bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Recrystallization in Al-Li Based Alloy during Equal Channel Angular Extrusion
Authors: Giribaskar Sivaswamy , Gouthama  , Prasad Rajesh
Published: April 2012

Development of bulk ultra-fine grained (UFG) materials by severe plastic deformation to attain improved mechanical properties is becoming more attractive and extensively studied nowadays. Equal channel angular extrusion (ECAE) is one of technique used effectively for obtaining bulk UFG materials. Novelty of this technique is one can build up significant amount of plastic strain by increasing the number of passes without much dimensional change. In present investigation dynamic recrystallization at deformation zones around the non-shearable second phase particles in Al-Li based alloy processed by ECAE is reported. Transmission electron microscopy technique involving imaging the regions of such deformation zones with different specimen tilt conditions is used. It is shown that the dynamic recrystallisation occurring in the proximities of second phase particles during the deformation at room temperature, leads to very fine grained microstructure. Observation of multiple active nucleation sites around even sub-micrometer sized non-deformable particles in the as-processed material indicates that the system exhibits efficiency >1 based on the concept of particle stimulated nucleation (PSN). Crystallites of ultra-fine/nanocrystalline size ranges are formed in the deformation zones around the non-deformable particles during deformation itself. Effect of short term post deformation annealing to understand the recovery and recrystallization was undertaken. Based on these results effect of optimal post deformation heat treatment conditions on the thermal stability of the microstructures is emphasized. It is suggested that with significant fraction of non-shearable particles it might be possible to get grain size in the nanocrystalline or ultra-fine range with relatively low effective strain levels using ECAE.
Tales of the Abnormal: Nanocrystalline Grain Growth at Low Temperatures
Authors: Paul Heiko , Dake Jules M. , Krill III Carl E.
Published: April 2012

Employing x-ray diffractometry and electron microscopy, we have investigated thermally induced microstructural evolution in ball-milled nanocrystalline Fe. At low annealing temperatures, the early-stage growth of the area-weighted and volume-weighted average grain sizes deviates strongly from the parabolic behavior expected for normal grain growth. Analysis of the ratio of these two averages indicates that the width of the grain-size distribution changes with time. This result is more consistent with the occurrence of a transient stage of abnormal grain growth than with a grain-size-dependent change in the rate-limiting mechanism for grain-boundary migration.
Texture Change during Grain Growth in Non-Oriented Electrical Steel
Authors: Arita Y. , Chan L. , Sintay S.D. , Rollett Anthony D.
Published: April 2012

Grain size and texture are very important for controlling the magnetic properties in non-oriented electrical steel. Grain size and texture are closely related because the texture usually changes during grain growth. In this study, texture changes with grain growth in non-oriented electrical steel are investigated. Two kinds of materials, Sample A and Sample B, were prepared in order to study the differences of the texture. Sample A, Fe-0.5wt%Si, is not annealed before cold rolling. Sample B, the same chemical composition as Sample A, is annealed before cold rolling. In Sample A, the {111} texture component increases markedly during grain growth. By contrast, in Sample B, the increase in {111} is less pronounced. The recrystallized orientations in both Samples are analyzed, and computer simulation is used to attempt to explain the texture changes during grain growth. In the case of Sample A, the simulations reproduce the experimental result well; for Sample B, however, the simulations do not agree as well. The microstructures before annealing exhibit strong alignment of the orientations, which will require a new approach to building the digital microstructures for instantiation of the simulations.
Self-Limited to Parabolic Grain Growth Kinetics in Metal Oxide Thin Films
Authors: Rupp Jennifer L.M. , Scherrer Barbara , Martynczuk Julia , Gauckler Ludwig J.
Published: April 2012

Distinctive microstructure engineering of amorphous to nanocrystalline electroceramic thin films is of high relevance for integration in low to high temperature operating MEMS-devices. Up to now, kinetic rules of nucleation, crystallization and grain growth of precipitation-based ceramic thin films are unknown. In this study, general rules for the crystallization and grain growth kinetics of a pure single-phase metal oxide thin film with only one kind of cation, i.e. ceria, made by spray pyrolysis from a precursor with one single organic solvent is discussed [1,. The near-and long range disorder is studied via Raman, DSC investigation of crystallization enthalpy, XRD, SEM and TEM for amorphous to fully crystalline state. These 400 nm thick-thin films were dense, crack-free and amorphous directly after deposition on a sapphire substrate. Briefly, above deposition temperature crystallization sets in with respect to temperature and persists over a broad temperature range from 400 to 950°C. In this regime, biphasic amorphous-crystallien films exist and grain growth proceeds simultaneously to crystallization. Isothermal grain growth studies showed that after short dwell times of 10-20h stable microstructures established following self-limited grain growth law [. In this state, driving force for the crystallization is the reduction of free enthalpy for phase transformation and interface diffusion prevails. A transition to classical grain curvature-driven parabolic grain growth kinetics appeared once the material reached the fully crystalline state for average grain sizes larger than 140 nm and higher annealing temperatures. Volume diffusion was then activated in addition to the interface diffusion. It was found that once crystallized the material shows independent on processing route equal XRD density and microstrain, as well as Raman characteristics. However, dependent on processing conditions i.e. choice of organic and, according, deposition temperature of the film amorphous states vary and affect strongly crystallization and grain growth history for the biphasic films.
A Model for Recovery Kinetics of Aluminum after Large Strain
Authors: Yu Tian Bo , Hansen Niels
Published: April 2012

A model is suggested to analyze recovery kinetics of heavily deformed aluminum. The model is based on the hardness of isothermal annealed samples before recrystallization takes place, and it can be extrapolated to longer annealing times to factor out the recrystallization component of the hardness for conditions where recovery and recrystallization overlap. The model is applied to the isothermal recovery at temperatures between 140 and 220°C of commercial purity aluminum deformed to true strain 5.5. EBSD measurements have been carried out to detect the onset of discontinuous recrystallization. Furthermore, comparison between the present model and a similar recently developed recovery model is made, and the result is discussed.
Thermal Behavior of Nickel Deformed to Ultra-High Strain by High Pressure Torsion
Authors: Zhang Hong Wen , Huang Xiao Xu , Pippan Richard , Hansen Niels
Published: April 2012

Polycrystalline Ni (99.5 %) has been deformed to an ultra-high strain ofεvM=100 (εvM, von Mises strain) by high pressure torsion (HPT) at room temperature. The deformed sample is nanostructured with an average boundary spacing of 90 nm, a high density of dislocations of >1015m-2and a large fraction of high angle boundaries (>15o) 68% as determined by transmission electron microscopy and 80% as determined by electron backscatter diffraction. The thermal behavior of this nanostructued sample has been investigated by isochronal annealing for 1h at temperatures from 100 to 600°C, and the evolution of the structural parameters (boundary spacing, average boundary misorientation angle and the fraction of high angle boundaries), crystallographic texture and hardness have been determined. Based on microstructural parameters the stored energy in the deformed state has been estimated to be 24 MPa. The isochronal annealing leads to a hardness drop in three stages: a relatively small decrease at low temperatures (recovery) followed by a rapid decrease at intermediate temperatures (discontinuous recrystallization) and a slow decrease at high temperatures (grain growth). Due to the presence of a small amount of impurity elements, the recovery and recrystallization are strongly retarded in comparison with Ni of high purity (99.967%). This finding emphasizes the importance of alloying in delaying the process of recovery and recrystallization, which enables a tailoring of the microstructure and properties through an optimized annealing treatment.
3D-EBSD Studies of Deformation, Recrystallization and Phase Transformations
Authors: Ferry Michael , Xu Wan Qiang , Quadir M. Zakaria , Zinnia Nasima Afrin , Laws Kevin J. , Mateescu Nora , Robin Lalu , Bassman Lori , Cairney Julie M. , Humphreys John F. , Albou Adeline , Driver Julian H.
Published: April 2012

A focused ion beam (FIB) coupled with high resolution electron backscatter diffraction (EBSD) has emerged as a useful tool for generating crystallographic information in reasonably large volumes of microstructure. In principle, data generation is reasonably straightforward whereby the FIB is used as a high precision serial sectioning device for generating consecutive milled surfaces suitable for mapping by EBSD. The successive EBSD maps generated by serial sectioning are combined using various post-processing methods to generate crystallographic volumes of the microstructure. This paper provides an overview of the use of 3D-EBSD in the study of various phenomena associated with thermomechanical processing of both crystalline and semi-crystalline alloys and includes investigations on the crystallographic nature of microbands, void formation at particles, phase redistribution during plastic forming, and nucleation of recrystallization within various regions of the deformation microstructure.
A Hybrid Modelling Approach Applied to the Evolution of Microstructure during Plane Strain Deformation
Authors: Das S. , Abbod M.F. , Zhu Q. , Palmiere Eric J. , Howard I.C. , Linkens D.A. , Sellars C.M.
Published: April 2012

This paper presents a modelling strategy that combines neuro-fuzzy methods to dene the material model with cellular automata representations of the microstructure, all embedded within a nite element solver that can deal with the large deformations of metal processing technology. We use the acronymnf-CAFE as a label for the method. The need for such an approach arises from the twin demands of computational speed for quick solutions for ecient material characterisation by incorporating metallurgical knowledge for material design models and subsequent process control. In this strategy, the cellular automata hold the microstructural features in terms of sub-grain size and dislocation density which are modelled by a neuro-fuzzy system that predicts the ow stress. The proposed methodology is validated on a two dimensional (2D) plane strain compression nite element simulation with Al1%Mg alloy. Results from the simulations show the potential of the model for incorporating the eects of the underlying microstructure on the evolving ow stress elds. In doing this, the paper highlights the importance of understanding the local transition rules that aect the global behaviour during deformation.
In Situ Measurements of Magnetically Driven Grain Boundary Migration in Zn Bicrystals
Authors: Günster Christoph , Molodov Dmitri A. , Gottstein Günter
Published: April 2012

The results of investigations of magnetically driven grain boundary migration in high purity (99.995%) zinc bicrystals are presented. In-situ measurements were conducted by means of a specially designed and fabricated polarization microscopy probe. The migration of planar tilt grain boundaries with various misorientation angles in the range between 60° and 90° was studied. The absolute grain boundary mobility and its temperature dependence was measured in the regime between 330°C and 415°C and the corresponding migration activation parameters were determined. The results revealed that there is a pronounced misorientation dependence of grain boundary mobility in the investigated angular range. The migration activation enthalpy was found to vary between 1.18 eV and 2.15 eV. The obtained activation parameters comply with the compensation law, i.e. the migration activation enthalpy changes linearly with the logarithm of the pre-exponential factor.
Grain Growth and the Puzzle of its Stagnation in Thin Films a Detailed Comparison of Experiments and Simulations
Authors: Barmak Katayun , Eggeling Eva , Sharp Richard , Roberts Scott , Shyu Terry , Sun Tik , Yao Bo , Ta'asan Shlomo , Kinderlehrer David , Rollett Anthony D. , Coffey Kevin
Published: April 2012

We revisit grain growth and the puzzle of its stagnation in thin metallic films. We bring together a large body of experimental data that includes the size of more than 30,000 grains obtained from 23 thin film samples of Al and Cu with thicknesses in the range of 25 to 158 nm. In addition to grain size, a broad range of other metrics such as the number of sides and the average side class of nearest neighbors is used to compare the experimental results with the results of two dimensional simulations of grain growth with isotropic boundary energy. In order to identify the underlying cause of the differences between these simulations and experiments, five factors are examined. These are (i) surface energy and elastic strain energy reduction, (ii) anisotropy of grain boundary energy, and retarding and pinning forces such as (iii) solute drag, (iv) grain boundary grooving and (v) triple junction drag. No single factor provides an explanation for the observed experimental behavior.
EBSD Coupled to SEM In Situ Annealing as a Tool to Identify Recrystallization Mechanisms - Application to Zr and Ta Alloys
Authors: Bozzolo Nathalie , Jacomet S. , Houillon M. , Gaudout B. , Logé Roland E.
Published: April 2012

A heating stage as been developed to performin-situannealing in a SEM equipped with an EBSD system in order to study recrystallization mechanisms. High temperature treatments could then be performed inside the SEM, up to 1180°C and with high heating-and cooling-rates (~100°C.s-1). Samples were cooled down to room temperature to perform EBSD orientation mapping in between successive short-duration heat-treatments. Microstructure evolution snapshots obtained this way are presented in this paper to show recrystallization in Zircaloy4 and in pure tantalum.
Substructure Dynamics in Crystalline Materials: New Insight from In Situ Experiments, Detailed EBSD Analysis of Experimental and Natural Samples and Numerical Modelling
Authors: Piazolo Sandra , Borthwick Verity , Griera Albert , Montagnat Mâurine , Jessell Mark W. , Lebensohn Ricardo A. , Evans Lynn
Published: April 2012

The understanding of the dynamics of substructures during deformation and annealing is fundamental in our ability to predict microstructural and physical properties such as rheological behaviour of crystalline materials. Here, we present an overview of new insights into substructure dynamics through a combination of in-situ heating experiments, detailed Electron Backscatter Diffraction (EBSD) analysis and numerical modelling.
Development of Cube Texture in Pure Ni Following Ultrahigh Straining by Accumulative Roll Bonding and Annealing
Authors: Bhattacharjee P.P. , Tsuji Nobuhiro
Published: April 2012

The evolution of cube texture has been investigated in pure Ni (~99.97%) following ultra high straining by Accumulative Roll Bonding (ARB) and annealing. Fully annealed sheets of pure Ni with average recrystallized grain size of ~28 (henceforth termed as fine grained starting material) and 650 µm (henceforth termed as coarse grained starting material) were used as the starting material for the ARB processing. ~50% reduction was imparted in each cycle of ARB and the process was carried up to 8 cycles resulting in an accumulated equivalent strain (εeq) of 6.4. The deformed materials were subsequently annealed at temperatures ranging between 300 to 800°C for one hour. In addition few samples were annealed at 300°C for different time intervals to observe the evolution of texture components. In all cases textures were carefully characterized using Electron Back Scatter Diffraction (EBSD) technique.
Abnormal Grain Growth Approached by Sub-Boundary Enhanced Solid-State Wetting
Authors: Hwang Nong Moon
Published: April 2012

Abnormal grain growth (AGG), which is also called the secondary recrystallization, often takes place after primary recrystallization of deformed polycrystalline materials. A famous example is the evolution of the Goss texture after secondary recrystallization of Fe-3%Si steel. A selective AGG of Goss grains has remained a puzzle over 70 years in the metallurgy community since its first discovery by Goss in 1935. We suggested the sub-boundary enhanced solid-state wetting as a mechanism of selective AGG of Goss grains. According to this mechanism, if Goss grains have sub-boundaries of low energy, they have an exclusively high probability to grow by solid-state wetting along a triple junction compared with other grains without sub-boundaries. This aspect has been confirmed by Monte-Carlo and Phase Field Model simulations. The simulations showed that if the abnormally-growing grain has a high fraction of low energy boundaries with the matrix grains, it favors the sub-boundary enhanced solid-state wetting and produces many island and peninsular grains frequently observed near the growth front of abnormally-growing Goss grains. For example, the {111}<112> orientation has a S9 relationship with a Goss grain. Therefore, grains with the {111}<112> orientation provide a favorable condition for sub-boundary enhanced solid-state wetting. Three or four-sided grains with convex-inward boundaries, which are observed on a two-dimensional section of polycrystalline structures, are not shrinking but are growing, indicating that they are growing by wetting along a triple junction. These and other microstructural evidences of solid-state wetting could be observed relatively easily near the growth front of abnormally-growing Goss grains. The existence of sub-boundaries exclusively in abnormally-growing Goss grains has been experimentally confirmed. In order to understand why only Goss grains have sub-boundaries, the cold rolling process of the hot-rolled Fe-3%Si steel was analyzed by finite element method (FEM). The analysis showed that a small portion of Goss grains formed during hot rolling survives after cold rolling; the survived Goss grains have the lowest stored energy and are expected to undergo only recovery without recrystallization, producing sub-boundaries.
Two-Dimensional Grain Growth Simulation by Local Curvature Multi-Vertex Model
Authors: Tamaki Teruyuki , Murakami Kenichi , Homma Hotaka , Ushioda Kohsaku
Published: April 2012

A local curvature multi-vertex model was developed. This model is the straightforward two-dimensional topological network model based on the physical principles which are the curvatures of grain boundaries and the grain boundary tensions at triple junctions. The model was applied to the artificial random microstructure under some conditions of grain boundary characters. The misorientation distribution was changed very little under constant grain boundary energy and mobility, but it was change much under grain boundary character dependent on misorientation. Therefore, in order to discuss actual textures, it is important to take grain boundary characters into account.
Modelling of Recrystallization Nucleation at Hard Inclusions
Authors: Mitter Werner , Sommitsch Christof
Published: April 2012

During plastic deformation, a metallic structure is deformed inhomogeneously near hard inclusions. Hence both the materials strengthening and recovery and thus softening depends on the local position. There are thus high gradients of point defects, such as vacancies and interstitials, of the dislocation density and hence of the strain energy. Those gradients govern the diffusional flow, whose pile-up influences the climbing of edge dislocations, i.e. recovery and materials softening, respectively.
Molecular Dynamics Simulation of Grain Growth in Nanocrystalline Ni
Authors: Foiles Stephen M.
Published: April 2012

Grain growth in nanocrystalline Ni has been simulated by molecular dynamics. The simulations show the creation of a high density of twin boundaries during the growth as well as the formation of vacancies consistent with recent experimental observations. The growth follows parabolic kinetics with the diameter increasing with the square root of time consistent with behavior of conventional scale metals but in disagreement with prior simulation results.
Preparation and Thermal Stability of a Mechanically Alloyed Oxide Dispersion Strengthened Ferritic Steels
Authors: Wen Yu Ren , Liu Yong , Liu Dong Hua , Tang Bei
Published: April 2012

Oxide dispersion strengthened ferritic steels (so-called nanostructured ferritic alloys, NFAs), which are candidate structural materials in next generation nuclear power plant, have attracted much attention during recent years. In this work, iron oxide as oxygen carrier and titanium, yttrium hydrides were together mechanically milled with Fe-14Cr-3W gas-atomized powder. The thermal stability and recrystallization behaviour of the as-milled ferritic powder were studied by means of metallography, SEM, TEM and microhardness test. After ball milling for 48h, complete solid solution of bcc-Fe was formed in the as-milled powder. The thermal analysis results show that dispersed oxides with an average diameter of 5nm precipitate from the supersaturated matrix at about 850 °C. During annealing at temperatures from 800 to 1000 °C, a large number of equiaxed grains as fine as few hundreds of microns were found embedding in the matrix; the recrystallized grains stay quite stable and show minor dependence on annealing temperature and time. After being heated to 1200 °C for extended time, abnormal grain growth took place and resulted in bimodal grained structure. The effect of secondary particles on the thermal stability and recrystallization behavior of the ferritic steel was also discussed.
Quantitative Analysis of EBSD Data in Rocks and other Crystalline Materials: Investigation of Strain Induced Recrystallisation and Growth of New Phases
Authors: Wheeler John , Mariani E. , Piazolo S. , Prior D.J. , Trimby P.J. , Drury M.R. , McNamara D. , Pearce M.A.
Published: April 2012

Misorientation can be calculated over large datasets and a theme of this paper is the usefulness of examining the results statistically. Comparing the statistics of misorientations calculated from neighbouring pixels (or grains) with those calculated from pairs of pixels (or grains) selected at random helps to indicate deformation and recrystallisation mechanisms. Taking boundary length into account provides a link to grain boundary energy, and boundary length versus misorientation data should be used to examine how boundaries with different misorientations evolve through time. Time lapse misorientation maps indicate how orientation changes through time at particular points in a microstructure during in situ experiments. The size of areas which have changed orientation by particular amounts can be linked to boundary length and boundary migration velocities. When dealing with different phases, the statistics of angular relationships, akin to intraphase misorientation analysis, can indicate orientation relationships in the absence of prior knowledge, which is advantageous in investigating the plethora of minerals that make up the Earth.
A Step Forward in the Understanding of the Strain Reversal Effect on the Recrystallization Kinetics after Hot Working
Authors: Jorge-Badiola D. , Lanzagorta J.L. , Gutiérrez Isabel
Published: April 2012

A reversion of the strain produces a modification of the static recrystallization kinetics. Initially, the reversion increases the recrystallization time, that reaches a maximum at a certain strain, and decreases again for increasing reverse strains. This transient on recrystallization kinetics develops over a strain interval similar to that of the microstructural and stress-strain transients. At strains beyond the transient, the reversion can be regarded as a shift on the strain axis. However, at the authors knowledge there is no formulation able to describe the material behaviour during the transient. The present work introduces an equivalent strain concept based on the substructural dissolution/build-up processes taking place as a result of the strain reversal. This formulation allows including the effect of the strain path on recrystallization models.
Grain Refinement of a Cold Rolled TRIP Assisted Steel after Ultra Short Annealing
Authors: Petrov Roumen H. , Sidor Jurij J. , Kaluba Wlodzimierz , Kestens Leo
Published: April 2012

Recrystallization and austenite formation in a TRIP-assisted steel during conventional and ultra fast reheating for intercritical annealing are studied with the purpose to clarify the possibility for grain refinement. Partially recrystallized (or transformed) samples were prepared by reheating and water quenching to temperatures between 650 and 1050°C at reheating rates of 10, 50, and 3000 °C/s, respectively, without isothermal soaking from 95% cold rolled steel sheet with ferrite-pearlite microstructure. By monitoring the hardness and microstructure, it was shown that the increase of the reheating rate from 10 to 3000°C/s causes grain refinement from 5µm to 1µm in diameter and the final ferrite grain size depends significantly on both reheating temperature and reheating rate. It was observed that after an extreme reheating rate of 3000°C/s the α-γ phase transformation starts before the completion of the recrystallization. This opens up possibilities for further structural refinement and alternative texture control.
The Effect of Strain Path Reversal during Austenite Deformation on Phase Transformation in a Microalloyed Steel Subjected to Accelerated Cooling
Authors: Sun Lin , Muszka K. , Wynne Bradley P. , Palmiere Eric J.
Published: April 2012

In the present study, monotonic and cyclical torsional deformations of an X-70 microalloyed steel were conducted at austenite temperatures below the recrystallisation-stop temperature (T5%). The austenite deformation is followed by accelerated continuous cooling to allow the investigation of the strain reversal effect on the subsequent phase transformation mechanisms. The transformation behaviours were studied by a dilatometry method, and the microstructures of the transformed products have been analysed using electron back scatter diffraction (EBSD). The results of this study shows that although subjected to the same total cumulative strain and the same cooling rate, strain path reversal by cyclical torsion produces lower temperature transformation products involving mainly a displacive mechanism, comparing to simple strain path deformation which leads to higher temperature transformation by a reconstructive mechanism.
The Solute Drag Effect during Recrystallisation and Grain Growth in Austenite
Authors: Kranendonk W.
Published: April 2012

The relevance of the solute drag phenomenon to the hot rolling of modern steel grades is outlined. An overview of our present knowledge of solute drag in grain growth and recrystallisation in austenite is presented and recommendations for subsequent research are given.
Austenite Grain Refinement in Direct Charging Based Thermomechanical Processes
Authors: Rodriguez-Ibabe J.M. , López Beatriz
Published: April 2012

Thermomechanical processes based on direct charging routes combined with near net shape technologies have become one of the main industrial production routes. The singularity of the coarse as cast initial austenite grain size, combined with the limited total applied strain during hot working, requires a tailored design of the composition and deformation schedules in order to achieve the required mechanical properties. This becomes more and more complex as higher steel grades combined with thicker sections are incorporated into production. This paper reviews the role played by the interaction of dynamic-metadynamic-static recrystallisation and strain induced precipitation on achieving the finest and most homogeneous austenite microstructures as possible, prior to transformation in the case of Nb, Nb-Mo and Ti microalloyed steels. Special emphasis will be put on the relevance of the kinetics of combined postdynamic softening mechanisms before a complete stop of recrystallisation due to precipitation occurs.
The Weighted Burgers Vector: A Quantity for Constraining Dislocation Densities and Types Using Electron Backscatter Diffraction on 2D Sections through Crystalline Materials
Authors: Wheeler John , Mariani Elisabetta , Piazolo Sandra , Prior David J. , Trimby P.J. , Drury M.R.
Published: April 2012

The Weighted Burgers Vector (WBV) is defined as the sum, over all types of dislocations, of [(density of intersections of dislocation lines with a map) x (Burgers vector)]. It can be calculated, for any crystal system, solely from orientation gradients in a map view, unlike the full dislocation density tensor, which requires gradients in the third dimension. No assumption is made about gradients in the third dimension and they may be non-zero. The only assumption involved is that elastic strains are small so the lattice distortion is entirely due to dislocations. Orientation gradients can be estimated from gridded orientation measurements obtained by EBSD mapping, so the WBV can be calculated as a vector field on an EBSD map. The magnitude of the WBV gives a lower bound on the magnitude of the dislocation density tensor when that magnitude is defined in a coordinate invariant way. The direction of the WBV can constrain the types of Burgers vectors of geometrically necessary dislocations present in the microstructure, most clearly when it is broken down in terms of lattice vectors. The WBV has five advantages over other measures of local lattice distortion. 1. It is a vector and hence carries more information than any scalar measure of local misorientation. 2. It has an explicit mathematical link to the individual Burgers vectors of dislocations. 3. Since it is derived via tensor calculus, it is not dependent on the map coordinate system, in contrast to existing measures of local misorientation which are not only scalar but dependent on the coordinate system used. 4. Calculation involves no assumptions about energy minimisation. 5. The numerical differentiation involved in calculating the WBV may introduce errors, but there is a direct mathematical link to a contour integral. The net Burgers vector content of dislocations intersecting an area of a map can be simply calculated by an integration round the edge of that area, a method which is fast and complements point-by-point WBV calculations. Errors in orientation measurement will have a much smaller effect here, and dislocations can be detected which are otherwise lost in the noise of any local calculation.
A Rationale for SRX Regression Model of Hot-Deformed Austenite Using an Orthogonal Taguchi L8 Matrix Steels
Authors: Somani Mahesh C. , Karjalainen L. Pentti
Published: April 2012

In recent past, a linear regression model to predict the activation energy (Qrex) and kinetics of static recrystallisation for hot-deformed austenite was developed based on stress relaxation test results of over 40 different carbon steels. The model is able to predict satisfactorily the static recrystallisation (SRX) kinetics of common carbon steel grades (including microalloyed steels) and also several special steel grades. In this study, the main effects of seven alloying elements, viz., C, Mn, Cr, Ni, Mo, Nb and V, on the activation energy of recrystallisation were further examined by using eight experimental steels based on an orthogonal Taguchi L8 matrix. All steels contained constant additions of B, Ti and Si. Even though originally intended for studies on phase transformation characteristics and hardenability under direct quenching conditions, the L8 matrix steels were suitably employed for further validation of the SRX regression model. In addition, the SRX characteristics and kinetics of a set of new steel compositions including C-Mn, C-Mn-Nb and C-Mn-Nb-Ti types were examined in the light of model equations, which further confirm the suitability of the regression model.
Modelling of Particle Pinning in Dual Scale Using Phase Field Method
Authors: Shahandeh Sina , Militzer Matthias
Published: April 2012

Modelling the evolution of structures in polycrystalline materials with distributions of fine particles requires integration of multiple length scales. Grain boundaries interact with particles on the scale of the particle diameters. The particle pinning force controls the kinetics of grain growth. Grain diameters can be several orders of magnitude larger than particles. In this work, a methodology is proposed to combine two sets of phase field models at different length scales. At the smaller scale, the effect of particles on movement of a single grain boundary is modelled in a small domain with a high grid resolution. The interface moves in an array of particles with specified shape and size distributions. The average pinning force exerted by the particles, is calculated from the interface velocity. Then, an effective driving force model is developed to incorporate the obtained pinning force into the large scale where grain growth simulations are preformed. In this model, the particle pinning force is subtracted from the driving force in the phase field formulation. In this effective formulation, particles are not resolved in the calculation grid. Therefore, with the larger numerical mesh, modelling of larger systems is possible. Kinetics of grain growth was studied with 2 dimensional simulations. Keywords: Phase field modelling, particle pinning, grain growth
Phase Field Model of Grain Growth Using Quaternions
Authors: Biswas Santidan , Samajdar Indradev , Haldar Arunansu , Sain Anirban
Published: April 2012

The microstructure of a material determines its mechanical properties. Since microstructure can be tailored by thermo-mechanical processing of the metal, it is important to understand how the microstructure evolves under thermo-mechanical processing. We have constructed a phase field formalism to study recrystallization and grain growth in polycrystalline material. A unique feature of our model is that the Euler Angles (φ1,φ,φ2), obtained from Electron Back Scattered Diffraction (EBSD) data of a polycrystalline sample can be taken as an input to our model. In our model, the grain orientations at discrete grid points are represented by a non-conserved vector field, namely a quaternion. The free energy used for the evolution of the local orientations contains bulk energy for various preferred grain types and grain boundary energy. The grain orientations evolve in time following a Langevin dynamics. So far we have established that the rate of grain growth follows the usual L ~ t1/2scaling law when the grain boundary energy is independent of the misorientation angle between neighboring grains. Work on other aspects of this model is in progress.
Microstructural Evolution in 9%Cr Heat Resistant Steels under Creep Conditions
Authors: Kaibyshev Rustam
Published: April 2012

Microstructural design of a new generation of 9%Cr steels for fossil power plants is considered. It was shown that microstructural stability of 9%Cr steels impairs their creep resistance. Two types of restoration processes can occur in the heat resistance steels under creep conditions: (i) normal grain growth and (ii) dynamic recovery. The first process associates with the migration of high-angle boundaries (HAGB) of blocks of tempered martensite lath structure (TMLS). However, their migration is negligible even during creep deformation. Boundaries of packets and prior austenite boundaries (PAB) are effectively pinned by precipitations of M23C6and Laves phase Fe2(W,N). The second process consists of transformation of lath boundaries to subboundaries and their subsequent migration (subgrain coarsening) under creep. Under aging the migration of low-angle boundaries (LAGB) is retarded by uniformly distributed nanoscale M(C,N) dispersoids and particles of M23C6precipitated on these boundaries under tempering. Under creep the dissolution of M23C6carbides located along LAGBs and coagulation of uniformly distributed M(C,N) carbonitrides facilitates LAGB migration. It was shown that the normal grain growth is not important for deterioration of creep strength. Conversion of the lath boundaries into subgrain boundaries strongly decreases creep rate. In contrast, continuous subgrain coarsening is the main process restricting the ability of the 9%Cr steel for long-range service under creep conditions. Tertiary creep is attained due to the occurrence of subgrain coarsening.
Goss Texture Formation by Strain Induced Boundary Migration in Semi-Processed Nonoriented Electrical Steels
Authors: Park Jong Tae , Han Kyu Seok
Published: April 2012

Semi-processed nonoriented electrical steels are very attractive products whose magnetic properties are significantly improved through annealing treatment in customers plant. The improvement is due to strong Goss texture formation by strain induced boundary migration (SIBM). In order to the effect of temper rolling reduction on the strengthening of Goss texture, temper rolling reduction was changed in the range of 2% to 8%. The annealing times was changed from 10 minutes to 180 minutes. A mechanism of grain growth during SIBM is suggested from our experimental data. In the specimen temper-rolled by 2%, relatively strong {111}<112> texture develops, whereas in the specimens temper-rolled by 4% through 8%, strong Goss texture develops as a result of SIBM during final annealing. It can be found from observed EBSD data that the Goss grains have the lowest stored energy in all temper-rolled specimens, which is confirmed by average image quality value in EBSD measurements. However, for the Goss grains to grow preferentially, stored energy difference between Goss grains and their neighboring grains may have to be higher than a certain critical value.
Microstructure Evolution during Quenching and Tempering of Martensite in a Medium C Steel
Authors: di Schino Andrea , Alleva Laura , Guagnelli Mauro
Published: April 2012

The microstructural evolution of a quenched medium-C steel during tempering was analyzed by means of Orientation Imaging Microscopy (OIM). The steel was heat treated in order to develop fully martensitic microstructures after quenching with a different prior austenite grain size (AGS). Main results can be summarized as below: A very poor effect of AGS on packet size was found in comparison to bainitic steels. A finer packet was measured at mid-thickness with respect to surface after the quenching process. This phenomenon was attributed to the effect of thermal strain path on phase transformation during quenching. The through-thickness microstructural gradient remains after tempering. High-angle boundary grains do not significantly grow after tempering; on the contrary, low-angle grain boundaries (cells) move, fully justifying the hardness evolution with tempering temperature.
Growth History of Individual Grains in Polycrystals: Theoretical Model and Simulation Studies
Authors: Zöllner Dana , Streitenberger Peter
Published: April 2012

A 3D grain growth model is developed based on a generalised mean-field approach. It allows the prediction of the growth history of individual grains of a polycrystal during normal grain growth, which has been compared with results from Monte Carlo Potts simulations showing a good agreement. Based on a stochastic grain growth model the diffusivity of the Brownian-like motion of individual quadruple points and triple junctions in 2D sections can be related to the average growth rate providing a possibility for the determination of the average growth law of the grain ensemble solely from the stochastic growth behaviour of single grains.
Grain Refinement in Austenitic Stainless Steel during Warm Screw Rolling
Authors: Mogucheva Anna , Lopatin Nikolay , Belyakov Andrey , Kaibyshev Rustam
Published: April 2012

The development of dynamic recrystallization in a 304-type austenitic stainless steel during warm multi-pass screw rolling was studied. The fraction recrystallized depended significantly on the distance from the centre of rolled rods. The highly elongated original grains were mainly observed in the centre of processed samples, while the portions close to the sample edge were characterized by relatively fast development of dynamic recrystallization leading to formation of almost equiaxed fine grains with a size of about 1 μm. The volume fraction of fine grains in the edge areas increased with straining and exceeded 0.7 after rolling to 63% cross area reduction. The structural mechanism responsible for the grain refinement was considered as continuous dynamic recrystallization. The difference in the recrystallization kinetics across the sample is associated with the variation in strain intensity.
Role of Σ9 Boundaries in Abnormal Grain Growth of Goss Grains in Fe-3%Si Steel Approached by Solid-State Wetting
Authors: Park Chang Soo , Park Hyung Ki , Park Seung Chul , Han Chan Hee , Hwang Nong Moon
Published: April 2012

The pancake-shaped growth of Goss grains in Fe-3%Si steel is approached by solid-state wetting mechanism. The fraction of grains with Σ9 relation with Goss grains in the 0.3 mm thick specimens after primary recrystallization is higher near the surface than at the center. This result indicates that the probability of solid-state wetting is higher near the surface than at the center, leading to the pancake-shaped growth.
Mobility Driven Abnormal Grain Growth in the Presence of Particles
Authors: Fjeldberg E. , Holm Elizabeth A. , Rollett Anthony D. , Marthinsen Knut
Published: April 2012

Simulation of mobility-driven abnormal grain growth in the presence of particles in a 3D Potts Monte Carlo model has been investigated, and even though the driving force in this case is identical to normal grain growth, Zener pinning does not occur. Instead the particles seem merely to have a small inhibiting effect on the number of abnormal grains, and this effect only has a noticeable influence for volume fractions of particles above 5 vol%.
Migration of Dislocation Boundaries in a Modified P911 3%Co Heat Resistant Steel during Tempering, Ageing and Creep
Authors: Kipelova Alla , Kaibyshev Rustam , Belyakov Andrey , Molodov Dmitri A.
Published: April 2012

Effect of carbide precipitation on pinning force and migration mechanism of boundaries of martensite laths was considered in a 3%Co modified P911. The dimensions of second phase precipitations, martensite laths and dislocation densities were measured by means of transmission electron microscopy. The pinning forces retarding the motion of the lath boundaries, that arise from M(C,N) nanoscale precipitations and M23C6 particles were evaluated by using different models. The pinning pressure evaluated by taking into account a non-uniform distribution of M23C6 particles was high enough to stabilize the lath martensite structure during tempering and long term ageing. On the other hand, significant coarsening of martensite laths occurred in neck portions of samples subjected to long-term creep tests. Additional effects from dislocation density and applied stress on the motion of lath boundaries are considered in some details.
Modelling Interface Diffusion Creep: Single Phase Insights and Two Phase Challenges
Authors: Wheeler John , Ford J.M.
Published: April 2012

Numerical and analytic models for diffusion creep have commercial and geological uses. For single phase polycrystals, numerical models of interface diffusion creep illustrate how grains rotate and what the relative contributions of grain shape change and grain boundary sliding are to the overall strain. In particular they shows that an equi-axed starting material will initially show large grain angular velocities but that these slow down as grain become slightly elongate. A steady state microstructure with some grain elongation and little or no grain rotation is reached. Consequently the equi-axed grain shapes seen in superplastic deformation require additional processes for a full explanation. For two phase aggregates, the mathematical framework cannot be simply extended it breaks down as the system becomes mathematically overdetermined. Further work is required to solve this problem. If the second phase is insoluble, the mathematics can, though, be extended successfully, paving the way for models of diffusion creep with insoluble second phase particles.
Applicable Solvent Photoresist Strip Process for High-K/Metal Gate
Authors: Wada Masayuki , Takahashi H. , Snow J. , Vos Rita , Mertens P.W. , Shirakawa H.
Published: April 2012

In the very near future 32(28)-nm node device technology innovations will enter high volume manufacturing. New materials and structures, e.g. high-k (HK), high-k cap (HK cap), metal gate (MG) and SiGe channel, are being highly considered. Requirements for wet processing are varied according to metal-first or metal-last integration schemes. [1, 2, 3] One of the biggest challenges in wet processing for implementing new materials and structures is to achieve both high selectivity and low substrate loss. At some wet cleaning or etching processes, standard chemicals, e.g. APM, HF and O3, can be accommodated by optimizing the chemical condition. However, photoresist (PR) strip processes require the development of new chemicals or techniques, since SPM does not have sufficient compatibility against presently reported materials. This study focused on the PR strip technique via the dissolution and swelling effects in solvent, and an applicable process technique and its effectiveness for 32(28)-nm and beyond device fabrication is reported.
Optimized Post-CMP and Pre-Epi Cleans to Enable Smooth and High Quality Epitaxial Strained Ge Growth on SiGe Strain Relaxed Buffers
Authors: Loo Roger , Souriau Laurent , Ong Patrick , Kenis Karine , Rip Jens
Published: April 2012

Further improving complementary metal oxide semiconductor (CMOS) performance beyond the 15 nm generation likely requires the use of high mobility materials like Ge for pMOS devices. However, Ge pMOS devices made in relaxed Ge do not outperform current state of the art uni-axially strained Si pMOS devices. This explains the current interest in compressively strained Ge like bi-axially strained Ge grown on top of SiGe Strain Relaxed Buffers. From a device integration point of view, the surface smoothness of the strained Ge layer is an important parameter which has so far not widely been reported in literature, in contrast to other parameters like the material quality (crystallinity) and the threading dislocation density. In this paper we report the post-CMP and pre-epi cleans which are required to obtain contamination free SiGe surfaces to enable defect free strained Ge growth without reoccurrence of the surface roughening. We will demonstrate the epitaxial growth of fully strained 20 nm thick Ge epitaxially grown on top of SiGe Strain Relaxed Buffers with 85% Ge with a surface roughness as low as 1.6 Å (as measured on areas of 10×10 µm2).