bluuebunny/crossref_metadata_2025 huggingface dataset:
Current Steps in Poly(3-Hexylthiophene)/ZnO Nanobelt Hybrid Diodes
Authors: Guo Wen , Yang Ya , Qi Jun Jie , Zhang Yue
Published: June 2010

We report the poly(3iophene) (P3HT)/ZnO nanobelt hybrid p-n junction diodes characterized by using a conductive atomic force microscope (C-AFM). The diodes exhibited a turn-on voltage of about 2.5 V and ideality factor of about 11.6. The obvious current steps in the I-V characteristics under the reverse bias were clearly observed at room temperature. The origin of these steps is suggested to be attributed to the charge injection-trapping induced by nanoparticles on the surface of the ZnO nanobelt.
650°C Long-Term Structure Stability Study on 18Cr-9Ni-3CuNbN Heat-Resistant Steel
Authors: Yu Hong Yao , Dong Jian Xin , Xie Xi Shan
Published: June 2010

The Cu-containing austenitic heat-resistant steel 18Cr-9Ni-3CuNbN has been widely used as superheater and reheater tube material for modern ultra-super-critical (USC) power plants in the world. High temperature structure stability is considered to be an important factor for long-term service. Long-term aging at 650°C for this steel was conducted from 100 to 10,000hours. Effect of aging time on microstructure was studied by means of SEM, TEM and 3DAP (three dimensional atom probe). Micro-hardness tests were carried out after aging at 650°C for different times to be considered as a representative of strength. Experimental results show that Cu-rich phase, MX and M23C6 are major strengthening precipitates in this steel. With on increasing of aging time, fine nano-size Cu-rich phase particles precipitate in the grains and its size is in the range of several nanometers to 35nm till 10,000h at 650°C. The fraction of MX also increases with aging time and its average size is about 100nm till 10,000h. Carbide M23C6 mainly precipitates at grain boundaries and coarsens quickly. Investigation results show that the most important strengthening effect for 18Cr-9Ni-3CuNbN steel is contributed by Cu-rich phase and MX in the grains and M23C6 carbide at the grain boundaries.
In Situ TEM and APT Analysis on the Dislocations Associated with Solute Carbons in Strain-Aged Low Carbon Pipeline Steels
Authors: Seok Park Hyoung , Kang Ju Seok , Yoo J.Y. , Park Chan Gyung
Published: June 2010

Low carbon (~0.34 at.%) pipeline steels with high strength and high toughness are widely used for the transportation of petroleum and natural gas. These pipelines usually experience UOE (bending by U press, forming by O press, Expansion) piping followed by coating process at 250°C, which usually cause strain aging phenomenon with discontinuous yielding in service. In order to understand the major cause of the strain aging in these low carbon pipeline steels, the dislocations associated with solute carbon atoms have been investigated in three different types of steels (plate, pipe, and coated pipe). In-situ TEM heating up to 250°C for 30min did not cause any change of structure in both steel plate and pipe. However, APT results revealed the segregation of carbon atoms alone dislocation lines in ferrite region of both UOE pipes and coated pipes. It is believed that this solute segregation along the dislocations is the major cause in the case of strain aging of low carbon pipeline steels.
Susceptibility to Hydrogen Embrittlement of IF Steel with Ultrafine-Grained Structure Produced by Accumulative Roll-Bonding Process
Authors: Haruna Takumi , Nakagawa Yuichi , Terada Daisuke , Takata Naoki , Tsuji Nobuhiro
Published: June 2010

We have investigated the susceptibility to hydrogen embrittlement of interstitial-free (IF) steel with ultrafine-grained microstructure produced by accumulative roll-bonding (ARB) process. The ARB process was conducted to as-received IF steel at 773 K, and repeated to five cycles. The as-received and the ARBed IF steels were cut into tensile specimens, and then hydrogen was electrochemically charged to the specimens in a sulfuric acid solution of pH 2.5 at a cathodic current density of 50 A m-2 for several charging times. Immediately after the hydrogen-charging process, tensile test was conducted at ambient temperature and an initial strain rate of 3.3 x 10-4 s-1. Besides, state and amount of hydrogen absorbed in the specimen were determined with a thermal desorption gas spectroscopy (TDS) at a heating rate of 5.6 x 10-2 K s-1. As a result, almost no hydrogen was absorbed in the as-received IF steel charged for a long time of ca. 300 ks, and a fracture strain of the steel was independent of the charging time. On the other hand, amount of hydrogen in the 5-cycle ARBed steel increased with an increase in the charging time, and the fracture strain decreased with an increase in the charging time, indicating that the ARBed steel exhibited susceptibility to hydrogen embrittlement.
Mechanisms of Dynamic Recrystallization in Cu-Sn-P Alloy
Authors: Miura Hiromi , Watanabe Masato , Shirai Takashi , Ishibashi Akihiko
Published: June 2010

Dynamic recrystallization (DRX) behavior in a Cu-0.65Sn-0.025P (mass%) alloy (Cu-Sn-P), which had been newly developed for high strength copper tubes, was systematically investigated. For this purpose, an orientation-controlled bicrystal ( =28o); a model samples of the as-casted billet having coarse columnar grains, was hot deformed in compression at 1073 K at true strain rates from 2 x 10-3 s-1 to 2 x 10-1 s-1 in vacuum. Appearance of peak stress, where DRX sets in, was much delayed in Cu-Sn-P alloy compared with that in Cu and the other copper alloys. While nucleation of new grains preferentially took place at grain boundary, this tendency became more significant with decreasing strain rate. Almost all the new grains were annealing twins (3) formed behind the migrating grain boundary. The more preferential nucleation at grain boundary with decreasing strain rate could be, therefore, reasonably understood by easier and more extensive occurrence of grain boundary migration at lower strain rate.
Isothermal Martensitic Transformation in a Sensitized SUS304 Stainless Steel under Magnetic Field
Authors: Choi Ju Young , Fukuda Takashi , Kakeshita Tomoyuki
Published: June 2010

We have investigated effect of magnetic field at cryogenic temperature on the stability of austenitic phase in a sensitized SUS304 stainless steel. The sensitization of the steel was made by heat-treatment in vacuum at 973 K for 100h after the solution treatment at 1323 K for 0.5 h. Isothermal holding of the sensitized specimens was made under a static magnetic field of 5 T in the temperature range between 60 and 260 K for various holding times. As a result, the TTT diagram under the magnetic field corresponding to the formation of 0.5 vol. % of -martensite shows a double-C curve with two noses. We found that by the application of magnetic field, the nose temperature and the incubation time of upper part of the C-curve, that is due to the    transformation, become lower and shorter, respectively. On the other hand, the nose temperature of lower part of the C-curve, that is due to the      transformation, does not change under the magnetic field although the incubation time shortens by the application of magnetic field.
Researches on the Nucleation Behaviors of NH4Cl Crystal on Coarse Aluminum Surfaces
Authors: Wang Meng , Zhu Sen Feng , Zhang Ying , Lin Xin , Huang Wei Dong
Published: June 2010

Coarse aluminum surfaces were prepared by etching method, the wettability of NH4Cl -70wt%H2O solution on the surfaces was investigated, and then the substrates were undercooled and immerged into NH4Cl-70wt%H2O solution to trigger nucleation of NH4Cl crystals. Experimental results indicate that the aluminum surface with step-like micro-morphology shows a transformation from strong wettability to non-wettability during its exposure in the atmosphere, in the same time, nucleation density on the strongly wetting surface is significantly higher than that of the non-wetting surface. A hypothesis is proposed to explain the relationship between the wettability and the nucleation density: the capillary effect helps the solution infiltrate into the structures of the surface with strong wettability and drive the air out of the surface structures, so nucleation is effectively promoted by the sharp corners and hollows of the coarse surface; conversely, the air bubbles trapped in the non-wetting surface structures decrease the number of the effective nucleation sites, and leads to a higher nucleation energy barrier, thus the nucleation density is decreased.
The Character of Melt of A357 Alloy and Its Influences on the Solidification Microstructures
Authors: Zhang Rong , Zhang Li Min , Yang Zhi Huai , Liu Lin
Published: June 2010

The relativity between the alloy melt state and solidification microstructure has been received great interesting recently. Some previous studies proved that control the state of alloy melt can improve the microstructure and properties. In this paper, the character of melt of A357 alloy between 700°C-1150°C was studied by using DSC. The result indicates that there are exothermic reactions over liquidus which corresponds to dissolution of crystalline particle or cluster in the melt. In order to investigate the effects of character of melt on the microstructure, the alloys were first superheated at 720°C，820°C and 925°C respectively with different character of melt, held for 20min, then the melts cooled to 720°C before quenching in Ga-In-Sn melt. The microstructure of samples was analyzed. The results show that with the increase of superheating temperature, the secondary dendrite arm spacing (SDAS) of -Al trends to decrease, and the eutectic silicon becomes fine and dispersion and its morphology becomes spherity instead of coarse platelike. These results can be explained by improving of uniformity of the melt and the changing of the solidification parameters.
Effect of Rare-Earth Elements on the Ignition-Proof Behavior of Industrial Pure Magnesium
Authors: Zhao Wei Min , Shi Zhong Fang , Wang Zhi Feng , Li Yong Yan , Ding Jian , Hur Bo Young , Zhao Rui
Published: June 2010

The purpose of this research is to investigate effect of rare-earth elements (Y and Dy) on industrial pure Mg through the ignition point test and oxide film analysis. The results show that the 0.5%Y can make the ignition point of pure magnesium about 30°C higher. However, the ignition point of pure magnesium can be multiplied about 50°C by the mixed additions of 0.5wt%Y and 5wt%Dy. The SEM analysis indicates the oxide film of Mg-0.5Y-5Dy is more compact and tenacious than that of Mg-0.5Y. The XRD analysis indicates that the oxide film of Mg-0.5Y-5Dy consists of MgO, Y2O3 and Dy2O3. The most of all the three oxides are Dy2O3, which can prevent magnesium from further oxidizing.
Effect of Oxygen on the β-Grain Size of Cast Titanium
Authors: Bermingham Michael J. , McDonald Stuart D. , Dargusch Matthew S. , StJohn David H.
Published: June 2010

Grain refinement of titanium alloys during solidification is believed to have many benefits for processing and properties. Recent work has emphasized the importance of solute elements in grain refining cast titanium and it was demonstrated that the growth restriction factor is useful for predicting the grain refining effectiveness of solute elements in titanium. Despite oxygen being the major impurity element present in titanium alloys and having been previously identified as a theoretical growth restricting solute, its effect as a β-grain refiner is still unexplored. This paper investigates the effect of oxygen on the grain size in cast titanium alloys.
A Cellular Automaton Model with the Lower Mesh-Induced Anisotropy for Dendritic Solidification of Pure Substance
Authors: Lin Xin , Wei Lei , Wang Meng , Huang Wei Dong
Published: June 2010

A modified cellular automaton model for describing the dendritic solidification of pure substance was developed. Instead of using the high mesh-induced anisotropy capture rules, such as Von Neumann’s and Moore’s method, a new capture rule---random zigzag method was developed, which greatly reduced the mesh-induced anisotropy in crystallographic orientation. The calculation method for the solid/liquid interface curvature was also improved. The effect of interfacial energy anisotropy on the dendritic growth behavior was analyzed.
Homogenisation of Cast Microstructures: Thermodynamic Calculation and Kinetic Simulation
Authors: Guo Zhan Li , Miodownik Alfred Peter , Qin Rong Shan
Published: June 2010

This paper uses a combination of thermodynamic calculation and kinetic simulation to model the homogenisation process of cast microstructure for multi-component alloys. The approach assumes that the solute segregation profile across the half dendrite arm spacing can be scaled to the solute concentration profile during solidification as generated by a Scheil type calculation. When secondary phases dissolve during homogenisation, they are treated as an additional fraction of pseudo-eutectic to the initial solute concentration profile of the primary solution phase. The methodology is compared with the assumptions made by other authors, highlighting the significant advantages in the present treatment. Examples are drawn from a cast nickel-based superalloy.
Influence of Silicon on the Spheroidization of Cementite in Hypereutectoid Bearing Steels
Authors: Kim Kwan Ho , Lee Jae Seung , Lee Duk Lak
Published: June 2010

The influence of silicon on the spheroidization of cementite in hypereutectoid 1.0C-1.45Cr bearing steels has been investigated, on the basis of microstructural analysis and thermodynamic calculations. The silicon content was varied 0.25 to 2.00 in weight percent. Annealed at 790∼850°C for 6 hr, the 0.25Si and 1.00Si steels were entirely spheroidized at 790°C, while 1.50Si and 2.00Si steels at 830°C, respectively. This implies that the increase of silicon content in hypereutectoid steels retards the spheoridization of cementite. The thermodynamic calculations revealed that silicon atoms were partitioned into not cementite but austenite at annealing temperatures, and the increase of silicon content can raise the chemical potential of carbon atoms within austenite at austenite/cementite interfaces, causing the decrease of driving force for the diffusion of carbon atoms from cementite to austenite.
Thermal Modeling of Direct Digital Melt-Deposition Processes
Authors: Cooper Khershed P. , Lambrakos Samuel G.
Published: June 2010

Additive manufacturing involves creating three-dimensional objects by depositing materials layer-by-layer. The freeform nature of the method permits the production of components with complex geometry. Deposition processes provide one more capability, which is the addition of multiple materials in a discrete manner to create “heterogeneous” objects with locally controlled composition. The result is direct digital manufacturing (DDM) by which dissimilar materials are added voxel-by-voxel (a voxel is volumetric pixel) following a predetermined tool-path. A typical example is functionally-graded material such as a gear with a tough core and a wear resistant surface. The inherent complexity of DDM processes is such that process modeling based on direct physics-based theory is difficult, especially due to a lack of temperature-dependent thermo-physical properties and particularly when dealing with melt-deposition processes. To overcome this difficulty the inverse problem approach is adopted to develop thermal models for multi-material, direct digital melt-deposition. This approach is based on the construction of a numerical-algorithmic framework for modeling anisotropic diffusivity such as that which would occur during energy deposition within a heterogeneous work-piece. This framework consists of path-weighted integral formulations of heat diffusion according to spatial variations in material composition and requires consideration of parameter sensitivity issues.
A Multi-Scale Constitutive Model in High Temperature Deformation of Near Alpha Ti-5.6Al-4.8Sn-2.0Zr Alloy
Authors: Li Miao Quan , Luo Jiao
Published: June 2010

Isothermal compression of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy is conducted on a Thermecmaster-Z simulator at the deformation temperatures ranging from 1173 K to 1333 K, the strain rates ranging from 0.001 s-1 to 10.0 s-1 at an interval of an order magnitude and the height reductions ranging from 50% to 70%. The primary grain size is measured at an OLYMPUS PMG3 microscope with the quantitative metallography SISC IAS V8.0 image analysis software. A multi-scale constitutive model coupling the grain size, volume fraction and dislocation density is established to represent the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation, in which the flow stress is decomposed a thermal stress and an athermal stress. A Kock-Mecking model is adopted to describe the thermally activated stress, and an athermal stress model accounts for the working hardening and Hall-Petch effect. A genetic algorithm (GA)-based objective optimization technique is used for determining material constants in this study. The mean relative difference between the predicted and experimental flow stress is 5.98%, thus it can be concluded that the multi-scale constitutive model with high prediction precision can efficiently predict the deformation behavior of near alpha Ti-5.6Al-4.8Sn-2.0Zr alloy in high temperature deformation.
Role of Microstructure in Susceptibility of X70 Pipeline Steel to Hydrogen Embrittlement
Authors: Hejazi D. , Haq A.J. , Yazdipour N. , Dunne D.P. , Barbaro Frank J. , Pereloma Elena V.
Published: June 2010

In order to investigate the susceptibility of steels to hydrogen embrittlement as a function of their microstructure X70 steel was chosen in different conditions: normalized transfer bar, as-received hot rolled strip and heat affected zone (HAZ). Notched and fatigue pre-cracked samples were subjected to electrochemical hydrogen charging to achieve 2 ppm hydrogen content. Three point bend tests were conducted on as-received and hydrogen charged samples. The results showed that HAZ samples are more susceptible to hydrogen embrittlement than the others. This was supported by fracture surface observations.
The Material Flow Analysis in the Modified Orbital Forging Technology
Authors: Nowak Jaroslaw , Madej Łukasz , Grosman Franciszek , Pietrzyk Maciej
Published: June 2010

The main aim of this work is the computer aided design of the new orbital forging process. The finite element model was developed and used in research on possibility of modification of the classical orbital forging technology based on the Marciniak press to obtain more effective process. Obtained numerical results from simulations of the new orbital process are compared with the experimental analysis, performed on the orbital press with the developed device. However, due to the novelty of the developed approach the investigation on direction of material flow during deformation is of particular interest in this work. Direction of material flow and strain path change effect due to incremental character of deformation is analyzed. Obtained results confirm good predictive capability of the FE model and are the basis for the comparison of the two processes and discussion on the effectiveness of the modified incremental forming process.
Determination of Interphase Thickness and Mechanical Properties of Effective Nanofillers in Polymer Nanocomposites by Molecular Dynamic Simulation
Authors: Xu Wen , Zeng Qing Hua , Yu Ai Bing , Paul Donald R.
Published: June 2010

The properties of interphase in polymer composites are often different from those of bulk polymer matrix, which may include chemical, physical, microstructural, and mechanical properties. The nature of interphase is critical to the overall properties and performance of polymer materials, in particular in nanofiller reinforced composites. Experimental efforts have been made to determine the effective interphase thickness and its properties, for example, by nanoindentation and nanoscratch techniques. Yet, it is very difficult to quantify the interphase and its properties because of its nanoscale nature and the unclear boundary. In this regard, computer simulation, e.g., molecular dynamics, provides an effective tool to characterize such interphase and the properties. In this work, molecular dynamics simulations are applied to quantify the interphase thickness in clay-based polymer nanocomposites. Then, the mechanical properties of the so-called effective nanofiller (i.e., the physical size of nanofiller plus the thickness of interphase) will be determined by a series of simulations.
First-Principles Investigation of the Electronic Structure and Magnetic Properties for Co-Doped Fe3O4
Authors: Hou Yu Hua , Zhao Yu Jun , Zeng De Chang , Liu Zhong Wu , Wen Li Shi
Published: June 2010

The electronic structure and magnetic properties of the (Co1-xFex)Tet(CoxFe2-x)OctO4 spinels (x is deﬁned as the degree of inversion) scenario are investigated theoretically from first-principles, using generalized gradient approximation (GGA) method for the systems with strong coulomb correlations, which gives a correct description of the electronic structure. The GGA+U method gives an improved qualitative result compared with the GGA not only for the excited-state properties such as energy gaps but also for the ground-state properties such as magnetic moments and crystal parameters. The nominal valence of the transition metal elements and the ground state structure have been established based on the study of variation of the cation distribution (x=0.0, 0.25, 0.5, 0.75 and 1.0) over the tetrahedral and octahedral sites. The site-preference calculation on bulk systems indicates that Co2+ ions strongly prefer the octahedral B sites, and the electronic structure and magnetic properties of cobalt ferrites highly depend on the cation distributions even though the chemical composition of the compound does not change. The results are in good agreement with the available experimental data and most of the other theoretical results.
Study of Deposition of Aluminum Nitride Thin Films by Hollow Cathode Electron Beam Vapor Deposition Method
Authors: Mu Zong Xin , Mu Xiao Dong , Wang Chun , Dong Chuang
Published: June 2010

Aluminum nitride (AlN) thin films were deposited on (100) oriented silicon wafers substrates by Hollow Cathode Electron Beam Vapor Deposition system (HCEBVD) under various Ar/N2 mass flow ratio. The films were characterized by Atomic Force Microscopy (AFM), Glancing Incident X-ray Diffraction (GIXRD) techniques and Ultraviolet/Visible Spectrophotometer (UV/VIS). It was found that the thin films are polycrystalline and have a hexagonal wurtzite structure with (002) preferred orientation, as revealed by GIXRD. AFM analysis indicates that the surface of the thin films is smooth, with average RMS (Root Mean Square) roughness Ra of 0.7nm, which is suitable for application in surface acoustic wave devices. The film thickness and optical refractory properties of the AlN thin films were investigated.
Fabrication of Co/Cu Multilayered Nanowires Using a Pulsed Current Deposition Technique
Authors: Ohgai Takeshi , Hashiguchi Keisuke , Morimura Takao , Takao Keizo , Kagawa Akio
Published: June 2010

Co/Cu multilayered nanowires with 40 nm in diameter were fabricated using a pulsed current deposition technique into a nanoporous template with numerous nanochannels. To determine the optimum electrodeposition condition of Cu and Co into the template, cathodic polarization behavior was examined at a wide range of cathode potential. Time-dependence of deposition current was monitored to determine the growth rate of Co and Cu nanowires. Co layer and Cu layer thicknesses were adjusted to several tens nanometers, by controlling the deposition times. With decreasing the each layer thickness, the coercive force of Co/Cu multilayered nanowires was decreased and the soft magnetic property was improved.
Effect of Iodine Doping on Surface and Optical Properties of Polyterpenol Thin Films
Authors: Bazaka Kateryna , Jacob Mohan V.
Published: June 2010

This study presents the effect of iodine doping on optical and surface properties of polyterpenol thin films deposited from non-synthetic precursor by means of plasma polymerisation. Spectroscopic ellipsometry studies showed iodine doping reduced the optical band gap from 2.82 eV to 1.50 eV for pristine and doped samples respectively. Higher levels of doping notably reduced the transparency of films, an issue if material is considered for applications that require high transparency. Contact angle studies demonstrated higher hydrophilicity for films deposited at increased doping levels, results confirmed by XPS Spectroscopy and FTIR. Doping had no significant effect on the surface profile or roughness of the film.
Scale-Bridging Analysis of Stress Partitioning in High Nitrogen Steel
Authors: Ojima Mayumi , Adachi Yoshitaka , Tomota Yo
Published: June 2010

To understand the reason of high work hardening in high nitrogen steel, a scale-bridging analysis consisting of in situ neutron diffraction, in situ electron backscattering diffraction measurement during tensile deformation and weak beam transmission electron microscopy was performed with particular attention to stress partitioning. This study demonstrates the contribution of stress partitioning, back stress due to dislocation pile-up at grain boundaries and dislocation interaction to work hardening at each strain level.
Effect of Interlayer Thickness on Stress and Dielectric Properties of MgTiO3 Modified (Ba,Sr)TiO3 Multilayer Thin Films
Authors: Lu Sheng Bo , Xu Zheng Kui
Published: June 2010

Ba0.6Sr0.4TiO3 (BST)/MgTiO3 (MT)/ Ba0.6Sr0.4TiO3 multilayer thin films were deposited on LaNiO3 (100)/Pt/Ti/SiO2/Si (100) substrates by pulsed laser deposition. It was found that the film orientation and dielectric properties of BST/MT/BST multilayer thin films are strongly dependent on MT interlayer thickness. Pure BST thin film exhibits a (100) preferred orientation, while BST thin films with a MT interlayer exhibit a random orientation. Residual stress is relaxed dramatically due to a closer match of thermal expansion coefficients between the BST and MT interlayers. The largest figure of merit of 18.7 is achieved in the multilayer thin film with a 50-nm-thick MT interlayer, which exhibits a tunability of 30% and a lost tangent of 0.016. Dielectric constant and loss tangent decrease with increasing MT interlayer thickness due to a series dielectric dilution effect.
Numerical Simulation for Surface Modification of Thermal Barrier Coatings by High-Current Pulse Electron Beam
Authors: Qin Ying , Qu Wei , Mei Xian Xiu , Hao Sheng Zhi , Zhao Ji Jun , Lu Wen , Dong Chuang
Published: June 2010

High current pulsed electron beam is an effective technique for surface sealing of ceramic thermal barrier coatings prepared by electron beam physical vapor deposition. Due to the rapid remelting and solidification, the outer layers of ceramic coatings become smooth and dense, and the protective performance for turbine blades is effectively improved. Because of the complex multi-layered structures in the coatings, a high-current pulsed electron beam treatment requires specific parameter inputs which are related to the temperature field induced by electron energy deposition in the coatings. In this paper, a two-dimensional temperature simulation was performed to demonstrate the melting depth and temperature evolution in ceramic coatings treated by high-current pulsed electron beam. Different energy densities and pulses were studied and discussed for obtaining optimized parameters.
Multilayered Approach to Step-Edge Josephson Junctions
Authors: Shcherbakova Olga V. , Pan Alexey V. , Fedoseev Sergey , Dou Shi Xue , Lam Simon K.H. , Du Jia , Foley Cathy P.
Published: June 2010

Multilayered approach to YBCO-based Josephson junction manufacture is introduced. Properties of monolayer YBa2Cu3O7 (YBCO) and multilayer YBCO/NdBCO/YBCO junctions of similar thickness grown by pulsed-laser deposition on MgO (100) substrates has been analysed and compared. The influence of the multilayered structure on junction behaviour and properties are presented and discussed.
Investigation of Super-Hydrophobic Coatings with Hierarchical Structures Surface on Mild Steel
Authors: Zhang Zhan Ping , Qi Yu Hong , Zhang Yan , Mo Gui Ke , Wang Jing Zhao
Published: June 2010

A hierarchical roughness surface with micro-and nano-structures was fabricated on mild steel by chemical etching with a mixture acid (2%HNO3 + 6%H2SO4 + 6%H3PO3) solution. The surface was modified by fluoroalkylsilane. The wettability of the modified surfaces was studied by contact angle method and Electrochemical Impedance Spectroscopy (EIS), and their morphology was investigated by Scanning Electron Microscopy (SEM). The roughness of the steel etched consisted of fine micro-steps in grains. The treated surface exhibited super-hydrophobic properties, water contact angle is high to 152° after modification for 6 min at room temperature. The results indicated that with the increase of etching time, the hierarchical structure gradually formed on the surface and the contact angle gradually decreased.
The Investigation of the Interdiffusion Barrier in TiAl/MCrAlY System
Authors: Wang Wen , Cheng Yu Xian , Zhu Sheng Long , Wang Fu Hui , Xin Li
Published: June 2010

TiAl based alloys are promising candidates for structural applications at high temperature. However, the poor oxidation resistance above 800oC obviously restrains their applications. Although NiCrAlY overlay coatings can remarkably improve the high temperature oxidation resistance of TiAl, serious inward diffusion of Ni from the coating to the substrate occurs which could reduce the lifetime of the coating/substrate system. Apparently, the development of interdiffusion barrier could overcome the disadvantage of the NiCrAlY/TiAl system. In this work, Ta, TiN and Cr2O3 interlayers were deposited between NiCrAlY coating and γ-TiAl substrate as diffusion barrier (DB). The interdiffusion behavior of the TiAl/DB/NiCrAlY system was investigated at 1000°C. The results showed that the metallic and nitride interlayers cannot retard the interdiffusion of Ni effectively. As an active diffusion barrier, the oxide interlayer obviously suppressed the inward diffusion of Ni from the coating to the substrate by the formation of alumina-rich layers at both the TiAl/DB and DB/NiCrAlY interfaces.
Influence of Cryomilling on Microstructure, Phase Stability and Oxidation Behavior of NiCrAlY Bond Coat in Thermal Barrier Coatings: Experimentation and Mechanistic Investigation
Authors: Ma Ka Ka , Schoenung Julie M.
Published: June 2010

Improved thermal cycling lifetime has been observed in thermal barrier coatings (TBCs) with cryomilled NiCrAlY bond coat. To understand this improved behavior, a robust experimental investigation is coupled with mechanistic explanations to describe the influence of cryomilling on microstructure, phase stability and oxidation behavior of the bond coat. It is found that cryomilling results in two significant changes in the NiCrAlY bond coat: unintentional Fe additions and creation of a homogeneous distribution of ultrafine oxide/nitride dispersoids. Through extensive microstructural analysis combined with computational simulation using Thermo-Calc® software, it is determined that the presence of Fe stabilizes the high temperature γ and β phases in the NiCrAlY bond coat, corresponding to a decrease in the transformation temperature. The results are explained on the basis of the Gibbs free energy for the individual phases. Characterization of the thermally grown oxide (TGO) in TBCs after isothermal oxidation with rigorous statistical evaluation indicates that the TGOs in the TBCs with the cryomilled bond coats are more uniform in thickness and slower growing. Both behaviors are attributed to the more homogeneous distribution of oxide dispersoids, which are a direct result of the cryomilling, yet remain stable after extensive thermal exposure.
High Temperature Corrosion of Fe-Cr, Fe-Al, Fe-Si and Fe-Si-Al Alloys in CO2-H2O Gases
Authors: Gheno Thomas , Li Huan , Zhang Jian Qiang , Young David J.
Published: June 2010

Iron and model alloys containing 2.25, 9, and 20 wt% Cr, 2, 4 and 6 wt% Al, 1, 2 and 3 wt% Si, and dilute Fe-Si-Al ternaries were reacted in dry and wet Ar-CO2 gases at 800°C. External oxide scales grew on Fe according to fast, linear kinetics in dry CO2. Additions of H2O accelerated the reaction until steady-state parabolic kinetics were achieved. High Cr content alloys developed slow-growing chromium-rich oxide scales. Dry CO2 mixtures produced faster rates than wet gas mixtures. Lower Cr alloys developed thicker iron oxide scales, featuring cavities, cracks and poor adherence, and sustained internal oxidation. The presence of H2O led to even higher oxidation rates. Aluminium additions to iron of up to 4 wt% provided no protection, but instead caused internal oxidation. A level of 6 wt% significantly slowed oxidation by forming a continuous Al2O3 layer. Silicon additions had little effect, apart from promoting internal oxidation. However, simultaneous alloying with aluminium and silicon strongly depressed corrosion rates. The effectiveness of different alloy additions is discussed, along with the effects of water vapour and carbon activities, in the context of oxyfuel combustion technology.
Surface Modification for Enhanced Corrosion Resistance Using Fluid Bed Reactor Chemical Vapour Deposition (FBR-CVD)
Authors: Ralston Kevin D. , Fabijanic Daniel , Birbilis Nick
Published: June 2010

The use of materials with otherwise desirable mechanical properties is often problematic in practice as a result of corrosion. Susceptibility may arise for a number of reasons, including an electrochemically heterogeneous surface or destabilisation of a passive film. These shortcomings have historically been overcome through the use of various coatings or claddings. However, a more robust surface layer with enhanced corrosion resistance could possibly be produced via local surface alloying using a fluidised bed. A fluidised bed treatment allows a surface to be alloyed, producing a distinct surface layer up to tens of microns thick. Surface alloying additions can be selected on the basis of whether they are known or suspected to enhance the corrosion resistance of a particular material, whilst at a minimum, surface alloying likely provides a more electrochemically homogeneous surface. Electrochemical evaluations using potentiodynamic polarisations in NaCl electrolytes have shown chromised plain carbon and stainless steel surfaces have decreased rates of corrosion, decreased passive current densities, and ennobled pitting potentials relative to untreated specimens.
Corrosion Behavior of 6000 Series Aluminum Alloys Produced by Conventional and Powder Extruded Process through Electrochemical Impedance Method
Authors: Sunada Satoshi , Nunomura Norio , Majima Kazuhiko
Published: June 2010

In this study, the electrochemical measurements such as the potentiodynamic polarization and the electrochemical impedance spectroscopy (EIS) tests were carried out in order to clarify the corrosion behavior of the aluminum alloys fabricated by powder extruded (P/E) process compared with those by ingot metallurgy (I/M) process, using 6000 system aluminum alloys. Two kinds of aluminum specimens; one is fabricated by the conventional I/M specimen and the other is fabricated by the P/E process, were used for the electrochemical experiment in the sulfuric acid solution with 0.5 kmol/m3 concentration. Both of I/M and P/E specimens showed the linear relationship between the electrochemical potential (E) and the common logarithm of current density (icorr) in the cathodic region where Tafel law was recognized irrespective of stirring of the test solution though the icorr was slightly increased by stirring for both specimens. On the other hand, in the anodic region, both of the two specimens indicated the almost the same icorr irrespective of stirring. These experimental results interpret that the corrosion is controlled by the chemical reaction. The EIS test indicated that the maximum charge transfer resistance (Rct) was observed at -0.55 V which is 0.11 V higher potential than the corrosion potential (Ecorr) for both of the two specimens.
Environmental Impact Evaluation and Rationalization of Ceramics Process on the Basis of Exergy Analysis
Authors: Kita Hideki , Hyuga Hideki , Nagaoka Takaaki , Kondo Naoki
Published: June 2010

In order to lower environmental impact in manufacturing, it is necessary to know the processes of consumption and emission of resource and energy with bird’s eyes view point. In this paper, exergy analysis was conducted in case when heater tube used in the molten aluminum was made of steel and ceramics. As results, it is revealed that ceramics have effectiveness in the reduction of environmental burden through the lifecycle process, while ceramics consumes much higher exergy than the steel one in production stage.
Optimization of Dielectric Properties of Glass Added BaxSr1-xTiO3 Ceramics for Pulsed Power Applications
Authors: Zhang Qing Meng , Wang Lei , Luo Jun , Tang Qun , Du Jun
Published: June 2010

BaxSr1-xTiO3 (0.2≤x≤0.5) ceramics with 10 vol% BaO-SiO2-B2O3 glass addition were prepared. The microstructure and dielectric properties were investigated by XRD, SEM, ferroelectric tester and impedance analyzer. The results show that with the decrease of x, the pulse breakdown strength of the samples is increased, and the dielectric constant and dielectric loss is decreased gradually. In the frequency from 10 kHz to 20 MHz, the dielectric constant of all the samples show good frequency stability. For x=0.2, the samples exhibit high breakdown strength of 37.7 kV/mm, moderate dielectric constant of 311 and low dielectric loss of 5×10-4,which is a promising dielectric for pulsed power applications.
Effect of Ti Content on Microstructure and Mechanical Properties of Si3N4/Si3N4 Joints Brazed with Ag-Cu-Ti+Mo Composite Filler
Authors: Zhang Jie , He Yan Ming
Published: June 2010

Mo particles have been introduced into Ag-Cu-Ti brazing alloy for the joining of Si3N4 ceramic. Effects of Ti content on microstructure and mechanical properties of the joints were investigated. The results present that a compact reaction layer which is composed of TiN and Ti5Si3 was formed at the Si3N4/solder interface. The central part of the joint was composed of Ag based solid solution, Cu based solid solution, Mo particles and Cu-Ti intermetallics. By increasing Ti content in the composite filler, both the thickness of reaction layer and the amount of Cu-Ti intermetallics in the joint increased, which is beneficial for the joint strength. However, the reaction between Ti and Si3N4 proceeded more excessively. Simultaneously, more Cu-Ti intermetallics were precipitated while elevating Ti content to 6wt.%, leading to deterioration of the bonding strength. The maximum bending strength (429.4MPa) was obtained when Ti content is 4wt.% in the composite filler.
Influence of Fiber Properties on the Performance of Piezoelectric 1-3 Composites
Authors: Peng Wei Wei , Zhou Jing , Xu Lei , Chen Wen
Published: June 2010

In this work, 1-3 composites, which required for different devices applications, with the (PZT)-based (PZT-5, PMnS-PZN-PZT and PSN-PZN-PZT) piezoelectric fibers produced via a VPP method have been investigated. The relationship between the dielectric and piezoelectric properties of the 1-3 composites and different ceramic fibers with various aspect radios has been compared. We conclude that the properties of the 1-3 composites are well followed with the properties of the piezoelectric fibers, so the performance of the 1-3 composites can be improved for various devices by tuning the fiber properties.
Mathematical Modeling of Polymer Biodegradation and Erosion
Authors: Chen Yu Hang , Li Qing
Published: June 2010

The biodegradable polymers are widely used in therapeutic surgery and pharmaceutics, in which the degradation process has drawn significant attention in recent years. In this paper, we propose a mathematical model to predict the polymer degradation in tissue engineering applications. A stochastic model is introduced to characterize the hydrolysis reaction in an elemental basis and the mass transport is also performed to investigate the diffusive transport of polymer erosion. Two representative polymeric films in different configurations are studied. It is found that for biodegradable systems, mass transport plays an important role in controlling the erosion pathway, in which the matrix configuration could be one of the key factors that determine the characteristics of erosion and drug release rates. The proposed model makes a useful benefit to the design optimization of the matrix architectures for biodegradable devices.
Effect of the Addition of Gd on Ni53Mn22Co6Ga19 High-Temperature Shape Memory Alloy
Authors: Ma Yun Qing , Yang Shui Yuan , Lai San Li , Tian Shi Wen , Wang Cui Ping , Liu Xing Jun
Published: June 2010

The rare earth element Gd is added to Ni53Mn22Co6Ga19 high-temperature shape memory alloy to refine the grain size and adjust the distribution of γ phase, and their microstructure, martensitic transformation behaviors, mechanical and shape memory properties were investigated. The results show that the grain size is obviously decreased and the γ phase tends to segregate at grain boundaries with increasing Gd content. Small amounts of Gd-rich phase were formed with 0.1 at.% Gd addition. The martensitic transformation temperature abruptly increases with 0.1 at.% Gd addition, then almost keeps constant with further increasing Gd content. The addition of 0.1 at.% Gd is proved to be beneficial to both tensile stress and strain before fracture, but negative to the shape-memory effect.
A Pilot Rolling Mill Designed for High Strength Steels
Authors: Jiao Zhi Jie , Li Jian Ping , Sun Jie
Published: June 2010

High strength steels, such as austenitic stainless steel, Transformation Induced Plasticity (TRIP) steel and silicon steel, have significant work hardening during cold rolling, which in turn induces a quickly increased rolling force. Tension plays a very important role in the reduction of the rolling force. However, coiler tension control system used in the classic experimental rolling mill requires long-scale strip, which cannot be satisfied for most experimental cases. To overcome this drawback, a new pilot rolling mill has been developed. The horizontally located hydraulic cylinders and clamps have been used to apply tension to the rolled short-scale strip. With this rolling mill, the austenitic stainless steel strip, TRIP steel strip and other high strength strips have been studied.
Effect of Nitrogen Addition on Mechanical Property of Ti-Cr-Sn Alloy
Authors: Nakahira Yuichi , Inamura Tomonari , Kanetaka Hiroyasu , Miyazaki Shuichi , Hosoda Hideki
Published: June 2010

Effect of nitrogen (N) addition on mechanical properties of Ti-Cr-Sn alloy was investigated in this study. Ti-7mol%Cr-3mol%Sn was selected and less than 0.5wt% of N were systematically added. The alloys were characterized by optical microscopy, X-ray diffraction analysis and tensile tests at room temperature. The apparent phase was β (bcc) phase, whereas the presence of precipitates was confirmed in 0.5wt%N-added alloy only which did not exhibit sufficient cold workability. The grain size was not largely affected by N addition being less than 0.5wt%. Tensile tests revealed that less than 0.5wt%N addition improves the strength which is due to the solution hardening by interstitial N atoms.
Effect of Aging on Mechanical Properties of Ti-Mo-Al Biomedical Shape Memory Alloy
Authors: Hosoda Hideki , Taniguchi Makoto , Inamura Tomonari , Kanetaka Hiroyasu , Miyazaki Shuichi
Published: June 2010

Effects of single- and multi-step aging on mechanical properties and shape memory properties of Ti-6Mo-8Al (mol%) biomedical shape memory alloy were studied using tensile tests at room temperature (RT). The solution-treated alloy at RT was two phase of bcc β and martensite α". Tensile tests revealed that the solution-treated alloy exhibited good shape memory effect. As for the single-step aging, (1) pseudoelastic shape recovery by unloading was observed after aging at 623K, (2) the alloy became brittle after aging at 773K due to ω embrittlement, and (3) strength was improved with small shape memory effect by aging at 1023K. On the other hand, after a multistep aging at 773K-1023K-1123K, the alloy was strengthened and showed perfect shape recovery. The improvement must be achieved by the formation of fine and uniform hcp α precipitates.
Grain Refining Technique and Mechanical Properties of the Biomedical Co-Cr-Mo Alloy
Authors: Kurosu Shingo , Li Yun Ping , Matsumoto Hiroaki , Chiba Akihiko
Published: June 2010

Thermomechanical processes combined with reverse transformation from -hcp and M2N) dual-phase to -fcc phase of biomedical Co-Cr-Mo-N alloys were examined. According to XRD analysis, the reverse transformation from  to  is completed after heat treating at 1223 to 1373 K without deformation, while after heat treating at 1223 and 1273 K contained residual M2N particles in the  matrix. After the subsequent hot compression at condition at 1273 K and strain rate less than 1 s-1, and 1223 K and strain rate less than 10 s-1, ultra fine grains less than 1 m with residual M2N were obtained. Therefore, it is suggested that the residual M2N suppressed further growing of DRXed grain. The obtained microstructure with ultra fine grain dispersed with residual M2N was obtained to demonstrate both grain refining strengthening and precipitation strengthening.
Effect of Grain Boundary Segregated Dopant on Phase Stability in Tetragonal Zirconia Polycrystal
Authors: Takigawa Yorinobu , Yamamoto Takahisa , Higashi Kenji
Published: June 2010

The effect of grain boundary segregated dopant on phase stability of tetragonal zirconia polycrystal (TZP) is examined by accelerated exposure tests ageing in hot water. The materials used in this study are 3 mol%Y2O3 stabilized TZP (3Y-TZP) and 0.1mol%SiO2-doped 3Y-TZP. Accelerated exposure tests in an autoclave reveal that the tetragonal phase stability of 3Y-TZP in water is highly affected by the grain boundary segregated dopant and the grain size. When the grain size of TZP is about 0.55μm, the change in phase transformation behavior with dopant is explained from the change in grain boundary diffusivity of hydroxyl ion. Grain boundary diffusion of hydroxyl ion must be blocked by the presence of some segregated ion which reduces the effective area of grain boundary diffusion. On the other hand, when the grain size is about 0.35μm, the phase transformation behavior seems to be controlled by the grain boundary stress. Decreased grain boundary stress by the segregation of some dopant must enhance the phase transformation of 3Y-TZP.
Evaluation of Mechanical Properties of Regenerated Bone by Nanoindentation Technique
Authors: Ishimoto Takuya , Nakano Takayoshi
Published: June 2010

To evaluate the material parameters of regenerated bone, it is important to clarify the mechanical performance of the regenerated portion. In general, the shape and size of regenerated bone tissue is heterogeneous. It is often difficult to elucidate material properties by means of conventional mechanical tests such as compressive and/or tensile tests and bending tests. The nanoindentation technique has been utilized to evaluate the material properties of small or microstructured materials because they do not necessarily require a large well-designed specimen. Thus, this technique may be useful for the evaluation of the material properties of regenerated bone tissue. In this study, this technique was applied for the assessment of the Young’s modulus and hardness of regenerated and intact long bones of a rabbit. The regenerated bone exhibited a significantly lower Young’s modulus and hardness than the intact bone. The regenerated long bone also exhibited impaired mechanical properties, which may have been caused by the difference in the nano-organization of its collagen fibers and mineral crystals (the main components of bone tissue), from that of the intact bone.