bluuebunny/crossref_metadata_2025 huggingface dataset:
Anodic Oxide Coatings on Ti Alloys and their Osteoconductivity
Authors: Yamamoto Dai , Kuroda Kensuke , Ichino Ryoichi , Okido Masazumi
Published: January 2012

Titanium and Ti alloys are widely used as substitutional materials for natural bone because of their good biocompatibility, high strength, and high corrosion resistance. In our previous studies, TiO2 coating on Ti with Ra (arithmetical means of roughness) < 0.1 μm formed by anodizing had much higher osteoconductivity than that of pure Ti. It can be expected that TiO2 coating with fine surface can improve the osteoconductivity of Ti alloys. In this study, the effects on the osteoconductivity of TiO2 coatings on different kinds of Ti alloys were investigated by in vivo study. TiO2 coatings with Ra < 0.1 μm were formed on 4 kinds of Ti alloys (Ti-6Al-4V (Ti64), Ti-6Al-7Nb (Ti67), Ti-29Nb-13Ta-4.6Zr (TNTZ), Ti-13Cr-1Fe-3Al (TCFA)) using anodizing in H3PO4 aqueous solution. Surface properties of these coatings were evaluated using SEM, XRD, and XPS. In in vivo study, samples were implanted in rats’ tibia for 14 days, and then removed. Cross section of the sample was observed with optical microscope and bone-implant contact ratio (RB-I) at the interface between body tissue and bone was used as a parameter of osteoconductivity. Anatase type TiO2 coatings with Ra < 0.1 μm were uniformly formed on all of the Ti alloys by anodizing at low voltage. These oxide coatings contained the ions of other alloy elements. TiO2 coatings on Ti64 and Ti67 indicated high osteoconductivity similar to that of TiO2 coating on pure Ti. On the contrary, TiO2 coating on TNTZ and TCFA showed low osteoconductivity. It was thought that ions of alloy elements brought bad influence on the osteoconductivity of TiO2.
Electrophoretic Deposition of Organic - Inorganic Composites for Biomedical Applications
Authors: Ma Rong , Zhitomirsky Igor
Published: January 2012

Electrophoretic deposition method has been developed for the fabrication of organic-inorganic composite films, containing bioglass and hydroxyapatite in a hyaluronic acid matrix. The film composition and deposition yield were varied by variation of the electrochemical bath composition and deposition time. The films were studied by scanning electron microscopy, thermogravimetric analysis and X-ray diffraction methods. The deposition method offers the advantages of room temperature processing and allows the fabrication of composite films for biomedical applications.
Effect of Heat Treatment on Tensile Strength, Hardness and Thermal Conductivity of Blended Polymer Composite
Authors: Alallak Nidaa
Published: January 2012

Sometimes, there is a need for a material that has some properties of one polymer as well as some properties of another polymer. Instead of going back in to the laboratory and trying to synthesize a brand new polymer with all the needed
Mechanical Behavior of High Boron Content Al-B4C Metal Matrix Composites at Elevated Temperatures
Authors: Chen X.-G. , St-Georges Lyne , Roux M.
Published: January 2012

High boron content Al-B4C metal matrix composites are highly attractive as an excellent neutron absorber material for the storage of spent nuclear fuels. In the present paper, the mechanical properties of two composites with AA1100 matrix reinforced with 25 and 30 vol.% B4C at ambient and elevated temperatures have been investigated. The thermal stability of two composites at 300°C is experimentally determined. The microstructural features and the tensile fracture at different conditions are examined. It is found that the mechanical properties of both composites remain unchanged at 300°C after a long holding period up to 1000 h. The thermal stability of the mechanical properties of the composites is directly related to the stability of all microstructural compounds of the material. Finally, the effect of the tensile temperatures on the fracture mechanism is assessed.
Composite 316L+Al2O3 for Application in Medicine
Authors: Dudek Agata , Włodarczyk Renata
Published: January 2012

The demand for new materials in medicine is on the increase today. Long-lasting implants (joint prostheses, dentistry implants), made typically of metals and their alloys, are characterized with high mechanical properties, however their corrosion resistance and biocompatibility are relatively low. One of the methods to ensure particular functional properties is to employ composite implants, combining improved mechanical properties of metallic material with biocompatibility of ceramic materials. The study aimed to develop and analyse properties of metallic/ceramic composites made of the mixture of powders: austenitic steel (316LHD) and ceramics (Al2O3).
Evaluation of Cutting Process on the Tensile and Fatigue Strength of CFRP Composites
Authors: Harada Yoshihisa , Kawai Kyohei , Suzuki Takayuki , Teramoto Tokuo
Published: January 2012

Carbon fiber-reinforced plastics (CFRP) composite is most attractive materials to reduce the weight of transportations. To increase the production volume and the efficiency in the field of CFRP component, fast, highly precise and cost-efficient technologies are required. Although laser cutting meets these requirements, it is not used because of insufficient knowledge about the effect of thermal damage on the material behavior. In this study, the effect of several cutting processes on the static tensile strength and the fatigue strength was evaluated for CFRP consisting of thermoset resin matrix and carbon fibers. The CFRP was cut using two different-type of lasers; a CO2 gas laser and a single-mode fiber laser, an abrasive water-jet and a conventional mechanical tool. The mechanical cutting specimen produced a cut of high quality. The water-jet cutting specimen showed a moderate quality though was seen a trace of abrasive grain. While, the laser cutting specimens clearly showed a heat-affected zone (HAZ). The static tensile strength and the fatigue strength by laser cutting specimens clearly decreased in comparison with mechanical or water-jet cutting specimen. The laser cutting specimen exhibited a linear dependency of the tensile strength on the HAZ, indicating that the main effect resulted from thermal destruction of CFRP within the HAZ.
Investigating the Potential of TiB2-Based Composites with Ti and Fe Additives as Wettable Cathode
Authors: Heidari Hamed , Alamdari Houshang , Dubé Dominique , Schulz Robert
Published: January 2012

In this work, porous TiB2 ceramics were consolidated by pressureless sintering method using metallic Ti and Fe as additives in order to perform sintering at temperatures lower than 1700°C. It was shown that processing parameters including milling time of the starting mixture had a considerable effect on final properties of sintered specimens and their behavior in molten aluminum. Microstructural studies were carried out using optical microscope, SEM and EPMA. It was found that specimens with uniform and crack-free microstructure could be produced using the pre-mixed powders milled for as low as 30 min prior to compaction and sintering. Sessile drop test was performed on the specimens milled for 30 and 240 minutes. Their interaction with molten aluminum was also studied. It was found that 30 min milling time resulted in better electrical conductivity, wettability and stability in liquid aluminum.
Fabrication of Metal-Based Functionally Graded Grinding Wheel by a Centrifugal Mixed-Powder Method
Authors: Miura-Fujiwara Eri , Sato Hisashi , Yamada Motoko , Watanabe Yoshimi
Published: January 2012

Metal-bonded diamond grinding wheel was fabricated by a centrifugal mixed-powder method. The centrifugal mixed-powder method is a novel and effective casting process to obtain functionally graded material (FGM). At the beginning, we performed fundamental experiments using Al-Si alloy system for the purpose of knowing the migration behavior of mixed-powder under centrifugal force. Al-Si hypereutectic alloyed-powder or mixed-powder of Al and Si particles was placed into the mold, and then Al molten metal was cast under a centrifugal force. Cross sectional microstructure observation and quantitative analysis of Si content were conducted using an electron probe microanalyzer. Amount of Si decreased with receding from a mixed-powder region. Si concentration gradient in the sample fabricated Al-Si powder was smaller than the one fabricated using mixed-powder of Al and Si particles. Subsequently, φ 20 mm Cu/diamond grinding wheel was fabricated by the casting method. Graded diamond distribution was successfully obtained.
Microstructure and Superconductive Property of MgB2/Al Composite Materials
Authors: Mizutani Manabu , Tokai Daisuke , Matsuda Kenji , Nishimura Katsuhiko , Kawabata Tokimasa , Hishinuma Yoshimitsu , Aoyama Shigeki
Published: January 2012

MgB2 has the higher critical temperature of superconducting transition (TC : 39K) among the intermetallic compound superconductive materials, however, MgB2 is hard for practical use because of its unworkable and lower critical current density (JC) in a high magnetic field than Nb-based superconductive materials. We have developed the original method of three-dimensional penetration casting (3DPC) to fabricate the MgB2/Al composite materials. In the composite material we made, MgB2 particles dispersed to the matrix uniformly. Thus, these composite materials can be processed by machining, extrusion and rolling. The TC was determined by electrical resistivity and magnetization to be about 37～39K. In this work, we made composite material with ground MgB2 particle with the purpose of extruding thinner wires of composite material, successfully produced φ1mm wire and changed the matrix from pure Al to Al-In alloy. JC of composite materials with the matrix of Al-In alloy was calculated from the width of the magnetic hysteresis based on the extended Bean model. The result was better than that of MgB2/Al composite material without Indium. Microstructures of these samples had been confirmed by SEM observation.
Degradation Mechanism of Polycrystalline Silicon Carbide Fiber due to Air-Exposure at High Temperatures
Authors: Morishita Kohei , Ochiai S. , Okuda H. , Ishikawa Toshihiro , Sato M.
Published: January 2012

For description of the mechanical performance of SiC/SiC composites and for safety design for practical use, it is needed to reveal the degradation mechanism especially of fiber under the oxygen atmosphere. In the present work, the fracture behavior and microstructure of the polycrystalline silicon carbide fiber exposed in air at 1173-1873 K for 20 and 3.6 ks were studied with monofilament tensile test, microstructure observation and fracture toughness determination test using newly developed FIB(focused-ion-beam)-method.
Microstructure of the New Route Wire Fabrication of V3Ga Compound Superconducting Wire Using High Ga Content Cu-Ga/V Precursor Composite Material
Authors: Murakami Satoshi , Mizutani Manabu , Matsuda Kenji , Nishimura Katsuhiko , Kawabata Tokimasa , Hishinuma Yoshimitsu
Published: January 2012

Our co-worker, Hishinuma et. al. has established a new route Powder-In-Tube (PIT) process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V3Ga compound wire. In this study, we investigated microstructure of this high Ga content Cu-Ga/V composite superconducting wire. The different contrasts of matrix, V-Ga phase and Cu-Ga core were observed by SEM observation in cross section of 19 multifilamentary wire. And V-Ga phase was confirmed by SEM mapping. The area fraction of V-Ga phase increased when Ga content increased from 30% to 50%. Thin film sample with V-Ga phase for TEM was fabricated by FIB and observed by TEM in detail. Selected area diffraction pattern was obtained for V matrix, V-Ga phase and Cu-Ga core. The ratio of V to Ga for V-Ga phase was probably V3Ga according to the EDS result. There was a linear interface between V matrix and V-Ga phase, while the interface between Cu-Ga core and V-Ga phase was not linear. On the other hand, there were some granular grains observed in V-Ga phase wear Cu-Ga core.
Mechanical Properties, Aging Behavior and Microstructure Evolution of Mg-Nd-Zn-Zr Based Magnesium Matrix Composite Reinforced with Alumina Fibers
Authors: Peng Li Ming , Hu Bin , Ding Wen Jiang
Published: January 2012

Metal matrix composites reinforced with discontinuous reinforcement (short fiber, whisker or particle) are attractive for applications requiring higher stiffness and strength than traditional alloys. Unlike continuously reinforced composites, where the properties are mainly influenced by fibers, the properties of the discontinuously reinforced composites seem to be influenced more by matrix properties. Most of the discontinuously reinforced composites are based on age-hardenable light alloys, so that aging treatments can be applied to develop the optimum properties of the composites. The aging behavior of discontinuously reinforced composites has been a subject of great interest both from scientific and technological view points. Recently developed NZ30K (Mg-3wt.%Nd-0.5wt.%Zn-0.5wt.%Zr) alloys exhibit higher specific strength at both room and elevated temperatures, better strength and creep resistance than the existing commercial magnesium alloys. Accordingly, this alloy can be considered as a candidate material for potential automobile applications, such as engine blocks and pistons, which experience high service temperature. Its use could save considerable mass weight in powertrain systems. However, low elastic modulus and wear resistance of magnesium alloys limit their widespread applications. Metal matrix composites have been proposed as the feasible and economical solution. The aim of this study is to investigate the effect of alumina fibers on the aging hardening kinetics and age-hardening efficiency of squeeze cast NZ30K/Saffil/15p magnesium matrix composite. The aging behavior has been examined using Vickers, combined with microstructure observation developed during heat treatment by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM).
Magnesium Alloy Development for Automotive Applications
Authors: Luo Alan A. , Mishra Raja K. , Powell Bob R. , Sachdev Anil K.
Published: January 2012

This paper summarizes the development of new cast and wrought magnesium alloys using computational thermodynamics tools and experimental approach. The Mg-Al-Ca alloys show excellent creep resistance due to the formation of high-temperature (Mg,Al)2Ca phase. The Mg-Al-Sn alloys are designed for mechanical properties and corrosion resistance through the optimization of Mg17Al12 and Mg2Sn phases in the microstructure. In the Mg-Zn-Ce system, Zn provides strength through solid solution strengthening while Ce increases the ductility via improved texture. Mg-Nd-Zn is a heat-treatable alloy system based on the precipitation hardening of Mg12Nd phase.
Functionally Graded Biocomposites
Authors: Barzegari Mohamad Reza , Rodrigue Denis
Published: January 2012

Functionally graded materials (FGM) are characterized by a gradual change in the volume fractions of two or more components as a function of position along certain dimensions. FGM has been introduced as an alternative to laminated composites where a mismatch in properties across each layer interface is the origin of stress concentration and a source of delamination/failure. In addition, the use of natural wood fibres as reinforcement has the advantage of easy manufacturing, low cost, biodegradability, negligible health hazards and high specific properties. Using short fibres in a controlled manner to produce functionally graded composites can provide more balanced properties and lead to improved stiffness/strength properties across thickness. The aim of this paper is to evaluate the mechanical behavior of functionally graded natural fibre composites. To study the effect of composite property variation, the functionally graded composite is divided into a number of homogeneous layers in order to evaluate the mechanical behavior. In particular, the effect wood fibre content variation across thickness on the tensile properties of the composites is presented.
Fabrication of Vapor Grown Carbon Fiber Reinforced Aluminum Composites by Spark Sintering
Authors: Sasaki Gen , Xu Zhe Feng , Choi Yong Bum , Sugio Kenjiro , Mastugi Kazuhiro
Published: January 2012

As vapor grown carbon fiber (VGCF) possesses the good mechanical properties, high thermal conductivity, high electrical conductivity and low thermal expansion, VGCF/ Al composites are expected to be suitable materials for a high performance radiator. In this study, VGCF were dipped and treated with ultrasonic vibration in some kinds of solution at first. Then, the mixed powders including three kind of average particle size of Al (1, 3 and 30µm) was milled by wet process with three kinds of solution, which are acetone, ethanol and butanol. Ethanol is most suitable for mixing solution because of homogeneous distribution of VGCF and Al powders. The mixed powders were spark-sintered in order to obtain dense VGCF/Al composites. The densification mechanism of VGCF/Al composites was divided into the plastic deformation (2nd stage) and creep deformation (3rd stage) after the 1st stage of rectangular wave pulse discharge. The densification rate of VGCF/Al composite powder depended on Al powder for matrix, but independent on VGCF. VGCF are dispersed uniformly in the VGCF/1 µm Al composite. But the aggregations of VGCF exhibited a preferential orientation in VGCF/30 µm Al composite, which results from the deformation of Al powders under the uniaxial pressure during the hot pressing in sintering process.
Microstructure and Compression Behavior of Cenosphere Filled Aluminum Syntactic Foams
Authors: Zhang Qiang , Wu Gaohui
Published: January 2012

Aluminum syntactic foams were fabricated by pressure-inﬁltrating liquid pure aluminum into packed preforms of cenosphere fly ash. The morphology, true density and porosity of fly ash microballoons were characterized. The microstructure of the syntactic foams demonstrated uniform distribution of the microballoons in the aluminum matrix and seldom infiltration of cenosphere fly ash. These foams were subjected to quasi-static uniaxial compression tests and behaved like high strength aluminum foams under compressive deformation, exhibiting an extended plateau region in the stress–strain curves. With the decreasing of fly ash diameter, the plateau stress and absorbed energy of the syntactic foams increased. X-ray microcomputed tomography was used to examine the foam microstructures after interrupted compression and reveal the damage evolution. The current work provides a better understanding on the structure and mechanical properties of aluminum matrix syntactic foams.
Nanofragmentation Controlled by a Shock-Induced Phase Transition in Mullite Related Ceramics and its Application
Authors: Atou T. , Kawai N. , Yubuta K. , Ito S. , Kikuchi M.
Published: January 2012

Mullite (3Al2O3•2SiO2) undergoes a phase transition at 30 GPa with forming aligned nanocrystalline fragments in an amorphous phase. The direction of the crystal axes of mullite nanocrystals with the grain sizes less than 10 nm is that preserved from the starting specimen. To clarify the mechanism of the nanofragmentation in mullite, compositional and structural effects are investigated by comparative studies using several mullite-related aluminosilicates. Consequently, we proposed that the oxygen vacancies in the crystal structure in mullite play an important role to formation of the nanofragmentation textures. Also, we performed impact experiments using mullite as a bumper material, simulating a Whipple bumper shield for spacecrafts. Damage of impact could be considerably less with mullite bumper shield than with aluminum alloy bumper shield, suggesting that mullite could be an candidate for a Whipple bumper materials in the next generation.
Explosive Welding of Molybdenum/Copper Using Underwater Shock Wave
Authors: Manikandan Palavesamuthu , Lee Joo Noh , Mori Akihisa , Hokamoto Kazuyuki
Published: January 2012

In this research, surface modification of copper with molybdenum was made using explosive welding technique. The underwater shock waves derived from the detonation of explosives was used to bond thin films of molybdenum on copper. Visual observation shows a sound joining of Mo/Cu. Microstructural characterization reveals the bonding interface with a clear wave formation between the participant metals. A clear wavy interface is formed when the weldable conditions lie in the weldability window. When the weldable conditions lie near the right limit or lower limit, a jet trapped region was formed.
Dynamic and Quasi-Static Compression Tests for Polylactic Acid Resin Foam
Authors: Kobayashi Hidetoshi , Horikawa Keitaro , Watanabe Keiko , Ogawa Kinya , Nozaki Kensuke
Published: January 2012

In this study, the effect of strain rate on the strength and the absorbed energy of polylactic acid resin foam (PLA-foam), which is generally known as one of carbon-neutral and environmentally-friendly polymers, were examined by a series of compression tests at various strain rates from 0.001 to 750 s-1. For the measurements of the impact load and the displacement of specimen, a special load cell and a high-speed video camera were used, respectively. The flow stress of the PLA-foam strongly depends upon not only strain rate but also density of specimens. Thus, a new technique to eliminate the effect of the difference in the specimen density was proposed and successfully applied. It was also found that the strain-rate dependency of PLA-foam can be expressed by a simple power law.
Formation of Whisker in Pure Sn under Tensile Stress and a Method of its Suppression
Authors: Nakai Kiyomichi , Sakamoto Tatsuaki , Miyamoto Takeaki , Kobayashi Sengo
Published: January 2012

Effect of dislocation behavior on formation of whisker in pure Sn has been investigated. Slip system in β-Sn was determined; slip plane is , and Burgers vector b is . The magnitude of Burgers vector is larger than the smallest interatomic spacing in β-Sn. This means that there is broad space under the extra half plane of edge dislocation. It sould be noted that pipe diffusion along the edge dislocation is enhanced in β-Sn, resulting in easy supply of Sn atoms at the root of Sn whisker [1, 2]. Si-bearing particles, which precipitate on surface of bulk Sn by heat-treatment in quartz tube, suppress the accumulation of both edge and screw dislocations to same area. It is greatly effective for the suppression of the nucleation of Sn whisker.
Transition Joints of Aluminum and Magnesium Alloy Made by Underwater Explosive Welding Technique
Authors: Manikandan Palavesamuthu , Lee Joo Noh , Mizumachi Kotaro , Ghaderi Seyed Hadi , Mori Akihisa , Hokamoto Kazuyuki
Published: January 2012

In this study, aluminum alloy A5052 and magnesium alloy AZ31 were joined by conventional parallel setup of explosive welding and underwater explosive welding. Microstructural characterization of conventional welded joints revealed a characteristic wave formation with vortices and contact surface melting layer containing intermetallics. In order to reduce the vortices and melting layer, underwater explosive welding was used. The welding parameters are regulated to reduce the kinetic energy loss during collision. The low kinetic energy loss in underwater explosive welding resulted in the formation of small waves with less vortices and no melting layer.
Effect of Temperature on Crater Formation and Ejecta Composition in Aluminum Alloy Targets
Authors: Nishida Masahiro , Hayashi Koichi , Nakagawa Junichi , Ito Yoshitaka
Published: January 2012

The influence of temperature on crater formation and ejecta composition in thick aluminum alloy targets were investigated for impact velocities ranging from approximately 1.5 to 3.5 km/s using a two-stage light-gas gun. The diameter and depth of the crater increased with increasing temperature. The ejecta size at low temperature was slightly smaller than that at high temperature and room temperature. Temperature did not affect the size ratio of ejecta. The scatter diameter of the ejecta at high temperature was slightly smaller than those at low and room temperatures.
High Strain Rate Torsion and Bauschinger Tests on Ti6Al4V
Authors: Peirs Jan , Verleysen Patricia , Verbeken Kim , Coghe Frederik , Degrieck Joris
Published: January 2012

An accurate isotropic and kinematic hardening model and description of the strain rate dependent material behaviour is necessary for simulation of fast forming processes. Consequently, the material model parameter identification requires experiments where large strains, high strain rates and strain path changes can be attained. Usually, quasi-static tension-compression Bauschinger tests are used to assess the materials kinematic hardening. Hereby it’s important to have the same specimen geometry and boundary conditions in the forward and reverse loading step which is not easily achieved in high strain rate testing techniques. In this work, high strain rate split Hopkinson bar torsion experiments on Ti6Al4V are carried out to study the constitutive material behaviour at large plastic strain and strain rate. In torsion experiments, due to the absence of cross sectional area reduction, higher strains than in tensile tests can be obtained. In addition, a modified torsional split Hopkinson bar setup is developed to perform dynamic Bauschinger tests. A shear reversed-shear load is applied instead of the classical tension-compression load cycle. The test results are analysed to find out if the technique can be used for characterisation of the kinematic material behaviour. Digital image correlation and finite element simulations are used to improve the interpretation of the experimental results.
Response of Silica-Nylon6 Nanocomposites to Static and Dynamic Loading
Authors: Shim V.P.W. , Guo Y.B. , Gu H. W. , Li Xu
Published: January 2012

Silica-nylon6 composites were fabricated using two types of silica nanoparticle fillers with different surface modifications. Type A particles (treated with hexamethyldisilazane) were uniformly dispersed but only displayed weak long-range interaction with the nylon6 matrix; in contrast, type B particles (modified with 3-aminopropyltriethoxysilane) formed covalent bonds with the nylon6 chains but their dispersion is not good. The silica-nylon6 composites synthesized were subjected to quasi-static and dynamic tension to study the effects of strain rate and nanoparticle fraction. Results show that compared to quasi-static loading, both pure nylon6 and the composites exhibit a higher strength but lower ductility under dynamic loading. With respect to the influence of the nanoparticles, both particle types cause an increase in the elastic modulus and tensile strength. The effect of the two particles on ductility differs – particle A reduces ductility, while particle B decreases ductility under quasi-static loading but enhances it noticeably for dynamic loading. Particle B enhances the mechanical properties more significantly, especially in terms of ductility. These results suggest that ensuring strong particle-matrix bonding is more crucial than good particle dispersion.
Hot Dynamic Densification of Materials by Utilizing Underwater Shock Wave
Authors: Tomoshige Ryuichi , Ii Seiichiro , Fujita Masahiro , Chiba Akira
Published: January 2012

Hot dynamic densification method was developed by combining self-propagating high temperature synthesis (SHS) with explosively shock powder compaction technique. This method is extremely short time processing. The main purpose in this study is to perform from synthesis to densification of TiB2-TiN system high temperature ceramic composites and TiB2-TiNi-Cu system functionally graded materials (FGMs) in one step. In TiN-TiB2 ceramic composites, they showed up to 95% of relative density. It was appeared by TEM observations that both the two phases joined tightly each other. The FGMs also were produced by the same technique. They indicated no interlayer exfoliation and no macro cracks after thermal shock tests from 973 K to room temperature. It was shown that thermoelastic property of intermetallic TiNi phase as intermediate layer between ceramics and metal layers operated effectively.
Effect of Random Defects on Dynamic Response of Honeycomb Structures
Authors: Zheng Zhi Jun , Yu Ji Lin
Published: January 2012

The dynamic crushing behavior of cellular metals is closely related to their microstructure. Two types of random defects by randomly thickening/removing cell walls are investigated in this paper. Their influences on the deformation modes and plateau stresses of honeycombs are studied by finite element simulation using ABAQUS/Explicit code. Three deformation modes, i.e. the Homogeneous Mode, the Transitional Mode and the Shock Mode, are used to distinguish the deformation patterns of honeycombs under different impact velocities. The critical impact velocity for mode transition between the Homogeneous and Transitional modes is quantitatively determined by evaluating a stress uniformity index, defined as the ratio between the plateau stresses on the support and impact surfaces. It is found that the critical impact velocity decreases with increasing thickening ratio but increases with increasing removing ratio. The plateau stress on the impact surface heavily depends on the impact velocity due to the inertia effect. The random defects lead to a weakening effect on the plateau stress. For the honeycombs with randomly removing cell walls, the weakening effect is especially obvious at a moderate impact velocity. For the honeycombs with randomly thickening cell walls, the weakening effect is particularly severe at a low impact velocity, but this effect almost disappears when the impact velocity is high enough.
Centrifugal Separation of Primary Silicon during Solidification in Al-Si Alloy for Solar Silicon Feedstock
Authors: Cho Ju Young , Kang Bok Hyun , Kim Ki Young
Published: January 2012

Various metallurgical refining processes of SOG (Solar Grade)-Si are being developed aiming its cost reduction for the PV (Photovoltaic) market. High purity silicon can also be obtained from Al-Si alloys using solidification theory. Since the solubility of impurity elements in silicon decreases rapidly with temperature decrease much above the Al-Si eutectic temperature, the removal of impurities from silicon at low temperature is expected to be effective. Most of impurity elements with small segregation coefficient can be removed during solidification. Key technology in this process is to separate the primary solid silicon from the liquid eutectic matrix during solidification. Some methods by an electromagnetic force or by combining flocculation and filtration techniques have been proposed to separate the solid silicon. The present study describes a new way to extract the primary silicon crystal from Al-Si alloys using centrifugal force during solidification for a silicon solar feedstock. Primary silicon was separated in the shape of foam during solidification, and pure Si flakes after acid leaching could be obtained.
Atomic Resolution Investigations of Phase Transformation from TaN to CrTaN in a Steel Matrix
Authors: Danielsen Hilmar Kjartansson , Hald John
Published: January 2012

In development of 12%Cr high temperature steels used for fossil fired power plants, the precipitation of large Z-phase particles, CrMN, has been identified as a major problem since they replace small and finely distributed MN particles. This causes a premature breakdown in the long-term creep strength of the steel. The Cr content promotes Z-phase precipitation, making MN strengthening of these materials unfeasible, since 12%Cr is necessary for oxidation resistance. The authors have suggested an acceleration of Z-phase precipitation to obtain a fine and stable distribution of CrMN instead of MN, thus preserving long-term creep strength. This can be done by alloying with Ta instead of Nb and V. Recent investigations have indicated a direct transformation of MN into CrMN to take place, not the traditional nucleation/dissolution process. In this paper atomic resolution microscopy shows how Cr atoms diffuse from the steel matrix into TaN precipitates and physically transform them into CrTaN. The crystal structure of the precipitates changes from that of a typical MN NaCl type crystal structure to a Z-phase crystal structure with alternating double layers of Cr and TaN. Since there is a large contrast between heavy Ta atoms and light Cr atoms, the ordering of the Cr layers inside the TaN particles can clearly be observed.
Microstructural Evolution of Ultrafine Ferrite during Plate Steel Processing Using Intermediate Cooling
Authors: Hamre D.J. , Matlock David K. , Speer John G.
Published: January 2012

A 0.12 wt.% C – 1.26 wt.% Mn steel was studied to evaluate phase transformations that occurred during a specific thermal processing method designed to simulate steel plate surface layer microstructural evolution during processing with intermediate cooling. All process simulations used a Gleeble thermomechanical simulator along with thermal practices developed previously. After intermediate cooling was completed during processing, slight reheating of the plate surface layer region would occur due to heat retained in the plate core. Microstructural evaluation of Gleeble samples quenched at several points along the thermal profile allowed interpretation of microstructural evolution during processing. The microstructure that was present at the point where deformation would be applied consisted of approximately 75% ferrite, 25% austenite and some small, undissolved cementite particles.
Microstructural Investigation on Tungsten for Applications in Future Nuclear Fusion Reactors
Authors: Deodati Paolo , Donnini Riccardo , Montanari Roberto , Ucciardello Nadia
Published: January 2012

Tungsten is a promising armour material for plasma facing components of nuclear fusion reactors. Two materials with different density and purity have been examined by optical microscopy, X-ray diffraction (XRD), instrumented indentation tests (FIMEC) and mechanical spectroscopy. For both the materials yield stress and elastic modulus strictly depend on the residual porosity. Moreover, the material with higher porosity (≈ 9%) is not stable and remarkable modulus variations are observed during heating. The IF spectrum exhibits a relaxation Q-1 peak superimposed to an exponentially increasing background. The peak is a single Debye peak with activation energy H = 74.86 kJ mol-1 and pre-exponential factor τ0 = 1.76 x 10-9 s that has been ascribed to dislocation interaction with intrinsic point defects (autointerstitial and substitutional).
Effect of Tempering on Mechanical Properties and Microstructure of a 9% Cr Heat Resistant Steel
Authors: Dudko Valeriy , Belyakov Andrey , Kaibyshev Rustam
Published: January 2012

Effect of tempering temperature ranged from 400 to 720°C on mechanical properties and microstructure of a P92-type creep resistant steel was investigated. The hardness value of 400 HB, which was obtained after solution treatment, increased to 430 HB with increasing the tempering temperature to 525°С. Further increase in the tempering temperature resulted in gradual decrease in hardness, which approached a level of about 220 HB after tempering at 720°С. The equiaxed particles of MX-type carbonitrides with a size of about 30 nm were precipitated randomly after tempering under all conditions. At temperatures below 525°C, the tempered martensite lath structure (TMLS) was characterized by a random distribution of fine M3C-type carbides and MX-type carbonitrides. The precipitation of M23C6 was observed after tempering at T ≥ 525°C. At 525°C, the M23C6 carbides appeared as thin films on high-angle boundaries (HAB), while M23C6 particles having almost equiaxed shape and located on various boundaries including low-angle lath boundaries precipitate at higher temperatures.
A Differential Scanning Calorimetry (DSC) Study of Phase Changes in an As-Received Zr-2.5Nb Pressure Tube Material during Continuous Heating and Cooling
Authors: Fong R.W.L. , Saari H. , Miller R. , Teutsch J. , Vogel Sven C.
Published: January 2012

Differential scanning calorimetry (DSC) has been used to study the phase changes in samples of as-received Zr-2.5Nb pressure tube material by continuous heating and cooling. Two different heating rates (5 and 20°C/min) were used to heat the sample up to 1050°C. After a short time hold at 1050°C, all the samples were continuously cooled to 300°C at a rate of 20°C/min. On continuous heating, the DSC signals obtained showed two endothermic transitions. The low-temperature transition, occurring between about 500 and 650°C, is attributed to a thermal decomposition of metastable niobium-stabilized β-phase. The highertemperature transition, occurring between 600 and 950°C, is due to phase transformations of hcp α-Zr to bcc β-Zr, as previously confirmed in a companion study on the same pressure-tube material that was examined in-situ by neutron diffraction. The neutron diffraction results provided a positive identification of the two phases and also a quantification of the β-phase present in the sample at different heating temperatures, and thus provided a guide to extract the volume fraction of β-phase from the DSC signals obtained in this study. The DSC signals revealed only one exothermic transition which is correlated to the reverse transformation of β-Zr to α-Zr, as previously identified in the companion neutron diffraction study of the same pressure tube material.
Fast Melting and Refining of Recycled Silicon Powders from the Wafer Back Grinding Process for Solar Cell Feedstock
Authors: Seo Kum Hee , Kang Bok Hyun , Kim Ki Young
Published: January 2012

A new way to melt and refine recycled silicon powders from the wafer back grinding wastes was proposed. We designed a new equipment using induction heating for the fast melting and directional solidification of the recycled silicon powders, and investigated the feasibility of utilizing them as silicon feedstock for solar cells through lab-scale experiments on the melting and refining them. Silicon particles recovered from back grinding slurry were flake like and very fine, about 3um and was covered with very thin silicon oxide. Slag was observed on the top of the melt during melting, which was composed of oxygen, silicon and carbon which was believed to come from the graphite crucible. Complete melting and subsequent feeding of powders into the melt were prevented by the slag formed during melting, which could be solved by changing the melting atmosphere. Slow growth rate made the impurities such as Al, Ti, Fe, Zr segregate to the top of the ingot purifying the lower part. Over 5N purity was obtained in the middle and lower part of the ingot by the fast melting and directional solidification.
Evolution of Intermetallic Phase Fe2(W, Mo) in 9% Cr Steel during Creep Rupture Tests at 650°C
Authors: Korneev Aleksey , Zmienko D.S. , Gudenko A.S. , Kozlov P.A. , Korneev A.E.
Published: January 2012

Our report deals with investigation of evolution of AB2 phase in three melts of new 9% Cr heat resistant steel with different chemical compositions during creep rupture tests at 650°C in the course of 10000 hours. For each sample the following research procedure was applied: (i) identification of all second phases precipitations using differential X-ray analysis method; (ii) study of spatial distribution of second phases using scanning electron microscope and transmission electron microscope; (iii) numerical investigation of mass fraction and average size of AB2 particles using developed algorithm of statistical processing of images from electron microscope. It was found that for all melts mass fraction-time curve has global maximum and the rate of subsequent reduction of mass fraction depends on content of alloying elements.
Structural Changes of Liquid Pb-Bi Eutectic Alloy
Authors: Deodati Paolo , Gauzzi Franco , Montanari Roberto , Varone Alessandra
Published: January 2012

Liquid Pb–Bi eutectic (LBE) alloy has been selected as coolant and neutron spallation source for the development of MYRRHA, an accelerator driven system (ADS). The alloy has been characterized in liquid state from melting (125 °C) to 750 °C by mechanical spectroscopy, i.e. internal friction (IF) and dynamic modulus measurements. The experiments have been carried out using hollow reeds of austenitic stainless steel filled with Pb-Bi alloy and sealed at the extremities. Dynamic modulus showed a remarkable drop in the range 350-520 °C. In the same temperature range radial distribution functions (RDFs), determined from X-ray diffraction patterns, evidenced variations of the mean distance between the 1st nearest neighbour atoms. The phenomenon has been explained as a structural re-arrangement of atoms in the liquid metal.
Pulsed Laser Deposition of Pseudocapacitive Metal Oxide Thin Films for Supercapacitor Applications
Authors: Yang Dong Fang
Published: January 2012

Thin films of manganese oxides have been prepared by pulsed laser deposition (PLD) process on silicon and stainless steel substrates at different substrate temperatures and oxygen gas pressures. By proper selection of temperature and oxygen pressure during the PLD process, pure phases of Mn2O3, Mn3O4 as well as an amorphous phase of MnOx were successfully fabricated and characterized by X-ray diffraction. The pseudo-capacitance behaviors of those manganese oxides of different phases have also been evaluated by the electrochemical cyclic voltammetry in 0.1 M Na2SO4 aqueous electrolyte. Their specific current and capacitance determined at different scan rates were calculated and compared. The results show that polycrystalline Mn2O3 phase has the highest specific current and capacitance, while the values for polycrystalline Mn3O4 films are the lowest. The amorphous phase MnOx films have the values sitting in between those of Mn2O3 and Mn3O4. The specific capacitance of Mn2O3 films reaches 200 F/g at 1 mV/sec scan with excellent stability and cyclic durability. This work has demonstrated that PLD is a very promising technique for supercapacitor material research due to its excellent flexibility and capability of controlling microstructures and phases of various materials.
Hot Working Defines Thermomechanical Processing (TMP) for Aluminum Alloys and Composites
Authors: McQueen H.J. , Evangelista E.
Published: January 2012

TMP of Al alloys includes hot working with dynamic substructures and deformation bands for texture components combined with static recovery or recrystallization as well as cold working altered by annealing. The above processes are separately tailored for solute (Al, Mg), dispersoid (Al-0.7Fe) and precipitation hardening alloys; aging combined with deformation can raise strength or improve fatigue or corrosion resistance. Hot and cold rolling with suitable holding intervals are managed to combine deformation and annealing textures for planar anisotropy or for producing less fibrous grains to avoid delamination corrosion; grains may be severely refined by discontinuous or continuous recrystallization for superplastic sheet. In hot-billet and impact extrusion as an addition to substructure and texture strengthening, the intense heating near the die may be employed for precipitate solution with exit quenching for press heat treatment to T5 temper. Similarly, friction stir surface treatment and welding provide intense hot straining with additional softening as metal is swept behind the pin. In combination with some of the above, forging provides grain and dispersoid fibering oriented for crack retardation; semi solid forming competes with this.
Study of Modified Layer on Exterior Surface of Superheater Tubes
Authors: Zmienko Dmitry , Korneev Aleksey , Bogachev Vladimir
Published: January 2012

Renewal of overhaul period of power plants equipment, especially superheater tubes, is important problem in energy sector of every country. Investigation of processes on tube’s surfaces is necessary to obtain information of equivalent temperature during maintenance. In this work the austenitic chrome-manganese steel 10Cr13Mn12Si2Ni2Cu2Nb (DI59) and chrome-nickel steel 12Cr18Ni12Ti were studied. Application of these steels provides the desired heating resource of the steam superheater (100000 h) and reliable exploitation of the boilers at high temperature (~650°C). Between the oxide layer and the base metal layers with different crystal structure compared with matrix are observed. Qualitative and quantitative electron microscopic techniques, optical metallography and X-ray phase analysis are employed to investigate the morphological evolution, elemental redistribution in the alloy system and formation and growth of discovered layers. In steel DI59 the discovered layer had a ferrite structure. In steel 12Cr18Ni12Ti it was first shown that this layer is consist of different sulfides which disposed in FeNi3 matrix. This intermetallic phase and ferrite layer are ferromagnetic. Changes in the structure of steel on its surfaces are caused by high exploitation temperature and type of fuel which is used in power plants (combination of natural gas and mazut). This opens the possibility to use connection between thermal irregularity in metal and thickness of discovered layers in order to search most damaged part of tubes with ferrite meter.
Influence of the Impurities on Cathodic Copper on the Ductility of Copper Wires
Authors: Camurri Carlos , Carrasco Claudia , Pagliero Antonio , Leite Rodrigo
Published: January 2012

The main characteristic of cathodic copper is the concentration of impurities because it depends on mechanical characteristics, i.e. ductility, of the derived copper wires. The standard mechanical tests that evaluate their ductility, are quick elongation and spiral elongation tests. The results of these essais shown that there is not a clear correlation among the impurities content in cathodes and wire ductility. Also, the two mechanical tests actually used are not able to discriminate differences on the copper ductility associated to variations in impurities concentration, at ppm level. In this work, a design of new specimen for traction test, with a reduced gage length of 10 mm that clearly discriminate differences on copper ductility associated to variations in impurities concentration is exposed. In addition, from traction tests to copper wires and observation of their fracture surfaces by means of SEM and EDS it is concluded that the principal impurity affecting the ductility of the copper wires is the oxygen, mainly incorporated during the melting of the cathodes and casting of the rods. Also, the traditional annealing to the samples previous to the tensile tests must to be avoid since produces a dispersion on the matrix of the Cu2O oxides and so the deleterious effect of the oxygen on the copper ductility cannot be detected.