bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Properties of E21-base Co3AlC and the Correlation with the Ordering of Carbon Atoms and Vacancies
Authors: Kimura Yoshisato , Wei Fu-Gao , Ohtsuka Hideyuki , Mishima Yoshinao 
Published: April 2011

ABSTRACTTargeting to develop E21 Co3AlC based heat resistant alloys, phase stability of E21 Co3AlC and (Co, Ni)3AlC has been investigated together with the magnetic properties of E21’ Co3AlC0.5 which is formed by the extra ordering of carbon atoms accompanying anti-phase boundary (APB). The correlation of ferromagnetism with APB in E21’ Co3AlC0.5 was evaluated using single crystals by high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer. Anti-phase domain (APD) size affects the ferromagnetism: for instance, the saturation magnetization becomes larger as the APD size is smaller. Local atomic configuration at APB was clearly observed by HRTEM image.
Thermal Analysis of Relaxation Processes of Supersaturated Vacancies in B2-Type Aluminides
Authors: Nakamura Ryusuke , Yoshimi Kyosuke , Yamauchi Akira , Hanada Shuji 
Published: April 2011

ABSTRACTRelaxation behavior of supersaturated vacancies in water-quenched and rapidly solidified B2 type CoAl and NiAl with the stoichiometric composition was studied by differential scanning calorimetry (DSC). In both CoAl and NiAl quenched from 1773 K, a single exothermic peak due mainly to the recovery of supersaturated vacancies appeared near 950 K. On the other hand, the exothermic peak was also observed in as-spun rapidly solidified CoAl and NiAl ribbons, and the temperature range of the peak was much broader than that of quenched-in bulks, suggesting that the peak in the rapidly solidified ribbons results from not only a single recovery process of vacancies but also those of some other lattice defects. TEM observation showed that a large amount of dislocations were introduced in the NiAl ribbon and that comparatively many voids as well as an amount of dislocations were introduced in the CoAl ribbon.
Parameters of Dislocation Structure and Work Hardening of Ni3Ge
Authors: Koneva N. A. , Solov'eva Yu.V. , Starenchenko V. A. , Kozlov E. V. 
Published: April 2011

ABSTRACTOrientation dependence of the yield stress temperature anomaly in Ni3Ge single crystals with the L12 structure was investigated during compression tests. The measurements were carried out in the 4.2 K-1000 K temperature interval for two orientations of single crystals, [001] and [234]. The dislocation structure was studied by TEM. Quantitative measurements of different parameters of dislocation structure were carried out. The values of the scalar dislocation density, ρ, were determined for different temperatures in the deformation interval from the yield stress up to fracture. Temperature dependence of the friction stress τF (T) and the interdislocation interaction parameter α(T) were also obtained. The change in the fraction of straight dislocations as a function of temperature was analyzed.
High Temperature Oxidation Behavior of Al Added Mo / Mo5SiB2in-situ Composites
Authors: Yamauchi Akira , Yoshimi Kyousuke , Hanada Shuji 
Published: April 2011

ABSTRACTIsothermal oxidation behavior of Mo/Mo5SiB2in-situ composites containing small amounts of Al was investigated under an Ar-20%O2 atmosphere in the temperature range of 1073–1673 K. The Mo/Mo5SiB2in-situ composites, (Mo-8.7mol%Si-17.4mol%B)100-xAlx (x=0, 1, 3, and 5mol%), were prepared by Ar arc-melting, and then homogenized at 2073 K for 24 h in an Ar-flow atmosphere. Without addition of Al, Mo/Mo5SiB2in-situ composite exhibits a rapid mass loss at the initial oxidation stage, followed by passive oxidation after the substrate is sealed with borosilicate glass in the temperature range of 1173–1473 K, whereas it exhibits a rapid mass gain around 1073 K. On the other hand, small Al additions, especially of 1 mol%, significantly improve the oxidation resistance of Mo/Mo5SiB2in-situ composites at temperatures from 1073–1573 K. The excellent oxidation resistance is considered to be due to the rapid formation of a continuous, dense scale of Al-Si-O complex oxides. The protective oxide scales contain crystalline oxides, and the amounts of the crystalline oxides obviously increase with Al concentration.
Nucleation of (Mo) Precipitates on Dislocations During Annealing of a Mo-rich Mo5SiB2 Phase
Authors: Sekido Nobuaki , Sakidja Ridwan , Perepezko John H. 
Published: April 2011

ABSTRACTUpon annealing an as-cast Mo-10Si-20B alloy at high temperatures, a Mo solid solution phase precipitates within a supersaturated Mo5SiB2 phase. The precipitation behavior of the Mo solid solution was investigated by means of transmission electron microscopy and X-ray diffractometry. It is found that the Mo5SiB2 phase in a Mo-10Si-20B alloy contains a significant amount of structural vacancies in the as-cast state. The excess vacancies are removed to form dislocations during annealing, which provides the heterogeneous nucleation sites for the (Mo) precipitates.
Structural Properties and Magnetic Behavior in the Pseudobinary Alloys CoFe-CoAl
Authors: Tadachi Nobutoshi , Ishibashi Hiroki , Kogachi Mineo 
Published: April 2011

ABSTRACTStructural properties and magnetic behavior in pseudobinary alloys CoFe1−x Alx are studied. The B2-phase exists stably over wide ranges of composition and temperature and the Heusler-phase appears around the stoichiometric composition (0.4< x< 0.6 ) below about 973K. The mean magnetic moment in the B2-phase region decreases nearly linearly with increase in x in x > 0.2. Further, it decreases with increase in quenching temperature in x < 0.4, while it remains almost constant in x > 0.4. The mean magnetic moment of Heusler alloy Co2FeAl (x = 0.5) has the value of 1.30μB/atom, nearly the same as in the B2-phase, and shows no remarkable quenching temperature dependence.
The Creep Behaviors of Two Fine-grained XD TiAl Alloys Produced by Similar Heat Treatments
Authors: Zhu Hanliang , Seo Dongyi , Maruyama Kouichi , Au Peter 
Published: April 2011

ABSTRACTThe microstructural characteristics and creep behavior of two fine-grained XD TiAl alloys, Ti-45Al and 47Al–2Nb–2Mn+0.8vol%TiB2 (at%), were investigated. A nearly lamellar structure (NL) and two kinds of fully lamellar (FL) structures in both alloys were prepared by selected heat treatments. The results of microstructural examination and tensile creep tests indicate that the 45XD alloy with a NL structure possesses an inferior creep resistance due to its coarse lamellar spacing and larger amount of equiaxed γ grains at the grain boundaries, whereas the same alloy in a FL condition with fine lamellar spacing lowers the minimum creep rates. Contrary to 45XD, the 47XD alloy with a NL structure exhibits the best creep resistance. However, 47XD with a FL structure with finer lamellar spacing shows inferior creep resistance. On the basis of microstructural deformation characteristics, it is suggested that the well-interlocked grain boundary and relatively coarse colony size in FL and NL 47XD inhibit sliding and microstructural degradation at the grain boundaries during creep deformation, resulting in better creep resistance. Therefore, good microstructural stability is essential for improving the creep resistance of these alloys.
Formation and Morphology of Kurnakov Type D022Compound in Disordered fcc γ-(Ni, Fe) Matrix Alloys
Authors: Suzuki Akane , Takeyama Masao 
Published: April 2011

ABSTRACTFormation and morphology of D022compound Ni3V in γ-fcc alloys were investigated as a model case in order to understand fundamentals for microstructure control of new class of austenitic steels strengthened by Kurnakov-type GCP intermetallic compound. The formation process of the D022phase in γ matrix varies, depending on the composition and heat treatment temperature, and precipitation of D022takes place at temperature above T0in the γ+D022two phase region. The morphology of coherent precipitates of the D022compound is sensitive to misfit strains against matrix and can be controlled by alloying addition. The habit planes between the two phases become irrational, parallel to both directions of the invariant line and an a-axis of D022, since the lattice misfit becomes negative along a-axis (δa) and positive along c-axis (δc) of the D022. The calculation based on the lattice invariant theory as well as experimental results clearly demonstrate that the misfit strain ratio δc/δais a dominant factor to determine the habit plane. In addition, the shape of D022phase, either prism or plate, depends strongly on the magnitude of |δa|. These findings will extend to Ni-Fe-Nb-V quaternary system, by partial replacement of Ni with Fe and that of V with Nb.
Rationalization of the plastic flow behavior of Polysynthetically-twinned (PST) TiAl crystals based on slip mode observation using AFM and Schmid's law
Authors: Chen Yali , Pope David P. 
Published: April 2011

ABSTRACTPST TiAl samples of different orientations were prepared and deformed by compression at room temperature. The deformation structures on the free surfaces were scanned using an AFM. It was found that when the angle between the lamellar interfaces and the loading axis is between 20 degree and 80 degree, PST samples deform primarily by shear in slip planes parallel to the lamellar interfaces. When the angle is below 20 degree, both the gamma phase and the alpha 2 phase deform by shear in slip planes inclined with the lamellar interfaces, but the shear vectors lie in the interface. When the angle is close to 90 degree, complex deformation behavior occurs. Shear in planes parallel to the lamellar interfaces contributes more to the overall strain in the directions perpendicular to the loading axis and the out-of-plane shear contributes to the strain in the compression direction. The characteristic U-shape curve of the yield stress versus the angle between the loading axis and the lamellar interfaces can be explained quite well using different C.R.S.S. for the three different deformation modes.
Fatigue Testing of microsized samples of γ-TiAl based material
Authors: Halford Timothy P. , Takashima Kazuki , Higo Yakichi 
Published: April 2011

ABSTRACTHigh strength γ-TiAl based alloys, such as Ti-46Al-5Nb-1W (Alloy 7), which were originally developed for gas turbine and automotive applications are now being considered for application in Micro Electro Mechanical Systems (MEMS). This requires the evaluation of these materials upon the microscale. As international standards do not currently exist for the evaluation of the mechanical properties of samples with dimensions equivalent to those required by MEMS devices, the development of new methods was required. The method developed here is intended for the fatigue testing of samples measuring ≈ 10μm (B) × 20μm (W) × 40μm (L). This is completed using a machine recently developed at Tokyo Institute of Technology to load samples of lamellar γ-TiAl based material to failure in compressive bending. This method is intended to work alongside methods previously developed for the fracture toughness testing of similar microsized cantilever bend specimens.In this work sample cantilevers of Alloy 7 are Focussed Ion Beam (FIB) machined from foil ≈ 20μm thick and their stress - life (S-N) fatigue behaviour evaluated. The dependence of fatigue life upon lamellar orientation for a given peak stress / stress range is considered. The effect of the reduced scale of these samples upon the mean and scatter of these sample lifetimes is also considered through comparison with previous data obtained from the S-N testing of macrosized samples of the same material.
An Electron Microscope Study of Mechanical Twinning in a Precipitation–Hardened TiAl Alloy
Authors: Appel Fritz 
Published: April 2011

ABSTRACTThe high temperature capability of TiAl alloys can be significantly improved by the implementation of precipitation reactions. From the engineering viewpoint the challenge is to establish the hardening mechanism without compromising desirable low temperature properties such as ductility and toughness. With this perspective in mind, twin structures were investigated in a TiAl alloy containing Ti3AlC carbides, in order to identify mitigation strategies for overcoming precipitation induced embrittlement. The study is focussed on the nucleation and immobilization of twins at precipitates. The results are discussed in the context of the plastic anisotropy and fracture behaviour of TiAl alloys.
Internal Friction of a High-Nb Gamma-TiAl-Based Alloy with Different Microstructures
Authors: Weller M. , Clemens H. , Dehm G. , Haneczok G. , Bystrzanowski S. , Bartels A. , Gerling R. , Arzt E. 
Published: April 2011

ABSTRACTAn intermetallic Ti-46Al-9Nb (at%) alloy with different microstructures (near gamma, duplex, and fully lamellar) was studied by internal friction measurements at 300 K to 1280 K using different frequency ranges: (I) 0.01 Hz to 10 Hz and (II) around 2 kHz. The loss spectra in range I show (i) a loss peak of Debye type at T ≈ 1000 K which is only present in duplex and fully lamellar samples; (ii) a high-temperature damping background above ≈ 1100 K. The activation enthalpies determined from the frequency shift are H = 2.9 eV for the loss peak and H = 4.1–4.3 eV for the high-temperature damping background. The activation enthalpies for the visco-elastic high-temperature damping background agree well with values obtained from creep experiments and are in the range of those determined for self-diffusion of Al in TiAl. These results indicate that both properties (high-temperature damping background and creep) are controlled by volume diffusion-assisted climb of dislocations. The loss peak is assigned to diffusion-controlled local glide of dislocation segments which, as indicated by transmission electron microscopy observations, are pinned at lamella interfaces.
Impact Properties of Hot-Worked Gamma Alloys with BCC β-Ti Phase
Authors: Shindo Kentaro , Tetsui Toshimitsu , Kobayashi Toshiro , Morita Shigeki , Kobayashi Satoru , Takeyama Masao 
Published: April 2011

ABSTRACTImpact resistance of a hot-forged TiAl alloy with a composition of Ti-42∼44Al-5∼10M: M=V, Mn(at%), consisting of lamellar, γ and β grain of which the hot-workability was improved by introducing β phase, has been investigated using an instrumented Charpy impact test, tensile test at high strain rate and foreign object attack test. In instrumented Charpy impact test the absorbed energies for crack initiation and propagation were measured, and the effect of microstructure on the absorbed energies has been analyzed, by paying attention to the grain size, interlamellar spacing and lamellar area fraction. In tensile test at high strain rate, the dependence of strain rate of hot-extruded TiAl alloy is obtained and compared with that of Nickel based superalloy, Inconel 713C. In foreign object attack test with taper plate specimen modified turbine blade and brass ball as foreign object, the relation between impact damage and thickness of specimen at attack point is investigated. A limit of impact energy, at which there isn't a crack on buck of attack point, is obtained with each thickness about hot-forged TiAl alloy, Ti-42Al-5Mn. Therefore, the method of improvement of toughness and assessment of impact resistance of TiAl alloy is shown in this study.
Effects of long-period superstructures on plastic properties in Al-rich TiAl single crystals
Authors: Nakano Takayoshi , Hayashi Koutaro , Umakoshi Yukichi , Chiu Yu-Lung , Veyssière Patrick 
Published: April 2011

ABSTRACTIn Al-rich TiAl crystals, several long-period superstructures may appear depending on Al composition, annealing temperature and annealing time. Amongst these, Al5Ti3 and h-Al2Ti contain pure Al (002) layers, as in the L10 structure of the matrix, alternating with Ti (002) layers that exhibit an ordered arrangement of the Al atoms in excess. In single crystals with compositions ranging from Ti-54.7at.%Al to Ti-62.5at.%Al annealed at 1200°C, the Al5Ti3 long-period superstructure embedded in the L10 matrix develops with increasing Al concentration to finally transform fully into h-Al2Ti for Ti-62.5at.%Al. On the other hand, Al5Ti3 precipitates grow with annealing time at 500°C in Ti-58.0at.%Al.The effects of the Al5Ti3 and h-Al2Ti superstructures on slip properties of 1/2<110] ordinary dislocations are examined both at a macroscopic and a microscopic level. The CRSS for 1/2<110] ordinary slip increases with Al5Ti3 ordering depending on Al composition, or of annealing time in the case of Ti-58.0at.%Al. Dislocations with 1/2<110] Burgers vector group into fourfold configurations to avoid the trailing of extended APBs in Al5Ti3. The CRSS for slip in the <110] direction further increases with the formation of h-Al2Ti particles within the L10 matrix in Ti-62.5at.%Al. By contrast, Ti-62.5at.%Al fully transformed into Al5Ti3 exhibits a CRSS significantly lower than that of the two-phase alloy.
Influence of Micro-alloying on Oxidation Behavior of TiAl
Authors: Yoshihara Michiko , Taniguchi Shigeji 
Published: April 2011

ABSTRACTThe influence of a wide range of elements on oxidation behavior of TiAl was investigated by micro-alloying using ion implantation with ion doses of 1019 to 1022 m−2 and at acceleration voltages of 40 to 340kV. The oxidation resistance was assessed by a cyclic oxidation test at 1200K in a flow of purified oxygen under atmospheric pressure. The implanted elements can be classified into several groups according to their effect and mechanism. The mechanisms by which the oxidation resistance is improved are as follows: (1) Formation of a protective Al2O3 layer through β-phase formation, which was confirmed by TEM observations, in the modified surface layer by the implantation. (2) Reduction of TiO2 growth rate due to doping effect of the implanted element. (3) Protective Al2O3 layer formation through migration of volatile halide. (4) Enrichment of oxide of the implanted element in the scale. On the other hand, the oxidation resistance is decreased by (1) enhanced TiO2 growth due to doping effect, (2) lattice defects induced by the implantation, and (3) decreased scale strength and enhanced scale spallation.
Carbon Nanotube Reinforced Bombyx mori Nanofiber Composites by the Electrospinning Process
Authors: Ayutsede Jonathan , Gandhi Milind , Sukigara Sachiko , Ko Frank 
Published: April 2011

AbstractA nanocomposite of silkworm silk and single wall carbon nanotubes (SWNT) was produced by the electrospinning process. Regenerated silk fibroin dissolved in a dispersion of carbon nanotubes in formic acid was electrospun and the morphological, chemical and mechanical properties of the electrospun nanofibers were examined. The mechanical properties of the SWNT reinforced fiber show increases in Young's modulus up to 460 % in comparison with the un-reinforced aligned fiber.
Correlated Single Molecule Fluorescence and Scanning Probe Microscopies: Applications to the Study of Soft Materials
Authors: Slade Andrea L. , Shaw James E. , Yang Guocheng , Chhabra Neetu , Yip Christopher M. 
Published: April 2011

AbstractWe recently developed an integrated imaging platform that combines single molecule evanescent wave fluorescence imaging (and spectroscopy) with in situ scanning probe microscopy. The advantages, challenges, and potential represented by this coupled tool will be described in the context of the structure-function characteristics of nanostructured biomaterials and thin lipid films.
Nanoindentation of Bone in a Physiological Environment
Authors: Akhtar R. , Morse S. , Mummery P.M. 
Published: April 2011

ABSTRACTNanoindentation has been established as an effective method to measure the mechanical properties of bone tissue at the micron and sub-micron length scale. Although it is well-documented that the mechanical properties of macroscopic bone specimens vary depending on whether the samples are tested dry or wet, nanoindentation is generally conducted on dehydrated bone tissue at room temperature, primarily because nanoindentation systems are extremely sensitive to changes in environmental conditions such as humidity and temperature. In this study, these problems were overcome by using a specially constructed liquid cell with an extension piece that allowed the indenter tip to be submerged under 5 mm of liquid. The custom setup was used to test cortical bovine bone and cancellous human bone specimens in three distinct conditions – dehydrated, rehydrated in simulated body fluid (SBF) at 20°C, and rehydrated in SBF at 37.5°C. A heating element with a temperature control unit was used to test at 37.5°C. The hardness and elastic modulus of the bone samples were found to decrease when dry specimens were rehydrated and tested in physiological conditions. It is suggested that nanoindentation in physiological conditions gives a better estimate of the mechanical properties of the microstructural components of bone in vivo rather than nanoindentation under conventional conditions.
Lessons for New Classes of Inorganic/Organic Composites from the Spicules and Skeleton of the Sea Sponge Euplectella aspergillum
Authors: Mayer G. , Trejo R. , Lara-Curzio E. , Rodriguez M. , Tran K. , Song H. , Ma W. H. 
Published: April 2011

ABSTRACTStudies have been carried out on the structures and mechanical characteristics of an unusual family of sea sponges under the classification of Hexactinellida, genus Euplectella. The sponge spicules have been of interest to materials scientists because of their potentially important optical, coupled with mechanical, properties. The structures of the class Hexactinellida are characterized by a concentric ring appearance in the cross-section, which is a composite of hydrated silica, coupled with silicatein as a thin layer at the ring interfaces. The mechanical behavior and the toughness of the spicules have been examined with the aid of a special fiber testing method, coupled with scanning electrom microscopy (SEM) observations. It appears that there may be common mechanisms underlying toughness in rigid natural composites with high ratios of mineral/organic phase. In addition, novel pressurization tests of a portion of the sponge skeleton have provided information about the resilience of the skeleton, which resembles a selfsupporting glass winding of a cylindrical composite structure.
Mechanical Properties of Biomimetic Composites for Bone Tissue Engineering
Authors: Verma Devendra , Katti Kalpana S. , Mohanty Bedabibhas 
Published: April 2011

ABSTRACTA biomimetic process involving in situ mineralization of hydroxyapatite (HAP) is used to design new composite biomaterials for bone tissue engineering. Surface and bulk properties of HAP composites have been studied for hydroxyapatite mineralized in absence (ex situ) of polyacrylic acid (PAAc) and in presence (in situ) of PAAc. XRD studies show existence of structural disorder within in situ HAP. It has been observed that PAAc increases the rate of crystallization. FTIR studies indicate calcium deficiency in structure of both in situ and ex situ HAP. PAAc provides favorable sites for nucleation of HAP. During crystallization of HAP, PAAc dissociates to form carboxylate ion, which binds to HAP. Porous and solid composites of in situ and ex situ HAP with polycaprolactone (PCL) in 50:50 ratio have been made to evaluate their applicability as bone scaffold. Mechanical tests on solid samples indicate ex situ HAP/PCL composites have higher elastic modulus (1.16 GPa) than in situ HAP/PCL composites (0.82 GPa). However, in case of porous composites, in situ HAP/PCL composites are found to have higher elastic modulus (29.5 MPa) than ex situ HAP/PCL composites (10.4 MPa). Nanoindentation tests were also performed at different loads to evaluate mechanical properties of the composites. In situ HAP mineralized using non-degradable polymers has thus been shown to improve mechanical response in porous composites.