shuangquan
Published: March 2009

The effects of vacuum degree, pattern density, pouring temperature and metallic static head on the mold-filling velocity of AZ91D alloy in the expendable pattern casting (EPC) process have been investigated in the paper, and the influencing law of these technological factors on the mold-filling velocity are obtained. The results indicate that the influence of vacuum degree on the mold-filling velocity of AZ91D alloy in the EPC process is greatest, pattern density and pouring temperature are next respectively, and metallic static head is small relatively.
Research on the Homogenization of ZK60 Magnesium Alloy Ingot
Authors: Zhang Ding Fei , Peng Jian , Jiang Bin , Yang Chun Mei , Ding Pei Dao
Published: March 2009

The influence of various homogenizing parameters on the microstructure of ZK60
magnesium alloy ingot has been investigated. By means of metalography observation and micro-hardness measurement, the effect of annealing temperature and time on the homogenization processes were studied, which indicated that the homogenized microstructure was more sensitive to annealing temperature than to annealing time. An optimized homogenizing process 470°Cx14h was suggested to improve the deformability of ZK60 alloy.
The Grain Size Evolution of AZ31 Profiles as a Function of Different Casting Conditions
Authors: Pravdic Franka , Kilian H. , Brandecker M. , Wögerer C. , Traxler G.
Published: March 2009

The present paper describes the microstructural evolution of AZ31 alloy along the
process chain, from the melt treatment, the direct chill casting up to the extrusion process. Each step in the process chain will be considered in order to design the appropriate properties of the endproducts. The research has been done in industrial scale at ARC Leichtmetallkompetenzzentrum Ranshofen GmbH (LKR), in order to analyse the grain size dependency of AZ31 alloy on different casting conditions. The casting trials with and without grain refinement were carried out at the vertical direct chill casting machine MAGNUMCAST®. After the extrusion process metallographic
analysis and mechanical tests were carried out.
Investigation on Pore Formation during Hybrid Laser-Tungsten Inert Gas Arc Welding of Magnesium Alloy AZ31B
Authors: Liu Li Ming , Song Gang , Wang Ji Feng
Published: March 2009

This study seeks to analyze the presence method and quantity of pore during hybrid
laser-tungsten inert gas arc (TIG) Welding of Magnesium Alloy AZ31B by radiography, optical microscopy and electron probe microanalysis (EMPA). At the same time, it identifies both the mechanism of pore formation and a remedy for this problem. The experimental results indicate that lacking of shielding gas for laser beam is the dominant cause of macro-porosity formation during the hybrid of laser-TIG welding of magnesium Alloys AZ31B plate, and hydrogen is not main cause to
form large pores. A favorable weld without porosity can be obtained by appending lateral shielding gas for laser beam.
Grain Refining of Magnesium Alloy AZ 31 by Equal Channel Angular Extrusion
Authors: Wang Jian Yih , Chen Yung Hung , Yang Yi Lang , Lee Shyong
Published: March 2009

Among the conventional and alleged bulk deformation processes in metalworking, equal channel angular extrusion (ECAE) is an innovative and attractive method to refine grain structures effectively. Grain refining by this process on magnesium alloy AZ31 was studied and compared to published data. An interesting and unique question is proposed and studied - that is, how dominant is the accumulated strain as obtained through multiple angular extrusion passes. Tensile tests were performed at room and high temperatures, and processed AZ31 was examined with optical and
transmission electron microscopy as well as x-ray diffraction.
Plastic Deformation Behaviors and Microstructures of a Wrought Mg-Zn-Rare Earth Alloy
Authors: Yu Kun , Li Wen Xian , Wang Ri Chu , Xiao Yude , Ma Zhengqin
Published: March 2009

The hot compression simulation of an experimental Mg-Zn-Nd alloy at different
temperatures is studied by the Gleebe-1500 equipment. The deformation is performed with the strain rates 0.1s-1, 0.01s-1 and 0.002s-1. The plastic deformation behavior is analyzed at different temperatures and the deformation activation energy is calculated. The microstructures of experimental alloy during the deformation process are observed. The results show that the working hardening, dynamic recovery and dynamic recrystallization (DRX) operate under different
temperatures and strain rate. The DRX starts when the temperature is over 473K and the DRX grain size after hot deformation is only 5~10μm. So the refined grains improve both the tensile strength and elongation of alloys at room temperature. The precipitate phase Mg12Nd impede the movement of dislocations, it benefit to the mechanical properties and grain refining of magnesium alloy.
Development of Semi-Solid Processes for Hot Extrusion of Magnesium Alloys
Authors: Koren Z. , Rosenson H. , Rosen G.I. , Segal G.
Published: March 2009

Technological barriers that relate to limited capability of magnesium extrusion
technology still exist, especially for the higher alloyed grades. Part of this is associated with the unfavorable crystallographic structure of the magnesium, which is Hexagonal Close Packed (HCP). This work suggests an innovative and novel technology for reducing the production cycle from cast to finished product. A unique Semi-Solid casting system was designed and constructed in order to enable casting of large scale commercial billets having thixotropic properties. These have been
further hot extruded via conventional direct extrusion press. It is shown that all essential parameters have improved significantly. These include extrusion temperature reduction (up to 1500C), press pressure reduction, increase of extrusion rate (up to four times), and, enhancement of surface quality. In addition good mechanical properties and corrosion resistance were achieved.
TiN Coating on Magnesium Alloy by Arc-Aided Glow Discharge Plasma Penetrating Technique
Authors: Cui Cai E. , Miao Qiang , Pan Jun De , Zhang Ping Ze
Published: March 2009

Arc-aided glow discharge plasma penetrating technique is a new surface coating method. With the help of vacuum arc discharge, a cold cathode arc source continually emits ion beams of coating elements with high currency density and high ionizing ratio. As the ion bombard working on, nitrogen is let in the chamber simultaneously. Then the surface of the parts formed ceramic coatings. Under lab condition, a commercial magnesium alloy Az91 had been coated with TiN film layer with the aim of improving the corrosion resistance. This paper mainly summarizes the testing and analyzing of the coating layer. The composition and microstructure of the coating layer had been analyzed by means of X-ray diffraction (XRD) and glow discharge spectrum (GDS), and the surface appearance had been surveyed by scanning electronic microscope (SEM). The adhesion strength between film and matrix had been evaluated by experiments of sticking-tearing. The results indicated that the coated layer on magnesium alloy were homogeneous, dense and robustly adherent.
Synergistic Fluoropolymer Coating on Magnesium Alloys
Authors: Zou Hong Qing , Lu Ji Cheng , Zhang Jin , Wu Hou Chang , Fang Min
Published: March 2009

The synergistic fluoropolymer self-lubrication coatings on magnesium alloys were
studied. Magnesium alloy was firstly treated by electroless nickel plating. Then micropores of electroless nickel plating layer was enlarged. Then the fluoropolymer particles were infused into micropores, precise vacuum heat treatment ensured thorough infusion with fluoropolymer, finally the synergistic coating was formed. The hardness of the coating reached 600HV, the dynamic coefficient of friction of the coating was less than 0.15, and the low coefficient of friction could be kept during a long duration wear to realize the permanent dry lubrication. The corrosion resistance
was also excellent to endure 5% neutral salt spray test for 500 hours. Also the structure and composition of the coating were observed and studied.
Dynamic Crack Propagation Behavior of the Mg-Li Alloys under High-Speed Impact Loading
Authors: Sha Gui Ying , Xu Yong Bo , Han En-Hou
Published: March 2009

The dynamic experiments for the Mg-Li alloys with single phase structure were carried out using the Hopkinson pressure bar. The dynamic crack propagation behavior and fracture mechanism of the alloys were investigated. The results show that the dynamic crack propagation is a deceleration process for the Mg-Li alloys under high loading rate. The fastest crack propagation velocity for Mg-3.3Li alloy is m/s 37 . 1253 , and 935.36m/s for Mg-14Li alloy. Observations of the fracture by SEM reveal that the dynamic fracture surface for Mg-3.3Li alloy mainly appears to be
brittle fracture along grain boundaries. Whereas, the Mg-14Li alloy is ductile fracture mode under high loading rate. The main reason for these may be the transformation of hcp→bcc structure and the precipitation of the MgLi2Al and AlLi, as increase of Li in Mg-Li alloy.
Effect of Si, Ca and Sr on the Creep-Resistance of AZ91D Alloy
Authors: Wang Yan , Xiong Shou Mei , Li Wen Hui , Zou Zhi Wen
Published: March 2009

In present work, Sr, Ca and Si elements were added into AZ91D and cast into a metallic mold. The influence of these elements on AZ91D magnesium alloy were studied systematically with the purpose of developing a new magnesium alloy with good mechanical properties at both room and high (150°C~200°C) temperature. Additionally, a simple method to qualitatively analyze the high-temperature creep performances of magnesium alloys was designed and implemented.
Mechanical Properties and Deformation Features of AZ31-Sb Alloy
Authors: Tian Su Gui , Sohn Keun Yong , Kim Kyung Hyun
Published: March 2009

Mechanical properties and high temperature deformation behavior of AZ31-0.84%Sb
alloy have been studied. The results show that small additions of antimony to AZ31 alloy effectively enhanced the creep resistance and the ultimate tensile stress of the alloy at elevated temperature. One of the reasons for the improved high temperature properties is the high volume fraction (~20%) of the precipitates, as Mg3Sb2, which effectively hindered the movement of dislocations during the elevated temperature deformation. Considerable amounts of twins were formed during creep failure of AZ31-0.84%Sb alloy. Within the twins, many dislocation pile-ups were present on both basal and non-basal plane of magnesium matrix.
Environmental Impact and Corrosion Behaviour Assessment of Magnesium Castings
Authors: DeBenedetti Bruno , Angelini E. , Grassini S. , Marino M. , Fracassi F. , Palumbo F.
Published: March 2009

The use of magnesium and its alloys is limited by their high susceptibility to corrosion,
that may be attributed to the presence of critical impurities and the high chemical reactivity of the magnesium itself. Such characteristic justifies the great interest of performing coating technologies for the protection of magnesium parts by using environmentally friendly and cheap processes, with particular relevance in the framework of the European context. While magnesium technologies are rapidly taking advantages of the research results obtained during the last years, some more efforts are necessary to evaluate the impacts of its production on the environment and on the use of existing energy resources. Following this main lines, the paper
presents some results obtained in NANOMAG (“Development of Innovative Nanocomposite Coatings for Magnesium Casting Protection” – Growth Programme n. 40548), a research project sponsored by the European Commission in which magnesium and its coating processes are evaluated taking into account also their environmental performances with a life-cycle approach.
Compressive Behavior of Extruded SiCw/AZ91 at Temperatures close to and above the Solidus of the Matrix Alloy
Authors: Gan Wei Min , Zheng Ming Yi , Li S.B. , Wu Kun
Published: March 2009

Compressive deformation behaviors of extruded SiCw/AZ91 were investigated in
Gleeble-1500 thermal simulator at temperatures from 743 K to 783 K and strain rates from 6.4×10-2 s-1 to 1.0×101s-1. Results showed that high strain rate sensitivity (~0.5) occurred during compression; deformation activation energy normalized by threshold stress was higher than the lattice self-diffusion activation energy of magnesium. Dynamic recovery (DRV) and dynamic recrystallization (DRX) took place during compression, which refined the grains. The increase of deformation energy was attributed to non-basal planes slip and climbing of dislocations and also the presence of liquid phase.
Phosphoric Conversion Coating and Chromic Conversion Coating for Die-Cast Magnesium Alloy ZM5
Authors: Hu Yong , Du Nan , Zhao Qing , Zhou Ya , Meng Linggang
Published: March 2009

In the present paper, phosphoric and chromic conversion coatings were prepared for the die-cast magnesium alloy ZM5. Both two kinds of chemical converting coatings are of evident corrosion resistance. Their compositions, morphologies and crystal characteristics were discussed.
Effects of Alloying Elements on Mechanical Properties of Mg-Al Alloys
Authors: Chung Yeon Jun , Park Jung Lae , Kim Nack , Shin Kwang Seon
Published: March 2009

The effects of alloying elements on the microstructure and high temperature mechanical properties of Mg-Al alloys were investigated in this study. In order to improve the high temperature mechanical properties, Sr or Mm was added to the Mg-9Al alloy. The effect of Sn on the Mg-9Al alloy was also examined since Sn was expected to improve the high temperature mechanical properties by forming the thermally stable Mg2Sn phase. The specimens used in this study were produced on a 320 ton cold chamber high-pressure die casting machine. The microstructures of the specimens were examined by optical and scanning electron microscopy and tensile and creep tests were performed at elevated temperatures. Tensile tests were carried out at room temperature, 150oC and 200oC using an initial strain rate of 2×10-4/sec. In addition, tensile creep tests were conducted at the stress levels of 50 MPa and 70 MPa. From the microstructure analyses of the specimens after heat
treatment at 400oC for 12 hours, it was found that most of the Mg17Al12 precipitate dissolved into the matrix, while the thermally stable phases continued to exist. The high temperature mechanical properties of the Mg-9Al alloys were found to improve significantly with the additions of Sr, Mm and Sn, due to the formation of the thermally stable precipitates.
Effects of Biaxial Stress Condition for Fatigue Properties of Magnesium Alloy
Authors: Ito Yasumi , Shimamoto Akira
Published: March 2009

Fatigue crack propagation tests of magnesium alloy were conducted under conditions of biaxial and uniaxial loading by using a cruciform specimen with the biaxial fatigue tester. The purpose of this study is to investigate the effect of biaxial stress on the fatigue crack growth properties ⊿KⅠ-da/dN. From these comprehensive experiments, the remarkable effect was found in the specific biaxiality ratio σx 0/σy 0 on the ⊿KⅠ-da/dN relationship. When biaxiality ratio was 0.5,
it turned out that the fatigue crack propagation velocity of a magnesium alloy becomes very slow. In other biaxiality ratios, fatigue crack propagation velocity was influenced in some extent. Fatigue crack propagation velocity decreases a little as the stress which acts in parallel with a crack increases.
Fundamental Magnesium Researches in Japan
Authors: Kojima Yo , Kamado Shigeharu
Published: March 2009

In the current four-year term project in Japan, new platform science and technology is proposed as a core concept of research and development of advanced magnesium alloys together with understanding of their intrinsic characteristics. The research fields related to advanced super-light magnesium alloys for 21st Century have been focused to the selected three categories; ecomaterial design and processing, high qualification of mechanical performance, and high performance design and processing in functionality. On the basis of the obtained results, platform science and technology for environmentally benign and high performance magnesium alloys is constructed as an industrial base material for the next generation. As a result, numerous large-scale joint research and development projects on magnesium alloys based on partnerships between industries, academia and government has already started towards practical utilization since last year.
Approximate Analytical Formulae to Evaluate the Uncertainty in X-Ray Stress Analysis
Authors: François Manuel , Ferreira C. , Guillén Ronald
Published: March 2009

The global uncertainty, in X-ray stress analysis, is due to many factors but one of the most important is the uncertainty on peak positions due to counting statistics and other random errors on peak positions. Although a lot of work has been done to estimate the latter, very little work has been devoted to its propagation through the least square regression. This work presents some analytical results in the general case of triaxial stress state (elliptic curve fit) and proposes approximate formulae to easily compute the uncertainty on normal and shear stress components from acquisition parameters such as the number N of y tilts and the maximum y value. It was found that the latter only influences significantly the uncertainty on the normal stress component and that the dependency of the uncertainty on N does not necessarily follow a 1/ N relation.
Inter and Intra Granular Strain Analysis by Microdiffraction Kossel
Authors: Berveiller Sophie , Dubos Pascal , Inal Karim , Eberhardt André , Patoor Etienne
Published: March 2009

We have developed a new convenient tool for local stress and strain analysis in the
scanning electron microscope. It is based on the Kossel diffraction, physical phenomenon that is known for a long time because of its high accuracy for lattice constant determination in micron regions. The pattern is recorded on a CCD camera allowing a fast and reliable analysis. This technique has been applied to several materials. In-situ tensile tests were performed on a shape memory alloy. During loading, we observe clearly a shift of Kossel lines on the diagram, whose magnitude depends on the (hkl) crystallographic planes. The stress can be deduced from the diffracting plane strain measurement using a single crystal stress analysis.
Residual Stresses Induced by Laser FreeForm Fabrication
Authors: Peng Ru Lin , Johansson Sten Å.H. , Ericsson Torsten , Thorsson Lena
Published: March 2009

In this paper we report our attempts to use the neutron and X-ray diffraction techniques to characterize residual stresses in specimens manufactured by laser FreeForm technique. The aim of our work has been to understand how residua stresses develop during forming and their possible correlation with the microstructure, in particular the pore density which varies with the laser scan
speed. The specimens under investigation were built by layer-sintering a ferritic-steel powder with a Cu-based-alloy powder as the binder material. Limited results have been obtained for the ferrite steel phase and are presented in the paper.
Feasibility Study of FGM Technology in Space Solar Power Systems (SSPS)
Authors: Niino Masayuki , Kisara Katsuto , Mori Masahiro
Published: March 2009

In this paper, we introduce research and development in SSPS (aimed at global energy supply) in Japan. To build SSPS, we must develop ultra lightweight materials and high efficiency energy conversion materials. Feasibility of adapting FGM concept for those new demands and advanced research theme for future FGM research are also introduced in this paper.
Structure of Dental Resin-Based Adhesive Materials
Authors: Fano L. , Fano V. , Ma W.Y. , Wang X.G.
Published: March 2009

This study aimed to show that the polymerization contraction of dental light cured resin-based materials, when it was used as adhesives on hard substrate, produces voids at the material/substrate interface. Two liner/base systems, one glass-ionomer, one restorative composite resins and two compomers were cured using mirror-like glass slide as a compliance-free reference substrate. The adhesive surface was analyzed by atomic force microscopy, and the polymerization contraction of bulk material was tested by laser beam scanning method. Nanoperiodic structure of 3D images, section analysis and roughness characteristics (Ra and Rz)) indicated that polymerization contraction
produced voids at the interface. In visible light-cured (VLC) materials, the interface porosity decreased when an irradiation pause was carried out during gelation.
The Synthesis of Indium Tin Oxide Nano – Powders by Solvothermal Process
Authors: Lee Jin Seok , Choi Sung Churl
Published: March 2009

Well-crystallized and nano-sized indium tin oxide (ITO) powders were prepared by a solvothermal process from a mixed solution consisting of indium nitrate and tin chloride. The characteristics of the solvothermally synthesized ITO powders were studied to investigate the contribution of the processing variables on the physico-chemical properties of powders. The results of this study show that the nano-sized blue ITO powders with a single phase could be directly obtained by changing the medium from water to organic solvent.
Fracture Analysis of Functionally Graded Thermal Barrier Coating with Interface Crack by Computational Micromechanics Method
Authors: Yang Shu Yong , Liu Li Sheng , Zhang Qing Jie
Published: March 2009

The fracture of the functionally graded thermal barrier coating (TBC) under the thermal loads is a key for the engineering application of this kind of materials. In the previous studies, the functionally graded TBC is usually simplified into a laminate by homogenizing the material of each interlayer as an isotropic layer. Nevertheless, this method is a macro equivalent method, which neglected the microstructure characteristics of materials. In this paper, the computational micromechanics method (CMM) is employed to study the fracture problem of the functionally graded TBC with the interface crack. Essentially, CMM is a finite element analytical method based on the real microstructure of materials, which combines the digital image processing technique, the auto mesh generation technique with the finite element method. Firstly, the microstructure photos of the functionally graded TBC are required. Secondly, the digital image processing technique and the auto mesh generation technique are used to construct the finite element model. Finally, the finite element method is utilized for the fracture analysis of the functionally graded TBC under the thermal shock loads. Moreover, the problem is also analyzed using the macro equivalent method and the results from the two methods are compared. The temperature field obtained using CMM is basically consistent with the one obtained from the macro equivalent method and the influences of the interface crack on the temperature fields are limited in a local region. But results of the driving forces for the crack propagation, J-integrals, from the two methods are quite different. Comparing with the CMM results, J-integrals from the macro equivalent method are smaller. It means that the macro equivalent method tends to underestimate the driving force of the interface crack. On the other hand, the prediction of the critical location of the interface crack from the two methods is also different. Since the influence of the microstructure is taken into account by CMM, results of the present work may suggest that CMM is a more useful and accuracy method for the fracture analysis of the functionally graded TBC.
Electron-Probe Microanalysis: Some Revelations in the Investigation of Defects in Steel Products
Authors: Ray Amitava
Published: March 2009

The unique imaging and microanalytical capability of the electron-probe microanalyser (EPMA) has been exploited in conjunction with light microscopy for exploring the genesis of some defects, which are detrimental to steel product quality. Investigations of surface and internal defects have revealed that defects in the finished steel product are often inherited at upstream stages and accentuated in the later stages of steel processing. While the occurrence of surface defects such as “slivers” in hot-rolled sheets and “linear cracks” in hot-rolled rounds has been largely attributed to subsurface non-metallic inclusions and slag/casting powder entrapment, microprobe analysis of internal defects such as “centre-line
cracking” of thick plates have revealed the deleterious role of C and Mn macrosegration inherited during the continuous casting of steel slabs. The paper elucidates some of these findings, as unravelled by both qualitative and quantitative microprobe analysis.
Infrared to Visible Upconversion Luminescence in Yb3+, Ho3+: Y2O3 Nanocrystalline Powders
Authors: Zhang Jian , Wang Shi Wei , An Li Qiong , Liu Min , Chen Li Dong
Published: March 2009

Yb3+, Ho3+ co-doped Y2O3 nanocrystalline powders were synthesized via a reverse-strike co-precipitation method using nitrates and ammonia as raw materials. The as-prepared powders are cubic Y2O3 after fired at 7000C for 2 h. Field emission scanning electronic microscopy revealed that most of the particles are nearly spherical and the average diameter of the particles is in the range of 60-80 nm. Under the excitation with a 980 nm continuous wave diode laser, two main emission bands, i.e., green emission centered at 549 nm and red emission centered at 666 nm is observed, respectively. The green emission is attributed to the transition of (5S2, 5F4-5I8) levels of Ho3+; while for the red emission, the transition of 5F5-5I8 levels is suggested. In addition, near infrared emission centered at 755 nm is also detected, corresponding to the transition of (5S2, 5F4-5I7) levels. The dependence of the intensity of upconversion emissions upon the pump power of the diode laser suggests that two-photon absorption mechanism be involved in these processes.
Ultra-Hard Nanostructured Al-Si Thin Films
Authors: Radmilović Velimir , Mitlin D. , Dahmen U.
Published: March 2009

We show that it is possible to use high rate co-evaporation of Al and Si onto room
temperature substrates to achieve a novel two-phase nanoscale microstructure. These nanocomposites have a hardness as high as 4GPa (Al-23at.%Si), and display noticeable plasticity. Films with compositions of Al-12at.%Si and pure Al (used as baseline) were analyzed using transmission electron microscopy (TEM). The scale of the Al-12at.%Si microstructure is an order of magnitude finer compared to that of pure Al films. It consists of a dense distribution of spherical nanoscale Si particles separating irregularly-shaped small Al grains. These new
structures may have a mechanical performance advantage over conventional single phase nanomaterials due to the role of the dispersed hard phase in promoting strain hardening.
Particle Size Effect: Methanol Oxidation on Supported Pt Catalysts
Authors: Tripković A.V. , Jovanović V. , Lović J.D. , Popović K.Dj. , Kowal A.
Published: March 2009

The methanol oxidation was studied at two differently prepared supported Pt
electrodes (Pt-C/GC and Pt/GC) in 0.5 M H2SO4 and 0.1 M NaOH. The supported Pt electrodes were characterized by AFM, STM TEM and HRTEM. The higher activity of Pt-C/GC than of Pt/GC catalyst, as well as negligible differences in the activities between the supported Pt catalysts and the corresponding single crystal electrodes oriented as the sites in the catalyst deposits in which Pt particles are dominant, clearly suggest the influence of the particle size effect on the catalyst
activity.
Evidence of Dopant-Matrix Interaction in Optical Spectra of Rare Earth Ions
Authors: Antić-Fidančev E.
Published: March 2009

Complex emission spectra of europium doped rare earth calcium oxoborates, EuCa4O(BO3)3 - EuCOB, and GdCa4O(BO3)3: Eu3+- GdCOB: Eu3+, were finely analyzed for better understanding of some local perturbations detected in these solid media. Highlighting a “size effect” of dopant / matrix ions, the interaction between the host lattice and the embedded ion is demonstrated. The evolution of the crystal field strength of R3+ ions along the rare earth series is presented for C-type RE2O3 oxides. According to R3+ - RE3+ ionic radii difference (R3+ for a dopant ion and RE3+ for a matrix ion), two opposite standings are evidenced along a series. Effect of high concentration doping on spectral line broadening is illustrated following a half-height width of 2P1/2 level of Nd3+ ion in A-type La2O3 oxide.