bluuebunny/crossref_metadata_2025_split huggingface dataset:
Primary Creep of Ni3(Al, Ta) Single Crystals at Room Temperature
Authors: Uchic M. D. , Nix W. D. 
Published: April 2011

ABSTRACTThis study examines the time-dependent deformation of Ni3(Al, Ta) at room temperature. Tension creep experiments have been performed on single crystals with one {111}<101> slip system active at the start of the test, where the applied stress ranged from 66.4 MPa (the measured 0.01% flow stress) to 143 MPa (which produced approximately 9% plastic strain). All creep curves displayed primary creep leading to eventual exhaustion, where the measured creep strain declined at a rate faster than predicted for logarithmic creep. However, no correlation between the applied stress and the form of the declining creep rate can be made at this rime. Many creep curves can be obtained from one sample, as the creep curves from both virgin samples and samples with prior deformation history (at the same test stress) were indistinguishable. At the beginning of an incremental creep test, where the stress is increased by a small amount to reinitiate plastic flow in an exhausted sample, a significant retardation of the plastic response of the sample occurred when the stress increment was below 4 MPa. Preliminary TEM studies of a sample strained to 6% suggest that room temperature creep tests may not be ideal for examining the flow of Anti-Phase-Boundary (APB) dissociated dislocations.
Microstructural Stability of Directionally Solidified Eutectic NiAl-Mo Under Static and Thermal Cycling Conditions
Authors: Kush M. T. , Holmes J. W. , Gibala R. 
Published: April 2011

ABSTRACTThe quasi-binary eutectic NiAl-9% Mo with faceted molybdenum fibers was subjected to both thermal annealing conditions and to annealing under thermal cycling conditions to determine the microstructural stability of this alloy. The static temperature tests were run at 0.85TM- 0.97TMin an argon gas atmosphere. The thermal cycling tests were performed between temperatures of 700°C and 1200°C by induction heating disk-shaped specimens in an argon gas atmosphere using time-temperature heating and cooling profiles to approximate potential engine applications. To quantify microstructural changes, the fiber size and size distribution and number of fibers per unit area were measured as a function of time at temperature. The overall results demonstrate that the directionally solidified eutectic NiAl-9Mo subjected to thermal fatigue conditions exhibits cell boundary coarsening and large shape changes, whereas the microstructure under static stress-free annealing is stable.
TEM In-Situ Study of Dislocation Motion in B2 NiAl Single Crystals
Authors: Ghosh B. , Crimp M. A. 
Published: April 2011

ABSTRACTIn an effort to understand dislocation mobility in stoichiometric NiAl single crystals, in-situ tensile deformation experiments have been performed in a transmission electron microscope. Commercially pure and high purity single crystals with <001> and <110> orientations have been examined. Two different thermal treatments were adopted in order to effect the mechanical response. Dislocation motion was observed in all samples. Pre-existing dislocations, either isolated or tangled, were not observed to move at any point leading up to sample failure. Cross-slip of the mobile dislocations was observed in some cases. In commercially pure single crystals, dislocations were found to move at a much slower rate and uniform manner in contrast to motion in high purity single crystals which occurs by rapid jumps.
Slip Transition and Dislocation Structures in Off-Stoichiometric NiAl Single Crystals
Authors: Srinivasan R. , Savage M. F. , Daw M. S. , Noebe R. D. , Mills M. J. 
Published: April 2011

ABSTRACTCompression tests have been performed on hard-oriented Ni-44A1 single crystals for several temperatures and strain levels. There is a slip transition from a<111> type slip to non-a<111> type slip which corresponds with the observation of yield points. Transmission electron microscopy studies provide evidence for decomposition of a<111> dislocations into a<101> and a<010> dislocations near the “knee” of the yield strength curve. The mechanism of this slip transition and the nature of the dislocation processes both below and above the “knee” are described.
Deformation of Diffusion-Bonded Bi-Pst and Directionally Solidified Crystals of TiAl
Authors: Kishida K. , Johnson D. R. , Shimada Y. , Masuda Y. , Inui H. , Yamaguchi M. 
Published: April 2011

ABSTRACTWith a data base now available on the microstructural characteristics and the deformation, fracture and macroscopic flow behavior of polysynthetically twinned (PST) crystals of γ/α2 TiAl-base alloys, an approach to achieve a good combination of strength, ductility and toughness in γ/α2 TiAl-base alloys was proposed using directional solidification (DS) techniques to produce a columnar grain material with the lamellar orientation aligned parallel to the growth direction. Such alignment of the lamellar microstructure was recently accomplished in γ/α2 TiAl-base alloys of near equiatomic compositions using an appropriately oriented seed crystal from the Ti-Al-Si system.At the same time, bi-PST crystals, each containing a planar boundary parallel to the loading axis were prepared by directional solidification and diffusion bonding of two PST crystals. Such bi-PST crystals were deformed in tension at room temperature and their deformation behavior was examined in terms of the compatibility requirements imposed at the grain boundary and the interaction of the two component PST crystals.In this paper, (i) the current status of our DS processing efforts, (ii) some results of microscopic characterization of grain boundaries in diffusion bonded bi-PST crystals and (iii) results of deformation experiments of bi-PST crystals prepared by DS processing and diffusion bonding, will be reported.
Notch-TIP Deformation of Ni3Ai Single Crystals
Authors: Schulson E. M. , Xu Y. 
Published: April 2011

ABSTRACTThe notch-tip deformation field of Ni3AI single crystals doped with boron is characterized by fan-shaped sectors within which one slip system dominates. Cracks initiate and propagate along slip planes on both sides of the notch plane.
Recent Work on Environmental Embrittlement in Silicides
Authors: Chen Guoliang , Peng Jihua , Wang Xitao 
Published: April 2011

ABSTRACTThis paper reviewed the recent progress in the environmental embrittlement of suicide. On the surface of suicides, the Si in the suicides such as Fe3(Si,Al) alloy reacts with both oxygen and water vapor more easy than with iron. A molecular hydrogen machanism of surface reaction, i. e. Si + 2H2O = SiO2 + 2H2, can be derived. The moisture-induced embrittlement of suicides can be considered to be an embrittlement in a localized high pressure molecular hydrogen condition. It is a kinetic hydrogen gas embrittlement. Suicides may have more severely intrinsic brittleness than iron aluminides due to their special electronic structure and bonding mechanism, leading to elucidate the role of environment on ductility with difficulty. The improvement of both the intrinsic brittleness and moisture-induced embrittlement are critical for the development of suicides.
Effects of Rhenium Alloying on the Microstructures and Mechanical Properties of Directionally Solidified NiAl-Mo Eutectic Alloy
Authors: Misra A. , Wu Z. L. , Gibala R. 
Published: April 2011

ABSTRACTLow ductility of the reinforcing bcc metal phase at room temperature and weak interfaces can limit the intrinsic toughness and ductility of NiAl-bcc metal eutectic composites. The potential of rhenium (Re) addition, which is known to solid solution soften and lower the ductile-to-brittle transition temperature of various bcc metals, to enhance the ductility and toughness of a directionally solidified NiAl-9 at.% Mo eutectic alloy was investigated. Re partitioned to the bcc metal phase and formed a substitutional solid solution. The interface morphology was changed from a faceted to a non-faceted one. Re alloying caused softening of the Mo fibers, and as a result NiAl-Mo(Re) alloys were softer in compression and flexure and had ∼20% higher fracture toughness values as compared to the transverse orientation toughness of NiAl-9Mo alloy. The toughness of the NiAl-Mo(Re) alloys was lower man the longitudinal orientation toughness of the NiAl-9Mo alloy due to the poor alignment of the Mo(Re) phase with the growth direction. The toughening mechanisms have been evaluated and schemes for processing NiAl-Mo(Re) alloys for higher toughness in the longitudinal orientation are suggested. The role of the residual interstitial impurities and partitioning of Ni and Al to Mo fibers on the mechanical properties are highlighted.
Al2O3 Composites Containing Fe, Nb and Zr Aluminides
Authors: García D. E. , Schicker S. , Bruhn J. , Krupp A. , Janssen R. , Claussen N. 
Published: April 2011

ABSTRACTA reactive powder-processing technique involving controlled exothermic solid-state reactions between Al and oxides has been used to produce nearly fully dense composites with interpenetrating networks of aluminides and Al2O3. The process consists of the in situ formation of aluminides and Al2O3 from compacts of intensively milled oxide-Al powder mixtures followed by pressureless sintering. The reactions take place usually at temperatures below the melting point of Al. At temperatures >1000°C, the reaction products start to sinter yielding microstructures with very fine and uniform phase distribution. The present paper discuses processing parameters such as attrition milling, heating cycle and atmosphere controlling microstructural development and mechanical properties of Al2O3 composites containing Fe, Nb and Zr aluminides.
Strengthening Epoxy/High Impact Polystyrene Interfaces Using End Grafting Polymer Chains
Authors: Sha Y. , Hui C. Y. , Kramer E. J. , Hahn S. F. , Berglund C. A. 
Published: April 2011

AbstractThe fracture toughness Gc of epoxy/high impact polystyrene (HIPS) interfaces was measured as a function of grafting chain density Σ of dPS-COOH chains of various degrees of polymerization N. For short chains, no effective entanglements can be formed between the dPS chains and the PS matrix of the HIPS, thus no enhancement in Gc over that of a bare interface. For very long chains, even though each chain is well entangled with the HIPS, the maximum grafting density achievable is very low and such an interface fails by scission of the grafting chains so that the interface fracture toughness is also low. Large values of Gc are observed at intermediate chain lengths where both effective entanglements can be formed and a large Σ can be achieved. Under these conditions the interface fails initially due to the formation of crazes and the subsequent break down of one of these crazes at the interface. The transition areal chain density from chain scission to crazing, Σc,is independent of N.
Effect Of Drying on Permeability of Multilayer Polymeric Films
Authors: Nagarkar P. V. , Ko C. S. 
Published: April 2011

ABSTRACTPhotographic applications rely greatly on the permeability and swelling behavior of multilayer thin films. This behavior is, at least, a function of (I) material properties such as particle size, percent solids and solubility, and (II) processing conditions that affect film formation, such as rate of drying, maximum web temperature and nature of underlying layers.In order to test permeability of multilayer structures, an alkaline medium is allowed to permeate sample. In the structure under test, the bottom most layer is acidic in nature. This acid neutralizes the alkali as it permeates through the layers. Neutralization causes a change in ionic concentration in the sample and this is measured using a high frequency cavity sensor (commercially available as the conductivity Puntex technique) that changes its resonant frequency in response to change in conductivity of the sysytem. This frequency change can be monitored to to give a time transient for permeability. In the event that frequency changes even before neutralization has occured, it can be correlated to capacitance changes within the layers produced by swelling and water uptake.For a porous layer within the sample, the permeation proceeds along two paths. One through the porosity and the other through the bulk. In this case the bulk signal is superimposed over the signal from porous component. For such a system, a transient of the time derivative of resonant frequency proved to be a useful tool to study interfacial interactions between the acid layer and the layer above it. Impact of drying was also inferred from similar measurements. Data indicate that the higher temperature of drying of constituent layers resulted in a microstructurally tighter film, that took longer time for the alkali to permeate.
Polymer Blends made from Ionomer and Ionomer Precursor Polymer
Authors: Bellinger M. A. , Ma X. , Tsou L. , Sauer J. A. , Hara M. 
Published: April 2011

ABSTRACTRigid-rigid blends made of an ionomer and an ionomer precursor polymer, based on either polystyrene (PS) or poly(methyl methacrylate)(PMMA), were studied. A positive deviation from the rule of mixtures in both strength and toughness was observed over the entire composition range; and an especially significant enhancement was observed at low ionomer composition (e.g., 10 wt.%). This is attributed to a fine dispersion of the rigid ionomer phase in the matrix polymer together with good interfacial adhesion between the phases. The adhesion arises from entanglements due to athermal interactions between the same monomeric units of both the ionomer and the ionomer precursor. In addition, all the blend samples are found to be transparent due to similar refractive indices of the two components.
Laser Induced Decohesion Spectroscopy: A New Technique for Measuring Polymer Interfacial Adhesion
Authors: Meth J. S. , Sanderson D. , Mutchler C. , Bennison S. J. 
Published: April 2011

ABSTRACTWe present a new technique, laser induced decohesion spectroscopy (LIDS), which is capable of measuring the practical work of adhesion G between a transparent polymer film and an opaque substrate. In LIDS, a laser pulse directed onto the sample creates a blister at the film/substrate interface. The blister's internal pressure depends on the laser pulse energy, and at a critical pressure the sample fractures. We have derived a theoretical analysis of this experiment based on elasticity theory and fracture mechanics, and present the results. By measuring physical variables such as the thickness of the transparent polymer, the blister radius, and the blister curvature, it is possible to deduce G between the two coatings. Here we report G for a matrix of automotive finish systems consisting of four opaque basecoats of various colors (black, white, red, green) coated with a clearcoat of various thicknesses. We expect G to be a system parameter for each basecoat independent of clearcoat thickness. The values of G for the different basecoats yield the relative adhesion of the various pigmented paint formulations.
Production of Crucible Steel by Co-Fusion: Archaeometallurgical Evidence from the Ninth-Early Tenth Century at the Site of Merv, Turkmenistan
Authors: Feuerbach Ann , Merkel John F. , Griffiths Dafydd R. 
Published: April 2011

ABSTRACTVarious methods were used to produce steel in early Islamic times. According to early Islamic texts, three methods are described for indirect production of steel (fuladh). The methods are solid-state carburization of wrought iron, partial decarburization of cast iron or a high carbon steel, and co-fusion of cast iron with wrought iron. Evidence from a metallurgical workshop at Merv, dated to the ninth-early tenth century A.D., provides an illustration of the co-fusion method of steel production in crucibles. The primary investigations of the crucibles are presented. The crucible slag was found to contain droplets of cast iron and steel and the crucible fabric contains mullite.
European White Glass Trade Beads as Chronological and Trade Markers
Authors: Hancock R.G.V. , Aufreiter S. , Kenyon I. 
Published: April 2011

ABSTRACTEuropean explorers and traders, on their arrival in North America, found the aboriginal peoples willing to exchange furs and other goods for European-made metal objects and glass beads, the remains of which may be found at archaeological sites. Specific trade goods, including multi-coloured or curiously shaped glass beads that are visually distinctive, are used as chronological markers by archaeologists. Most of the single coloured, mainly blue or opaque white beads are very common and cannot be visually, chronologically differentiated. Non-destructive analysis (INAA) of turquoise blue or white beads from known-age archaeological sites in Ontario has revealed chemical changes in glass manufacturing compositions over time. This allows these otherwise nondescript, single coloured beads to be used as chronological and trade markers. Although the turquoise beads were always coloured by Cu, the white beads employed different opacifiers over time. First came Sn-rich beads (early to late 17th century); then Sb-rich beads (late 17th century to mid-19th century); finally As-rich beads (very late 18th century to early 20th century) and even F-whitened beads (19th century to 20th century). Within each major group, it appears that changes in glass making recipes may be found using the Na, K, Ca, Al and Cl contents. Therefore, chemical analysis of white glass trade beads may be as profitable as chemical analysis of turquoise blue trade beads in establishing chemical chronologies.
An Investigation of the Sources of Bronze Age Pottery from Göltepe and Kestel, Turkey by Neutron Activation
Authors: De Sena E.C. , Friedman E.S. 
Published: April 2011

ABSTRACTAs part of a broader research scheme intended to examine the relationship between the ceramic and metal industries of Bronze Age Anatolia, a program of compositional analysis by neutron activation was performed on ceramic material dated to the third millennium BC from Göltepe and Kestel, Turkey, the earliest known tin mining and processing sites in the Near East. Fifty-one archaeological samples representing five classes of pottery (crucibles, burnished ware, micaceous ware, fine-slipped ware, and metallic ware) and three local clay samples were analyzed in order to clarify problems related to the sources of the archaeological ceramics. Evidence provided by these experiments indicates that the four classes of domestic pottery and the crucibles derive from at least two distinct sources. One of these sources, the alluvial clay outcrops in the vicinity of Göltepe, was exploited for the manufacture of two types of domestic pottery (burnished ware and micaceous ware), as well as the “industrial” crucible refractories. Metallic ware appears to represent a distinct source group; however, the specific location of the source remains unclear. The geochemical relationship between fine-slipped ware and the other ceramics remains unclear.
Amber from 1000-Year Old Prehispanic Tombs in Northern Peru
Authors: Shimada Izumi , Anderson Ken B. , Haas Herbert , Langenheim Jean H. 
Published: April 2011

ABSTRACTHundreds of large, shaped and perforated amber beads excavated from two Middle Sicán elite shafttombs at Huaca Loro on the northern coast of Peru represent the first scientifically documented case of amber use in prehispanic South America. Amber was highly valued and formed a key component of Sicán sumptuary good production. This paper describes the analytical procedures and archaeological and botanical background for source identification and cultural understanding of amber beads found on pectorals, necklaces and gold alloy objects. Samples were initially identified by XRD and FT-IR microscopy, followed by a more detailed and conclusive analysis using pyrolysis GC-MS. Radiocarbon dating points to a minimum age of 50,000 years. Results were compared with amber from known sources in the New World. Various lines of evidence suggest that the amber was derived from a heretofore unknown source, probably an ancient species ofHymenaea, possibly related toH. oblongifolia(family Leguminosae) occurring today in upper Amazonia.
La Virgincita: Technical Study of an Indo-Christian Statue
Authors: Susan Barger M. , Gong Weiliang 
Published: April 2011

ABSTRACTA small stone statue of the Virgin Mary was recently found that is one of two free-standing Indo Christian sculptures known to be in the United States. The Indo-Christian style of art marks the transition from pre-Columbian art to Christian art and most examples of this style are found on buildings in Mexico. The statue,”la Virgincita,”is patterned after an European engraving, however the decorative details in the stone carving are Aztecan. This paper is a description of the materials characterization of the statue and a study of its technical details using scanning electron microscopy, transmission electron microscopy, and electron microprobe analysis.
Metallography and Corrosion Product Studies on Archaeological Bronze Fragments from the Qu Cun Site
Authors: Chase W. T. , Wang Quanyu 
Published: April 2011

ABSTRACTThe authors studied a suite of fragments of corroded bronzes from the Tienma-Qu Cun site, a Western Zhou city and cemetery complex dating from ca. 1000 to ca. 650 B.C‥ Conventional metallographic techniques were used along with scanning electron microscope, electron microprobe and x-ray diffraction. The bronzes are very varied in structure and composition. Most are cast, moderate-tin bronzes, but some are high or low in tin or lead. A few show a worked and annealed structure, and some of the cast bronzes were also heat treated (possibly by use as cooking pots). corrosion patterns also vary greatly, from almost uncorroded to total mineralization. Periodic and esquential corrosion phenomena were detected, as well as patination applied when the bronzes were made. We had hoped to be able to ascertain the causes of the different penetration of corrosion in these samples, but that must remain for future work.
Determination of the Three-Dimensional Atomic Structure at Internal Interfaces by Electron Energy Loss Spectroscopy
Authors: Browning N. D. , Wallis D. J. , Pennycook S. J. 
Published: April 2011

ABSTRACTThe fine structure of a core-loss edge contains detailed information on the local atomic environment. It can be used as an extremely sensitive probe of the fluctuations in structure and bonding that can occur at internal interfaces. Interpretation of such fluctuations requires only a knowledge of the location of the electron probe when the spectrum is acquired and a means of interpreting the spectrum. The location of the probe can be controlled with atomic precision in the STEM by the use of the Z-contrast image, while the real space cluster methodology of multiple scattering analysis is ideally suited to the task of interpretation. This approach is used here to derive 3-dimensional models for tilt grain boundaries in TiO2 and SrTiO3.
Stress Induced Structural Changes of Interphase Boundaries and Mechanical Twins in two-Phase γ-Titanium Aluminides
Authors: Appel F. , Wagner R. 
Published: April 2011

ABSTRACTConventional and high-resolution electron microscopy has been used to examine the interfacial structures in (α2+ γ) titanium aluminide alloys. Accommodation of misfit which arises because of differences in lattice parameters and crystal structure leads to dense structures of interfacial dislocations and coherency stresses. During deformation stress induced structural changes of misfitting interfaces occur. These are closely related to the generation of perfect and twinning partial dislocations. At elevated temperatures diffusion controlled structural changes take place at an atomic level and seem to limit the structural stability of the material.