bluuebunny/crossref_metadata_2025 huggingface dataset:
Spray Casting of Al-25Si Alloy and Hot Deformation Behavior
Authors: Park Woo Jin , Ha Tae Kwon , Ahn Sang Ho , Chang Young Won
Published: March 2009

The spray forming process was used to produce Al-25Si alloy in this study. The
microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles with average diameter of 5~7 µm. To deduce the extrusion condition, a series of compression tests has been conducted at temperatures ranging from RT to 500oC. The strain rate sensitivity parameter (m) of this alloy has been found to be very low ( ≤0.1) below 300oC and reached maximum value of about 0.13 at 500°C. The extrusion has been successfully conducted at the temperatures of 300°C and above with the ratio of area reduction of 28 and 40. The processing map for hot working has also been constructed.
Effects of Silicon and Chromium on the Fatigue Properties of Al-Zn-Mg-Cu Cast Alloy
Authors: Kim In Bae , Park Yong Su , Kim Kyung Hyun , Kim In Gon
Published: March 2009

Effects of Si and Cr additions on the fatigue properties of Al-Zn-Mg-Cu cast alloy were investigated by low and high cycle fatigue tests. It was found that in the low cycle fatigue test, fatigue life of base alloy showed the maximum value of 3,075 cycles, whereas in Si and Cr containing alloys, it was 2,993 and 1,413 cycles, respectively. The same trend was obtained in high cycle fatigue test, i.e., the fatigue strength in base alloy showed the highest value of 104MPa and decreased to 100MPa for Cr containing alloy and 81MPa for Si containing alloy. The fatigue ratio was about 0.20 for all three alloys. The tensile strength of base alloy also showed the maximum value of 513MPa, and decreased with the addition of Si and Cr to 400 and 500MPa, respectively. Metallographic observation revealed that the fatigue crack initiated at the surface and propagated along the grain boundary.
A Study on Tactile Friction and Wear - Frictional Wears Characteristics of Human Fingers on Various Soft Materials
Authors: Oda Yoshihito , Sugishita Junji , Usami Hatsuhiko , Hattori Tomokazu
Published: March 2009

The tactile wear ("tezure" in Japanese) is an abrasion phenomenon caused by the contact of humans hand with the surfaces of materials over a long period of time. Though this phenomenon has been the focus of various articles, an extensive study with regard to the wear characteristics is of profound importance. To date, we have several remarkable examples such as the statue of Pindola Bharadvaja (Buddhist) and the St. Peter statue (Christian). Followers of the respective religions who are deeply attached and rooted have been touching the statues as part of their rituals for many generations over centuries. In this study, an attempt is done to verify the friction and wear characteristics of the human finger with various soft materials and woods.
Model for the Protective Oxidation of Mg-Ca Alloys Containing Be at Elevated Temperature
Authors: Huang Y.B. , You Bong Sun , Choi Byung Ho , Park Won Wook , Chung Il Sup , Suh S.K.
Published: March 2009

The liquid oxidation behavior of Mg-Ca base alloys containing Be has been presented in this paper. The ignition temperature test and microbalance measurement indicated that the oxide film formed at elevated temperature was protective, resulting in the improved oxidation resistance and ignition-proof properties. A Ca-rich zone was found at the very near surface of oxide layer. With Be addition the oxide layer became dense and compact, which was impermeable for the rapid diffusion of oxygen and magnesium through the oxide layer. It was concluded that the formation of BeO in the oxide layer suppressed the continuous growth of the oxide layer.
Tensile Deformation Characteristics of Commercial Mg Alloys Processed by Equal Channel Angular Pressing
Authors: Chang Si Young , Lee Sang Woong , Kim Jin Chun , Kim Young Seok , Shin Dong Hyuk
Published: March 2009

The commercial AZ31 and AZ61 Mg alloys were subjected to equal channel angular
pressing (ECAP) after hot rolling at 673 K. The hot-rolled AZ31 alloy could be ECA pressed at 493 K. The 4 ECA pressed AZ31 alloy revealed the microstructure of dynamically recrystallized grains with a grain size in range of 1 to 10μm. Despite the dynamic recrystallization during ECAP at higher temperatures ( > 1/2 Tm), the yield stress and tensile strength of AZ31 and AZ61 alloys drastically increased after 1 pressing. The yield stress gradually decreased with increasing the number of pressings, which contrasts with the behavior of the ECA pressed Al and Fe alloys, while the tensile strength increased slightly. In particular, the alloys showed nearly 3 times higher elongation than as-annealed one after 4 ECAPs, without sacrificing the tensile strength. These tensile deformation characteristics were explained based on the observation of the deformed microstructure in the vicinit of fracture surface.
Mechanical and Fracture Behaviors of (Al2O3+SiCp)/AZ91 Hybrid Mg Matrix Composite
Authors: Park Ik Min , Choi Il Dong , Cho Kyung Mok
Published: March 2009

Hybrid AZ91 Mg matrix composites reinforced with ceramic short fiber (Al2O3) and particle (Si or SiCp) were fabricated by squeeze casting method. Microstructure of hybrid Mg matrix was examined and mechanical and fracture properties were characterized. It was found that squeeze casting is effective method for the fabrication of hybrid Mg matrix composites with fairly well distributed reinforcement and near defect-free solidification microstructure. Strength and wear resistance were enhanced with hybridization of reinforcements. To investigate fracture properties of hybrid Mg matrix composites, in-situ micro-fracture experiment was performed in SEM. Crack was initiated and propagated mainly by decohesion of interfaces between Mg matrix and reinforcements. Large ceramic particles tend to fracture and thus seem to be undesirable for mechanical and fracture behavior of hybrid Mg matrix composites.
Characteristics of the Electroless-Deposited Cu Film as Interconnect on a TaN Diffusion Barrier
Authors: Kim Jung Sik
Published: March 2009

In the present study, thermal properties of the electroless-deposited Cu thin film were investigated. The Cu thin film of good adhesion was successfully deposited on the TaN barrier layer by a electroless deposition method. The multilayered structure of Cu/TaN/Si was prepared by electroless-depositing the Cu thin layer on the TaN diffusion barrier which was deposited by MOCVD on the Si substrate. In order to investigate the effect of post-heat treatment the specimen was annealed in H2 reduction atmosphere. Crystallization and agglomeration of the electroless-deposited Cu film occurred through annealing at H2 atmosphere and resulted in the decrease of film resistance. Thermal stability of Cu/TaN/Si system was maintained up to the annealing temperature of 600°C in H2 atmosphere above which the intermediate compound of Cu-Si was formed through diffusion into the TaN layer
High Performance Materials Development in the 21st Century: Trends and Directions
Authors: Williams James C.
Published: March 2009

Product performance including the cost of ownership is becoming increasingly
dependent on the availability of high quality, high performance, affordable materials of
construction. Today, the requirements placed on a new material for a high performance structural application extend well beyond the improvement of one or more material properties. This makes the introduction of a new material a multi-faceted activity.
Modern structural materials derive their performance from a combination of
composition and processing, the results of which are inextricably intertwined. This
statement pertains to both metallic alloys and to fiber reinforced composite materials. In addition, material cost and the reproducibility of material properties are becoming more central as acceptance criteria for incorporating new materials into new products.
This paper will use examples of recent developments in materials for aircraft gas
turbines to depict the materials introduction process. Some of these developments have been successful and others have not. These examples illustrate the changing picture that represents the successful introduction of a new structural material, even in a high performance, high value product such as a gas turbine. Specific examples will include metal matrix composites, Ni-base alloys and improved reliability Ti alloys. The basis for successful introduction, or lack thereof will be discussed. While the examples are specific to gas turbines, they are generally instructive and depict the growing complexity of the process of developing and introducing new materials into a high value product.
An additional issue for all new materials introduction is the time required to achieve
product readiness. As the time required for product design decreases, there has been little commensurate reduction in materials development cycle time. This matter also will be discussed and some possible reasons and potential solutions will be described.
Direct Growth of SiC Nanorods on Si Using APCVD and Single Precursors
Authors: Rho Daeho , Kim Jae Soo , Byun Dong Jin , Yang Jae Woong , Jhin Jung Geun , Kim Nari
Published: March 2009

SiC nanorod was grown by APCVD using TMS. Grown SiC nanorods had a 10 ~ 60nm diameters and lengths of several micrometers. Nanorod.s diameters and lengths were different by kind of catalysts. Nanorod.s growth scheme was divided by two regions with diameter.s variations. At first region, nanorod was grown by VLS mechanism, but at the second region, nanorod growth was made by VS reaction. These differences were made from limitations of growth rate and deactivation effects. Growth temperature, time and flow rates of source gases were affected nanorod.s diameters and its lengths. And the kind of catalysts and coating methods were affected growth direction and microstructures too.
Design and Fabrication of Bi-Convex Variable Focusing Lens Arrays Using Liquid Crystal for Integral Photography
Authors: Hwang Yong-Seok , Kim Jae Chang
Published: March 2009

In this work, we propose integral photography using bi-convex variable focusing lens
arrays (hereafter will be abbreviated as bi-convex VFLA-IP) to obtain wider viewing angle and faster response time and the enhanced depth without decreasing resolution of integrated image. We designed a bi-convex lens structure to apply to 3-dimensional moving pictures. We fabricated twodimensional bi-convex liquid crystal lens arrays using lithography. The response time and the focal lengths of the lens array are measured. Applied voltage to the cell alters the effective refractive
index of the liquid crystal layer and results in a change of the focal length. From the results of measuring electro-optic properties of the fabricated cell, we discovered that synchronized elemental image array for real or virtual mode can be integrated in front of or behind the lens array without decreasing resolution by adjusting the focal length.
Determination of Diffusion Kinetic Parameters and Potential Barrier Height at the Grain Boundary of the Semiconducting SrTiO3 Ceramics
Authors: Park Myung Beom , Cho Nam Hee
Published: March 2009

The chemical and electrical characteristics of the grain boundary of the polycrystalline semiconducting SrTiO3 ceramics, which were synthesized by hot-press sintering Na-coated semiconducting SrTiO3 powders, were investigated in terms of process parameters such as sintering temperature. Diffusion kinetic parameters such as diffusion coefficients and activation energy of diffusing ions at particular heat-treatment conditions were obtained by fitting experimental data with computer-simulated results as well as electrical features near the grain boundary of the ceramics.
Photoluminescence Properties of Ba-Substituted SrAl2O4:Eu Phosphor
Authors: Park W.S. , Kim S.J. , Kim Ji Soon
Published: March 2009

The synthesis of Sr1-XBaXAl2O4 :Eu 2+ (x = 0, 0.1, 0.2 and 0.3 mol) phosphor and its properties of photoluminescence and long-phosphorescence were investigated as a function of sintering condition. The single phase of SrAl2O4 was obtained by sintering the mixtures of SrCO3, BaCO3, Eu2 O3, Al2O3 and 3wt% B2 O3 powders over 1100°C in Ar/H2 atmosphere. Stuctural properties were analyzed by a X-ray diffractometer, microstructural properties by a SEM, and photoluminescent properties by a PL measuring system. The optimum sintering condition for the long-phosphorescent phosphor of Sr1-XBaXAl2O4:Eu2+ was found at 1400 °C. Substitution of Ba about 0.2mol in SrAl2O4
:Eu 2+ enhanced the photoluminescence and long-phosphorescence.
On Ultrasonic Characteristics in Carbon/Phenolic Matrix Composite Materials
Authors: Sim Jae Ki , Im Kwang Hee , Hsu David K. , Kim Ji Hoon , Lee Hyun , Hwang Jae Jung , Bak Kyung-Youn
Published: March 2009

In order to assess material properties and part homogeneity in carbon matrix
composite (CMC) brake disks we have performed nondestructive evaluation, which are originally developed for aerospace applications. In this paper we have adopted several ultrasonic techniques to evaluate carbon matrix composites for the material properties that are attributable to the manufacturing process. In a carbon matrix composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of the CMC composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Optical micrograph had been examined on the surface of the CMCs using a destructive way. Also a motorized system was adopted to measure ultrasonic velocity on the point of the CMC materials under the same coupling conditions. Manual results were compared with those obtained by the motorized system with using dry-coupling ultrasonics and through transmission method in immersion.
Thermal Expansion Behavior of the Multiphase Composite System
Authors: Park Chong Sung , Hong Hyun Seok , Kim Myung Ho , Lee Chong Mu
Published: March 2009

A new approach for the CTE on the basis of Ashelby.s cutting and welding process was made for the analysis of the thermal expansion behaviors of Al-Si alloys and composites. In this theoretical approach, it was considered that relaxation of residual stress could create an elastoplastic zone in the matrix around a particle during cooling. A comparison of the measured CTEs with the calculated ones for the Al-Si-SiCp and Al-Si-Al2O3 composite systems was performed in terms of the volume percent and the size of reinforced phases. The calculated results revealed that the linear CTE of the both composite depends on the size of the reinforce phases, especially at the composite systems with a low volume percent of the reinforce phases. The increase in the volume percentages of Al2O3, SiCp and Si phase lowers the linear CTEs of the systems. The measured CTEs was deviated less than about ten percents from the calculated ones at composites with a high volume percent. The deviations of the CTEs of reinforced phases are about 4 - 6 vol% from real composite systems.
Microwave Behavior of α-Fe/Fe3B/Y2O3 and ε-Fe3N/Y2O3 Resin Composites in GHz Range
Authors: Machida K. , Liu J.R. , Itoh M.
Published: March 2009

Nanocompositesα-Fe/Fe3B/Y2O3 and ε-Fe3N/Y2O3 were prepared by a melt-spun
technique, and the subsequent hydrogenation, oxidation and nitrogenation treatments, respectively. The effective electromagnetic wave absorption (RL<-20 dB) was obtained in a frequency range of 2.7-6.5 GHz on resin composites of 80 wt% α-Fe/Fe3B/Y2O3 powders, with thickness of 6-3 mm; the ε-Fe3N/Y2O3 resin composites exhibited good microwave absorption properties in the 0.6-4.4 GHz range.
High Temperature Oxidation Mechanism of TiAl-W-Si Alloys
Authors: Lee Dong Bok , Woo Seung Wan
Published: March 2009

The oxidation of Ti-(43~52%)Al-2%W-(0~0.5%)Si alloys between 900 and 1050°C in air progressed via the outward diffusion of Ti ions to form the outer TiO2 layer, and the inward transport of oxygen to form the inner (TiO2+Al2O3) mixed layer, between which the intermediate Al2O3 barrier layer existed. Tungsten tended to diffuse inward to be incorporated below the intermediate Al2O3 layer, while Si outward to exist over the entire oxide layer. Both W and Si tended to be dissolved in the oxide layer, rather than forming independent oxides.
Oxidation of (Al+12.5%Cu)3Zr Intermetallics Synthesized by Mechanical Alloying
Authors: Lee Dong Bok , Jang Y.D. , Kim Sung Jin
Published: March 2009

The (Al+12.5 at.%Cu)3Zr alloy was prepared by mechanical alloying followed by cold isostatic pressing and sintering at high temperatures. The oxidation between 673 and 973 K in air progressed by oxygen dissolution arisen by the zirconium.s high affinity and solubility of oxygen. The porous (Al+12.5 at.%Cu)3Zr alloy oxidized even faster than Ti3Al alloys, because no Al2O<3/sub> barrier layers formed.
Yield Stress Anomalous Behavior in β-CuZn Alloy
Authors: Lee K.A. , Chang Young Won , Lee Chong Soo
Published: March 2009

A series of tensile and load relaxation behaviors in B2 type β-CuZn alloy have been examined to clarify the strain rate & the temperature dependence of yield stress anomaly. As strain rate increased, the anomalous peak moved to a higher stress and temperature region. The anomalous yielding region below peak temperature (Tp) revealed slightly positive strain rate dependence, while the region above Tp showed considerably positive strain rate dependence. Based on the different tendency of temperature and strain rate dependence of anomalous yielding, two types of deformation modes were suggested and incorporated into the yield stress vs. temperature curve analysis, which was in accord well with the experimental results. The less sensitive strain rate dependence of yield stress anomaly indicated that the yield stress anomalous behavior in β-CuZn alloy mainly seemed to be attributed to the vacancy hardening.
Tensile Properties of MoSi2 at Elevated Temperatures
Authors: Shan Ai Dang , Wu Jian Sheng , Hashimoto Hitoshi , Park Yong Ho
Published: March 2009

The tensile properties of two MoSi2 alloys with different grain sizes (1 micrometer and 10 micrometer) were evaluated in vacuum at temperatures ranging from 1400 to 1600K and initial strain rates ranging from 1×10-5/s to 1×10-3/s. For the alloy with 10micron grain size an m vale of 0.35 and an activation energy value of 350 kJ/mol were observed in the lower strain rate range while an m value of 0.12 and an activation energy value of 760 kJ/mol were observed in the higher strain rate range. For the alloy with 1micron grain size, a uniform m value of 0.55 and an activation energy value of 160 kJ/mol were observed. Moreover these two alloys showed remarkable ductility (maximum 33%) in the test temperatures. The deformation mechanism and the remarkable ductility are discussed in the light of the microstructural observations through SEM and TEM.
Fatigue and Contact Damage of Layered Machinable Ti3SiC2 Ceramics
Authors: Wang Zhong Guang , Zhang H. , Zang Q.S. , Zhang Zhe Feng , Sun Z.M.
Published: March 2009

Ti3SiC2 has been widely investigated for their intriguing physical and mechanical properties [1]. In the past decades, dense and pure polycrystalline Ti3SiC2 has been fabricated by some techniques [1,2]. Studies on deformation and fracture behavior at elevated temperature showed that Ti3SiC2 exhibited substantial plasticity with high strength [3]. It is pointed out that Ti3SiC2 can be possibly used for some contact applications, such as bearings, for its relative high compression strength, self-lubricating and machinability [1]. In the present paper, fatigue crack-growth rates and Hertzian contact damage of Ti3SiC2 were studied. Shielding ability of Ti3SiC2 was investigated specially in the small crack region. Damage evolution and strength degradation under Hertzian contact were studied to reveal damage behavior and mechanisms in Ti3SiC2.
Effects of Material Properties on Elastic Characteristics of Cold Forged Part
Authors: Lee Young Seon , Lee J.H. , Kwon Yong Nam , Ishikawa T.
Published: March 2009

The dimension of cold forged part is larger than that of the die cavity. The difference could be originated from the various features, such as the elastic characteristics of die and workpiece, thermal influences, and machine-elasticity. Among these features, elastic behavior of die and workpiece has been considered as the most important element for the precision cold forging. In the present study, the effect of material properties of both workpiece and die on the dimensional precision of forged part was investigated using FE and experimental analyses. Three materials, such as SCM420H, Cu-OFHC and Al6061 alloy, were used to divide the effect of the elastic modulus and flow stress on the dimension specifically. From the results of FEA, the elastic deformation of die was found to be more dominant than that of workpiece. The die expansion depends on the flow stress of workpiece during a loading stage. On the other hand, the die contraction during unloading was affected by both the flow stress and elastic modulus of workpiece. The elastic modulus of workpiece affects the elastic recovery of forged part after ejecting stage.
Elastoplastic Line Contact in Cylindrical Indentation
Authors: Muto Hiroyuki , Sakai Mototsugu
Published: March 2009

A novel indentation method is proposed to study the mechanical properties of porous
and/or heterogeneous materials by the use of a cylindrical indenter with line loading on test specimens. The problems in line contact are examined. The indentation load P versus penetration depth h relation in line contact is expressed in terms of the radius R of cylindrical indenter and the contact length L. An application of a cylindrical indentation to a polycrystalline graphite leads to a successful determination of the Young's modulus and the yielding strength. It is concluded that the line contact rather than the conventional pyramidal point contact is more efficient for the experimental deternination of mechanical properties of porous and/or heterogeneous materials.
Thermal Fatigue Behavior of the Surface Treated Hot Die Steel Depending on Test Temperature
Authors: Rhyim Young Mok , Youn Kuk Tae , Yoo Wee Do , Na Y.S. , Lee J.H.
Published: March 2009

The influence of thermal fatigue test temperature on crack propagation behavior of the surface treated tool steel for die-casting was investigated. For this purpose, thermal fatigue system consisted of induction heating and water spray quenching unit was constructed to simulate the service condition and Lm is proposed as the index representing the susceptibility to crack initiation and propagation. The thermal fatigue tests were conducted at the maximum temperature of 600°C, 700°C and 720°C using as-heat treated or nitrided specimens. The ion nitrided specimen showed lower Lm value than as-heat treated at all test temperature. But in the case of maximum and average crack length, the ion nitrided specimen exhibited higher value than those of as-heat treated specimen.
Effect of Temperature on Strength and Residual Stress Distribution in Silicon Nitride to 304 Stainless Steel Brazed Joints
Authors: Seo Do Won , Yoon Ho Chel , Lee Jin Yi , Lim Jae Kyoo
Published: March 2009

Ceramics are significantly used in many industrial applications due to their excellent
mechanical and thermal properties such as high temperature strength, low density, high hardness, low thermal expansion and good corrosion properties. To combine the specific advantages of ceramics with that of metals, they are often used together within one composite component. In this study, the effect of temperature on fracture characteristics of silicon nitride joined to 304 stainless steel brazed with Ti active alloy are investigated in room and high temperature regions. And analytical studies on the residual stress of dissimilar brazed joint are performed by the finite element method. Four-point bending strength and deflection of interlayer increase with increasing strain rate in room temperature. As the test temperature increases, the bending strength decreases, but the deflection of interlayer is almost constant. The residual stresses redistribute after cutting of joint and the maximum tensile stress occurs on the new free surface at the ceramic near the interface. The singularity of residual stresses at the ceramic near the interface is characterized by elastic-plastic properties of ceramic and inserted materials.­
Interfacial Morphology of Duplex Stainless Steel Joints Brazed with Ni-Cr-Si-B Filler Metal
Authors: Lee H.K. , Kang Chung Yun , Woo C.S. , Kim S.H. , Kim Dae Up
Published: March 2009

Microstructures of 0.18wt% nitrogen-contained duplex stainless steel, SUS329J3L brazed in a vacuum furnace of 10-4 torr, have been investigated as a function of bonding temperatures (1453-1523K) and holding times (0-1.8ks). An amorphous alloy, MBF50 (Ni-19.5wt%Cr-7.3wt%Si -1.5wt%B), was used as an insert metal. At an early stage at 1453K and 1473k, a morphology change of the insert metal, BN and CrB phase appeared only at the joints. The BN and Cr-Si-N phase were observed at the interface of the joints brazed under other conditions. The volume fraction of BN increased rapidly at an early stage and decreased with increasing holding time. The phase seemed to have been formed by dissolution of the base metal and the diffusion process. BN was formed easily due to the lowest Gibbs free energy.
Boron content in liquid insert metal becomes low due to the formation of a large number of BNs at the bonded interlayer by holding for a few minutes at brazing temperature. This caused the rapid isothermal solidification of the liquid insert metal. Thus, it is clear that the isothermal solidification process of this bonding is controlled by the formation of boron nitrides as opposed to the diffusion process of depressant elements(B and Si) in the base metal.
Effect of Argon Ion Bombardment on Diffusion Bonded Joint of Various Metals
Authors: Wang Airu , Ohashi Osamu , Yamaguchi N.
Published: March 2009

Specimens of aluminum (Al), austenitic stainless steel (SUS304L), pure iron (Fe) and Oxygen-free high conductivity copper (Cu) were treated by argon ion bombardment, and then were bonded by diffusion bonding method. The effects of argon ion bombardment on diffusion-bonded joints of four kinds of metallic materials were compared from the tensile strength at real bonded area and the fractographs. The results showed that bonding temperature was lowered by argon ion bombardment treatment for four kinds of materials. The effect of argon ion bombardment on diffusion-bonded joint depended strongly on the chemistry of the surface to be bonded, and increased in Al, SUS304L, Fe, and Cu in turn.
Comparison of Pd/Ge/Ti/Pt and Pd/Si/Ti/Pt Ohmic Contacts to N-Type InGaAs for AlGaAs/GaAs HBTs
Authors: Kim Il Ho
Published: March 2009

Pd/Ge/Ti/Pt and Pd/Si/Ti/Pt ohmic contacts to n-type InGaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In both ohmic contacts, low-resistance and non-spiking planar interfaces were obtained by rapid thermal annealing. RF performance of the AlGaAs/GaAs HBT was also examined by employing these contact systems.
Influence of Biaxial Surface Stress on Mechanical Indenting Deformations
Authors: Lee Yun Hee , Jang Jae Il , Kwon Dong Il
Published: March 2009

A theoretical model has been proposed to assess quantitative residual stress from a
stress-induced shift in an indentation curve, but the assumption in this model of equibiaxial surface stress has obstructed its application to real structures in complex stress states. Thus we investigated the influence of non-equibiaxial surface stress on contact deformation through instrumented indentations of a biaxially strained steel plate in order to extend the model to a general surface stress
by considering a ratio of two principal stresses.
Isothermal Crystallization of Zr55Al10Ni5Cu30 Bulk Amorphous Alloy Near the Glass Transition Temperature
Authors: Hu Zhuang Qi , Zhang Q.S. , Zhang Haifeng , Ding B.Z. , Rao Z.M.
Published: March 2009

Isothermal crystallization of Zr55Al10Ni5Cu30 bulk amorphous alloy near the glass
transition temperature has been investigated. The microstructures and thermal stability of the annealed amorphous alloy were examined by HRTEM, XRD and DSC. The amorphous phase in the Zr55Al10Ni5Cu30 bulk amorphous alloy crystallized at 420°C through the following processes of amorphous →amorphous with clusters + metastable phases→metastable phases.
Deformation Behavior of Ni-Based Metallic Glass Matrix Composites Reinforced by Brass Short-Fibers Synthesized by Warm Extrusion of Powders
Authors: Bae Dal Hee , Lee Myung Hyun , Kim D.H.
Published: March 2009

Deformation behavior of Ni-based metallic glass matrix composites reinforced by
short brass-fibers, synthesized by warm extrusion of gas atomized powders, has been investigated under the uniaxial compression condition at room temperature. The brass-fibers are well distributed in the metallic glass matrix and enhanced macroscopic plasticity is observed due to the formation of multiple shear bands, initiated from the interface between brass-fiber and metallic glass matrix, as well as their confinement between the brass-fibers, stemming from the constrained plastic deformation of the reinforcing brass phase.
Heat Capacities of Ln2MnNiO6 (Ln = Rare Earth)
Authors: Sato Hirohisa , Ochi K. , Kamegashira Naoki
Published: March 2009

Ln2MnNiO6 were synthesized by the usual ceramic method for Ln = Sm, Eu, Gd, Tb and
Dy and by the wet method for Ln = La, Nd Ho and Er. Heat capacities of these compounds were
measured by using DSC and ACC. The thermal anomalies accompanying by magnetic transition
from ferromagnetism to paramagnetism were observed for some rare earths and the magnetic
contribution of heat capacity was estimated
Structural Analysis of a Complex Oxide Eu2Mn2/3Nb4/3O7 with a Pyrochlore-Related Structure
Authors: Chen G. , Nakano Hiromi , Sato Hirohisa , Kamegashira Naoki
Published: March 2009

The complex oxide Eu2Mn2/3Nb4/3O7 structurally characterized by powder X-ray
diffraction (XRD) and transmission electron microscopy (TEM). The results of XRD structure
analysis shown that the X-ray diffraction profile calculated with monoclinic C2/c model is in a good
agreement with the observed X-ray diffraction patterns. In addition to fundamental reflection peaks,
super lattice lines could be also assigned with C2/c symmetry. Therefore, it is derived that
Eu2Mn2/3Nb4/3O7 phase has not a pyrochlore structure but has a zirconolite-type structure
(pyrochlore-related structure) with a C2/c space group. Eu2Mn2/3Nb4/3O7 has two kinds of distorted
MO6 octahedra and HTB layers, which deviates from the regular forms. The microstructure of
Eu2Mn2/3Nb4/3O7 investigated by TEM also proved the results of XRD structural analysis. It was
viewed that HRTEM image of a characteristic twin structure in Eu2Mn2/3Nb4/3O7 which a
zirconolite-type structure has.
Molecular Dynamics Analysis of Structure and Intrinsic Stress in Amorphous Silicon Carbide Film with Deposition Process Parameters
Authors: Kim Ju Young , Lee Baik Woo , Nam Ho Seok , Kwon Dong Il
Published: March 2009

Amorphous silicon carbide (a-SiC) films were deposited using molecular dynamics
simulations employing the Tersoff potential. The structure and intrinsic stress of a-SiC films changed
dramatically with changes in such principal deposition process parameters as substrate temperature
and incident energy. Changes in structure and intrinsic stress with deposition process parameters were analyzed.
Characteristics of ZnO Thin Film by Atomic Layer Deposition for Film Bulk Acoustic Resonator
Authors: Kim S.G. , Jung Seung Boo , Oh Ji Hun , Kim H.J. , Shin Yong Hyeon
Published: March 2009

Polycrystalline ZnO thin films were for the first time deposited on SiO2/Si (100)
substrate using 2-step deposition; atomic layer deposition (ALD) and RF magnetron sputtering, for
Film Bulk Acoustic Resonator (FBAR) applications. The film deposition performed in this study
was composed of following two procedures; the 1st deposition was using ALD method and 2nd
deposition was using RF magnetron sputtering. The ZnO buffer layer ALD films were deposited
using alternating diethylzinc (DEZn)/H2O exposures and ultrahigh purity argon gas for purging.
Exposure time of 1 sec and purge time of 23 sec yielded an ALD cycle time. Two-step deposited
ZnO films revealed stronger c-axis preferred-orientation than one-step deposited. Therefore, this
method could be applied to the FBAR applications, since FBAR devices require high quality of thin
films.
Characteristic Investigations of Stoichiometric LiNbO3 Single Crystal Fiber Co-Doped with Tb and Mn
Authors: Lee S.M. , Shur J.W. , Shin T.I. , Yang W.S. , Kim G.Y. , Baek S.W. , Yoon D.H.
Published: March 2009

[MnO2(1.0mol%) : Tb4O7(0.5mo%)] doped stoichiometric LiNbO3 (Mn:Tb:SLN) single
crystals of 0.5~1.0 mm in diameter and 30~35 mm in length were grown by micro pulling
down(µ-PD) method. We investigated the photoluminescence (PL) properties of Mn:Tb:SLN single
crystal. The OH- absorption band of the single crystals observed infrared the absorption spectra by
using an FT-IR spectrophotometer at room temperature. Homogeneous distributions of Mn and Tb
concentration were confirmed by the EPMA and observed defects by optical microscopy.
Electrical/Optical Properties of Thin Transparent Oxide Films Deposited Using DC Magnetron Sputtering
Authors: So Byung Soo , Kim Sung Moon , Pyo Young Sin , Kim Young Hwan , Hwang Jin-Ha
Published: March 2009

Amorphous indium tin oxide (ITO) thin films were grown on plastic substrates, PES (polyethersulfone) using low temperature DC magnetron sputtering. Various post-annealing techniques are attempted to optimize conductivity, transmittance, and roughness: i) conventional thermal annealing, ii) excimer laser annealing, and iii) UV irradiation. The electrical/optical properties were measured using Hall-measurement, DC 4-point resistance measurement, and UV spectrometry along with micro-structural characterization. Optimized UV treatment exhibits enhanced conductivity and smooth surface, compared to those of conventional thermal annealing and excimer laser annealing.
Mesoscale Simulation of Grain Growth
Authors: Kinderlehrer D. , Lee Jee Hyun , Livshits Irene , Rollett Anthony D. , Ta'asan Shlomo
Published: March 2009

Simulation is becoming an increasingly important tool, not only in materials science in a general way, but in the study of grain growth in particular. Here we exhibit a consistent variational approach to the mesoscale simulation of large systems of grain boundaries subject to Mullins Equation of curvature driven growth. Simulations must be accurate and at a scale large enough to have statistical significance. Moreover, they must be sufficiently flexible to use very general energies and mobilities. We introduce this theory and its discretization as a dissipative system in two and three dimensions. The approach has several interesting features. It consists in solving very large systems of nonlinear evolution equations with nonlinear boundary conditions at triple points or on triple lines. Critical events, the disappearance of grains and and the disappearance or exhange of edges, must be accomodated. The data structure is curves in two dimensions and surfaces in three dimensions. We discuss some consequences and challenges, including some ideas about coarse graining the simulation.
Mesoscale Simulation of the Evolution of the Grain Boundary Character Distribution
Authors: Kinderlehrer D. , Livshits Irene , Rohrer Gregory S. , Ta'asan Shlomo , Yu Peng
Published: March 2009

A mesoscale, variational simulation of grain growth in two-dimensions has been used to explore the effects of grain boundary properties on the grain boundary character distribution. Anisotropy in the grain boundary energy has a stronger influence on the grain boundary character distribution than anisotropy in the grain boundary mobility. As grain growth proceeds from an initially random distribution, the grain boundary character distribution reaches a steady state that depends on the grain boundary energy. If the energy depends only on the lattice misorientation, then the population and energy are related by the Boltzmann distribution. When the energy depends on both lattice misorientation and boundary orientation, the steady state grain boundary character distribution is more complex and depends on both the energy and changes in the gradient of the energy with respect to orientation.
Grain Growth in Films with Initial 3D Microstructure
Authors: Novikov Vladimir Yu.
Published: March 2009

Grain growth in films with h/〈D〉0=3.5−7.5, where h is the film thickness and 〈D〉0 the
initial average grain diameter, was studied by means of computer simulation. The growth kinetics during 3D®2D microstructure transformation do not obey the parabolic law commonly used for the grain growth description. By the end of the transformation, 〈D〉/h is not grater than 2. The drag effect of thermal grooves also results in 〈D〉/h < 2 to the end of the microstructure transformation.
Stability of Ultra-Fine ‘Grain Structures’ Produced by Severe Deformation
Authors: Prangnell Philip B. , Bowen Jacob R. , Berta M. , Apps P.J. , Bate Pete S.
Published: March 2009

Severe deformation techniques allow metallic alloys to be deformed to ultra-high plastic strains, without any geometrical change to the work piece. They thus offer potential for the cheap production of submicron grained materials, in a bulk form. After processing severely deformed materials do not have conventional, idealized, grain structures, contain significant fractions of low angle boundaries, and are often heterogeneous. Due to their high stored energy, they are unstable on annealing and in most cases can be thought of as continuously recrystallizing. However, locally discontinuous behaviors are often observed, due to the retained less mobile low angle boundaries, as well as abnormal grain growth at elevated temperatures. Monte-Carlo-Potts models have been used to show the sensitivity of the annealing behavior to the initial starting structure present after deformation. The effect of coarse (~1µm) particles and fine dispersoid particles are also discussed.
Grain Growth and Texture Development in Nanostructured Invar Alloy
Authors: Kim Jong Kweon , Seo Jun Hyuk , Park Yong Bum
Published: March 2009

In the present work, a nanocrystalline Invar alloy (Fe-36wt%Ni) foil was fabricated by using a continuous electroforming method. This material exhibited outstanding mechanical properties and a relatively low thermal expansion coefficient as compared to conventional Invar alloys. The as-deposited texture was of fibre-type characterized by strong <100>//ND and weak <111>//ND components. Grain growth occurred during annealing beyond 350°C and resulted in such texture change that the <111>//ND fibre texture strongly developed with the minor <100>//ND components. It was clarified using orientation imaging microscopy that abnormal growth of the <111>//ND grains in the early stages of grain growth plays an important role on the texture evolution. The mechanism of the abnormal grain growth has been discussed in terms of the orientation dependence of energy density.
Hot Strain Diagrams, Strengthening and Recrystallization of Nitrogen Alloyed Steels
Authors: Kaputkina Liudmila M. , Prokoshkina Vera , Lojnikov Yu.I.
Published: March 2009

Kinetics of deformation strengthening, polygonization and recrystallization processes
have been studied, effects of alloying by nitrogen, combined carbon and nitrogen as well as by various other elements (Cr, Mo, Ni, Mn, V etc.) have been estimated for steels of different compositions and applications. Strain diagrams and structure state maps for the studied steels are presented. Strain diagram shape and attainable hot strength depend on the deformation conditions and basic alloying which determine strain hardening and diffusional processes of post-deformation
softening. Alloying by nitrogen increases hot and cold strain hardening and retards recrystallization. Maximum strengthening obtained by cold deformation is accompanied by lowering of ductility and fracture toughness. Hence, it is applicable mainly to the austenitic steels. Nitrogen alloying enhances the austenite stability against g ® a transformation and consequently allows extending a composition range of steels which can be strengthened by cold deformation with large strains. The high-temperature thermomechanical treatment is more effective as a treatment improving a combination of mechanical properties. The schemes and regimes of thermomechanical strengthening treatments are proposed for low- and high- nitrogen containing steels of various structure classes.
Prediction of Static Recrystallisation after Extrusion of Shaped Aluminium Sections
Authors: Peng Zhi , Sheppard Terry
Published: March 2009

Extrusions experience large deformations at discontinuities when they traverse the die land, leading to considerable modifications to the average deformation parameters when compared to the remainder of the extrusion. The distribution of structure is therefore greatly inhomogeneous. Reference to both empirical and physical models of the recrystallisation process indicate that nucleation and growth will differ at these locations in those alloys that are usually solution treated and aged subsequent to the deformation process. Since static recrystallisation has a significant influence on many of the properties of the extrudate, it is therefore essential to provide the methodology to predict these variations. In the work presented, a physical model based on dislocation density, subgrain size and misorientation is integrated into the commercial FEM codes, FORGE2® and FORGE3® to study the microstructure changes. Axi-symmetrical and shape extrusion are presented as examples. The evolution of the substructure influencing static recrystallisation is studied. The metallurgical behaviour of axi-symmetric extrusion and that of shape extrusion are compared. The predicted results show good agreement with experimental measurement. The distribution of equivalent strain, temperature compensated strain rate and temperatures are also presented to aid in interpretation.
Development of Two-Dimensional Vertex Type Model
Authors: Piękoś K. , Tarasiuk Jacek , Wierzbanowski Krzysztof , Bacroix Brigitte
Published: March 2009

The recrystallization process in polycrystalline material was studied using the newly developed two–dimensional model based on the vertex concept. In the model presented below the microstructure of polycrystalline material is represented by two-dimensional network of grains. The initial microstructure is characterized by topology, crystal orientations and stored energy values of the grains. The boundary energies and mobilities are anisotropic in general. Additional driving forces in recrystallization, are exerted on vertices and are derived from the stored energy gradients between adjacent grains. The nucleation mechanism of a given type is selected at the start of the calculations. Two different nucleation types were tested. Deformation texture, stored energy distribution and initial microstructure are input parameters of the model. The goal of the calculations is the prediction of texture and microstructure modification during recrystallization. A comparison of predicted and experimental characteristics enables the verification of the model assumptions.
Microstructure Modeling as a Tool to Optimize Forging of Critical Aircraft Parts
Authors: Stockinger Martin , Tockner Johann
Published: March 2009

Forging of high strength nickel base superalloys 720 and 718 for aircraft parts requires the usage of finite element simulations to ensure a proper thermo-mechanical treatment. Because of the strong mechanical requirements and narrow specifications of such parts not only a correct, defect free final geometry is necessary, but also a defined microstructure. The crucial point is therefore, to control all process parameters in a way to achieve the demanded properties. The typical forging processes like hydraulic, screw press and hammer forging imply a broad spectrum of strain rates. The influence of this different strain rates as well as forging temperature and strain on dynamic and post-dynamic recrystallization have been examined experimentally. Annealing tests at various temperatures and
time periods have been performed, to investigate the grain growth behavior and dissolution processes in this before mentioned materials during heating periods. The obtained data was used to build phenomenological models, which were implemented into finite element code of a commercial special purpose finite element program. 2D and 3D Simulations of multiple step thermo-mechanical processes are compared with microstructure examinations of forged parts to show the usability and accuracy of such models as a tool to optimize complex forging processes of critical aircraft parts. In combination with systematic process data collection during production a stable processes and satisfactory mechanical product properties are guaranteed.
Grain Boundary Dynamics in High Magnetic Fields. Fundamentals and Implications for Materials Processing
Authors: Molodov Dmitri A.
Published: March 2009

The latest research on dynamics of grain boundaries in non-magnetic materials in high magnetic fields is reviewed. A control of grain boundary migration means control of microstructure evolution, which is a key for the design of materials with desire properties. Grain boundary motion can be affected by a magnetic field, if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free energy. In contrast to curvature driven boundary motion, a magnetic driving force also acts on planar boundaries so that the motion of crystallographically well-defined boundaries can be investigated, and the true grain boundary mobility can be determined. The results of migration measurements obtained on bismuth and zinc bicrystals are addressed. Selective growth of new grains in locally deformed zinc single crystals driven by a magnetic force is reported as well. Implications for materials processing, in particular the effect of magnetic fields on texture development in hcp metals are finally discussed.
Five-Parameter Grain Boundary Character Distribution in Fe-1%Si
Authors: Bennett Tricia A. , Kim Chang Soo , Rohrer Gregory S. , Rollett Anthony D.
Published: March 2009

The grain boundary character distribution in an Fe-1%Si steel has been measured as a function of lattice misorientation and boundary plane orientation. There is a weak texture in the space of grain boundary planes that favors the {110} orientation. At specific misorientations, the anisotropy is larger. For example, when the lattice misorientation is 60° around [111], symmetric tilt boundaries comprised of two {110} planes on either side of the interface dominate the population. The results are consistent with observations suggesting that in a range of crystalline
materials, the low energy, low index surface planes are found to dominate the distribution of internal interfaces.
Grain Boundary Roughening Transition
Authors: Yoon Duk Yong , Cho Young Kyu , Jang Hyun Min
Published: March 2009

Flat surfaces and grain boundaries lying on low crystal planes are singular corresponding to the cusps in the polar (Wulff) plots of their energy against their orientation. The theoretical analysis of the entropy effect at high temperatures shows that these interfaces undergo roughening transitions. The molecular dynamics simulations also show disordering to liquid-like structures at high temperatures that can be interpreted as the roughening transition. Experimentally, singular flat surfaces and grain boundaries become curved at high temperatures or with additives, indicating their roughening transition. The grain boundaries in polycrystals are often faceted with hill-and-valley shapes and their defaceting at high temperatures also show their roughening transition.