bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interface-Stabilized Nanoscale Quasi-Liquid Films and Interfacial Prewetting and Premelting Transitions
Authors: Luo Jian , Gupta Vivek K , Qian Haijun 
Published: June 2019

AbstractEquilibrium-thickness, intergranular films (IGFs) have been observed in various ceramic materials. Recently, surficial amorphous films (SAFs) of similar character have also been found. Furthermore, a series of studies revealed the stabilization of disordered (quasi-liquid) IGFs and SAFs well below the bulk solidus or eutectic temperatures, wherein analogies to the phenomena of premelting and prewetting can be made. Accordingly, combined interfacial premelting and prewetting models have been developed using a diffuse-interface theory. This paper outlines the key results of two model experiments in support of the above theory: namely observation of quasi-liquid grain boundary films (metallic IGFs) in W-Ni and searching of a complete wetting transition for Bi2O3 on ZnO where SAFs become macroscopically thick. We propose that simple combined interfacial premelting and prewetting models apply to metallic IGFs, but only serve as a basis to understand IGFs and SAFs in ceramics where additional interactions, e.g. dispersion forces and space-charges, should be added separately and may result in more complex behaviors.
Phase Transformation Crystallography of Lath Martensite
Authors: Ma Xiao , Pond R.C. 
Published: June 2019

AbstractOur current understanding of martensitic transformations has been based on the Phenomenological Theory of Martensite Crystallography developed in the 1950s. Recently, a Topological Model of martensitic transformations has been presented wherein the habit plane is a semi-coherent structure, and the transformation mechanism is shown explicitly to be diffusionless. This approach is used here to model phase transformation crystallography of lath martensite in ferrous alloys. A range of network geometries is predicted corresponding to orientation relationships varying from Nishiyama-Wasserman to Kurdjumov-Sachs. Experimental observations from the literature of the dislocation and disconnection arrays, habit plane and orientation relationship are in good agreement with the model.
Influence of Processing Parameters on Microstructure of Pulsed Laser Deposited Au Thin Films
Authors: Kulovits Andreas , Leonard John , Wiezorek Jorg 
Published: June 2019

AbstractIt has long been recognized that thin film polycrystalline microstructures are determined by the thermodynamics and kinetics associated with physical vapor deposition, but it is quite process dependent and not easily quantified. We have examined the microstructure in polycrystalline Au films obtained by pulse laser deposition (PLD) under various conditions and interpret the results in terms of three fundamental parameters common to all physical vapor deposition: Flux kinetic energy, substrate temperature, and deposition rate. With this model, it is predicted that nanocrystalline films are formed in the limits of low temperature, flux, and high deposition rate. The deposited films are analyzed with X-ray diffraction and SEM to determine texture and grain morphology, which are found to fit well within the process maps.
Nucleation-Initiated Solidification of Thin Si Films
Authors: Hazair S. , van der Wilt P. C. , Deng Y. , Chung U.-J. , Limanov A. B. , Im James S. 
Published: June 2019

AbstractThin Si films on SiO2 that are completely melted by pulsed laser irradiation cool rapidly and eventually solidify via nucleation and growth of solids. It has been observed that a variety of solidified microstructures can be obtained, depending primarily (but not exclusively) on the degree of supercooling achieved prior to the onset of nucleation. This paper focuses on investigating one particular and unusual polycrystalline microstructure that consists of “flower-like” grains, the interiors of which can be described as being made up of two distinct regions: (1) an extremely defective core region consisting of fine-grained material, and (2) an outer region consisting of relatively defect-free crystal “petals” that radiate outwards. After considering the microstructural details and experimental behavior of the microstructure, we have formulated a growth-based physical model to account for the formation of the microstructure. The model is found to be also capable of accounting for the other complex and unusual microstructures obtained via nucleation and growth in the complete melting regime.
The Origin and Implications of (111)-Textured Grains Obtained via Nucleation and Growth of Solids in Pulsed-Laser-Quenched Al Films on SiO2
Authors: Choi J. B. , Choi Min H. , Chung U.-J. , Limanov A. B. , Im James S. 
Published: June 2019

AbstractWe have investigated excimer laser irradiation of 2000-Å-thin as-deposited Al films on SiO2. Microstructural analysis of the irradiated films conducted with AFM and EBSD techniques reveals that there exists a wide energy density interval over which large equaxed grains with a strong (111) texture are obtained. Based on thermal, transformational, and microstructural considerations, we propose a heterogeneous nucleation model to account for the observed behaviors, and discuss the implication of the model on the phenomenon of heterogeneous nucleation of crystalline solids in condensed systems as regards the thermodynamic role played by the orientation of subcritical clusters.
Solute-Driven Melting Kinetics in the Sn-Bi System
Authors: Yasensky David , Abbaschian Reza 
Published: June 2019

AbstractThe goal of the present study was to gain insight into the mechanisms and behavior of solute driven melting processes. Solute-driven melting refers to melting whose driving force originates from a change in composition, i.e., solute content, rather than a change in temperature. This kind of melting has been known to cause casting defects in superalloys and other metals.An experimental apparatus was designed and a series of experiments were carried out on Sn-Bi alloys. The apparatus involved diffusing Bi into solid Sn cast inside a glass capillary to cause it to melt. The Bi source was an enriched liquid Sn-Bi alloy contained in a reservoir. The Sn in the capillary was kept at a constant temperature below its melting point so that the melting was caused by the increasing Bi composition. The progression of the interface was monitored by quenching the process at various times for the same conditions.The apparatus was successful in delivering data for the displacement of the interface against time. It was found that interface position was approximately proportional to the square root of time, and so the process may be diffusion controlled as conjectured in previous literature. Rough calculations are made relating the temperature and supersaturation to the displacement coefficient A in the equation z = At½ where z is displacement and t is time. By comparing data at different temperatures with the same supersaturation, an activation energy Q of ~60,000J/mol is calculated. This value is between the activations energies for diffusion of Bi through the liquid and the solid. Suggestions for modification of the apparatus to include in-situ interface monitoring are made.
Formation of Domain Structures in Ordering Processes of B2 and D03 Types
Authors: Oguma Ryuichiro , Matsumura Syo , Eguchi Tetsuo 
Published: June 2019

AbstractTime-dependent Ginzburg-Landau (TDGL) formulation on a continuous medium has been developed for ordering processes of B2 and D03 types in binary alloy systems. The results of 2-dimensional simulations reproduce well the formation of B2 and D03 ordered domains in the processes in an Fe3Al alloy.
Effect of Temperature on the Kinetics of Nanocluster Nucleation and Growth in Polymeric Media
Authors: Gazit Oz , Tannenbaum Rina 
Published: June 2019

AbstractThe synthesis of metal nanoclusters in a polymeric environment has been shown to yield nearly monodisperse particles, whose size is controlled by the strength of the polymer/metal interactions. Although the phenomenon is quite general, little is known regarding the mechanism by which the polymer controls nanocluster size. Previous studies of the kinetics of nanocluster growth in polymeric melts above the glass transition temperature (Tg) showed that the nanoparticle size is set by the critical cluster size rather than the rate of metal precursor transport. In this paper we examined the kinetics of iron-oxide (Fe2O3) nanocluster formation in two polymer melts below their Tg: polystyrene (PS) and poly(methyl methacrylate) (PMMA). We found that the rate of particle formation is nucleation-controlled for both PS and PMMA, similarly to the same process above Tg, while the growth stage is diffusion limited. Transmission electron microscopy (TEM) revealed needlelike particles morphology with larger average dimensions as the temperature is elevated towards polymer matrix Tg. The stabilizing effect of the polymer chains on the growth of the nanoparticles was dominant when the synthesis was performed in solution or in the melt, allowing the polymer to adsorb on the cluster. However, below its Tg the chains were not free to move and conform to the nanocluster surface, and hence, capping occurred when the cluster growth limitation was imposed by the geometric confines set by the voids in the polymer matrix.
Microstructure and Mechanical Properties of an Extruded Fe30Ni20Mn25Al25 Alloy
Authors: Loudis J. A. , Boyd T. C. , Coen D. A. , Baker I. 
Published: June 2019

AbstractA spinodal alloy, Fe30Ni20Mn25Al25, was produced by casting followed by hot extrusion. The microstructure consisted of coherent, 20-30 nm wide rods of alternating body-centered cubic (b.c.c.) and ordered B2 phases aligned along <100>. The room temperature mechanical properties were determined under compression over a range of strain rates. The as-extruded yield strength, which was strain-rate dependent, was ~1400 MPa. Annealing at 550°C led to the precipitation of large unit cell cubic phase and to an increase in hardness. Post-mortem TEM analysis of the compressed specimens identified dislocations having <111> Burgers vectors.
Effects of Dislocation and Microstructure on Pseudoelasticity in D03-Type Fe3Al Single Crystals
Authors: Umakoshi Yukichi , Nakajima Takashi , Yasuda Hiroyuki Y. 
Published: June 2019

AbstractNew type pseudoelasticity in Fe3Al with the D03 structure was examined using the single crystals. The pseudoelasticity occurred due to a reversible motion of 1/4<111> superpartials dragging the nearest-neighbor anti-phase boundaries. The chemical composition and microstructure of Fe3Al alloys strongly influenced the shape recovery ratio and Fe-23.0at%Al alloy with fine domain structure was the most favorable for the appearance of the pseudoelasticity. The recovery ratio of Fe-23.0at%Al exceeded 80 % in the wide temperature range from -50 to 200 oC.
First-principle Thoery of Phase Stability, Phase Equilibria and Phase Transition of Ordered Compounds
Authors: Mohri Tetsuo 
Published: June 2019

AbstractFirst-principles theory of alloys is based on electronic structure calculation at the ground state and statistical mechanics calculation at finite temperatures. The former clarifies the stability of an ordered compound against competing phases and the latter is employed mainly to derive a phase diagram. The author performed a series of first-principles investigations on binary alloy systems including noble metal alloys, semiconductor alloys and Fe-based alloy systems by combining FLAPW electronic structure total energy calculations with Cluster Variation Method. Recently, the theoretical framework is extended even to calculate microstructural evolution process. By exemplifying Fe-based alloy systems, the progress of the first-principles calculation is reviewed and future prospect is discussed.
Control of Microstructure Driven by Magnetic Field in Ferromagnetic Intermetallics
Authors: Kakeshita Tomoyuki , Fukuda Takashi 
Published: June 2019

AbstractMagnetic field has been known to be effective in solidification processes. Recently, however, it has been revealed that the magnetic field is also effective for controlling the arrangement of variants, which are formed in association with a solid-solid transformation, in some ferromagnetic intermetallic-based alloys with a large magnetocrystalline anisotropy. In this presentation, we will show two of such cases: one is the rearrangement of martensite variants by magnetic field in intermetallic-based ferromagnetic shape memory alloys (Ni2MnGa and Fe3Pt), and the other is formation of mono-variant state by ordering heat-treatment under magnetic field in a L10-type CoPt. The former process is diffusionless and proceeds by the movement of twinning plane under a magnetic field. The latter is a diffusion controlled process. For both the cases, a large magnetocrystalline anisotropy is essentially important for controlling the arrangement of variants, although kinetics of the two processes is quite different each other.
Microstructural Evolution during Post Deposition Annealing of Pulsed Laser Deposited Fe(100-x) Pdx Thin Films
Authors: Kulovits Andreas , Leonard John , Wiezorek Jorg 
Published: June 2019

AbstractFePd belongs to a group of L10 - intermetallics with attractive uniaxial hard-ferromagnetic properties. In this study thin films of different composition FeXPd1-X, X= 50, 60, were deposited by pulsed laser deposition (PLD) on amorphous SiO2 and Si3N4. We characterized the microstructural evolution during the different order/disorder phase-transformations during post-deposition annealing relative to the as-deposited state in terms of morphology, grain size, texture and presence of short-range order using SEM, XRD and TEM. VSM measurements were used to monitor magnetic properties. Differences in these microstructural parameters are due to different ordering reactions FCC to L10 ordering and concomitant phase separation of ?-Fe vs. FCC to L10 ordering upon heat treatment. The relationships of the different phase transformation products to properties are discussed. Support from NSF-DMR-Metals is gratefully acknowledged.
Thermoelectric Properties of Half-Heusler Compounds N-type MNiSn and P-type MPtSn (M = Hf, Zr)
Authors: Kimura Yoshisato , Kuji Tomoya , Zama Akihisa , Lee Taiki , Mishima Yoshinao 
Published: June 2019

AbstractTo design and to develop Half-Heusler based high-temperature thermoelectric materials, thermoelectric properties of n-type MNiSn and p-type MPtSn (M = Hf, Zr) were investigated based on two respective strategies. For the n-type (Hf, Zr)NiSn, a combined process of optical floating zone melting and hot-pressing was applied aiming to reduce thermal conduction through the lattice contribution. For the p-type HfPtSn, power factor and hence figure of merit ZT were dramatically improved by the p-type doping of Ir and Co targeting for Pt-site, which effectively lower electrical resistivity. The additions of Ir and Co are expected not only to increase carrier concentration but also to suppress the lattice thermal conduction by substituting for Pt.
Compression and Compressive Creep Behaviors in Titanium Aluminides Alloyed with Vanadium comprizing Gamma + Beta Dual Phase Microstructures
Authors: Takahashi Tohru , Kojima Yohji , Otsuka Koshiro 
Published: June 2019

AbstractFine grained gamma+beta dual phase microstructures were obtained in aluminum-titanium-vanadium ternary alloys containing 40 at.% aluminum and 60 at.% (titanium and vanadium). Average grain size was about 5, 3, and 2 micrometers in the recrystallized materials containing 20, 30, and 40 at.% vanadium, and the phase constitution was around 50vol.% gamma phase and 50vol.% beta phase. Compression behavior was investigated at temperatures ranging from the room temperature up to 1200K, and compressive creep tests were carried out at 1050-1200K in order to characterize the temperature and chemical composition dependences of strength and deformation. These gamma+beta microduplex materials showed very high strength at room temperature; 0.2% proof stress was around 1200MPa. The compression deformability decreased from about 0.2 to 0.05 true strain with increasing vanadium content. The grain size effect was not clarified yet, but it was rather disappointing that smaller-grained material with Al40Ti20V40 composition did not show effective improvement either in strength or in deformability. 0.2% proof stress showed a considerable weakening at temperatures higher than 900K; the onset temperature of softening became lower as the vanadium content increased. In Al40Ti40V20 material with about 5 micrometer grains, both gamma and beta grains were flattened up to 1000K, however, above 1100K the gamma grain showed no significant shape change even after a heavy deformation. This is probably because the gamma grains were relatively stronger than the beta grains. The gamma grains showed tendency toward agglomeration, which is similar to rafting of precipitate particles. Surface relief was observed after high temperature deformation suggesting activity of boundary sliding on grain boundaries and interfaces. Compressive creep behavior was investigated under a constant true stress in vacuum. Creep curves consisted of a small amount of normal primary transient, the minimum creep rate region, and a steady or slightly accelerating creep region. Stress exponent decreased to about 2 with decreasing vanadium content. It was rather unexpected that smaller grained Al40Ti20V40 material showed larger stress exponent around 3.
Synthesis of FeAl Hetero-Nanostructured Bulk Parts via Spark Plasma Sintering of Milled Powder
Authors: Grosdidier Thierry , Ji Gang , Bernard Frédéric , Launois Sébastien 
Published: June 2019

AbstractSpark plasma sintering (SPS) has been used in order to introduce nanocrystalline grains within fully dense FeAl consolidated parts. Hetero-nanostructured parts, consisting of nano, ultrafine and micrometric grains, have been successfully processed when milled - Y2O3 reinforced - FeAl powder was used. The large temperature differences that are spontaneously generated during the SPS process as well as the use of milled powder account for the formation of such interesting structures. The grain size distribution - that is suggested to be very potent to improve both strength and ductility - could be significantly modified by a proper selection of sintering temperature and holding time.
TEM Observation of Vacancy Clustering Process in FeAl Single Crystal
Authors: Tsunekane Masafumi , Yoshimi Kyosuke , Maruyama Kouichi 
Published: June 2019

AbstractNanoporous surfaces are formed in B2-type FeAl single crystals by quenching into iced water, followed by surface treatment and aging heat treatment. From our previous works, it was indicated that the nanoporous phenomenon is caused by the clustering of supersaturated thermal vacancies. In this study, the clustering process of supersaturated thermal vacancies was systematically investigated by transmission electron microscopy (TEM). An irreversible exothermic peak was detected for as-quenched specimens by differential scanning calorimetry (DSC). The isochronal changes of surface morphology and substructure around the exothermic peak temperature were clarified by TEM observation. The average size of the surface pores monotonously increased with increasing the temperature. Dislocations whose Burgerse vectors are parallel to <100> existed in the isochronally-heated single crystals, and its density was changed with heat treatment temperature. On the other hand, there was no dislocation zone from surface to the depth of several tens nanometers. A growth model of the surface pores is discussed
Synthesis, Microstructure, and Mechanical Properties of FeCo-VC Composites
Authors: Bei Hongbin , George E. P. 
Published: June 2019

AbstractFe-Co-V-C quaternary alloys were drop cast and directionally solidified to obtain an in situ composite. It is found that the fully eutectic structure occurs at a composition of Fe - 40.5Co -10.4V- 8.6C (at. %) in a drop-cast alloy. Directional solidification of this composition in a high-temperature optical floating zone furnace produces a well-aligned microstructure, consisting of sub-micron VC fibers (~19% by volume) embedded in a FeCo-5V solid solution matrix containing ~ 1% C. The temperature dependencies of mechanical properties of this composite were examined by tensile tests and the composite was found to have higher yield strength and lower ductility than the matrix.
Atomic Disorder and its Relation to the Magnetic Behavior in CoFe1-xAlx Alloys
Authors: Fujiwara Tetsuya , Kikuchi Shigeyuki , Ishibashi Hiroki , Kogachi Mineo 
Published: June 2019

AbstractAtomic disorder is investigated for B2- and Heusler-phase CoFe1-xAlx alloys quenched from various temperatures by X-ray diffraction measurements. In the B2-phase region, with increase in quenching temperature, atomic disorder on the Co-site (Co-type disorder) proceeds for x=0.30 but not for x=0.70. In the Heusler-phase region (x=0.45, 0.50 and 0.55), atomic disorder between the Fe- and Al-sites (Fe-Al-type disorder) mainly proceeds. A relation between the magnetic behavior obtained in our previous work and the atomic disorder is examined. As a result, it is found that the Co-type disorder leads to a reduction of the magnetic moment in the B2-phase alloys and that the Fe-Al-type disorder does not significantly affect the magnetic behavior in the Heusler-phase alloys.
Plastic Deformation Behavior of Oriented Ni3V Crystals with D022 Structure
Authors: Hagihara Koji , Mori Mayumi , Umakoshi Yukichi 
Published: June 2019

AbstractPlastic deformation behavior of Ni3V with D022 structure was examined using the single crystals containing two dominant variants of three. Three deformation modes were confirmed to be operative depending on temperature and loading orientation. {111}1/6<112] twinning and/or {111}<110] slip is dominantly operative at low temperatures, but {111}1/2<112] slip is activated at high temperatures accompanied by a rapid drop of yield stress.
Microstructure Control of Nb-Si Alloy Doped with Zr and Mg through Eutectic and Eutectoid Reactions and its Deformation Behavior
Authors: Miura Seiji , Murasato Yuki , Ohkubo Kenji , Kimura Yoshisato , Sekido Nobuaki , Mishima Yoshinao , Mohri Tetsuo 
Published: June 2019

AbstractIn order to overcome the brittleness of Nb-Si intermetallic compounds, a novel microstructure control through a eutectic solidification and a eutectoid decomposition reactions has been proposed for obtaining Nb matrix alloys with Nb-silicide dispersion by the present authors. As the additions of Zr and Mg accelerate the eutectoid decomposition rate and spheroidization of Nb-silicide during heat treatment, the effects of these additives on the eutectic microstructure are investigated. The effect of the growth rate during the uni-directional solidification on the microstructure of a selected alloy was examined and it was found that the following eutectoid reaction rate is strongly affected by the growth rate.
Effect of Cr Addition on the Phase Equilibria of the Nb-Si System
Authors: Bewlay B. P. , Yang Y. , Casey R. L. , Jackson M. R. , Chang Y. A. 
Published: June 2019

AbstractNb-silicide based in-situ composites are promising materials for future high-temperature structural applications. Nb-silicide composites are typically alloyed with Hf, Ti, Cr, and Al to provide a balance of mechanical and environmental properties. A thermodynamic description of the Nb-Cr-Si system has been developed previously in literature based on reported isothermal sections. According to the previously calculated phase diagrams, selected alloys were directionally solidified. The as-solidified microstructures could not be interpreted using the liquidus projection calculated from the existing thermodynamic descriptions. Therefore, an improved thermodynamic description was developed by incorporating the new experimental data.