bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Water on Mechanical Properties of Mineralized Tissue Composites
Authors: Bembey Amanpreet Kaur , Oyen Michelle L , Ferguson Virginia L. , Bushby Andrew J. , Boyde Alan
Published: June 2019

In the current study, the effects of polar solvents on tissue volume and mechanical properties are considered. Area shrinkage measurements are conducted for mineralized, bone tissue samples soaked in polar solvents. Area shrinkage is used to calculate approximate linear and volume shrinkage. Results are compared with viscoelastic mechanical parameters for bone in the same solvents (as measured previously) and with both shrinkage measurements and mechanical data for nonmineralized tissues, as taken from the existing literature. As expected, the shrinkage of mineralized tissues is minimal when compared with shrinkage of nonmineralized tissues immersed in the same polar solvents. The mechanical changes in bone are also substantially less than in nonmineralized tissues. The largest stiffness values are found in shrunken bone samples (immersed in acetone and ethanol). The mineral phase in bone thus resists tissue shrinkage that would otherwise occur in the pure soft tissue phase.
Nanomechanics of Knockout Mouse Bones
Authors: Kavukcuoglu N Beril , Mann Adrian B.
Published: June 2019

Osteocalcin (OC) and osteopontin (OPN) are among the most abundant non-collagenous bone matrix proteins. Both have drawn interest from investigators studying their function in osteoporosis and it is known that mutations of these proteins can also have dramatic effects on the properties of bone. Other proteins including fibrillin 1 and 2 (FBN2) have been less widely studied, but can be mutated in some individuals resulting in connective tissue disorders. It has been reported that abnormal fibrillin may play a role in decreased bone mass. In this study bones from osteopontin (OPN), osteocalcin (OC) and fibrillin-2 (FBN2) knockout mice have been investigated. The study has identified how these proteins affect the bone's nanomechanical properties (hardness and elastic modulus). Nanoindentation tests were performed on the radial axis of cortical femora bones from the knockout mice and their wildtype controls. The results showed that young (age< 12 weeks) OPN knock-out bones have significantly lower mechanical properties than wild-type bones indicate a crucial role for OPN in early bone mineralization. After 12 weeks of age, the OPN knockout and wild-type control bones did not show any statistical difference. In OC deficient mice the mechanical properties were found to increase in the cortical mid-shaft of femora from 1 year old mice, suggesting an increase in bone mineralization, but 3 month old FBN2 deficient mice bones showed a decrease in mechanical properties across the cortical radial axis of the mid- femora.
Multiscale Modeling of Carbon Nanotube Adhesion for Dry Adhesives
Authors: Xia Zhenhai , Liang Jianyu
Published: June 2019

Geckos have extraordinary ability to move on vertical surfaces and ceilings. The secret of the climbing ability stems from their foot pads, a special hierarchical hairy structure. Mimicking such structure would lead to dry adhesives for many applications. Recent experiments showed that the adhesion of multiwalled carbon nanotubes is larger than that of a gecko foot-hair. To explore the adhesive mechanisms of the nanotubes, we have developed a multiscale approach to simulate the adhesion process of carbon nanotubes. A molecular dynamics is used to simulate the deformation and damage of the nanotubes when contacting with a rough surface at atomic scale. A coarse graining method is developed to predict the interactions and adhesion of larger scale nanotube array. The parameters used in the coarse graining method are determined by the detailed molecular dynamics. The preliminary results show that the nanotube bending under pre-applied pressure increases the contact area and therefore enhances the adhesion. The nanotube breakage during pre-loading will reduce the adhesion in post cycles. These results are consistent with the experiments found in literature.
Atomistic Simulations of Strain Rate Dependent Deformation Behavior at Continuum Timescales
Authors: Tomar Vikas
Published: June 2019

A majority of computational mechanical analyses of nanocrystalline materials or nanowires have been carried out using classical molecular dynamics (MD). Due to the fundamental reason that the MD simulations must resolve atomic level vibrations, they cannot be carried out at the timescale of the order of microseconds. Additionally, MD simulations have to be carried out at very high loading rates (∼108 s−1) rarely observed in experiments. In this investigation, a modified Hybrid Monte Carlo (HMC) method that can be used to analyze time-dependent (strain rate dependent) atomistic mechanical deformation of nanostructures at continuum timescales is established. In this method there is no restriction on the size of MD timestep except that it must be such that to ensure a reasonable acceptance rate between consecutive Monte-Carlo (MC) time-steps. For the purpose of comparison HMC analyses of Cu nanowires deformation at two different strain rates (108 s−1 and 109 s−1) (each with three different timesteps 2 fs, 4fs, and 8 fs) are compared with the analyses based on MD simulations at the same strain rates and a MD timestep of 2 fs. As expected, the defect formation is found to be strain rate dependent. In addition, HMC with timestep of 8 fs correctly reproduces defect formation and stress-strain response observed in the case of MD with 2 fs (for the interatomic potential used 2 fs is the highest MD timestep). Simulation time analyses show that by using HMC a saving of the order of 4 can be achieved bringing the atomistic analyses closer to the continuum timescales.
Grain Boundary Responses to Local and Applied Stress: An In Situ TEM Deformation Study
Authors: Miller Bryan , Fenske Jamey , Su Dong , Li Chung-Ming , Dougherty Lisa , Robertson Ian M.
Published: June 2019

Deformation experiments at temperatures between 300 and 750 K have been performed in situ in the transmission electron microscope to investigate dislocation interactions and reactions with grain boundaries and other obstacles. Dislocations, both partial and perfect, as well as deformation twins have been observed being emitted from grain boundaries and, in some cases, even the same grain boundary. The ejection of dislocations from the grain boundary can result in its partial or total annihilation. In the latter case, the disintegration of the grain boundary was accompanied by grain growth and a change in misorientation.
On the Characterization of Thin Film-only Mechanical Property Based on the Indentation Image Analysis
Authors: Lee Yun-Hee , Kim Yong-Il , Jang Hoon-Sik , Nahm Seung-Hoon , Kim Ju-Young , Kwon Dongil , Jang Jae-il
Published: June 2019

Conventional nanoindentation testing generally uses a peak penetration depth of less than 10 % of thin-film thickness in order to measure film-only mechanical properties, without considering the critical depth for a given thin film-substrate system. The uncertainties in this testing condition make hardness measurement more difficult. We propose a new way to determine the critical relative depth for general thin-film/substrate systems; an impression volume analyzed from the remnant indent image is used here as a new parameter. Nanoindents made on soft Cu and Au thin films with various indentation loads were observed by atomic force microscope. The impression volume calculated from 3D remnant image was normalized by the indenter penetration volume. This indent volume ratio varied only slightly in the shallow regime but decreased significantly when the indenter penetration depth exceeded the targeted critical relative depth. Thus, we determined the critical relative depth by empirically fitting the trend of the indent volume ratio and determining the inflection point. The critical relative depths for Cu and Au films were determined as 0.170 and 0.173, respectively, values smaller than 0.249 and 0.183 determined from the hardness variation of the two thin films. Hence the proposed indent volume ratio is highly sensitive to the substrate constraint, and stricter control of the penetration depth is needed to measure film-only mechanical properties.
Size Effect in the Initiation of Plasticity for Ceramics in Nanoscale Contact Loading
Authors: Zhu Tingting , Hou X.D. , Walker C. J. , P'ng K. M.Y. , Dunstan D. J. , Bushby A. J.
Published: June 2019

In nanoindentation, the plasticity size effect has been observed for several years, where a higher hardness is measured as indenter size decreases. In this paper, we report the size effect on the initiation of plasticity in ceramics by using spherical indenters. Here, we show a clear method that is able to determine the details of the onset of plasticity in nanoindentation. This enables us to measure the yield pressure with a high degree of accuracy and over a large range of indenter radii (hundreds of nanometers to several tens of micrometers). Our data shows clearly that there is a significant yield strength enhancement, which is inversely proportional to the cube root of the indenter radius. Also after normalization by the bulk yield strength, the increase in yield strength with decreasing indenter radius is shown to follow a single relation for all the ceramics studied in agreement with recent results for metals [1], and consistent with critical thickness theory for the initiation of yielding over a finite volume.
Thermal Effects of Phase Transformations: A General Approach
Authors: Umantsev Alex
Published: June 2019

All stages of phase transformations in materials, nucleation, growth, and coarsening, are subjected to thermal effects that stem from the redistribution of energy in the system like, release of latent heat and heat conduction. The thermal effects change the rate and outcome of the transformation and may result in appearance of unusual states or phases, in particular in nanosystems. This paper is not a complete account of the theory of thermal effects; it is rather a guide through many seemingly unrelated effects in different phase transformations, which in fact have unified origin. Although the dynamical Ginzburg-Landau approach will be used for the analysis of the effects, they are robust and independent of the employed theoretical methods. Another purpose of this review is to bring these effects to the attention of experimenters and motivate them on conducting new experiments in the area of phase transitions.
Interface-Stabilized Nanoscale Quasi-Liquid Films and Interfacial Prewetting and Premelting Transitions
Authors: Luo Jian , Gupta Vivek K , Qian Haijun
Published: June 2019

Equilibrium-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

Our 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

It 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

Thin 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

We 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

The 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

Time-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

The 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

A 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

New 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

First-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

Magnetic 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

FePd 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

To 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

Fine 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

Spark 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

Nanoporous 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

Fe-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

Atomic 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

Plastic 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

In 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

Nb-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.
Toughening Effect and Oxidation Behavior of MoSi2 -ZrO2 Composites
Authors: Gong Karin , Yao Yiming , Sundberg Mats , Li Xin-Hai , Ström Erik , Li Changhai
Published: June 2019

Toughening effect of ZrO2-particles on MoSi2-based materials is one of the important toughening mechanism. In this work, the influence of particle size and volume percentage of unstabilized ZrO2-addition on toughening in MoSi2-matrix composites was studied. The measured data revealed that the fine particle size, < 1 ìm, with certain volume percentages around 20% have given more effective toughening results. The tested materials were prepared by two different sintering processes: pressure-less sintering (PLS) and PLS + Hipping sintering. The results on sintered density, RT-hardness and RT-toughness indicated that the PLS process could be a practical and economical method for producing MOSi2-ZrO2 composites in industry. Oxidation behavior of MoSi2-ZrO2 composites was also studied in the work. Clearly, the ZrO2-addition made the composites having a worse oxidation resistance than the monolithic MoSi2, which means that a low ZrO2-addition should be used in the composites, as far as an acceptable toughening effect was reached.
Control of the Si Vacancy Concentration and Arrangement in ReSi1.75 by Al and P Additions
Authors: Harada Shunta , Tanaka Katsushi , Kishida Kyosuke , Inui Haruyuki
Published: June 2019

The concentration and arrangement of Si vacancy in aluminum or phosphorus containing ReSi1.75 based silicides have been investigated. Both aluminum and phosphorus are substituted with silicon. In addition to the (001)C11b twins usually observed in binary ReSi1.75, planar defects are heterogeneously formed in both of the silicon substituted ternary alloys with small amount. By using the high resolution electron micrograph (HREM) technique, the planar defects are assigned as crystallographic shear (CS) planes lying on (109) C11b and (107) C11b in aluminum and phosphorus containing ReSi1.75, respectively. The CS vector in both ternary alloys is [100]C11b. Since the concentration of vacancies in the ReSi1.75 structure is changed by the introduction of these crystallographic shear, ternary alloys with silicon substituted by aluminum and phosphorus contain more or less amount of vacancies than the binary alloy, respectively. This implies us that concentration of Si vacancies changes so as to retain the average number of valence electron. We can control the concentration of Si vacancy in the ReSi1.75 based alloys.
Theoretical investigation of Pt monosilicide and several germanides: electronic structure, surface energetics, and work functions
Authors: Niranjan Manish K. , Kleinman Leonard , Demkov Alexander A.
Published: June 2019

We present a theoretical study of the electronic structure, surface energies and work functions of orthorhombic Pt monosilicide and germanides of Pt, Ni, Y and Hf within the framework of density functional theory (DFT). Our calculated bulk structures are within 1-2% of reported experimental values. Calculated work functsions for the (001) surfaces of PtSi, NiGe and PtGe are 5.12, 4.57 and 4.83 eV, respectively, suggesting that these metals and their alloys can be used as self-aligned contacts to p-type silicon and germanium. Work functions for Y and Hf germanides range from 2.4 to 4.3 eV making them a possible n-type contact material. In addition, we also report an ab-initio calculation of the Schottky-barrier height at the Si(001)/PtSi(001) interface. The p-type Schottky barrier height of 0.28 eV is found in good agreement with predictions of a simple metal induced gap states (MIGS) theory and available experiment. This low barrier suggests PtSi as a low contact resistance junction metal for silicon CMOS technology. We identify the growth conditions necessary to stabilize this orientation.
Magnetic Behavior due to Quenching Temperature in Co-based Heusler-type Alloys Co2MnZ (Z=Si, Ge, Sn)
Authors: Kikuchi Shigeyuki , Fujiwara Tetsuya , Ishibashi Hiroki , Kogachi Mineo
Published: June 2019

Magnetic behavior in Co-based Heusler alloys Co2MnZ (Z=Si, Ge, Sn) is investigated as a function of quenching temperature. The mean magnetic moment decreases with increase in quenching temperature in Co2MnSi and Co2MnGe while it remains almost constant in Co2MnSn. Relation between the magnetic behavior and the atomic disorder is discussed.

The results of the lattice constant and the electrical resistance measurements are also reported.
Effect of Ti3Si on Texture in Ti-Nb Based Shape Memory Alloys
Authors: Shimizu Ryutaro , Masumoto Kei , Fukui Yusuke , Inamura Tomonari , Wakashima Kenji , Hosoda Hideki , Miyazaki Shuichi
Published: June 2019

Effect of Ti3Si particles on recrystallization texture of Ti-Nb based superelastic alloys has been investigated using X-ray pole figure measurement and electron backscatter diffraction (EBSD) technique. The alloys used were Ti-24mol%Nb-3mol%Al-Xmol%Si (X=0~0.9, termed XSi) and Ti-24mol%Nb-3mol%Si alloy (termed 3Si). The apparent phase at room temperature was β-phase (bcc). Besides, (Ti, Nb)3Si particles with PTi3 type crystal structure were formed in the alloys with Si content higher than 0.7mol%. After the cold rolling of 99% reduction in thickness, a rolling texture of the β-phase was formed to be mainly {001}β<110>β regardless of the presence of the (Ti, Nb)3Si particles. After the solution treatment at 1273K, a recrystallization texture formed to be {112}β<110>β in all the alloys except for 3Si. The average grain size of the recrystallized alloys was 20~40μm. On the other hand, the solution treated 3Si exhibited the {001}β<110>βn texture and the average grain size of 3μm. It is concluded that the {001}β<110>β texture with fine grains of the solution treated 3Si is obtained by the suppression of grain boundary migration due to the existence of the (Ti, Nb)3Si particles.
Phase Constitution, Crystal Structures and Hardness of Ti60-xAu40Cox and Ti34-xAu44Co22+x (x=0, 2 and 4) Ternary Alloys
Authors: Tsugane Yasuhito , Inamura Tomonari , Wakashima Kenji , Hosoda Hideki
Published: June 2019

It was previously found that two B2 phases (matrix and precipitates) appeared in Ti-32mol%Au-18mol%Co superelastic alloy. In this study, each B2 single phase alloy was tried to be fabricated individually, and phase constitution, crystal structures and hardness were investigated. The chemical compositions were Ti60-xAu40Cox and Ti34-xAu44Co22+x (x=0, 2 and 4), and the alloys were fabricated by Ar-arc melting followed by a hot-forging at 1423K for 43.2ks and a solution treatment at 1173K for 3.6ks. It was found by X-ray diffraction analysis that Ti60-xAu40Cox (called Co-poor alloys) were composed of B19 (Ti, Co)Au and A15 Ti3Au two phases, instead of B2 single phase expected. It was also found that Ti34-xAu44Co22+x (called Co-rich alloys) were composed of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) two phases, instead of B2 single phase expected. These unexpected phase constitutions appeared in this work may be due to the difference in cooling rate and/or phase transformation from B2 to C11b. Lattice parameters of the obtained phases were precisely determined. The hardness of C11b Ti(Au,Co)2 and C36 Co2(Ti,Au) are HV480 and HV780, respectively. The hardness change of Co-rich alloys can be understood in terms of the volume fraction change of these phases.
Microstructures and Hydrogen Permeability of Nb-NiTi Eutectic Alloys Prepared by Directional Solidification
Authors: Yamaguchi Yuji , Kishida Kyosuke , Tokui Sho , Ishikawa Kazuhiro , Tanaka Katsushi , Aoki Kiyoshi , Inui Haruyuki
Published: June 2019

The Nb-NiTi eutectic alloys were directionally solidified (DS) in an optical floating zone furnace. Columnar grains of eutectic structures containing rod-shaped Nb in the NiTi matrix is observed in the DS ingots irrespective of the alloy composition. Well-aligned rod-type eutectic microstructures can be obtained for samples with a composition of Nb-41Ni-40Ti grown at relatively slow growth rates below 2.5mm/h. The hydrogen permeability along the direction parallel to the Nb rods of Nb-41Ni-40Ti DS alloy grown at 1mm/h is 2.60×10-8mol H2m-1 Pa-1/2 at 673K, which is over 20 times higher than that measured perpendicular to the Nb-rod direction. No hydrogen embrittlement is observed between 573 and 673K indicating that the eutectic structure itself is favorable in suppressing the hydrogen embrittlement of Nb.
High Temperature Mechanical Behavior of a Mo-Si-B Solid Solution Alloy
Authors: Jain Padam , Kumar K. S.
Published: June 2019

Multi phase alloys at the Mo-rich end of the Mo-Si-B system have drawn recent attention because of their high temperature performance capabilities. Previous studies on two- and three-phase alloys have confirmed the central role of the Mo-rich solid solution phase in affecting creep resistance and low-temperature toughness in these multiphase alloys. Thus, it is important to understand the intrinsic mechanical response of the matrix solid solution. In this study, compression and tensile tests were conducted over a nominal strain rate regime spanning 10-4 s-1 to 10-7 s-1 and temperature ranging from 1000°C to 1300°C in vacuum on a Mo-Si-B solid solution alloy (Mo-3Si-1.3B in at.%) that contained a low fraction (~5 %) of the T2 phase. The microstructure of the deformed specimens was examined to elucidate the underlying deformation mechanisms.
Pseudoelastic Behavior of Fe3Ga Single Crystals with D03 Structure
Authors: Yasuda Hiroyuki Y. , Aoki Mitsuhiro , Fukushima Kouki , Umakoshi Yukichi
Published: June 2019

Pseudoelastic behavior of Fe3Ga single crystals regardless of a thermoelastic martensitic transformation was investigated focusing on the dislocation structure and the phase constituent. Large pseudoelasticity of 5 % recoverable strain appeared in Fe3Ga single crystals sufficiently annealed in the D03 single-phase region. In the crystals, uncoupled and paired 1/4[111] superpartial dislocations moved dragging the nearest-neighbor (NN) and next-nearest neighbor (NNN) anti-phase boundaries (APBs) during loading, respectively. During unloading, these APBs pulled back the superpartials resulting in large pseudoelasticity, which is similar to D03-ordered Fe3Al crystals. The dislocation configuration was closely related to the ordered domain structure developed in the D03 phase. Moreover, the precipitation of the thermally stable L12 phase was so slow that the metastable D03 phase developed even if the crystals were annealed in the (a+ L12) and (D03+ L12) phase fields in Fe-Ga equilibrium phase diagram. The metastable D03 phase also demonstrated large pseudoelasticity of which recovery ratio was above 80 %. On the other hand, if the L12 phase precipitated by long time annealing in the (a+ L12) region, the reversible motion of 1/4[111] superpartials was suppressed by the L12 phase resulting in a decrease in recovery ratio. In addition, the crystals aged in the (a+ D03) phase region showed small strain recovery.
Texture Formation in High Niobium Containing TiAl Alloys
Authors: Stark Andreas , Bartels Arno , Schimansky Frank-Peter , Clemens Helmut
Published: June 2019

Texture formation was studied in high Nb bearing g-TiAl based alloys with compositions of Ti-45Al-(5,7.5,10)Nb-(0,0.5)C (compositions are in atomic percent). In order to start with texture-free material hot-isostatically pressed powder compounds were used. The deformation was performed either in uniaxial compression or by hot rolling. After compression at 700 °C and 800 °C fiber textures with <110> and <302> components occur. These deformation textures can be verified by computer simulations using a yield surface model of g-TiAl. With higher deformation temperatures the <110> fiber vanishes and new accumulations of orientations are formed, which are due to dynamic recrystallization.

Hot rolling was performed at temperatures in the upper part of the (a+g) phase field and, therefore, with more than 50% a-phase existing. The co-deformation of a- and g-phase during rolling leads to correlated components in the independently measured textures of both phases. The texture of the g-phase shows a maximum of orientation around the Goss2 component and the texture of the a-phase exhibits an orientation maximum around the transversal component. The correlation is the Blackburn orientation relation, although the textures are not caused by phase transformations, but by co-deformation. Hot rolling with many passes and reheating between the passes lead to the formation of a cube component with an alignment of the c-axes in transverse direction. In general, this is a typical recrystallization-induced component in hot rolled TiAl.
Effect of SPS processing temperature on the microstructure and properties of a Ti49Al47Cr2Nb2 alloy
Authors: Couret Alain , Molénat Guy , Galy Jean , Thomas Marc
Published: June 2019

The sintering of TiAl alloys by the Spar Plasma Sintering (SPS) technique is investigated in the present paper. Compactions are conducted between 1100°C and 1225°C on a Ti49Al47Cr2Nb2 powder. Single phased and lamellar microstructures are generated at low and high temperatures, respectively. The former exhibits enhanced tensile properties at room temperature but at the expense of a limited creep resistance. On the other hand, the latter suffers from a poor ductility.

The deformation systems which are activated are determined by post-mortem transmission electron microscopy. The behavior of the single phased-alloy is analyzed in terms of the Hall-Petch law.