bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microscopic View on Grain Nucleation and Growth Kinetics During Solidification of Aluminum Alloys
Authors: Iqbal N. , van Dijk N. H. , Offerman S. E. , Moret M. , Katgerman L. , Kearley G. J. 
Published: April 2011

ABSTRACTX-ray diffraction with hard X-rays (E = 70 keV) was used to investigate the grain nucleation and grain growth during solidification of a grain refined Al-0.3Ti-0.02B (wt.%) alloy. The investigations showed for the first time the nucleation profile during solidification and how nucleation rate increases with cooling rate. The results indicate that the nucleation process is complete for solid fraction below 30 %, irrespective of the cooling rate. This is explained in terms of the release of latent heat during solidification. The growth of individual aluminium grains during solidification is experimentally observed and compared to model predictions for the diffusion limited grain growth. The experimental results are only in agreement with the theory in the first stage of the transformation. The difference between the experiment and the theory is discussed qualitatively.
In-Situ Neutron Diffraction Study of Strain-Induced Martensite Formation in 304L Stainless Steel at a Cryogenic Temperature
Authors: Tao Kaixiang , Wall James J. , Brown Donald W. , Li Hongqi , Vogel Sven C. , Bourke Mark A. M. , Choo Hahn 
Published: April 2011

ABSTRACTIn-situ, time-of-flight neutron diffraction was performed to investigate the martensitic phase transformation during quasi-static uniaxial compression testing of 304L stainless steel at 300K (room temperature) and 203K. In-situ neutron diffraction study enabled the bulk measurement of intensity evolution for each hkl atomic plane during the austenite (fcc) to martensite (hcp and bcc) phase transformation. The neutron diffraction patterns show that the martensite phases started to develop at about 2.5% applied strain (600 MPa applied stress) at 203K. However, at 300K, the martensite formation was not observed throughout the test. Furthermore, from changes in the relative intensities of individual hkl atomic planes, the selective phase transformation can be well understood and the grain orientation relationship between the austenite and newly-forming martensite phases can be determined. The results show that the fcc grain families with {111} and {200} plane normals parallel to the loading axis are favored for the “fcc to hcp” and “fcc to bcc” transformations, respectively.
Probing Mesoscopic Strain Evolution during Creep Deformation: An In-Situ Neutron Diffraction Study
Authors: Choo Hahn , Brown Donald W. , Bourke Mark A. M. , Swindeman Robert W. 
Published: April 2011

ABSTRACTThe development of lattice strain was studied using in-situ time-of-flight neutron diffraction during constant-load tensile creep deformation of an austenitic 316FR stainless steel at 180, 240, and 300MPa at 873K (a power-law creep regime) with time resolution of 900 seconds. The macroscopic (global) and mesoscopic (lattice) strains were measured simultaneously during creep using an extensometer and neutron diffraction, respectively. The hkl-specific lattice strains were measured to gain insights into the plastic anisotropy at various stages of creep deformation (i.e., primary, secondary, and tertiary regimes). Furthermore, the creep-induced lattice strain behavior was compared to the result obtained from a quasistatic tension test at 873K. The lattice strain evolution in the axial direction (direction parallel to the tensile loading axis) during the primary and secondary creep (dislocation creep) is quite similar to the quasistatic case (slip). However, in the tertiary creep regime, the creep-induced lattice strain accumulation is smaller than the quasistatic case at a given total strain, except the (111) reflection.
Micro-Raman Mapping and Analysis of Indentation-Induced Phase Transformations in Germanium
Authors: Jang Jae-il , Lance M. J. , Wen Songqing , Huening J. J. , Nemanich R. J. , Pharr G. M. 
Published: April 2011

ABSTRACTAlthough it has been confirmed by diamond anvil cell experiments that germanium transforms under hydrostatic pressure from the normal diamond cubic phase (Ge-I) to the metallic β-tin phase (Ge-II) and re-transforms to Ge-III (ST12 structure) or Ge-IV (BC8 structure) during release of the pressure, there are still controversies about whether the same transformations occur during nanoindentation. Here, we present new evidence of indentation-induced phase transformations in germanium. Nanoindentation experiments were performed on a (100) Ge single crystal using two triangular pyramidal indenters with different tip angles - the common Berkovich and the sharper cube-corner. Although the indentation load-displacement curves do not show any of the characteristics of phase transformation that are well-known for silicon, micro-Raman spectroscopy in conjunction with scanning electron microscopy reveals that phase transformations to amorphous and metastable crystalline phases do indeed occur. However, the transformations are observed reproducibly only for the cube-corner indenter.
Modeling indentation in linear viscoelastic solids
Authors: Cheng Yang-Tse , Cheng Che-Min 
Published: April 2011

ABSTRACTUsing analytical and finite element modeling, we study conical indentation in linear viscoelastic solids and examine the relationship between initial unloading slope, contact depth, and viscoelastic properties. We will then discuss whether the Oliver-Pharr method for determining contact depth, originally proposed for indentation in elastic and elastic-plastic solids, is applicable to indentation in viscoelastic solids.
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.
Nanomechanical Properties of UV Degraded TiO2/Epoxy Nanocomposites
Authors: Scierka Stephanie , Drzal Peter L. , Forster Amanda L. , Svetlik Stephanie 
Published: April 2011

ABSTRACTModel epoxy nanocomposite thin films containing one of three types of titanium dioxide (TiO2) particles were degraded using an integrating sphere-based ultraviolet weathering chamber. Instrumental Indentation Testing (IIT) was used to measure nanomechanical changes in the surface region of thin films resulting from UV exposure. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC) were used to support the mechanical results with chemical and thermal data. The unfilled epoxy was the most photosensitive sample tested, exhibiting the highest rates of chemical oxidation, the largest decrease in the glass transition (Tg), and the greatest increase in elastic modulus with increased exposure. Similar trends were observed in the nanocomposite films, but the rates of change were much lower than the unfilled epoxy and decreased with increasing volume fraction of nanoparticles.
Nano Scratching of Clear Coats and Relation to Mechanical Material Properties
Authors: Nothhelfer-Richter Rolf , Klinke Eugen , Eisenbach Claus D. 
Published: April 2011

ABSTRACTThe nano single scratch experiment has been proven to be a suitable method to evaluate the scratch resistance of a coating. Single scratch damage and its recovery have been studied for a variety of clear coats under dry as well as wet conditions; these investigations were complemented by multi-scratch tests. Bulk mechanical materials properties of free standing films of the clear coats were determined by tensile tests and dynamic mechanical analysis (DMA). It was found that the recovery of the scratch groove is inversely related to the maximum value of the loss tangent (tan δ) as obtained from DMA analysis. The results of our comparative experiments and implications for the evaluation of the scratch resistance of organic coatings will be discussed.
The atomic scale removal mechanism during chemomechanical polishing of Silicon: An atomic force microscopy study
Authors: Katsuki Futoshi , Watanabe Junji 
Published: April 2011

ABSTRACTThe pressure dependence of the microwear of an oxidized Si surface under aqueous electrolyte solutions has been investigated using an atomic force microscope with a single crystal Si tip. The removal ratio of Si tip to SiO2 surface is found to be highly sensitive to the contact pressure. We present a microscopic removal mechanism which is determined by an interplay of the diffusion of H2O in Si and SiO2.
Microstructures of LENS™ Deposited Nb-Si Alloys
Authors: Dehoff Ryan R. , Sarosi Peter M. , Collins Peter C. , Fraser Hamish L. , Mills Michael J. 
Published: April 2011

ABSTRACTNb-Si “in-situ” metal matrix composites consist of Nb3Si and Nb5Si3 intermetallic phases in a body centered cubic Nb solid solution, and show promising potential for elevated temperature structural applications. Cr and Ti have been shown to increase the oxidation resistance and metal loss rate at elevated temperatures compared to the binary Nb-Si system. In this study, the LENS™ (Laser Engineered Net Shaping) process is being implemented to construct the Nb-Ti-Cr-Si alloy system from elemental powder blends. Fast cooling rates associated with LENS™ processing yield a reduction in microstructural scale over conventional alloy processes such as directional solidification. Other advantages of LENS™ processing include the ability to produce near net shaped components with graded compositions as well as a more uniform microstructure resulting from the negative enthalpy of mixing associated with the silicide phases. Processing parameters can also be varied, resulting in distinct microstructural differences. Deposits were made with varying compositions of Nb, Ti, Cr and Si. The as-deposited as well as heat treated microstructures were examined using SEM and TEM techniques. The influence of composition and subsequent heat treatment on microstructure will be discussed.
Microstructure and Thermo-Mechanical Behavior of NiAl Coatings
Authors: Dehm G. , Riethmüller J. , Wellner P. , Kraft O. , Clemens H. , Arzt E. 
Published: April 2011

ABSTRACTIn this study the thermo-mechanical behavior of a commercial Pt containing NiAl coating deposited on a Ni-base superalloy is compared with a Ni-rich NiAl coating sputter-deposited on a Si substrate. Both types of coatings possess high tensile room temperature stresses after thermal straining. The Pt-NiAl coating shows negligible plasticity as a result of solid solution and dispersion strengthening. In contrast, for the NiAl coatings on Si noticeable plasticity can be obtained if the film thickness exceeds the sub-micrometer range.
Complex Intermetallic Compounds: Defects, Disordering, Details
Authors: Sprengel W. , Baier F. , Sato K. , Zhang X. Y. , Schaefer H.-E. 
Published: April 2011

ABSTRACTA short overview will be given on the thermodynamics of the formation of thermal defects in intermetallic aluminides. We focus on thermal vacancies studied by the specific techniques of positron annihilation and time-differential dilatometry and discuss the results together with self-diffusion data. We then demonstrate that these techniques can be employed for studying vacancies in compound semiconductors specifically. Furthermore, structural order-disorder phase transitions can be investigated from an atomistic point of view by making use of positron annihilation as shown in the exemplary case of decagonal Al-Ni-Co quasicrystals.
Mechanical Aspects of Structural Optimization in a Bi-Te Thermoelectric Module for Power Generation
Authors: Nakatani Yujiro , Takaku Reki , Hino Takehisa , Shindo Takahiko , Itoh Yoshiyasu 
Published: April 2011

ABSTRACTThe thermal stress and strain occurring on a Bi-Te thermoelectric module subjected to variable thermal conditions were estimated based on three-dimensional elastic-plastic finite element method (FEM) analysis. The analysis showed that mechanical integrity of the interface between a Bi-Te thermoelement and electrodes of Al and Mo coatings formed by atmospheric plasma spraying was significantly reduced and that shear strain rose to 0.6∼1.1% in the vicinity of the interface. Furthermore, to estimate the sensitivity of configurational parameters of the module to the thermal strain, statistical sensitivity analysis based on the design of experiment (DoE) and response surface method (RSM) was conducted. The statistical analysis revealed that the thickness of electrode coatings of Al and Mo affected the thermal strain and that the thinner Al coating and the thicker Mo coating reduced the thermal strain. In this study, a thermal fatigue test machine was newly developed with a view to verifying these analytical studies.
Effect of Heat Treatment Conditions on Multistage Martensitic Transformation in Aged Ni-rich Ti-Ni Alloys
Authors: Nishida Minoru , Hara Toru , Morizono Yasuhiro , Matsuda Mitsuhiro , Fujishima Kousuke 
Published: April 2011

ABSTRACTIt has been demonstrated with systematic experiments that the appearance and disappearance of multistage martensitic transformation (MMT) in aged Ni-rich Ti-Ni alloys depend on the heat treatment conditions. No multistage transformation occurs when the evaporation of Ti and Ni and/or the preferential oxidation of Ti in the specimen are prevented and the purification of heat treatment atmosphere in an evacuated quartz tube is achieved. The heterogeneity in precipitation morphology of the Ti3Ni4 phase, which is responsible for the multistage transformation can be suppressed with the regulation of heat treatment atmosphere as mentioned above. We have concluded that the multistage martensitic transformation in aged Ni-rich Ti-Ni alloys is extrinsic in nature, and is an artifact during the heat treatment.
B2 Phases and their Defect Structures: Part I. Ab Initio Enthalpy of Formation and Enthalpy of Mixing in the Al-Ni-Pt-Ru System
Authors: Prins Sara , Arroyave Raymundo , Jiang Chao , Liu Zi-Kui 
Published: April 2011

ABSTRACTThe enthalpies of formation of the bcc phases in the Al-Ni-Pt-Ru system, particularly in the Al-Ru binary and Pt-Al-Ru ternary subsystems, were calculated by first principle methods. The enthalpies of formation for stoichiometric bcc-B2 phases have been calculated using both the GGA and LDA approximations, while the enthalpies of formation for B2 phases with large amounts of constitutional defects (both vacancies and anti-site atoms) were calculated using the Special Quasirandom Structures (SQS) approach. The enthalpies of mixing for the disordered bcc-A2 phases have also been calculated with SQS by mimicking the random bcc alloy with the local pair and multisite correlation functions. The calculated B2 lattice parameters for the different defect structures were compared with experimental results. These results are used as input values for the CALPHAD modified sublattice model to describe the A2/B2 phases with one Gibbs energy function.
Microstructure, Mechanical Properties and Wear Resistance of Fe-Al Based Alloys with Various Alloying Elements
Authors: Kim Han-Sol , Yeo In-Dong , Ra Tae-Yeub , Kim Won-Yong 
Published: April 2011

ABSTRACTWe report on microstructure, mechanical properties and wear resistance of Fe-Al based alloys with various alloying elements. The microstructures were examined using optical and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscope (EDS). Two types of alloys were prepared using vacuum arc melting; one is Fe-28Al based alloys (D03 structured) with and without alloying elements such as Mo and Zr. The other one is Fe-35Al based alloys (B2 structured) produced with same manner. For both types of alloys, equiaxed microstructures were observed by the addition of Mo, while dendritic structures were observed by the Zr addition. These microstructural features were more evinced with increasing the content of alloying elements. Concerning the mechanical properties and wear resistance, Fe-35Al based alloys with or without Mo addition superior to Fe-28Al based alloys especially in the high temperature region.
Phase Equilibria and Lattice Parameters of Fe2Nb Laves Phase in Fe-Ni-Nb Ternary System at Elevated Temperatures
Authors: Takeyama Masao , Gomi Nobuyuki , Morita Sumio , Matsuo Takashi 
Published: April 2011

ABSTRACTPhase equilibria in Fe-Ni-Nb ternary system at elevated temperatures have been examined, in order to identify the two-phase region of γ-Fe (austenite) and ε-Fe2Nb (C14). The ε single phase region exists in the range of 27.5 to 35.5 at.% Nb in the Fe-Nb binary system, and it extends toward the equi-niobium concentration direction up to 44 at.% Ni in the ternary system at 1473 K, indicating that more than half of the Fe atoms in Fe2Nb can be replaced with Ni. Thus, the γ+ε two-phase region exists extensively, and the solubility of Nb in γ phase increases from 1.5 to 6.0 at.% with increase in Ni content. The lattice parameters of a and c in the C14 Laves phase decrease with increasing Ni content. The change in a axis is in good agreement with calculation based on Vegard's law, whereas that of c axis is much larger than the calculated value. The result suggests that atomic size effect is responsible for a-axis change and the binding energy is dominant factor for the c-axis change. To extend these findings to development of new class of austenitic steels strengthened by Laves phase, an attempt has been made to control the c/a ratio by alloying. The addition of Cr is effective to make the c/a ratio close to the cubic symmetry value (1.633).
Massive Transformation in High Niobium Containing TiAl-Alloys
Authors: Bartels A. , Bystrzanowski S. , Chladil H. , Leitner H. , Clemens H. , Gerling R. , Schimansky F.-P. 
Published: April 2011

ABSTRACTMassive transformation in high Nb bearing γ-TiAl-based alloys, Ti-45Al-7.5Nb and Ti-46Al-9Nb (at.%), and the thermal stability of the resulting microstructure were investigated. Using a quenching dilatometer, a nearly complete massive transformation in Ti-45Al-7.5Nb was found at about 1050°C after annealing at 1305°C for 10min and subsequent cooling with a rate of 55K/s. Higher starting temperatures and higher cooling rates lead to incomplete massive transformation and small transformed areas situated at the grain-boundary triple points of the parent α-grains are observed. By means of EBSD only in one case the same orientation of the close-packed planes of parent α-grains and of massively transformed γM-areas was observed.The thermal stability of the microstructure of massively transformed Ti-46Al-9Nb sheet material was tested by annealing samples for 1 hour between 400 and 1200°C. Above 800°C a drop of hardness was measured and X-ray diffraction patterns show an increasing separation of (200)γ and (002)γ reflections as expected from a tetragonal γ-TiAl lattice. After annealing at 1100°C α2-phase segregates at grain boundaries and after 1200°C α2-lamellae appear insides the γM-grains parallel to all four {111}γ-planes.
Mechanical Behavior of a Pt-Cr Jewelry Alloy Hardened by Nano-Sized Ordered Particles
Authors: Jackson Kamili M. , Nzula Miyelani P. , Nxumalo Silethelwe , Lang Candace I. 
Published: April 2011

ABSTRACTThe materials engineering of platinum jewelry is interesting because only 5wt% can be used for alloying in order to maintain hallmarking. However, pure platinum is very soft and must be alloyed in order to be used effectively as jewelry. In several binary systems an increase in hardness has been found after cold working and annealing at low temperatures. The hardening in these alloys has shown to be a result of nano-sized ordered particles. In particular, the existence of the ordered particles has previously been confirmed for a Pt-Cr alloy by TEM. Extensive work has been done on the Pt-Cr alloy to understand the crystal structure and mechanisms of the ordered phase. Hardness tests were performed to measure mechanical properties after various heat treatments. In addition, tensile tests were conducted using a small-scale tensile testing machine. An 8mm long specimen is used, which significantly reduces the cost of the specimens while providing necessary properties. Tensile tests on the Pt-Cr alloys at various post deformation heat treatments show an increase in tensile strength with no effect on ductility. They confirm results of the hardness tests while providing additional properties data. In addition, the results show a fairly good relationship between strength and hardness.
The Correlation of Slip between Adjacent Lamellae in TiAl.
Authors: Molénat G. , Couret A. , Sundararaman M. , Singh J. B. , Saada G. , Veyssière P. 
Published: April 2011

ABSTRACTIn lamellar TiAl, concerted deformation occurs in adjacent true-twin related variants (O/OT). When deformation takes place in a given variant, O, by activation of the slip system with highest shear stress, slip proceeds in the companion variant, OT, by operation of a slip system of the same family in mirror orientation, including the slip direction. Depending on load orientation, the latter system may not necessarily exhibit the highest resolved shear stress. The correlation does not depend upon Burgers vector orientation with respect to the interface.This property applies to ordinary dislocations and twinning. The variant that conforms the Schmid law is referred to as the pilot variant, the twin-related variant is dubbed driven.
Examination of the Dynamic Mechanical Properties of Tissue Engineering Scaffolds
Authors: Kauth Heather , Klapperich Catherine 
Published: April 2011

AbstractScaffolds of both natural and synthetic materials have been widely utilized to provide a three dimensional environment for cell growth. The characteristics of these scaffolds play a vital, but sometimes ambiguous, role in tissue engineering constructs. Collagen-glycosaminoglycan matrices have been used clinically as artificial skin implants. Previous research in our laboratory on this model has shown that gene expression is regulated by mechanical stress applied to the matrix. In this work we begin the process of quantifying the effects of mechanical stress and preparation technique on a matrix comprised of type I collagen and chondroitin-6-sulfate. Compressive loads were applied to the matrices using a dynamic mechanical analyzer at 37 degrees Celsius and retrofitted with 5% carbon dioxide gas flow. All samples were tested hydrated in either simulated body fluid or PBS. Storage and loss modulus data are presented. Mechanical tests were performed on collagen-GAG meshes both seeded with humandermal fibroblasts and not seeded with cells. Continuing work includes gene expression analysis of the cells on the seeded matrices in order to identify differential gene expression induced by mechanicalloading.