bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Polyimide Dielectric Layer for the Passivation of High Electric Field and High Temperature Silicon Carbide Power Devices
Authors: Zelmat Samir , Locatelli Marie Laure , Lebey Thierry
Published: March 2009

Silicon carbide (SiC) is a wide bandgap semiconductor suitable for high-voltage, highpower and high-temperature applications [1]. However, and among other issues, the production of advanced SiC power devices still remains limited due to some shortcomings of the dielectric properties of the passivation layer [2]. Due to their supposed high operating temperature and dielectric strength [3], spin coated polyimide materials appear as a possible candidates for SiC device passivation and insulation purposes. As a matter of fact, they are already used in current commercial SiC devices allowing a maximum junction temperature of 175 °C. The aim of this paper is to study the ability of polyimide (PI) coatings to be used for a Tjmax up to 300 °C. Therefore, the main electrical properties (dielectric permittivity, leakage current and breakdown field) at different temperatures of a high temperature commercially available polyimide material (from HD Microsystems) in both Metal-Insulator-Semiconductor (MIS) and Metal-Insulator-Metal
(MIM) structures are presented and discussed.
The Reactive Neutral Beam Etching of SiC and its Application in p-n Junction Periphery Protection
Authors: Sarov G. , Cholakova T. , Kakanakov Roumen
Published: March 2009

This paper presents much more details on the process of etching n and p type SiC using a dc saddle field source. Here is described a method for stabilizing the dc discharge by adding controlled flow of O2 to SF6 in the source chamber. This kind of etching is used to fabricate 4H-SiC p-i-n diodes with a junction periphery protection. The effect of the junction periphery protection, the source power that terminates the etching process and testing environment on the breakdown
voltage are investigated. The optimised p-i-n diodes exhibit a stable reverse bias operation with a breakdown voltage of 1700 V.
Metal Bonding in SiC Based Substrates
Authors: Matko Igor , Chenevier Bernard , Madar Roland , Roussel H. , Coindeau Stephane , Letertre Fabrice , Richtarch Claire , Di Cioccio Lea
Published: March 2009

QuaSiC TM substrates can be obtained by transferring a single crystal SiC layer onto a poly SiC substrate using the Smart Cut TM technology. The structure evolution of metal bonding (W-Si silicide) layer has been investigated by Transmission Electron Microscopy and X-ray diffraction. Results indicate that the metal bonding film is made of W5Si3. The film is discontinuous and strained. Annealing releases stress at least partially.
Low On-Resistance in Normally-Off 4H-SiC Accumulation MOSFET
Authors: Okuno Eiichi , Endo Takeshi , Matsuki Hideo , Sakakibara Toshio , Tanaka Hiroaki
Published: March 2009

In our previous paper [1], we simulated an accumulation-mode MOSFET with an epitaxial layer channel (epi-channel) that had a high channel mobility. In this paper, we experimentally show that channel mobility is enhanced by the epi-channel. On varying the thickness of the epi-channel, the channel mobility improved from a few cm2/Vs to 100 cm2/Vs. Finally, we show that the “Normally-off” accumulation MOSFET with a 720 V breakdown voltage has a low on-resistance
(10.4 m1cm2) and that the 3 × 3 mm2 accumulation MOSFET operates over 10 A and its on-resistance is 19 m1cm2.
Short-Channel Effects in 4H-SiC MOSFETs
Authors: Noborio Masato , Kanzaki Y. , Suda Jun , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: March 2009

Short-channel effects in SiC MOSFETs have been investigated. Planar MOSFETs with various channel lengths have been fabricated on p-type 4H-SiC (0001), (000-1) and (11-20) faces.^Short-channel effects such as punchthrough behavior, decrease of threshold voltage and deterioration of subthreshold characteristics are observed. Furthermore, the critical channel lengths below which
short-channel effects occur are analyzed as a function of p-body doping and oxide thickness by using device simulation. The critical channel lengths in the fabricated SiC MOSFETs are in agreement with those obtained from the device simulation. The results are also in agreement with the empirical relationship for Si MOSFETs.
High Field Effect Mobility in 6H-SiC MOSFET with Gate Oxides Grown in Alumina Environment
Authors: Allerstam Fredrik , Gudjónsson G. , Ólafsson H.Ö. , Sveinbjörnsson E.Ö. , Rödle T. , Jos R.
Published: March 2009

Lateral inversion channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were manufactured on 6H-SiC and two gate oxidation recipes were compared. In one case the gate oxide was grown in N2O using quartz environment. The resulting peak field-effect mobility was µFE=43 cm2/Vs. In the other case the gate oxide was grown in oxygen using alumina environment and the resulting peak field-effect mobility was µFE=130 cm2/Vs. Oxidizing in an environment made
from sintered alumina introduces contaminants into the oxide that effect the oxidation in several^ways. The oxidation rate is increased and the resulting SiC/SiO2 interface allows higher inversion
channel mobility.
High Power Lateral Epitaxy MESFET Technology in Silicon Carbide
Authors: Konstantinov Andrey O. , Harris Chris I. , Ray I.C.
Published: March 2009

High impedance silicon carbide power RF transistors are reported, which
use the technology of Lateral Epitaxy Metal-Semiconductor FET (LEMES). The
LEMES transistor utilizes a heavily doped buried depletion stopper to increase output impedance and breakdown voltage and to eliminate undesirable hot-carrier trapping effects. A power density of 2-3 W/mm at 2 GHz is routinely achieved resulting in a total output power of 10W for packaged components. The value of input and output impedance is around 50 Ohms for a frequency of around 2 GHz.
Electrical Characteristics Temperature Dependence of 600V-Class Deep Implanted Gate Vertical JFET
Authors: Mizukami Makoto , Takikawa Osamu , Imai Seiji , Kinoshita Kozo , Hatakeyama Tetsuo , Domon Tomokazu , Shinohe Takashi
Published: March 2009

A 4H-SiC 600 V class Deep-Implanted gate Vertical JFET (DI-VJFET) is examined. The DI-VJFET exhibited a specific on-resistance of 13 mΩcm2, drain current of 5 A, and a blocking-voltage of 600 V. In this paper, the very high temperature dependence (R.T.~ 400 oC) of the I-V characteristics is
measured and the dominant factor of the on-resistance and the blocking-voltage is discussed. Moreover, the switching waveform of SiC DI-VJFET with SiC SBD is measured by using a half bridge, double-pulse circuit with inductive load at R.T. and 200 oC. The turn-off time is 300 ns at an inductance of 4 mH and an external gate resistance of 100 Ω.
BVCEO Versus BVCBO for 4H and 6H Polytype SiC Bipolar Junction Transistors
Authors: Balachandran S. , Chow T. Paul , Agarwal Anant K. , Scozzie Skip , Jones Kenneth A.
Published: March 2009

The letter presents a set of design curves that relate the open-base breakdown
voltage BVCEO to the open emitter breakdown voltage BVCBO for 4H (0001 and 11-20 orientations) and 6H SiC NPN and PNP Bipolar Junction Transistors. We also present design curves pertaining to the variation of BVCEO with base doping and minority carrier diffusion length in the base for (0001) 4H-SiC BJTs for a 4x1015 cm-3 doped and 12µm thick drift layer for both NPN and PNP BJTs.
Planar Schottky Microwave Diodes on 4H-SiC
Authors: Südow Mattias , Rorsman Niklas , Nilsson Per Åke , Zirath Herbert
Published: March 2009

Planar microwave Schottky diodes on 4H-SiC have been designed, processed and
measured. Different Schottky metals were tested to study the influence on the microwave performance. A maximum extrinsic cut-off frequency of 30.8GHz was achieved for a Tungsten/SiC-Schottky diode. The diode geometry dependence on both the cut-off frequency and the breakdown voltage was investigated. The breakdown voltage was found to be linearly dependent on the anode-cathode distance.
Drift-Free, 50 A, 10 kV 4H-SiC PiN Diodes with Improved Device Yields
Authors: Das Mrinal K. , Sumakeris Joseph J. , Hull Brett A. , Richmond Jim , Krishnaswami Sumi , Powell Adrian R.
Published: March 2009

The path to commericializing a 4H-SiC power PiN diode has faced many difficult
challenges. In this work, we report a 50 A, 10 kV 4H-SiC PiN diode technology where good crystalline quality and high carrier lifetime of the material has enabled a high yielding process with VF as low as 3.9 V @ 100 A/cm2. Furthermore, incorporation of two independent basal plane dislocation reduction processes (LBPD 1 and LBPD 2) have produced a large number of devices
that exhibit a high degree of forward voltage stability with encouraging reverse blocking capability. This results in a total yield (forward, 10 kV blocking, and drift) of >20% for 8.7 mm x 8.7 mm power PiN diode chips—the largest SiC chip reported to date.
Synthesis of SiC Ceramics from Coal Gangue
Authors: Jia Shu Hai
Published: March 2009

The synthesis and the sintering of SiC from coal gangue by carbothermal synthesized in N2 atmosphere are studied. The material, 5 percent carbon black added and sintered at 1400°C for 2 hours, had good properties and a bending strength of 137.8MPa. Too high temperature or too long holding time made the properties of the material to decrease. β-SiC found by observing the
microstructure is a major crystal phase in the synthesized ceramics, which would lead to fine mechanical properties.
Various Applications of Silver Nano-Particles by Ultrasonic Eco-Fabrication
Authors: Hayashi Yamato , Takizawa Hirotsugu , Saijo Yoshitaka , Sekino Tohru , Suganuma Katsuaki , Niihara Koichi
Published: March 2009

Applications of silver nano-sized metal particles were investigated for a new,
ecologically friendly and economical liquid-solid (silver oxide-alcohol) system. Silver metal oxides as starting materials have merits in metal particles fabrication because these materials are decomposed only by heating in air. That is, noble metal oxide does not use thestrong reduction atmosphere. This reduction is ecologically clean because many noble metal oxides are not toxic, and because O2 is evolved during decomposition. We reduced silver metal oxides by ultrasound and
fabricated silver nano metal nanoparticles at room temperature, and various applications were investigated. By choosing a suitable process and conditions, it is reasonable to expect that ultrasonic eco-fabrications can be extended to obtain various silver nano-particles containing materials.
Gas Sensing Characteristics of ZnO-doped SnO2 Sensors for Simulants of the Chemical Agents
Authors: Yun Kwang-Hyun , Yun Ky-Youl , Cha Geon-Young , Lee Bong Ho , Kim Jae Chang , Lee Duk-Dong , Huh Jeung Soo
Published: March 2009

After the 9∙11 terrorism and America-Iraq war, apprehension of mass destruction
weapons such as bio-chemical agents calls for much more sensitive sensors which can detect toxic gases. In this study, semiconductor gas sensors based on tin oxide were examined to detect chemical agent simulants: dimethyl-methyl-phosponate (DMMP), di(propylene glycol) methyl ether (DPGME), acetonitrile, and dichloromethane. DMMP((CH3O)3), DPGME(C7H16O3),
acetonitrile(CH3CN), and dichloromethane(CH2Cl2) gases are the simulants of nerve agent-sarin, vesicant agent-HN(N(CH2CH2Cl)3), blood agent-AC(HCN), and choking agent-CG(COCl2) gases, repectively. The SnO2 powder was prepared by a coprecipitation method from the mixture of tin chloride and zinc acetate dihydrate. Zinc oxide was doped into SnO2 from 1 wt% to 4 wt% to
improve its reliability and sensitivity. To fabricate a thick film, powders were made into paste with organic binder of ethyl cellulose and screen-printed on the alumina substrate. The phase development and morphology of ZnO-doped SnO2 film were investigated by XRD (X-ray diffraction analysis), BET (surface and pore size analyzer), and SEM (scanning electron microscope). The gas sensing characteristics for target gases were examined with a flow-type measurement system. The concentrations of simulants were controlled from 500 ppb to 1500 ppb, and working temperatures were regulated from 250 to 400 .
High Mechanical Properties of Cast Quasicrystal-Reinforced Mg-Alloys
Authors: Yuan Guang Yin , Ding Wen Jiang , Amiya Kenji , Kato Hidemi , Inoue Akihisa
Published: March 2009

Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the
quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.
Texture, Microstructure and Strain Sensibility in Compressed Magnesium Alloys
Authors: Yang Ping , Zhao Zude , Meng Li , Ren Xueping , Huang Shao Dong
Published: March 2009

Depending on its initial texture and external strain condition differences in deformation
mechanisms, kinetics of dynamic recrystallization or even superplastic behaviors may emerge in magnesium alloys leading to distinct microstructure and texture evolutions. When imposed strain condition is altered, e.g. from plane strain compression to rolling or uniaxial compression, the deformation anisotropy will decrease in different rates and basal slip and {1012} twinning will dominate deformation process. This work examines this strain sensibility by inspecting the σ-ε
curves, microstructures and textures in a quasi plane-strain compressed ZK60 alloy and compares the results with those of AZ31 alloy compressed in channel die.
Investigation on Microstructures of Heat Treated Mg-Zr and Mg-Mn Alloys
Authors: Li Jian Ping , Lorimer Gordon W. , Robson Joseph D. , Davis B.
Published: March 2009

The microstructure of three dilute Mg-Mn and two dilute Mg-Zr alloys which had been
heat treated at different temperatures and times were studied using optical microscopy and various electron optical techniques, including FEGSEM and TEM. It was found that the Mg-Zr alloys homogenized at 500°C and annealed at 350°C contained a fine dispersion of Zr-containing particles at grain boundaries and within grains. In contrast, annealing Mg-Zr alloys at 300°C for up to 3 h led to little modification of the as-cast structures. When the Mn content was less than 0.9 weight
percent, homogenization of the Mg-Mn alloys at 550 to 600°C resulted in the dissolution of small rod-like and needle-shape particles, which then grown up as fine particles when aged at 300°C. Mg- 0.6Mn and Mg-0.9Mn alloys annealed at 300 to 400°C without solution treatment contained a large volume fraction of nano-sized precipitates.
Diffusion Bonding in Superplastic ZK60 Magnesium Alloy
Authors: Yu Yan Dong , Li Qiang
Published: March 2009

In this paper, diffusion bonding of ZK60 superplastic material is investigated according to atom diffusion law. Gleeble-1500 testing machine is used in the diffusion bonding processing on the superplastic ZK60. In additional, shear tests of bonding joints are carried out on electronic universal testing machine. The optimized diffusion bonding conditions are obtained: a bonding time of 90 min at 653K at a pressure of 20MPa. The microstructures of the joints are observed through OM and SEM. It is concluded that the mechanism of diffusion bonding of the ZK60 superplastic material is the slide of original grain boundaries caused by atom diffusion and the grain growth, and sound joints with high shear strength are obtained through sufficient diffusion of the interface atoms.
Microstructure and Mechanical Properties of Rapidly Solidified AZ91HP Alloy
Authors: Cai J. , Lin Li , Liu Zhen , Zhang Haifeng , Hu Zhuang Qi
Published: March 2009

Bulk AZ91HP rods with a diameter of 8mm were prepared by copper mould casting. The microstructure and mechanical properties have been studied. The compressive strength, yield strength, elongation and microhardness of the rapidly solidified AZ91HP alloy are 392MPa, 183 MPa, 3.6% and HV87, respectively. It results from grain refinement and reinforcement of β-Mg17Al12 phase.
Microstructure and Mechanical Properties of Extruded Mg-Al-Ca Based Alloys
Authors: Chen Rongshi , Blandin Jean Jacques , Suéry Michel , Han En-Hou
Published: March 2009

Mechanical properties and microstructure of extruded AZ91(-Ca) alloys have been studied in this paper. The results showed that Ca has no significant effect on reducing grain size of the extruded AZ91 alloy. The ambient temperature tensile tests showed that the ultimate and yield strength of extruded AZ91 alloy decreased by addition of Ca. At elevated temperature, Ca addition improves the yield strength of both AZ91 alloy. The variations in microstructure and mechanical properties of the AZ91 alloy are also discussed in terms of the effects of Ca on grain refinement and
formation of constituent phases.
Theoretical and Practical Considerations of Grain Refinement of Mg-Al Alloys
Authors: Lu L. , Dahle Arne K. , Taylor John A. , StJohn David H.
Published: March 2009

The fundamentals of grain refinement are reviewed with particular focus on magnesium alloys. This is followed by considerations of the theoretical and practical aspects of grain refinement of Mg-Al alloys by carbon-based grain refiners. Finally, experimental results using Al4C3 as a potential grain refiner are presented and discussed.
Investigations on Laser-TIG Hybrid Welding of Magnesium Alloys
Authors: Song Gang , Liu Li Ming , Chi Mingsheng , Wang Ji Feng
Published: March 2009

This paper presents results of recent investigations on the weldability of several wrought (AZ31, AZ61) and cast magnesium-based alloys (AZ91) by laser-TIG welding process. The investigations showed that magnesium alloys can be easily welded by laser-TIG welding. The grain of the fusion zone was finer than that of in base metal. The width of the heat-affected zone welded by laser-TIG welding process was obviously narrower than that of welded by TIG. Besides, with the
Al content of magnesium alloys increasing, the width of the heat-affected zone (HAZ) was increased，as well as the content of β phase(Mg17Al12). The hardness in the fusion zone (FZ) and in HAZ of AZ61 and AZ91 has a large change to the base metal due to the existing of β phase, while no change relative for AZ31. It results from above discussing that laser-TIG welding is an excellent welding process for magnesium alloys.
Numerical Study on the Low Pressure Die Casting of AZ91D Wheel Hub
Authors: Peng Ying Hong , Li Da Yong , Wang Ying Chun , Yin Ji Long , Zeng Xiao Qin
Published: March 2009

Most magnesium alloy components available for automobile are made through die casting. In this paper, PAM-CASTTM, commercial die casting simulation software based on the finite difference method, is employed to simulate the low-pressure die casting process of magnesium wheel hub. The temperature field and velocity field during filling and solidification stages are analyzed; the evolution of temperature distribution and liquid fraction was numerically studied. Then, the potential
defects including the gas entrapments in the middle of the spokes, shrinkages between the rim and the spokes are predicted. The cooling performance of mould during casting is also investigated. Via analyzing the shrinkage defects generated under various cooling conditions, the cooling system set in the side mould is found to be more effective for enhancing the cooling capacity at the rim/spoke junction areas. With this cooling system, the hot spots at the junctions are obviously reduced and
product quality is improved.
The Microstructure and Processing in Twin Roll Casting of Magnesium Alloy Strip
Authors: Yang Chun Mei , Zhang Ding Fei , Ding Pei Dao , Pan Fu Sheng
Published: March 2009

Magnesium has a hexagonal close-packed crystal structure which makes it more difficult to deform than aluminum. Conventional strip production usually requires several process steps to reach the final strip thickness. Strip casting can reduce some of the process steps and make strip processing simpler and easier, especially for alloys with poor deformability. The twin-roll casting process can directly obtain strips with thickness less than one or two millimeters. In this paper, the metallurgical characteristics of the twin-roll strip casting process were analyzed and discussed. A
laboratory scale vertical twin roll caster in prepared AZ31 magnesium alloy strips, with 1.0 to 2.0 mm thick and 150mm wide. Process stability in the thin strip casting process of the alloy has been studied, the casting temperature (superheat) was proven to be a key factor influencing process stability and casting strip quality. The as-cast microstructure of the alloy was analyzed and evaluated by optical microscopy, which showed that the as-cast microstructure was composed of
developed dendrites when the superheat was high, and of a rosebush-like structure when the superheat was low. When the casting temperature was close to the liquid phase temperature，the as-cast microstructure became global or grainy, and the grain size of the cast strip was very small. This remarkably improved the deformability of the as-cast strip.
Rolling of Mg Sheet Metal
Authors: Li Xiang Yua , Lou Hua-fen
Published: March 2009

This paper analyzed the effect of deformation process of wrought magnesium alloys on the mechanical properties. The rolling technology and process key technology for Mg sheet metal are discussed. The technical flows of rolling processes are confirmed.
Thermal Flow Simulation on Twin Roll Casting Process for Thin Strip Production of Magnesium Alloy
Authors: Ju Dong Ying , Zhao Hong Yang , Hu Xiao Dong , Ohori Koichi , Tougo Mituo
Published: March 2009

Strip continuous casting by twin roll method is a rapidly solidifying process, which can directly produce thin strips,reduce energy consumption and product cost of various metal materials. However, the casting of magnesium alloys with large solidifying ranges lead to some problems such as surface and internal defect, variation of solidification finish point for Mg sheet. In this research, the process conditions for a twin roll caster are analyzed by thermal flow simulation. The effect of type and dimension of delivery nozzles on production of Mg alloy are studied. A proper match of the setback distance of thin nozzle and casting speed is studied by thermal flow simulation, based on the characteristics of Mg melt handling, flow dynamics control and solidification.
Improvement of Plastic Workability of Rolled AZ31 Alloy Sheet by Surface Thermo-Mechanical Treatment
Authors: Yoshida Yu , Arai Keita , Kamado Shigeharu , Kojima Yo
Published: March 2009

Ingots of AZ31 alloys were prepared for the present study. The ingots were hot rolled to 0.5 mm thickness. In order to develop rolled magnesium alloy sheet having excellent plastic formability, the authors attempted the grain refinement and randomization of the rolling texture of the alloy by means of surface modification utilizing wet-type shot blast (wet blast) and subsequent annealing. Then the microstructural observations including texture analysis and tensile tests were carried out. Furthermore, the bendability and stretch formability were investigated. After wet blast and subsequent annealing at 573K for 1h, the region of 50 µm depth from the sheet surface that experienced deformation by wet blast is recrystallized, and fine and equiaxed grains are generated. Although rolling texture remained in the central part of the sheet, the recrystallized grains near the surface of such specimens have random crystallographic orientation. The tensile strengths of both
rolled and wet-blasted specimens are almost the same but the elongation of the latter increases due to grain refinement and randomization of crystallographic orientation. Such a microstructural feature realizes bending with the radius of 1 mm without cracks and wrinkles and leads to an increase in limiting stretching depth by 1.5~2 mm.
Effect of Microstructures on Tensile Properties of AZ31 Mg Alloy Processed by ECAP
Authors: Miyahara Yuichi , Adachi Kazuhiko , Maehara Yasuhiro , Horita Z. , Langdon Terence G.
Published: March 2009

A commercial AZ31 Mg alloy was subjected to ECAP (equal-channel angular pressing) and the tensile properties were examined at room temperature. It is shown that the microstructure before ECAP significantly affects the performance of ECAP without breaking samples. When the initial structure before ECAP is homogeneous with equiaxed grains, subsequent ECAP is feasible at lower temperatures. The grain refinement is achieved more effectively as the temperature for ECAP is lowered and the number of ECAP pass is increased. The tensile ductility was reduced after 1 pass of ECAP at 473 K or 498 K. However, the ductility was improved with an increasing number of ECAP pass or by annealing at 473 K or 523 K after ECAP. The results demonstrate that a homogeneous distribution of fine equiaxed grains is important for ductility improvement in the AZ31 Mg alloy.
Superplastic Forming of AZ31 Mg Alloy Recycled by Solid-State Processing
Authors: Chino Yasumasa , Mabuchi Mamoru , Hoshika Tetsuji , Lee Jae Seol , Shimojima Koji , Hosokawa Hiroyuki , Yamada Yasuo , Iwasaki Hajime
Published: March 2009

Superplastic forming characteristics of AZ31 Mg alloy recycled by solid-state process were investigated. Cylindrical scraps and machined chips were recycled by hot extrusion and hot rolling in air. As a result of tensile test, elongation to failure of the specimens recycled from small and large cylindrical scraps was almost the same as that of the rolled specimen from a virgin ingot. On the other hand, the specimen from machined chips had much lower elongation at elevated temperatures. The
oxygen concentration of the specimen recycled from machined chips showed about 60 times higher value compared with that of the other specimens. In superplastic forming tests, the specimen from small and large cylindrical scraps exhibited excellent formability similar to the rolled specimen from a virgin ingot. However, the specimen from machined chips showed poor formability. Thus, oxide contamination adversely affected the formability of recycled Mg alloy.
Superplasticity of Magnesium Alloy ZK40 Processed by Equal Channel Angular Pressing
Authors: Yang Lin , Yang X.M. , Liu T. , Wu Shi Ding , Chen Li Jia
Published: March 2009

The superplasticity and microstructure of magnesium alloy ZK40 processed by ECAP for 1 and 4 passes were investigated. Tensile experiments at 523 K showed that the elongation of ZK40 was improved with the increasing passes. The elongation-to-failure of ZK40 processed by ECAP for 4 passes tested at 523 K and strain rate of 1×10-4s-1 was 660%. The microstructural analyses explained these results.
Material Properties Test and Numerical Simulation of Impact for Die Cast Magnesium Alloy
Authors: Zeng Xiang Guo , Wu Qing Wen , Liyuan L. , Fan Jing Hong
Published: March 2009

The poison’s ratio of plane plate samples taken from AM60 magnesium alloy was tested in this paper. A number of strain controlled fatigue experiments were also carried out on MTS to investigate the stress-strain behavior under different temperature conditions. The finite element analysis software ANSYS was employed to simulate impact process of shot blasting. Results indicated that at the specific temperature condition the residual stress and plastic strain increased with impact velocity increasing. At the specific impact velocity, residual stress reduced and plastic strain increased with temperature increment.
Corrosion Resistance of Surface Treated AZ91D Magnesium Alloys Outdoor Exposure after 10 Years
Authors: Nishinaka Kazuhito , Senzaki Manabu , Konno Akihiro , Umehara Hiroyuki , Takaya Matsufumi
Published: March 2009

The high-purity magnesium alloy specimens prepared by applying die-cast [1] paint and various types of surface treatments, and then the corrosion resistance of practical coating materials after ten-year outdoor exposure tests was evaluated. These tests were performed at the Choshi (long. 140°45' E, lat. 35°43' N), the Asahikawa (long. 142°18' E, lat. 43°47' N), and the Miyakojima (long. 125°20' E, lat. 24°44' N) Exposure Laboratories of the Japan Weathering Test Center. The
environmental factors generally believed to be associated with corrosion mechanisms (temperature, humidity, precipitation, wetness time, solar and UV radiation, and concentration of chloride and sulfur oxide) were measured. Evaluation of the adhesion of paint and corrosion resistance, chromate and anodic oxide films were superior as pretreatment paint films on AZ91D magnesium alloys;
these films were comparable to paint-coated ADC12 aluminum alloys.
Corrosion of New Wrought Magnesium Alloys
Authors: Na Young Gee , Eliezer Dan , Shin Kwang Seon
Published: March 2009

The development of new components with magnesium alloys for the automotive industry has increased in recent years due to their high potential as structural materials for low density and high strength/weight ratio demands. However, the limited mechanical properties of the magnesium alloys have led to search new kind of magnesium alloys for better strength and ductility. The main objective of this research is to investigate the mechanical properties and the corrosion behavior of new wrought magnesium alloys; Mg-Zn-Ag (ZQ) and Mg-Zn-Si (ZS) alloys. The ZQ6X and ZS6X samples were fabricated using hot extrusion method. Tensile tests and immersion tests were carried out on the specimens from the extruded rods, which contained different amounts of silver or silicon, in order to evaluate the mechanical properties and corrosion behavior. The microstructure was examined using optical and electron microscopy (TEM and SEM) and EDS. The results showed that the addition of silver improved the mechanical properties but decreased the corrosion resistance. The addition of silicon improved both mechanical properties and corrosion resistance. These results can be explained by the effects of alloying elements on the microstructures of the Mg-Zn alloys such as grain size and precipitates caused by the change in precipitation and recrystallization behavior.
Protective System for Magnesium Melt
Authors: Karger A. , Bach Friedrich Wilhelm , Pelz C.
Published: March 2009

The environmentally friendly alternatives are being examined by an R&D group funded by German Federal Ministry of Education and Research. The research goals of this group are to analyze the potential of known environmental friendly gases to serve as protective atmosphere, and also to develop and to evaluate new methods for protecting the surface of magnesium melts. One possible alternative is covering the magnesium melt with CO2-snow, which is deposited on the molten bath and decreases the surface temperature of the melt. On the other hand gas expansion is the result of the sublimation of the CO2-snow which displaces any oxygen at the surface of the molten magnesium.
Dynamic Fracture Behavior of Magnesium Alloy under Biaxial Stress
Authors: Hwang Do Yeon , Shimamoto Akira
Published: March 2009

In this study, dynamic behaviors of cracks under dynamic biaxial stress were investigated. We conducted static and dynamic loading fracture experiments on a magnesium alloy (AZ31B-O) under equitable and inequitable biaxial stress by using a hydraulic high-speed biaxial experimental machine. We processed specimens as the cross type with a crack. Different kinds of cracks were defined by their crack angles. We analyzed the results using the caustic method. The experiments revealed some important findings; there is a negative relation between the fracture toughness value and the plate thickness of the magnesium alloy sheet specimen; the fracture toughness value decreases when the crack has an angle different from the loading direction; the fracture toughness value decreases significantly under inequitable biaxial stress.
Effect of Al2O3 Thin Film on Corrosion Resistance of Pure Mg and Its Anodic Coating
Authors: Shan Da Yong , Zhang Rong Fa , Han En-Hou
Published: March 2009

Al2O3 thin film was formed on pure magnesium and its anodic coating by sol-gel method. SEM observation and EDX analysis showed that Al2O3 film could not totally cover the surface of base metal, but they blocked small pores when they were formed on anodic coating. Potentiodynamic polarization test indicated that Al2O3 films improved corrosion resistance of both anodizing coating and base metal, and the effect on anodizing coating was better than on base metal.
Ammoniation Technology for Dehydration of Hydrated Magnesium Chloride in China
Authors: Long Guangming , Ma Peihua , Chu Minxiong
Published: March 2009

Ammonination technique for dehydration of hydrated magnesium chloride is a special
kind of method for preparation of high-pure anhydrous magnesium chloride, which is requisite for electrolytically manufacturing metal magnesium. The technique has been developing for decades in the west world. China has now been exploiting the technique for his magnesium ore, especially the magnesium resource in the west of China. We started investigation of the method for several years, and several new progresses were arrived for preparation of anhydrous magnesium chloride. From
our study, ethanol, methanol and water solution can be used for the method, and each had an advantage over the others; the ammonia used in the technique for preparation of anhydrous magnesium chloride is less corrosive for the equipment, and friendly for environment. The method gives great potential application in industry of metal magnesium and magnesium matrix materials.
The Recrystallization Behavior of AZ31 and WE43
Authors: Lorimer Gordon W. , Mackenzie L.W.F. , Humphreys John F. , Wilks T.
Published: March 2009

The deformation and recrystallization behavior of two magnesium alloys, AZ31 and
WE43, have been investigated. The cast alloys were heat treated to produce various distributions of second phase particles and deformed in a channel die at a strain rate of 10-4 s-1 at temperatures between 523 and 673 K. The alloys were subsequently annealed at temperatures between 708 and 798 K.The AZ31 and WE43 were extruded at 555 and 633 K, respectively. The microstructures were
compared to those developed during channel die deformation. The tensile and compressive strengths and the texture of the alloys were determined in the as-extruded and recrystallised conditions.Optical microscopy and electron backscattered diffraction (EBSD) were used to characterize the microstructures of the alloys. The EBSD technique was used to determine the texture of the deformed
and annealed samples.
Neutron Diffraction Study of Extruded Magnesium during Cyclic and Elevated Temperature Loading
Authors: Oliver E.C. , Daymond Mark R. , Withers Philip J.
Published: March 2009

Neutron diffraction has been used to study the progress of deformation twinning and intergranular strain evolution in extruded magnesium during cyclic and monotonic loading at two temperatures. Differences in the intergranular strains generated during tensile and compressive tests are attributed to the operation of twinning in compression. Twinning activity is reduced relative to slip at higher temperature, leading to greater similarities between tension and compression. During cyclic loading, a distinct Bauschinger effect is observed after each compressive loading stage. The origin of this effect is identified as the reversal of twinning during unloading and subsequent tensile loading.
In Situ Observation of Thermal Stress in Nano-Size Thin Aluminum Films
Authors: Takao Hanabusa , Kusaka Kazuya , Shingubara Shozo , Sakata Osamu
Published: March 2009

In-situ observation of thermal stress in thin films deposited on a silicon substrate was made by synchrotron radiations. The specimens prepared in this experiment were nano-size thin aluminum films with SiO2 passivation. The thickness of the films was 10 nm, 20 nm and 50 nm. Residual stress in the as-deposited state was tensile. Compressive stress was developed in the heating cycle up to 300 oC and tensile stresses developed in the cooling cycle. The thermal stresses in the 50 nm film showed non-linear behavior in the first heating cycle from the room temperature to 300 oC. However, they linearly behaved in the first cooling cycle and the second thermal cycle. On the other hand, the thermal stresses in the 10 nm film behaved almost linearly without any hysteresis in the first and the second thermal cycles. The mechanism of thermal stress behavior of thin films is discussed.
Development of Multifunctional Materials (MFM): Bioabsorbable Drug-Releasing Hard Tissue Fixation Screws
Authors: Ashammakhi Nureddin , Veiranto Minna , Niemelä Sanna-Mari , Tiainen J. , Leinonen S. , Suokas Esa , Törmälä Pertti
Published: March 2009

To develop a successful bone fixation device that can also release therapeutic agents such as antibiotics one has to consider mechanical, drug release, and biocompatibility properties. We have used bioabsorbable polymers (PLGA 80/20 or PLDLA 70/30) as the matrix and ciprofloxacin (CF) as antibiotic to develop such an implant. Initial shear strengths of the studied ciprofloxacinreleasing screws were 152 MPa (P/L/DL)LA) and 172 MPa (PLGA). Studied screws retained their mechanical properties for least 12 weeks (P(L/DL)LA) and 9 weeks (PLGA) in vitro at the level that ensures their fixation properties. Pull-out tests indicated that the early version of screws have lower values as compared to controls. CF was found to be released after 44 weeks (P/L/DL)LA) and 23 weeks (PLGA) in vitro. It remained in the range of 0.06 – 8.7 µg/ml/day (for P(L/DL)LA) and 0.6 - 11.6 µg/ml/day (for PLGA) after the jump start. Release CF was demonstrated to significantly inhibit S. epidermides growth, attachment and biofilm formation different than controls. Histology showed no difference from plain polymer screws, except for increased giant cells at the implantation site. Accordingly, SR-P(L/DL)LA and SR-PLGA MF implants were considered appropriate to proceed to pilot clinical application.
A Process for Sintering of Diopside Prepared from Dolomite
Authors: Zouai S. , Mezahi F.Z. , Achour S. , Harabi Abdelhamid
Published: March 2009

Diopside CaMgSi2O6 is an attractive material because of its multi applications. It was prepared by sintering the mixture at different temperatures (900°C-1300°C). Starting materials were pure SiO2 and dolomite raw materials. In order to improve the properties of sintered samples, such as the density egg white (ovalbemin) has been added into diopside. Furthermore, the effect of P2O5 addition on the sintering of the prepared diopside in the range of 0.5 to 5.0 wt% was studied as a function of the sintering temperature. A density of 96.5% of theoretical has been achieved when 5.0 wt% P2O5 was added, at a sintering temperature of 1225°C, whereas the density of diopside samples, without P2O5 addition was lower than 83.0% of theoretical.
Functional and Structural Characteristics of Metallic Foams Produced by the SlipReactionFoamSintering (SRFS)-Process
Authors: Angel S. , Bleck Wolfgang , Harksen S. , Scholz P.-F.
Published: March 2009

Highly porous open- cell materials on the base of various metals and alloys are of increasing interest as they combine structural and functional properties. There is a wide range of possible applications for such materials, e.g. as heat exchangers, filters or catalysts. A new and promising method to produce open- cell metallic foams on base of iron powder, low and high alloyed steel powders as well as nickel alloy
powder is the SlipReactionFoamSintering (SRFS)- process. In comparison to other production processes of metallic foams, the SRFS- process provides several advantages: foaming at room temperature, allowing a very good process control by various parameters, foams of a great variety of metals are possible and a broad
spectrum of properties is achievable.
Stress Analysis of Powder Compacts with Graded Structures in Sintering Process
Authors: Shinagawa Kazunari , Hirashima Yasushi
Published: March 2009

During sintering of metal/ceramic functionally grade materials, cracks are often formed on the surface on the top ceramic layer due to the internal stress produced by mismatch shrinkage and warpage. The ways to reduce the internal stress are examined by using the finite element method as well as the plate theory for sintering. Uniaxial pressing, which gives the counter moment against the warping, can decrease the bending stress but only in the middle of the surface. Thinning the top layer is found to be effective in reducing the tensile stress on the surface when the
sintering properties of some layers are modified appropriately. The suppression of the surface cracking in the improved graded powder compacts is confirmed by experiment.
Particle Distribution and Orientation in Al-Al3Zr and Al-Al3Ti FGMs Produced by the Centrifugal Method
Authors: Sequeira P.D. , Watanabe Yoshimi , Rocha L.A.
Published: March 2009

Al-Al3Zr and Al-Al3Ti functionally graded materials (FGMs) were produced by a
centrifugal method from Al-5wt% Zr and Al-5wt% Ti alloys, respectively. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Microstructural characterization was performed to evaluate the intermetallic particles’ distribution and orientation. Knoop hardness tests were carried out, with the indenter’s long diameter normal to the centrifugal force direction. Both the Al3Zr and the Al3Ti
intermetallic particles are platelet in morphology. These platelets tend to be oriented normal to the centrifugal force direction. Higher applied centrifugal force increases both the intermetallic platelet volume fraction as well as their orientation in the outer regions of the fabricated FGM rings. Also higher orientation and volume fraction distribution are observed in the Al- Al3Ti FGMs. Knoop hardness measurements in general follow the same trend as the intermetallic particle volume fraction for each sample.
Processing of a Graded Ceramic Cutting Tool in the Al2O3-ZrO2-Ti(C,N) System by Electrophoretic Deposition
Authors: Vanmeensel Kim , Anné Guy , Jiang Dongtao , Vleugels Jef , Van der Biest Omer
Published: March 2009

In this study, the development of a functionally graded material (FGM) with hard outer surfaces and a tougher inner core was envisaged. The applicability of electrophoretic deposition (EPD) for the processing of FGM materials by continuously changing the suspension composition is shown. Optimisation of the colloidal processing technique was combined with hot pressing experiments on homogeneous composites in the Al2O3-ZrO2-Ti(C,N) system in order to create a
very hard functionally graded material with beneficial residual stresses. Finally, the residual stress distribution was briefly discussed using an existing analytical model.
Synthesis of Nano ITO Powders Prepared by Solvothermal Process
Authors: Ahn Sung Don , Choi Sung Churl
Published: March 2009

In order to provide higher driving forces for densification of Indium-Tin oxide(ITO)
sputtering targets, nano-sized ITO powders with uniform size distribution were prepared by solvothermal process. In this study, sintered bodies were densified by a spark plasma sintering (SPS) process at 950 oC. The experiments conduct the SPS method in order to achieve the highest density of sputtering targets. The phase and relative density of ITO sputtering targets were identified by X-ray diffractometry_(XRD) and Archimedes method, respectively. The surface microstructure and quanitative analysis of the targets were observed by scanning scanning electron microscopy (SEM), and ITO powders particle were measured by SEM, XRD-LB methods.
Fine Nanophased ZnO:Ru and ZnO:Pt Powder Synthesis through Aerosols
Authors: Mančić Lydia , Grgurić-Šipka S. , Djinović V.M. , Marinković Z. , Sabo T. , Milošević O.
Published: March 2009

Pt/Ru-doped ZnO nanophase particles were synthesized using ultrasonic spray pyrolysis. Particles were obtained through decomposition of zinc nitrate and newly developed Pt(IV) and Ru(III) complexes. The particle morphology, phase composition and chemical structure were revealed in accordance to various analysis methods (XRD, DSC, SEM/EDS, TEM) and discussed in terms of precursor chemistry and process parameters. The shape of DSC curves, indicating two exothermic effects above 6000C in both ZnO:Ru and ZnO:Pt, gave an indication of irreversible structural changes and high reactivity of as-prepared powders. The hexagonal wurtzite-type ZnO phase was revealed in both powdered samples. Small content of an intermediate Zn5(NO3)2(OH)8·2H2O and cubic Zn2PtO4 phase were detected in the Pt-doped ZnO particles. Structural refinements, performed by Koalariet-XFit, suggest the composite internal particle structure composed of primary particles sized less than 100 nm. The estimated values for the unit cell parameters and Zn-O bond lengths imply noble metal ions incorporation into ZnO matrix interstitially, probably in octahedral interstitial environment. It has been shown that different particle growing morphologies (either spheroidally or pyramidally shaped) were influenced by the precursor chemistry, processing parameters and the presence of noble metal ions. Among the many parameters, attaining of the particle shape uniformity and homogeneous distribution of the noble metal cations in as-prepared particles are regarded as the most important factors for dominating microstructure evolution.
Electrochemical Study of Hydrogen Electrode Reaction Kinetics on LmNi3.55Co0.75Mn0.4Al0.3 Alloy Electrode
Authors: Potkonjak N. , Sužnjević D. , Simonović B.R. , Mentus S.
Published: March 2009

The exchange current density and the peak current density of the hydrogen electrode reaction on LmNi3.55Co0.75Mn0.4Al0.3 alloy electrode in an aqueous 1M KOH solution, at low hydrogen contents (<0.1 H/M) and elevated temperatures (42-60°C), were studied using potentiostatic polarization techniques. Both measured quantities increased linearly with the increase in hydrogen content in the alloy. On the basis of the difference between the activation energy of the charge transfer and the hydrogen diffusion, it was concluded that the charge transfer reaction represented the rate-determining step of the hydrogen electrode reaction under applied experimental conditions. The decrease of each of these two activation energies with increasing hydrogen content was evidenced, which indicated the existence of other processes occurring in the electrode bulk accompanying the hydrogen diffusion.
Formic Acid Oxidation on Pt/Ru Nanoparticles: Temperature Effects
Authors: Tripković A.V. , Popović K.Dj. , Lović J.D. , Marković N.M. , Radmilović Velimir
Published: March 2009

The formic acid oxidation on Pt/Ru nanoparticles in acid solution over the temperature range 298-333 K has been studied by thin-film rotating disk method (RDE). Transmission electron microscopy in combination with scanning tunneling microscopy was used to determine the size (4.3 ± 0.3 nm) and shape (cuboctahedral) of the particles. Kinetic analysis revealed that at elevated
temperatures (313 K, 333 K) the reaction rate is much higher than at room temperature (295 K), indicating that formic acid oxidation on supported Pt/Ru catalyst is a highly activated process. Based on experimental kinetic parameters we propose that the HCOOH oxidation on the PtRu alloy most likely follows a dual pathway, but the branching ratio is still very high, i.e. Pt-like. The principal effect of opening the dehydration channel at steady-state (via the presence of Ru in the
surface) is to lower the coverage of COads on Pt sites and permit the dehydrogenation path to increase in rate.