bluuebunny/crossref_metadata_2025 huggingface dataset:
Unjamming in Dry Granular Matter: Second-Order Phase Transition between Fragile Solid and Dry Fluid (Bearing) by Intermittency.
Authors: Rivier Nicolas , Fortin Jean Yves
Published: July 2011

Dry granular matter, with inﬁnite tangential friction, is modeled as a connected graph ofgrains linked by purely repulsive contacts. The degrees of freedom of a grain are non-slip rotationon, and disconnection from another. The material stability under shear (jamming) is ensured by oddcircuits of grains in contact that prevent the grains from rolling on each other. A dense granularmaterial with high stiffness-to-load ratio has two possible states: fragile solid, blocked by odd circuits,and dry ﬂuid or bearing, in the absence of odd circuits, that ﬂows under shear by creation and glide ofa pair of dislocations as in plasticity of continuous media. In this paper, we introduce the notions of blob, a region of the material containing only even circuits, and of critical contact that closes an oddcircuit. The granular material is then represented, at low energies and critical applied shear, as a chainof blobs connected by critical contacts. The transition between dry ﬂuid and fragile solid occurs byintermittency.
Slow Bainite: an Opportunity to Determine the Carbon Content of the Bainitic Ferrite during Growth
Authors: Caballero Francisca G. , Miller Michael K. , Garcia-Mateo Carlos
Published: July 2011

The amount of carbon in solid solution in bainitic ferrite at the early stage of transformation has been directly determined by atom probe tomography at 200 °C, taking advantage of the extremely slow transformation kinetics of a novel nanocrystalline steel. Results demonstrated that the original bainitic ferrite retains much of the carbon content of the parent austenite providing strong evidence that bainite transformation is essentially displacive in nature.
Simulation of the Kinetics of Grain-Boundary Nucleated Phase Transformations
Authors: Jägle Eric A. , Mittemeijer Eric Jan
Published: July 2011

The kinetics of phase transformations for which nucleation occurs on parent-micro-structure grain boundaries, and the resulting microstructures, were investigated by means ofgeometric simulations. The inﬂuences of parent microstructure grain-boundary area density,parent grain-size distribution and parent→product kinetics were analysed. Additionally, thesimulated kinetics were compared with predictions from two kinetic models, namely a modelproposed for spatially random nucleation and a model proposed for grain-boundary nucleation.It was found that the simulated transformed fraction as function of time lies in between the twomodel predictions for all investigated parent microstructures and parent→product kinetics.
Thermodynamic Aspects of Liquid Phase Sintering B-Containing P/M Stainless Steels
Authors: Rodriguez J. Carlos , Lozada Lorena , Tojal Concepción , Gómez-Acebo T. , Castro F.
Published: July 2011

Being an effective sintering enhancer boron is gaining relevance for obtaining high density PM steels. Thermodynamic calculations are an important tool for studying the roll of alloying elements in the formation of a liquid during sintering. In the present work, the system Fe-Cr-B was obtained by combining up to date thermodynamic descriptions for the subsystems Fe-Cr, Cr-B and B-Cr. The calculations were carried out with Thermo-Calc software to predict isothermal sections for the ternary diagram for 1210 and 1250°C. The analysis of the isothermal sections indicates that the solid phases in equilibrium with the liquid are M2B and a-BCC solid solution. The generation of the liquid is based on a eutectic reaction (Lða+(FeCr)2B) involving the mixed borides previously formed. On the other hand, simulations for PM steels with constant boron but higher chromium content allowed realising that the formation of the liquid may be completely inhibited, within the temperature range under consideration, as materials with too high Cr/Fe ratios are used. This study was also supported by selected experiments which were in excellent agreement with the thermodynamic calculations.
Thermodynamic Modelling of Carbide Precipitation in Hot Work Tool Steels with Different Silicon Contents
Authors: Farina Alexandre Bellegard , Mesquita Rafael Agneli , Goldenstein Hélio , Kestenbach Hans Jürgen
Published: July 2011

New grades have been developed in high alloy tool steels, enabling improved mechanical properties by modifications on Si, Cr or Mo contents. The correlation between alloy modifications and mechanical properties were successively correlated to microstructural aspects in previous work, especially in terms of secondary hardening carbides. In the present paper, thermodynamic and kinetic simulations were carried out and correlated to these data, especially in terms of Si effect on M3C carbide precipitation. Free energy evaluation points to easier formation of M7C3 carbide in high Si steels, especially at high tempering temperatures, which are typical for hot work tool steels. Kinetic evaluations, based on the present simulations and literature, also show that cementite formation is retarded in high Si steels, which also lead to direct formation of M7C3. Regarding the low Si steels, cementite enrichment by Cr, Mo and V was also evaluated in terms of simulation. The results are in good agreement and help the explanation on the slower dissolution of cementite particles in low silicon steels, leading to important implications to the higher tempering resistance of these grades. Therefore, tempering simulation on the new hot work tool steel compositions aided the understanding of the microstructure modifications found experimentally.
An Equation of State of Amorphous β-Boron under High Pressure.
Authors: Siberchicot Bruno , Clérouin Jean
Published: July 2011

Beyond 100 GPa at ambient temperature, β-boron exhibits an amorphization [1]. This paper presents Quantum Molecular Dynamics simulations of the equation of state (EoS) of amorphous boron under pressure.
Micromechanical Modelling of Microtexture Formation in Low Alloy Steel Bainite
Authors: Lubin Sophie , Gourgues-Lorenzon Anne Francoise , Bacroix Brigitte , Réglé Hélène
Published: July 2011

A micromechanical model was developed to account for the particular microtexture of upper bainite in low alloy steels, i.e. the non-random spatial distribution of variants within a given former austenite grain. A self-consistent scheme and an Eshelby approach, considering both transformation shape strain and viscoplastic strain as eigenstrains, was applied to estimate coupling between parent austenite and two or more bainite variants without any applied stress. Model predictions concerning self-accommodation between variants are sensitive to the plane of the first “lattice invariant shear” in the crystallographic model used to determine the shape strain. No obvious effect of the constitutive equations of phases and of the other model parameters was found.
Atomic Density Function Simulations of Crystal Growth Kinetics of FCC Crystal and BCC-FCC Transition
Authors: Certain Marilyne , Zapolsky Helena , Khachaturyan Armen G.
Published: July 2011

Spontaneous self-assembling of interacting atoms prototyping crystallization and reconstructive phase transitions in crystalline state is discussed in terms of Atomic Density Function (ADF) theory. It is demonstrated that a multi-mode potential can reproduce any crystal structure. 3D computer modeling of formation of the FCC crystal and crystal lattice rearrangement in the FCCàBCC transformation is presented.
In Situ Analysis of Effects of Transformation Strain on the Austenite Phase during Martenistic Transformation of Cr-Ni Steel
Authors: Terasaki Hidenori , Shouyuan Zhang , Komizo Yu Ichi
Published: July 2011

A hybrid in-situ observation system has been developed to study the phase transformation behaviour simultaneously in both real and reciprocal lattice space. This paper presents the development of the observation system. Furthermore, as an example of the application of our developed system, martensitic transformation of Cr–Ni steel along a designed thermal cycle was in-situ tracked with the developed system. As a result of analysing the time-resolved X-ray diffraction data for the observed target, our system could directly detect the effect of transformation strain on austenite during martensitic transformation.
Structural Characterization of Reaction Product Region in Al/MgO and Al/MgAl2O4 Systems
Authors: Nowak Rafal , Sobczak Natalia , Sienicki Edmund , Morgiel Jerzy
Published: July 2011

The reaction product region, formed between molten aluminium and MgO and MgAl2O4 single crystals of three different crystallographic orientations, was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with X-ray energy dispersive spectrometry (EDS). The Al/MgO and Al/MgAl2O4 couples were produced under ultra high vacuum at 800, 900 and 1000°C. The observations proved the redox reactions of Al with both MgO and MgAl2O4. Independently of crystallographic orientation of initial oxide single crystals, the reaction product region (RPR) was formed and it was built of oxide particles surrounded by continuous metallic phase. For Al/MgO couples, the RPR was composed of two layers, where in the first layer, the oxide phase was Al2O3 while in the second layer, the MgAl2O4 was identified. In the case of Al/MgAl2O4 couples, a single layer was distinguished and only the Al2O3 phase was recognized.
Influence of Doping on the Structural Transformations of the Proton Conducting Perovskite BaCe1xYxO3-D
Authors: Trequattrini Francesco , Cordero Francesco , Deganello Francesca , La Parola Valeria , Roncari Edoardo , Sanson Alessandra
Published: July 2011

From neutron diffraction it is known that the BaCeO3 perovskite undergoes a sequence of phase transformations from high temperature cubic C to rhombohedral R, to orthorhombic O1 (Imma) and to orthorhombic O2 (Pnma). Doping Y3+ on the Ce4+ site introduces charge compensating O vacancies (VO) that may be partially filled with OH complexes with exposition to H2O, so making the material an ionic conductor. Anelastic relaxation experiments have been carried out on samples doped with 2%Y and 10%Y; the real part s’(T) of the complex elastic compliance presents softenings at the transitions, and the loss s’’/s’ curves allow the content of VO and H to be monitored. Doping has a strong effect on the temperature of the Pnma/R transition: with 10%Y in the fully hydrated state TO1-R increases up to 750 K while after full outgassing falls to 500 K, meaning that the introduction of ~5% VO shifts the transition of 250 K. While the effect of cation substitution on the transitions temperature is easily explained in terms of simple arguments usually valid for perovskites based on bond length considerations, the remarkable stabilization of the R phase by VO requires to take into account the anomalous sequence of phase transitions of undoped BaCeO3, where the R structure transforms into orthorhombic Pnma on cooling with the loss of an octahedral tilt system.
Phase-Field Simulation of D03-Type Antiphase Boundary Migration in Fe3Al with Vacancy and Solute Segregation
Authors: Koizumi Yuichiro , Allen Samuel M. , Ouchi Masayuki , Minamino Yoritoshi , Chiba Akihiko
Published: July 2011

Segregation of solute atoms and vacancies to migrating D03–type antiphase boundaries (APBs) in Fe3Al of the stoichirometric and an Al-rich compositions has been investigated in detail by a phase-field method developed in the previous study [Koizumi et al. Acta Mater 2009;57:3039] focusing on the quantitative relationship among the segregation, APB energy, driving-force, drag-force and APB mobility. It has been revealed that the drag-force by solute segregation depends considerably on the alloy composition and is responsible for the significant composition dependence of the migration kinetics of D03-APB whereas the composition dependences of driving-force and mobility are negligibly small.
Precursor Nanoscale Textures: from Tweed to Glassy Behaviour
Authors: Planes Antoni , Lloveras Pol , Castán Teresa , Porta Marcel , Saxena Avadh
Published: July 2011

We study spatially inhomogeneous states that occur as precursors of marten-sitic/ferroelastic transitions. We will show that cross-hatched modulations (tweed patterns)arise at temperatures above the phase transition in the limit of high elastic anisotropy or lowdisorder while a nano-cluster phase-separated state occurs at low anisotropy or high disorder.In the latter case, nanoscale inhomogeneities give rise to glassy behaviour while the structuraltransition is inhibited. Interestingly, in this case the ferroelastic system also displays a largethermo-mechanical response so that the low symmetry structure can be easily induced by theapplication of relatively small stresses within a broad temperature range.
Position of Incommensurate Satellites Appearing in Ti-Ni Based Shape Memory Alloys
Authors: Todai Mitsuharu , Fukuda Takashi , Kakeshita Tomoyuki
Published: July 2011

We have investigated electron diffraction patterns of a Ti-44Ni-6Fe alloy exhibitng a negative temperature dependence in electrical resistivity below Tmin = 210 K. The electron diffraction patterns taken near Tmin show diffuse satellites at gB2 + * when the zone axis is [111] and [001]. For both the beam directions, the value ζ is slightly smaller than 1/3. On the other hand, the satellites are missing when the zone axis is [110]. This means that the incommensurate phase has a modulated structure with the propagation vector * (ζ~1/3) and the displacement direction is one of <110> which is vertical to the propagation vector. This modulation is obviously the consequence of the phonon softening of TA2-branch with the propagation vector near * (ζ~1/3). In addition to the satellite at gB2 + * (ζ~1/3), satellites appear at gB2+* with ζ = 1/2 when the zone axis is [001] and rod-like steaks appear in <112>* direction when the zone axis is [110]. However, these satellites and rod-like streaks do not show clear temperature dependence, suggesting they are not directly related to the phonon softening of TA2-branch.
Promoting Isothermal Martensite Formation by High Temperature Heat Treatments in a Precipitation Hardening Austenitic Stainless Steel
Authors: San Martín David , Garcia-Mateo Carlos
Published: July 2011

This work investigates what phase transformations are taking place during a continuous heating as well as the influence of the solution temperature on the isothermal formation of martensite in a precipitation hardening semi-austenitic stainless steel. In previous studies in the stainless steel under investigation (12Cr-9Ni-4Mo-2Cu) only the isothermal mode of martensitic transformation has been experimentally detected. In this work it is shown that: 1) The AFtemperature is located around 1040 K; 2) The χ-phase present in the initial microstructure dissolves above ~1323 K; 3) above 1448 K the formation of delta ferrite is promoted at austenite grain boundaries; 4) the kinetics of isothermal martensite formation is strongly accelerated with increasing solution temperature. The kinetics has been monitored in-situ at room temperature by using high resolution dilatometry. A semi-empirical dilatometry model is used to convert the dilatometry signal into volume fraction of martensite transformed. The results are briefly compared with previous kinetic measurements under the influence of strong magnetic fields.
The Use of Barkhausen Noise to Study the Martensitic Phase Transformation
Authors: Huallpa Edgar A. , Farina Paula F. S. , Capo Julio , Padovese Linilson R. , Goldenstein Hélio
Published: July 2011

The use of magnetic Barkhausen (MBN) noise methods to detect the austenite to martensite phase transformation during cooling of steel specimens was explored, using three different configurations: conventional Barkhausen noise emission stimulated by an alternating magnetic field, the Okamura method, that measures magnetic noise emission under a fixed DC field and a novel experimental technique that measures spontaneous magnetic emission during transformation, in the absence of any external field. The phenomena associated with the phase transformation were also followed by electrical resistivity measurements and the resulting samples were characterized using optical and scanning electron microscopy. MBN measurements on a AISI D2 tool steel austenitized at 1473K and cooled to liquid nitrogen temperature exhibited a clear change near 225 K during cooling, corresponding to the Ms (martensite start ) temperature, as confirmed by resistivity measurements. Spontaneous magnetic noise emission measurements made in situ during cooling of a sample immerged in liquid nitrogen showed that individual “burst” phenomena could be detected, in a manner similar to acoustic emission (AE) measurements. This magnetic emission (ME) can thus be considered a new experimental tool for the study of martensite transformations in ferrous alloys.
Structural Transitions in a Co2NiGa Ferromagnetic Shape Memory Alloy
Authors: Craciunescu Corneliu , Mahesh Karimbi K. , Silva Rui Jorge C. , Braz Fernandes Francisco Manuel
Published: July 2011

The development of ferromagnetic shape memory for practical applications needs to overpass brittleness issues, in addition to the control of the magnetoelastic domains. The Co-Ni-Ga system can provide adequate structural particularities to increase the ductility. This paper reports on structural observations of the martensitic transformation in a Co2NiGa alloy, in the as-cast and in plastically deformed state. Characterization has been performed before and after the heat treatment, using in-situ X-ray diffraction, optical and electron microscopy, as well as DSC measurements performed on heating and cooling of the samples. The observations show a β + γ two-phase structure that can be further influenced by quenching. The structural contribution on the deformation capacity of the alloys is analyzed, based on the changes in the pattern of transformation. Severe plastic deformation by cold rolling leads to the disappearance of the thermoelastic phase transformation.
Microstructure of Cu-Zn-Al Shape Memory Alloys Joined by Electric Stored-Energy Welding
Authors: Mitelea Ion , Dorohoi Claudia M. , Craciunescu Corneliu
Published: July 2011

Electric welding with energy stored in condensers offers the advantage of a reduced welding power and a better balance of the energy supplied in the joining area of the components. It can also supply hard thermal regimes in a short time, while the heat is generated only by the contact resistance. This is a major advantage for welding materials with high thermal conductivity, among which are the copper “based shape memory alloys. Since the energy accumulation only needs a few seconds and is released in very short time, it has favorable influence on welding, so that the effect on the shape memory effect is reduced. The paper details the process of electric stored-energy point welding, the structural and phase transitions in the welded seam and in the heat affected zone, as well as the influence of the welding process on the shape memory effect.
Edge-to-Edge Matching at Ti-TiH Interfaces: Kinetics of Hydride Growth and Clustering of Precipitates with Different Orientation Relationships
Authors: Conforto Egle , Caillard Daniel
Published: July 2011

The motion of steps during the growth of hydride precipitates has been observed by in situ transmission electron microscopy. Precipitates in different orientation relationships (OR) are shown to obey to the rules of three-dimensional edge-to-edge matching. They form clusters in order to realize a more isotropic distribution of the volume expansion, and to decrease their total elastic energy.
The Topological Model (TM) of Martensite Transformations – some Improvements
Authors: Kelly Patrick M. , Qiu Dong
Published: July 2011

A minor, but crucial, modification to the original version of the TM was recently proposed in order to ensure that the model predictions were entirely consistent with those of the phenomenological theory of martensite crystallography (PTMC). In the present paper an analysis based on the principles of the Frank-Bilby equation is used to derive this modified version of the two-dimensional TM equation for the habit plane orientation from first principles. A considerably simpler and more accurate expression for the tilt rotation is also presented. Finally, a simple method for using the TM approach to calculate the shape strain, its magnitude and direction is described. The results of the predictions made with this improved version of the TM are compared with those of the original TM and with the corresponding PTMC predictions.
An Energetic Study on the Preference of the Habit Plane in Fcc/bcc System
Authors: Gu Xin Fu , Zhang Wen Zheng
Published: July 2011

The preference of the habit planes (HPs) developed from precipitation in the fcc/bcc system has been investigated. The interfacial energy of different interface orientations has been examined with variation of the orientation relationships (OR) and lattice parameters by a classical molecular dynamics method. The results show that interface has the lowest interfacial energy when it contains parallel Burgers vectors and a set of dislocations. The local minimum of interfacial energy may not associated with a maximum of dislocation spacing. It is also found that the near Kurdjumov-Sachs OR is more preferable than the near Nishiyama-Wasserman OR. Contrary to the previous interfacial energy calculations, which usually limit to rational ORs, the present work allows ORs to be irrational, which agrees with the observations.
Interfacial Properties and Critical Avalanche Exponents of Shape Memory Alloys and Related Materials
Authors: Salje Ekhard
Published: July 2011

Interfaces in martensites and ferroelastic crystals show internal structures which are not simply the interpolation of the two adjacent domains. These structures can influence solitary front propagation as observed for large depinning forces. They also contribute to local pinning of walls when the applied forces are close to the depinning threshold. Under these conditions, walls propagate in jerks and avalanches. Typical depinning is observed for very small forces in single ferroelastic needle domain. It is shown that jerks occur in elastically driven system both for planar walls (D=2) and for needle tips (which represents a line in the three dimensional crystal, D=1). The experimental power law exponents are ~ -2 for the energy exponent for collective avalanches, -1.3 for the elastic response function and -1.8 for an advancing needle domain in LaAlO3.
Analysis of Clustering Characteristics during early Stages of Cu Precipitation in bcc-Fe
Authors: Warczok Piotr , Shan Yao , Schober Michael , Leitner Harald , Kozeschnik Ernst
Published: July 2011

Formation of coherent Cu precipitates in supersaturated ferrite (1.5 at.%Cu) at 500°C is simulated using the Monte Carlo method. Bond energies used in the atomistic simulation are calibrated on the mutual solubilities given on the Fe-rich and Cu-rich side of the Fe(bcc)-Cu(bcc) phase diagram. The spatial extension of the precipitate phase is defined on basis of a composition criterion of the nearest neighbor shells. Various definition conditions are examined in terms of resulting particle densities, mean radii and composition of the precipitates, as well as the composition profiles across the precipitate/matrix interface. The predictions of the simulations are compared with the experimental results from atom probe analysis as well as small angle neutron scattering.
Influence of High Magnetic Field on Ferrite Transformation in Fe-C Base Alloys
Authors: Enomoto Masato , Zhang Guo Hong , Wu Kai Ming
Published: July 2011

The characteristics and the mechanism of ferrite transformation in alloy steels which contain a carbide-forming element have attracted considerable attention for past decades. Since it is reported that the nucleation and growth of ferrite in Fe-C base alloys is accelerated by high magnetic field, the influence of a magnetic field of 12 Tesla on ferrite transformation was studied in a Fe-C- Mo alloy. Whereas a significant amount of expedition was observed at lower temperatures, the principal features of ferrite transformation, namely, a marked retardation of transformation at intermediate temperatures and premature cessation of transformation before it reaches the final equilibrium amount below the bay temperature were essentially retained. In contrast, the influence of magnetic field was much less at higher temperatures. These results are discussed in terms of the influence of magnetic field on the phase equilibrium and coupled-solute drag effects on the migration a/g phase boundary.
Influence of Crystallography on Nucleation of Ferrite Precipitates at Austenite Grain Boundary Corners in a Co-15Fe Alloy
Authors: Zhang Guo Hong , Takeuchi Tomoaki , Enomoto Masato , Adachi Yoshitaka
Published: July 2011

The nucleation of bcc ferrite precipitates at austenite grain corners in a Co-15Fe alloy was studied by serial sectioning coupled with electron backscatter diffraction (EBSD) analysis. Grain corners were identified by recombination of triple points and triangular annihilation, whereas quite a few precipitates were surrounded by more than four matrix grains when twins were counted as individual grains. More than 40% of corners composed all of high angle grain boundaries were vacant at an undercooling of ~60°C from the g/(a+g) phase boundary. All the precipitates had K-S or N-W orientation relationship with at least one grain and a larger proportion of them had the OR with two and three grains. For half of vacant corners a hypothetical precipitate could have the OR with more than one grain. It is likely that not only the misorientations among the matrix grains, but also the orientations of the grain boundary planes have a major influence on nucleation potency even at grain corners.
Influence of Chromium Carbide Size on the Austenitization Kinetics of a Martensitic Stainless Steel Measured by Dilatometry
Authors: Kostoj Valérie , Mithieux Jean Denis , Fröhlich Thomas
Published: July 2011

The use of martensitic stainless steels is commonly due to high mechanical properties requirements. To obtain these high values from the industrial material (whose microstructure consists in ferrite and M23C6 carbides), a suitable heat treatment, consisting in an austenitization of the steel at a temperature higher than A3 point, followed by a fast quenching, is necessary. For economic reasons, the shortest the heat treatment time, the better it will be. Therefore, one essential point, to reduce austenitization time, is to obtain a final product made of ferrite and carbides, with the lowest carbides size as possible: the lowest they will be, the shortest time the transformation ferrite + carbides --> austenite will take. The formation of these carbides occurs during the batch annealing of the steel, at low temperature. To study the influence of carbides size on the austenitization kinetics of a 1.4006 grade martensitic stainless steel, several batch annealings were made at different temperatures. Carbides sizes were measured by electronic microscopy and austenitization kinetics were measured by dilatometry. Small carbides size logically induces fastest austenitization kinetics. The austenization occurs in three stages: a fast one which corresponds to the dissolution of the smallest carbides leading to a homogeneous repartition of carbon, a chromium gradient into ferrite and thus an austenitization until reaching Cr-rich ferrite. The second one is limited by the diffusion of chromium, inducing a slower transformation. The apparent third stage is an artefact of the second one, as it corresponds to an expansion of the austenite due to the diffusion of carbide, and an apparent increase of the transformation kinetics.
Precipitation in Aged N-Containing Steels
Authors: Saucedo-Muñoz M.L. , Victoria-Hernández V.M.
Published: July 2011

Three types of austenitic stainless steels JK2, JJ1 and JN1 were isothermally aged at temperatures from 873 to 1173 K for 10 to 1000 minutes in order to study the microstructural evolution. In general, the kinetics of precipitation for JN1 steel was faster than that of JJ1 steel, because of its higher interstitial solute content. The TTP diagrams showed that the intergranular precipitation of Cr23C6 and Cr2N preceeded to the intragranular precipitation of Cr2N and h phase in JN1 and JJ1 steels, respectively.
Spinodal Decomposition in Fe-Cr Alloys
Authors: Soriano Vargas Orlando , Avila-Davila Erika O. , Victoria-Hernández V.M. , Saucedo-Muñoz M.L.
Published: July 2011

The hardening behavior of precipitation was studied during aging of Fe-Cr alloys. This mechanical behavior is associated with the nanometric modulation structure of the coherent decomposed Fe-rich and Cr-rich phases formed by the spinodal decomposition of the supersaturated solid solution. The growth kinetics of spinodal decomposition was very slow and it increased during coarsening stage. The morphology of decomposed phases consisted of an interconnected irregular shape with no preferential alignment for short aging times and a further aging caused the change to a plate shape of the decomposed Cr-rich phase aligned in the <110> directions of the Fe-rich matrix. The rapid increase in hardness and embrittlement seem to be associated with the coherency and nanometer size of the spinodally-decomposed phases in the aged alloys.
Phase Transformations in Lutetium Borides at Heating in Vacuum
Authors: Taran Anatoliy , Voronovich Daniel , Shitsevalova Natalya , Levchenko Ganna , Filipov Volodymyr , Abashin Sergiy
Published: July 2011

The LuB12 ® LuB4 ® LuB2 phase transformations on annealing in vacuum (T=(1400÷1800) K, p < 10-2 Pa) are investigated with use of the parent single crystals. SEM and X-ray researches of the corresponding lutetium boride single crystals were carried out before and after their annealing. It is shown that the LuB12 → LuB4 phase transformation takes place in surface layer and transition region spreads inwards the single crystal bulk with time. According to the assessed Lu-B phase diagram the LuB4 phase transformation into other individual phases is impossible, and at first it is shown that under corresponding conditions the LuB4 → LuB2 spontaneous phase transformation takes place both on the surface and in the LuB4 single crystal bulk.
Influence of Copper Additions in Fe-10Ni (mass %) Alloys on Cooling Microstructures
Authors: Crozet Coraline , Antoni Zdziobek Annie , Lay Sabine , Coindeau Stéphane
Published: July 2011

Austenite/ferrite phase transformations in Fe-xCu-10Ni alloys, 0<x<15 (mass%), are studied under two different cooling conditions, ice-brined quenching or slow cooling in the dilatometer. The influence of copper addition and cooling rate on the microstructure of the alloys is studied. Metallographic examinations of quenched samples show that metastable transformations occur during cooling. As for Fe-Ni alloys, it is impossible to stabilize the high temperature phase (γFeNi) in the Fe-Ni-Cu alloys. Dilatometry measurements of the γ → α transformation temperature with a cooling rate of 2°C/min also indicate a metastable phase formation despite the low cooling rate. For all alloys, a mixture of massive and lath ferrite is observed, one being predominant depending on the cooling conditions and composition. It is shown that the cooling rate has nearly no influence on the microstructure of alloys with a small amount of Cu unlike the alloys containing more Cu. In all alloys containing Cu, nanometric γCu precipitates, much finer in the quenched samples, are detected in the ferrite grains.
A Mixed-Mode Model Considering Soft Impingement Effects for Solid-State Partitioning Phase Transformations
Authors: Chen Hao , van der Zwaag Sybrand
Published: July 2011

The original mixed-mode model is reformulated by considering the soft impingement effect and applying a general polynomial method of dealing with the concentration gradient in front of the interface. Comparison with the numerical solution shows that the reformulated mixed-mode model is more precise than the original model. The effect of soft impingement on the kinetics of partitioning phase transformation depends on both the growth mode and the degree of super-saturation.
Sequential Phase Formation during Reactive Diffusion of a Nanometric-Thick Mn Film on Ge(111)
Authors: Abbes Omar , Xu Feng , Portavoce Alain , Hoummada Khalid , Le Thanh Vinh , Girardeaux Christophe
Published: July 2011

In recent years, spintronics whose principle is based on controlling the spin of electrons in semiconductor layers is presented as a complementary or even an alternative solution for production of logic devices in microelectronics. It relies on the fact that electric current in a magnetic layer can be spin polarized. Manufacture of such components is based on the use of materials or heterostructures whose electronic properties depend on their magnetic state. The magnetic Mn-Ge system is interesting because of its possible development at high Curie temperature and its integration on Si substrate. Among all of the Mn-Ge phase compounds of the diagram, Mn5Ge3 seems the most interesting one for spintronics applications: it is a stable and ferromagnetic phase at room temperature. In this paper, we present first results of the study, by Reflection High Energy Electron Diffraction (RHEED), X-ray diffraction (XRD) and Atomic Force Microscopy (AFM), of the sequence of formation of the MnxGey phases in the case of reaction of a nanometric-thick Mn film (200nm) deposited by MBE on Ge (111).
Order and Disorder in Ni-Pt Single Crystals
Authors: Schönfeld Bernd , Engelke Markus , Ruban Andrei V.
Published: July 2011

Single crystals of Ni-25.6 at.% Pt and Ni-87.8 at.% Pt were investigated by diffuse x-ray scattering for states of thermal equilibrium (923 K and 603 K, respectively). The separated short-range order scattering showed local maxima at 100 positions. Effective pair interaction parameters, as determined by the inverse Monte Carlo method, show a strong composition dependence of the nearest-neighbor interaction parameter. First-principles calculations are consistent with this finding and reveal a large contribution due to lattice strain. Based on values of the ordering energy, NiPt3 with L12 structure was considered as a plausible new intermetallic phase, with Monte Carlo simulations giving an order-disorder transition temperature of 650 K. A single crystal of Ni-75.2 at.% Pt, quenched from 1073 K and aged at 613 K, showed L12-type ordering, reaching a long-range order parameter of 0.50(4) after 800 h.
Re-Examination of A1 → L10 Ordering: Generalized Bragg-Williams Model with Elastic Relaxation
Authors: Soffa William A. , Laughlin David E. , Singh Nitin
Published: July 2011

The tetragonal lattice relaxation has been included in the thermodynamics of the fcc→L10 ordering to produce a first-order character of the transition within the mean field description of the binary solution energetics. In view of growing interest in such systems e.g. Fe-Pd and Co-Pt alloys, which display a wide range of applications relevant to current and futuristic technologies, the fcc→L10 two-phase field is re-examined utilizing a generalized Bragg-Williams approach including first and second nearest neighbor interactions. The thermodynamic behavior is examined in the limit of T→0K and discussed in terms of the implications of the Third Law of Thermodynamics.
Effect of Magnetism on Short-Range Order Formation in Fe-Si and Fe-Al Alloys
Authors: Gorbatov Oleg I. , Gornostyrev Yuri N. , Kuznetsov Andrey R. , Ruban Andrei V.
Published: July 2011

Short-range order formation in dilute Fe-Si and Fe-Al alloys has been investigated by statistical Monte Carlo simulations with effective interactions deduced from first principles calculations for different magnetic structures of bcc Fe. We find that the variation of the magnetic order from ferromagnetic to paramagnetic leads to significant changes in effective cluster interactions and, as follow, in short-range order parameters of alloys. It is shown in agreement with experiment the B2 type short-range order is formed above the Curie temperature, TC, while the D03 type short-range order is preferred below TC.
Evidence of a Biphasic Domain in the UO2-Nd2O3 Diagram at Room Temperature: a Proof for a Miscibility Gap in UO2-Nd2O3 Phase Diagram ?
Authors: Desgranges Lionel , Marcet Mathieu , Pontillon Yves , Porcher Françoise , Lamontagne Jerome , Matheron Pierre , Iltis Xavière , Baldinozzi Gianguido
Published: July 2011

Several samples of (U,Nd)O2 with different Nd content (ranging from 2 to 50 in Nd2O3 mass. %) were prepared. For composition ranging from 6 to 20 in Nd2O3 mass %, two crystalline phases are unambiguously evidenced by X-ray and neutron diffraction, by optical microscopy, and by SEM-EDX and EPMA. The influence of the preparation route on the distribution of the domains made by these two phases is evidenced and discussed.
Kinetic of Formation of Ni and Pd Silicides: Determination of Interfacial Mobility and Interdiffusion Coefficient by In Situ Techniques
Authors: Hoummada Khalid , Mangelinck Dominique , Portavoce Alain
Published: July 2011

The formation of metal (Ni and Pd) silicide thin films on a Si wafer is analyzed using differential scanning calorimetry (DSC) and isothermal X ray diffraction measurements. The sensitivity of DSC is remarkable even in this experimental Ni/Si and Pd/Si(001) and allows to show two steps of growth for a phase formation (lateral and normal growth). This technique is shown being of main interest for characterization of silicide formation during microelectronic industrial processes. Combining X-ray diffraction measurements and DSC measurements, the interface mobilities and the effective diffusion coefficient characterizing Ni2Si and Pd2Si growth are measured. These quantities as well as the interface mobilility for lateral growth have been determined by using a model taken into account the nucleation and lateral growth as well as a normal growth controlled by diffusion and interface reaction.
A Model for Formation and Consumption of Transient Phase
Authors: Tellouche Gamra , Hoummada Khalid , Mangelinck Dominique , Blum Ivan
Published: July 2011

The phase formation sequence of Ni silicide for different thicknesses is studied by in situ X ray diffraction and differential scanning calorimetry measurements. The formation of a transient phase is observed during the formation of δ-Ni2Si; transient phases grow and disappear during the growth of another phase. A possible mechanism is proposed for the transient phase formation and consumption. It is applied to the growth and consumption of θ-Ni2Si. A good accordance is found between the proposed model and in situ measurement of the kinetics of phase formation obtained by x-ray diffraction and differential scanning calorimetry for higher thickness.
Multiscale Modelling of the Ageing Kinetics of a 2D Deposit
Authors: Berthier Fabienne , Maras Emile , Braems Isabelle , Legrand Bernard
Published: July 2011

We compare three models of 2D precipitation kinetics that give access to different time-space scales. Kinetic Monte Carlo simulations (KMC), cluster dynamics (CD) and nucleation-growth-coalescence model (NGCM), based on a same atomic model, lead to an excellent agreement as long as the interfacial free energy is evaluated accurately and the interaction between diffusion fields is taken into account in the CD. The NGCM model noticeably improves the previous approaches of the same kind by using a constrained-equilibrium hypothesis to describe the solid solution. Moreover, in the coalescence regime, we show that CD leads to cluster distributions that are wider and more symmetric than the LSW distribution due to the probabilistic feature of the growth law of a cluster, that makes it differ from the purely deterministic NGCM approach.
Martensite Midrib in an Fe-1C-17Cr Stainless Steel
Authors: Yang Jer Ren , Lee Hsin Yi , Yen Hung Wei , Chang Hsiao Tzu
Published: July 2011

An Fe-1.0C-17Cr (wt.%) stainless steel was subjected to subzero treatment to investigated the structure of martensite midrib. The midrib region appeared in the thin plate and lenticular martensites have been observed detailed by TEM. The TEM result reveals that the transformations of thin plate martensite and lenticular martensite are initiated at the same midrib region. The former keeps the lattice-invariant deformation mode of twinning during subsequent growth, whereas the latter combines both twinning and slip modes. Midrib region is a preferential position for carbide precipitations after tempering. M3C and M23C6carbide were found in this alloy, and related to the ferrite by Bagaryatsky OR and K-S OR, respectively.
Non-Equilibrium Properties of Au-Pd Nanoparticles
Authors: Atanasov Ivailo S. , Hou Marc
Published: July 2011

We address the question of the evolution of a nanostructured system in a metastable state to equilibrium. To this purpose, we use the case study of the transition of an AucorePdshell nanoalloy cluster containing up to about 600 atoms toward the equilibrium Au segregated configuration. We start from a molecular dynamics approach with an embedded atom potential. The way the transition develops at low temperatures is found to be very sensitive to the cluster morphology and the way energy is exchanged with the environment. The transition of icosahedral inverse core-shell Au-Pd clusters is predicted to nucleate locally at the surface contrary to clusters with other morphologies, and starting at lower temperatures compared to them.
Disordering and Ordering in a Severely Deformed FePd Alloy
Authors: Chbihi Abdelahad , Sauvage Xavier , Genevois Cécile , Blavette Didier , Gunderov Dmitriy , Popov Alexander G.
Published: July 2011

A Fe50Pd50 alloy was severely deformed by High Pressure Torsion (HPT). For a processing temperature ranging from 20°C to 300°C, the Severe Plastic Deformation (SPD) induces a significant grain size reduction (in a range of 50 to 150 nm) but also a strong disordering of the long range ordered L10 phase. However, Transmission Electron Microscopy (TEM) data clearly show that few ordered nanocrystals remain in the deformed state. The deformed material was annealed to achieve a nanoscaled long range ordered structure. The transformation proceeds via the nucleation and growth of ordered domains along grain boundaries. Aging at lower temperature (400°C) gives rise to a smallest domain size and thus the highest coercivity.
Interaction Deformation / Precipitation / Phase Transformation in Nb Micro-Alloyed Steels
Authors: Thibaux Philippe , Liebeherr Martin , De Avila Cossa Dominique
Published: July 2011

Characterization of the phase transformation of Nb-micro-alloyed steels has to be performed taking into account the effect of deformation and precipitation. In the present investigation, the austenite to ferrite phase transformation is characterized in continuous cooling experiments after deformation at high temperature. The resulting phase transformation kinetics and microstructure showed an influence of the soaking temperature. Detailed investigations of the possible causes of the change of mechanism of phase transformation indicate that the amount of niobium in solution correlates with the slowing down in phase transformation kinetics.
Effect of the Metallurgical State of Austenite on the Microtexture Properties of the Bainitic Transformation in a Low Alloy Steel
Authors: Lubin Sophie , Gourgues-Lorenzon Anne Francoise , Bacroix Brigitte , Réglé Hélène , Montheillet Frank
Published: July 2011

The effect of the metallurgical state of austenite (undeformed vs. deformed vs. deformed + recrystallised) on the properties of the austenite to bainite transformation were investigated thanks to thermal (Gleeble simulations) and thermomechanical (hot torsion) treatments. No obvious influence of the state of austenite was found, using electron backscatter diffraction, on the resulting microtexture. Advantages and drawbacks of using misorientation angle histograms vs. axis-angle pair distribution are discussed regarding investigations of local variant selection. For an austenite grain size higher than about 50 µm, a strong effect of the transformation temperature was evidenced, bainite formed at lower temperature (530°C) exhibiting a microtexture close to that of lath martensite in the same steel.
Instability of the Parent Phase in Nearly Ordered Fe3Pt Invar Alloys
Authors: Fukuda Takashi , Yamamoto Takuya , Yamamoto Masataka , Kakeshita Tomoyuki
Published: July 2011

The martensitic transformation in a nearly ordered Fe3Pt is weak first order, and the martensite phase shows a large magnetic field-induced strain of several percent. We have investigated the origin of this transformation from its electronic structure. A characteristic feature in the electronic structure is the existence of a relatively high peak in the density of states of the minority spin band just below the Fermi energy. This peak splits into two peaks by tetragonal distortion, and one of them shifts to lower energy by the distortion, suggesting that the band Jahn-Teller effect is the main cause for the transformation.
Non-Isothermal Austenite Grain Growth Kinetics in the HAZ of a Microalloyed X-80 Linepipe Steel
Authors: Banerjee Kumkum , Perez Michel , Matthias Militzer
Published: July 2011

Non-isothermal austenite grain growth kinetics under the influence of several combinations of Nb, Ti and Mo containing complex precipitates has been studied in a microalloyed linepipe steel. The goal of these studies is the development of a grain growth model to predict the austenite grain size in the weld heat affected zone (HAZ). A detailed electron microscopic investigations of the as-received steel proved the presence of Ti-rich, Nb-rich and Mo-rich precipitates. Inter and intragranular precipitates of ~5-150 nm have been observed. The steel has been subjected to austenitizing heat treatments to selected peak temperatures of 950, 1150 and 1350°C at various heating rates of 10, 100 and 1000°C/s. Thermal cycles have been found to have a strong effect on the final austenite grain size. The increase in heating rate from 100 to 1000°C/s has a negligible difference in the austenite grain size irrespective of the austenitizing temperature. However, the increase in grain size has been noticed at 10°C/s heating rate for all the austenitizing temperatures. The austenite grain growth kinetics have been explained taking into account the austenite growth in the presence of precipitates.
Effect of Partial Martensite Transformation on Bainite Reaction Kinetics in Different 1%C Steels
Authors: Smanio Véronique , Sourmail Thomas
Published: July 2011

Isothermal bainitizing of high carbon steel is used to obtain exceptionally high mechanical characteristics together with near zero distortion during heat-treating. Such heat-treatments are often carried out at temperatures close to but above the martensite start temperature, where transformation kinetics are unfortunately very sluggish. The formation of a small amount of martensite prior to isothermal holding is known to accelerate transformation kinetics. However, the influence of the amount transformed remains to clarify, and the consequence on final properties have not been explored. In the following, the influence of partial martensite formation on the kinetics of bainite formation is investigated in 100Cr6 (AISI 52100) and similar grades. It is shown that, although the formation of martensite allows for shorter heat-treatment durations, it does not seem to affect the bainite kinetics, inasmuch as the bainite formation kinetics after formation of X% martensite are identical to that which would be expected if the first X% transformation had been obtained through isothermal bainitic transformation.