bluuebunny/crossref_metadata_2025 huggingface dataset:
Matrix Coherency Strain and Hardening of Al-Mg-Si
Authors: Gulbrandsen-Dahl Sverre , Moen Knut E. , Ehlers Flemming J.H. , Marioara Calin D. , Pedersen Ketill Olav , Marthinsen Knut
Published: January 2010

Standard and high resolution transmission electron microscopy (TEM) and advanced post processing of the TEM images have been applied for quantitative characterization of the hardening particle structure of an Al-Mg-Si alloy optimized for formation of the metastable phase β’. The relation between the structural characterization and the mechanical properties has been developed. A first attempt is presented on visualization and quantification of the coherency strain field of β’, based on a combination of Vienna Ab-initio Simulation Package (VASP) calculations and continuum mechanical modelling.
Morphology of γ' Precipitates in Second Stage High Pressure Turbine Blade of Single Crystal Nickel-Based Superalloy after Serviced
Authors: Miura N. , Nakata K. , Miyazaki M. , Hayashi Y. , Kondo Y.
Published: January 2010

The morphology of the ’ precipitates in the single crystal nickel-based superalloy serviced as the second stage high pressure turbine blade of the aircraft engine was examined. The aim of this work was to estimate the temperature and the stress distribution, and the stress direction of the blade in service. The blade was cut into three parts parallel to (001) plane at 8, 40 and 64mm from the tip. These parts were named as the tip, middle and root parts. Furthermore, these three parts were cut into six parts parallel to {100} which were almost normal to the surface from the leading to the trailing edge at interval of 6mm. Microstructure observations by a FE-SEM were carried out on the thirty portions of each part parallel to (001) and {100} planes at the vicinity of the interface between the coating layer and the matrix in the suction and pressure sides. Most of the ’ precipitates contacted each other toward almost parallel to the surface at the vicinity of the interface in the blade. Especially, at the leading edge of the pressure side of the tip and middle parts, the rafted /’ structures start to collapse. Consequently, the blade in service, at the leading edge of the pressure side of the tip and middle parts were exposed to the highest temperature and stress conditions. And the multi-axial compressive stresses parallel to the blade surface were expected to act on the blade in service.
New Creep Deformation Concept Based on Creep under Lower Stresses
Authors: Matsuo Takashi
Published: January 2010

Through the analysis of many creep rate-time or creep rate-strain curves of -single phase Ni-20mass% Cr alloy single crystals with various stress axes, it was clarified that the creep deformation manners at lower stresses are drastically different to those at higher stresses.
These creep features at lower stresses are summarized into three ones as follows.
(i) The fully extended transient stage occupies the considerable ratio of rupture life.
(ii) The steady state stage disappears, because the transient stage directly connected with the accelerating stage.
(iii) The origin of the onset of accelerating stage is regarded as the formation of the dynamic recrystallized grain.
These difference in creep deformation manner were caused by the predominant operation of the primary slip system and then the homogeneous evolution of dislocation substructures.
Creep Behavior and Microstructure of 8Cr Oxide Dispersion Strengthened Martensitic Steel
Authors: Shinozuka Kei , Esaka Hisao , Tamura M. , Tanigawa Hiroyasu
Published: January 2010

In international thermonuclear experimental reactor (ITER), reduced activation ferritic/martensitic steels will be used for plasma-facing materials. However, it is necessary to raise the temperature of operation in order to elevate efficiency of electric power generation by using the material which is more excellent in strength at elevated temperature. Oxide dispersion strengthened (ODS) steels are promising candidate for high temperature materials of a nuclear fusion reactor. There are many reports that ODS steels show very high creep strength, but there are few reports on creep deformation mechanism. In this work, creep deformation behavior of 8 wt% Cr ODS steel was investigated. This ODS steel had high density of fine dispersed Y2Ti2O7 particles and -ferrite grains elongated along the hot-rolling direction. The creep curve showed a low creep strain rate until specimen ruptured. Vickers hardness of the gauge part of specimens in interrupted creep tests decreased with increasing the loading time. However, that of the grip part did not change significantly. Accordingly, although dynamic recovery occurred in the ODS steel, it had not affected the creep deformation rate.
Microstructure Evolution in a 9%Cr Heat Resistant Steel during Creep Tests
Authors: Skorobogatykh Vladimir , Schenkova Izabella , Dudko Valeriy , Belyakov Andrey , Kaibyshev Rustam
Published: January 2010

Dynamic structural changes during creep tests for about 103 hours at 600 and 650oC were investigated in a P92-type 9%Cr martensitic heat resistant steel. The structural changes are characterised by the development of relatively large equiaxed subgrains with relatively low dislocation densities in place of initial martensite laths. The coarsening of substructure was accompanied by a growth of second phase precipitates. The final grain/subgrain sizes and dislocation densities evolved after the creep tests were in rough correlation with applied stresses, i.e. larger (sub)grains developed under lower stresses. The structural mechanism responsible for microstructure evolution was considered as a kind of continuous dynamic recrystallization.
Effect of Thermomechanical Processes on Σ3 Grain Boundary Distribution in a Nickel Base Superalloy
Authors: Souaï Nadia , Logé Roland E. , Chastel Yvan , Bozzolo Nathalie , Maurel Vincent , Nazé Loic
Published: January 2010

According to various studies, Grain Boundary Engineering (GBE) is likely to enhance mechanical properties of polycrystalline materials. The present investigation highlights some relationships between thermomechanical process (TMP) parameters of a commercial nickel-base superalloy PER72, supplied by Aubert & Duval (equivalent to Udimet®720™) and the resulting microstructure. The long-term goal is to develop TMPs that modify the Grain Boundary Character Distributions (GBCD) in order to improve high temperature properties. In this context, Grain Boundary Engineering (GBE) techniques are considered, thinking of replacing standard forming processes by optimised thermomechanical treatments. Mechanical testing at high temperature (compression and torsion tests) has been carried out and it is shown that multi-step treatments promote twinning. Some clues are then presented in an attempt to explain when and how twins are created.
Study on the Ultrahigh Speed Grinding of Superhard Materials with Squeeze Film Damping Technology
Authors: Yu Tian Biao , Li Hu , Yang Jian Yu , Wang Wan Shan
Published: January 2010

In order to further improve machining quality of superhard materials, it was presented that adds a squeeze film damper on the wheel spindle of ultrahigh speed grinder as a assistant elastic sustain to attenuate the vibration of the wheel spindle. Work principle of squeeze film damper was analyzed; the squeeze film pressure distribution was researched through simulation and damper parameters effect on damping coefficient was studied. Base on the theory research the damper was designed and experiments was done. Experimental result shows the amplitude of the grinding wheel spindle can be reduced 20% and machining quality of superhard materials can be improved 10%～20%. Research works provides a new method for superhard materials machining.
The Effect of Grain Size on Strain Determination Using a Neutron Diffractometer
Authors: Wimpory Robert C. , Wasmuth Uwe , Rebelo-Kornmeier Joana , Hofmann Michael
Published: January 2010

The determination of strain from neutron diffraction data is normally based upon the fit of a Gaussian function to a Bragg reflection. The error in the fit is assumed to be that based on ‘counting statistics’ and this error propagates through the analyses until the final stress evaluation. This relies on there being a big enough number of diffracting grains/crystallites within the gauge volume to ‘approximate’ to counting statistics. The number of grains however depends on the gauge volume size chosen and the average size of the grains (and hence diffracting grains) within the gauge volume and this should be taken into account. The aim of this work is to give an estimate of the uncertainty due to these ‘grain-size statistics’ due to grain size, gauge volume, FWHM of the Bragg reflection (for angular dispersive diffractometers), scattering angle (2), size of detector (and hence number of diffracting grains ‘seen’ on the detector), hkl multiplicity (m) and eventually texture.
Development of Twin Fractions and Microstresses of the Hot Extruded Magnesium Alloy AZ31 under Cyclic Loading Conditions
Authors: Huppmann Michael , Reimers Walter
Published: January 2010

For investigating the twinning and detwinning behaviour under cyclic loading conditions in-situ stress measurements with different applied strain amplitudes were performed at the beamline 7T-MPW at BESSY II. Intensity measurements of the (10-10), (11-20) and (0002) reflections served for the determination of the twinned volume fraction. The measurements of the (hkil) dependent strains and stresses gave information on the load partitioning between different grain orientations.
The intensity measurements performed in the compression regime showed that the evolution of the (0002) reflection intensity depends on the strain amplitude. For strain amplitudes ≥ 0.75 % an increase in intensity is observed whereas for smaller strain amplitudes the (0002) intensity decreases with increasing cycle numbers. In the tensile regime an increase in the (0002) reflection intensity is found for the whole range of applied strain amplitudes.
Single Crystal Elastic Constants of the MAX Phase Ti3AlC2 Determined by Neutron Diffraction
Authors: Kirstein Oliver , Zhang Jian F. , Kisi Erich H. , Riley D.P. , Styles M.J. , Paradowska Anna Maria
Published: January 2010

The ternary ceramic Ti3AlC2 has an interesting combination of electrical, thermal and mechanical properties. Single crystal elastic constants under the Reuss approximation for the micromechanical state were obtained by analysing the shifts of neutron diffraction peaks while a polycrystalline sample was subjected to a compressive load varying from 5 to 300 MPa. The values of Young’s modulus and Poisson’s ratio computed from the single crystal compliances are in good agreement with those obtained directly from strain gauges and from the average changes in the a and c unit cell parameters.
Real Time Monitoring of the Strain Evolution during Rapid Heat Treatment of Steel Samples by Means of Synchrotron X-Ray Diffraction
Authors: Kostov Vladimir , Gibmeier Jens , Doyle Stephen , Wanner Alexander
Published: January 2010

An innovative experimental set-up for fast X-ray diffraction analysis on polycrystalline materials has been established at the synchrotron radiation facility ANKA (Karlsruhe, Germany). Key components of the set-up are two fast microstrip line detectors arranged symmetrically around the incident beam in the backscatter region. The capabilities of the set-up are tested by means of in-situ heat treatment experiments on SAE 4140 steel samples. In this feasibility study the heat was introduced by means of either a heating stage or by means of a gas tungsten arc welding torch. It will be shown that the evolution of thermal and elastic lattice strains can be monitored at a sampling rate of up to 4 Hz at a bending-magnet synchrotron beamline. Since the sampling rate may be increased further at a insertion device synchrotron beamline providing higher photon flux, our setup appears to be feasible for monitoring laser treatments in real time.
A Study on Area Detector Type Diffraction Stress Measurement and its Application to Shelling Problem in Railway Tracks
Authors: Sasaki Toshihiko , Yaguchi Osama , Kobayashi Yuichi
Published: January 2010

In order to study on the effects of grinding of rail head on rolling contact fatigue of rails, residual stress measurements were conducted for rails processed under different grinding conditions. In this study, residual stresses in rails used for a service line were measured with the method of X-ray stress measurement. The triaxial stress analysis was conducted using a new method for an area detector type X-ray stress analysis proposed by the authors. Four grinding conditions were used to rail specimens. The distributions of residual stresses in the surface layer of the rail head were obtained. It was found that the tensile residual stresses were generated at the field-side of the ground rai1, and that the triaxial stress state was formed in the surface of the rail head widely.
Residual Stress Depth-Profiling in Shot-Peened Al Alloy Components Subjected to Fatigue Testing
Authors: Azanza Ricardo Cristy Leonor , Degan G. , Bandini M. , Scardi Paolo
Published: January 2010

The residual stress profile in a shot-peened Al alloy component was studied by a recently proposed method based on the known procedure of progressive thinning and X-ray Diffraction measurements. The effect the cyclic stress on the fatigue life was studied in detail, showing the correlation between nominal load and residual stress relaxation. Besides showing the expected decrease of compressive stress with the load and number of cycles, the present work highlights the importance of changes in the through-the-thickness residual stress distribution.
Effect of Material Property Changes on the Performance of Al Rolling Mills
Authors: Karhausen Kai F. , Schneider Wolfgang
Published: January 2010

The industrial production of aluminium strip comprises a rather long process chain. One of the characteristics of aluminium alloys is that a number of final strip properties are influenced considerably already at very early process stages. Since it is practically impossible to run large variations of controlled process changes on an industrial mill experimentally, Through Process Modelling (TPM) has been in focus of research and has developed into a valuable tool to design process chains with a view to achieving desired properties. Metallurgical models in combination with (plasto-) mechanical/thermal models trace variables of state through the process chain down to the final operation. However, there are further important properties of the product, which may be generated as consequence of the total production history. Predominant examples are the strip profile and flatness and the product surface. These properties do not only result from the processes settings, they may also have a strong back-effect on the process performance itself. As a consequence they may also affect the metallurgical properties. This paper shows representative computations of in-dustrial aluminium rolling process steps to evaluate the interactions of different mechanisms taking place in the rolling processing chain, with a special attention to profile/flatness, surface and metal-lurgical properties.
A Step towards a Complete Uncertainty Analysis of Residual Stress Determination Using Neutron Diffraction
Authors: Wimpory Robert C. , Ohms Carsten
Published: January 2010

Up to now the tendency in residual stress determination (using neutron diffraction) has been to assess the uncertainties in terms of the propagation of ‘fitting uncertainty’ of the Bragg peaks only. There are many other sources of uncertainty, some more obvious than others, that should be taken into account or at least be considered in terms of their impact when interpreting the data. These cover not just the instrument calibration and characteristics and the technique itself but also the properties of the sample. A discussion of how best to combine the uncertainty of all contributing factors will be made. These factors (on the sample side) will include variations in chemical composition, grain size related problems, surfaces/interfaces cutting through the sampling volume, texture variations within the sampling volume, presence of intergranular strains (plastic anisotropy) etc. The knowledge of appropriate elastic constants, for example, and their uncertainty is necessary for a more reliable stress determination. One should also be aware of the more subtle influences on the elastic constants such as texture or chemical variation. This should be a step in the right direction for a ‘unified uncertainty analysis’ covering all possible aspects of uncertainty in residual stress determination using neutron diffraction.
Investigation of Sintering Processes by Tomography
Authors: Kieback Bernd , Nöthe Michael , Banhart J. , Grupp Rainer
Published: January 2010

Sintering especially of loose particle packings is accompanied by dimensional changes of the specimen. The growth of inter particle contacts under the influence of the Laplace pressure is well understood and described by the two particle model. On the other hand the understanding of other fundamental sintering phenomena i.e. cooperative material transport processes is rather vague. To overcome this limitation for near net-shape production of components by powder metallurgy an improved model of particle rearrangement processes is required. First efforts to obtain necessary experimental data were performed at 1D and 2D models. But recent improvements of high resolution synchrotron computer tomography (SCT) setups allow the acquisition of in-situ data of particle rearrangements.

In-situ studies of particle rotations during sintering were conducted at the ESRF in Grenoble. The rotations during free sintering of monocrystalline particles were investigated during continuous heating up to 1050 °C or with frequent interruptions of the heating by 1 hr dwell times every 100 °C. In contrast to 1D specimens measured by Wieters the 3D specimens showed negligible rotations. This must be attributed to the constraints in 3D samples. To obtain a more detailed insight in the rotations the particles of one sample were marked. It is possible to show that the particles perform intrinsic rotations. Therefore a new rotation model is developed. The intrinsic rotations are confirmed by complementary EBSD analyses as well.
Mathematical Modeling of Microstructure Evolution of V Steels during Hot Rolling of Seamless Tubes
Authors: Carvalho Ricardo Nolasco , Ferreira Marcelo A.C. , Santos Dagoberto Brandão , Barbosa Ronaldo
Published: January 2010

Torsion and compression testing have been used to simulate microstructure evolution of industry processes. Additionally, mathematical modeling of the industry hot rolling processes has been carried out by several researchers. These models employed equations published in the literature describing kinetics of softening, grain size evolution and grain growth. Validation of the models was carried, in some cases, by comparing the microstructure or the average stress per pass, the latter as calculated from industry rolling mill loads. In the present work, torsion simulation and industry trial results were used to validate the mathematical model presented. Equations used in the model were mostly taken from literature and appropriate modifications were implemented concerning basically two points: a) the transfer time between CMM and SRM, a step in the production line typical for seamless rolling and rather unusual for other industry rolling processes and b) the chemical composition used in tube rolling industry where C equivalent values are usually higher than those used in the rolling of flats.
Micro-Polar and Second Order Homogenization of Periodic Masonry
Authors: Bacigalupo Andrea , Gambarotta Luigi
Published: January 2010

Micro-polar and second order homogenization procedures for periodic elastic masonry are implemented to include geometric and material length scales in the constitutive equation. By the solution of the RVE equilibrium problems with properly prescribed boundary conditions the orthotropic elastic moduli of the higher order continua are obtained on the basis of an enhanced Hill–Mandel condition. A shear layer problem is analysed and the results from the heterogeneous models are compared with those ones obtained by the homogenization procedures; the second-order homogenization appears to provide better results in comparison to the micro-polar homogenization.
The Microstructure Change during Modeling of Conventional and Thermo-Mechanical Rolling of S355 Steel Bars
Authors: Stradomski Grzegorz , Dyja Henryk , Stradomski Z.
Published: January 2010

Substantial differences – mainly in plasticity – were found based on statistical analysis of hot rolled bars mechanical properties. Investigations presented in the paper were related to the possibility of modification of continuous bar mills used now in order to improve and stabilise plastic properties determined by the energy of breaking. The paper presents results of laboratory investigations representing processes of conventional and normalising rolling of bars from S355 steel. The experimental analysis of both rolling processes comprised assessment of actual changes occurring in the microstructure of bars, deformed acc. to suggested parameters corresponding to conventional and normalising rolling. The investigations included also the assessment of accelerated cooling after rolling influence on the microstructure of finished products.
The Analysis of the Process of Asymmetric Rolling of Plates
Authors: Kawałek Anna , Dyja Henryk , Knapiński Marcin
Published: January 2010

In this work there has been conducted theoretical analysis of the process of asymmetric rolling of plate in finishers of plate mills. On the basis of the carried out research the influence of asymmetry factor av, deformation ε and strip form h0/D on strip bend during the process of rolling has been determined. For this reason, the following resolutions have been pointed out: velocity of flow, pure shear and intensity of deformation in deformation zone.
Physical Simulation at Hot Deformation
Authors: Kawalla Rudolf , Müller Wolfhart , Jungnickel Werner
Published: January 2010

Today the numerical simulation of hot deformation processes is very advanced. But it requires mathematical models for metalphysical processes as for microstructure development, which take place during the deformation. Until now such models were developed for many steel grades and non-ferrous materials. For new steels as multi-phase steels laboratory investigations are required, in order to determine the optimal processing technologies of these materials. This applies also to the modelling. So far it is impossible, to calculate sole by mathematical solutions the manifold parameters of metalphysical processes and microstructure, for this reason laboratory trials and simulations are needed implicitly. Even for well known materials such procedures can be essential and useful. Using the multi-functional simulation system Gleeble HDS-V40 it is shown, which possibilities a physical simulation offers today. Starting with the annealing conditions, followed by microstructure development up to cooling, selected examples reflect the results of property development during hot deformation processes. The differences between conventional deformation after re-heating and deformation after direct-charging will be presented. The last-mentioned concept offers in its combination of near-netshape casting and direct charging special benefits, especially saving of energy.
Anisotropic Ostwald Ripening in Silicon Nitride: On the Reaction-Controlled Kinetics
Authors: Kitayama M.
Published: January 2010

A model for anisotropic Ostwald ripening was developed using a chemical potential (weighted mean curvature) difference as a driving force for mass-transport. Based on this model, grain growth simulations of silicon nitride during the phase transformation and Ostwald ripening were performed. Comparison with experimental results during the phase transformation suggests that grain growth be controlled by interfacial reaction. Simulations of Ostwald ripening predict that the growth exponent be 3 for the reaction-controlled case, and increases up to 5 as the growth kinetics shifts from reaction-controlled to diffusion-controlled. It was reported that the mean aspect ratio of silicon nitride crystals increased during the phase transformation, and decreased during Ostwald ripening. These behaviors were successfully simulated by this model. The concave depression at the tip of silicon nitride crystal that was experimentally observed. Simulations by the Ostwald ripening model demonstrated that it could be developed when the liquid phase was super-saturated, and further that the tip shape was a function of the liquid concentration.
The Physical Simulation of the Normalizing Rolling of the Steel Plate in Strength Category 350÷460MPa
Authors: Knapiński Marcin , Koczurkiewicz Bartosz , Kawałek Anna , Dyja Henryk
Published: January 2010

The article presents the results of physical simulations of the process of rolling plates of steel in the strength category 350÷460MPa on the finishing stand of a reversing mill. The simulations were performed for three steel grades and final plate thicknesses 40mm. The purpose of the simulations was to select the conditions of plate deformation to obtain, directly after rolling, structure of material corresponding to the structure obtained from normalizing annealing. Thus, the simulations reflected the normalizing rolling process. The research carried out has allowed to elaborate the new technology of production of rolling plate without an additional thermal treatment like normalization. It allow to decrease a time and total cost of production for this sort of product.
The Effect of Deformation on the Work Hardening Behaviour after Aging of Two Commercial Al-Mg-Si Alloys
Authors: Kolar Michal , Pedersen Ketill Olav , Gulbrandsen-Dahl Sverre , Brüggemann Thiemo , Marthinsen Knut
Published: January 2010

In order to investigate the effect of deformation on the aging response of Al-Mg-Si alloys, a series of tensile tests have been designed and carried out on two commercial aluminium alloys, i.e. AA6060 and AA6082. Extruded and solution heat treated specimens were pre-deformed 0%, 5%, and 10% (engineering strain), respectively followed by natural aging (NA). It was observed that the work-hardening rate increases with prolonged natural aging time and decreases with increasing pre-deformation prior to natural aging. The most significant effect of deformation was obtained for T4 temper i.e. after 1000 and 10000 minutes NA for the 6082 and 6060 alloy, respectively, when the amount of pre-deformation is 10%. A remarkable difference in work-hardening rate at the level of small plastic strains was observed compared to that of the material naturally aged for only 10 minutes. In addition to the tensile tests, transmission electron microscopy (TEM) has been used to characterize dislocation evolution for various combinations of pre-deformation and aging time.
Combined Discrete/Finite Element Multiscale Approach for Modelling of the Tool/Workpiece Interface during High Shear Processing: Hot Rolling and Friction Stir Welding Applications
Authors: Krzyzanowski Michal , Davies Peter S. , Rainforth W. Mark , Wynne Bradley P.
Published: January 2010

The concept of combining the latest finite element (FE) and discrete element (DE) multiscale numerical technologies for modelling of the tool/workpiece interface during high shear processing is described. The potential of FE tools and techniques merged with DE based transient dynamics is highlighted. Linking of the modelling scales is based on transferring the corresponding boundary conditions from the macro model to the representative cell, considered as the meso- level model. This meso- model consists of a large number of bodies that interact with each other. The transfer processes are described by the system of diffusion and motion equations including contact detection and interaction solutions for particles integrated in time. Modelling of the tool/workpiece interface including both mixing of the oxide particles into the subsurface layer during hot rolling of aluminum and heat generation during friction stir welding (FSW) are considered.
Simulative Accelerated Creep Test on Gleeble
Authors: Mandziej Stan T.
Published: January 2010

The simulative accelerated creep test (ACT) on Gleeble thermal-mechanical simulator was developed as a response to an overall need of gaining in a short time useful physical data for estimation of long-term behaviour of materials exposed to operation at elevated temperatures. While most of the design of components and estimation of power plants lifetime is based on long-term creep data, which are generally available for the plate and pipe creep resisting steels, in case of the welded joints on these components such data are not always easily found and e.g. for the repair welds are very often not available.
Next to its short duration, demanded from the accelerated creep testing procedure are the following conditions:
- The basic temperature and applied strains in the ACT must prevent odd transformations like secondary dissolution of carbides or intensive formation of non-equilibrium phases.
- The final deformation at fracture must be like at real creep – just a few pct in total.
- The depletion of weld metal or steel matrix in alloying elements must be achieved similar to that of crept steels and the carbide phases at onset of cracks must not be different.
To meet these requirements a low-cycle thermal-mechanical deformation-relaxation test was developed, during which the sub-structural processes characteristic of creep occurred much faster, transforming the initial microstructure of the creep resisting steels and welds to the near-to-equilibrium one in less than 30hours. The formation of dislocation configurations and the sequence of carbide precipitation and coagulation, as confirmed by TEM investigations, well resembled these of the conventional creep, so the testing procedure, hence called the simulative accelerated creep test – ACT, has been verified this way.
Simulation of Evolution of Dual-Phase Microstructure
Authors: Mandziej Stan T. , Waengler Sebastian , Noack Julio , Kawalla Rudolf
Published: January 2010

Dual-phase steels, developed in the 1970’s, found until now wide applications related to their optimum combination of strength and ductility, in particular as flat semi-products used for further shaping by deep drawing and cold forming operations. Actually the need appears to manufacture long semi-products of dual-phase steels for further processing by cold forging, in order to obtain high-strength final products, like e.g. fasteners, without additional heat-treatment. An additional aim has been to explore the possibility of achieving from the same chemical compositions dedicated properties for particular applications. In this work a thermo-mechanical route was developed of modifying an originally bainitic-martensitic low-alloy steel to achieve a dual-phase microstructure. For this purpose physical simulation was used on Gleeble 3800 thermal-mechanical simulator, programmed to affect austenite in its dynamic recrystallisation range followed by separation of microstructures in the two-phase austenite-ferrite range. Observation of relaxation was used to monitor advancement of transformation / recrystallisation in subsequent stages of the processing. In the simulated hot-warm rolling process it appeared possible to convert the original bainitic microstructure, having prior austenite grain size ~15μm and the martensite-bainite laths of usual length throughout these grains, to the dual-phase microstructure containing well-recrystallised ferrite of an average grain size 1*1.5μm and fine second-phase islands of less than 1.0μm diameter. SEM and TEM analysis have been applied to describe details of the resulting microstructures.
Numerical Simulation of the Portevin – Le Chatelier Effect in Various Material and at Different Scales
Authors: Maziere Matthieu , Forest Samuel , Besson Jacques , Wang Huai Dong , Berdin Clotilde
Published: January 2010

The Portevin Le Chatelier (PLC) effect appears in many metallic materials at different temperatures. Some numerical simulations of this effect for different alloys (aluminium, steel, nickel based superalloy) are presented in this article. The mechanical model remain the same for all studied materials but the behavior parameters and identification methods differ. The scale at which this effect is investigated also varies from the microstructure to aeronautic components.
A Model for Nucleation and Growth Processes of Tin Whisker
Authors: Nakai Kiyomichi , Sakamoto Tatsuaki , Kobayashi Sengo , Arakawa Kazuto , Mori Hirotaro , Takamizawa Masao , Murakami Koji , Hino Makoto
Published: January 2010

A model for the nucleation and growth processes of Sn whisker is offered. High density of localized screw dislocations by deformation form the dense spiral steps of atomic scale on Sn surface. The spiral steps would induce the nucleation of Sn whisker. Edge dislocations localized at the same region where the dense screw dislocations exist supply Sn atoms to Sn whisker through pipe diffusion. Both screw and edge dislocations would bend along almost one direction, namely, to relax the external shear stress. The image force also helps to bend the dislocations perpendicular to the whisker side-surface. The bending of dislocations at root of whisker leads the bend of whisker. The pipe diffusion of Sn atoms through edge dislocations from bulk Sn toward whisker is suppressed at the bent part of edge dislocation, resulting in release of Sn atoms inside whisker and leading to the growth of whisker near its root.
Modelling of Grain Boundary Stability of Materials under Severe Plastic Deformation and Experimental Verification
Authors: Saito Yoshiyuki , Masuda Chitoshi
Published: January 2010

Thermodynamic stability of Grain boundary in materials under severe plastic deformation was simulated by the Monte Carlo and the phase field methods. Computer simulations were performed on 3-dimensional textured materials. The Monte Carlo simulation results were qualitatively in good agreement with those by the phase field model. The classification of the solution of differential equations based on the mean-field Hillert model describing temporal evolution of the scaled grain size distribution function was in good agreement with those given by the Computer simulations. The ARB experiments were performed for pure Al and Al alloys-sheets in order to validate the computer simulation results concerning the grain boundary stability of textured materials. With use of the Monte Carlo and the phase field methods. Effect of grain boundary mobilises and interface energy given by the computer simulations.
Effect of Aging Treatment on Properties and Microstructure of an Al-7.5Zn-1.3Mg-1.4Cu-0.12Zr Alloy
Authors: Li Xi Wu , Xiong Bai Qing , Zhang Yong An , Wang Guo Jun , Li Zhi Hui , Zhu Bao Hong , Wang Feng , Liu Hong Wei
Published: January 2010

In this study, the effect of various aging treatment (T6 and T7 treatment) on the mechanical properties, electrical conductivity and the microstructure of an Al-7.5Zn-1.3Mg-1.4Cu-0.12Zr alloy has been investigated. The results show that with elevating the aging treatment temperatures, the aging response rate is greatly accelerated. When T6 temper is performed at 140°C for 12h, as compared to peak aging for 24h at 120°C, the UTS and the corresponding Elongation values keep the same level, whereas the TYS and the electrical conductivity obviously increase by 5% and 9%, which is up to 560 MPa and 22.6 MS/m, respectively. And there are clear PFZs along the grain boundary and slightly coarser precipitates inside the grain. GPI zones, GPII zones and η' phases are major precipitates for the alloy under T6 condition. When T7 temper is performed on the alloy, the main precipitates are GPII zones, η′ and η phases. The coarser precipitates inside the grain and discontinuous grain boundary precipitates are favorable to electrical conductivity, which decrease the strength of 5~17% compared to T6 treatment. After T76 treatment (i.e., 110°C/6 h + 160°C/6 h), the UTS, TYS, Elongation and electrical conductivity values were 540 MPa, 510 MPa, 16.7% and 23.5 MS/m, respectively.
Modeling and Optimization of Cross-Sectional Microstructure Distribution during Hot Rolling of HSLA Steel Plates
Authors: Xu Yun Bo , Deng Tian Yong , Yu Yong Mei , Hou Xiao Ying , Liu Xianghua , Wang Guo Dong
Published: January 2010

The metallurgical equations have been implemented into the finite difference model to predict the microstructure evolution at different locations in the plate cross-section. Recrystallization kinetics and grain size distributions instead of average grain size values were computed for different rolling schedules. For 20mm plate, the austenite grain sizes at the surface are smaller than at the center, with the exception of the conner where there are the largest grain sizes in throughout cross-section, and the smallest grain sizes can be found near the end of the horizontal central line. The fine austenite grain size and relatively high retained strain could be obtained by modifying rolling practice, such as changing the temperature and thickness at the entrance of finishing rolling and adopting intermediate water cooling. The ferrite grain size and its distribution have a good agreement with the measurements.
Multiscale Modelling of Gradual Degradation in Al2O3/ZrO2 Ceramic Composites under Tension
Authors: Sadowski Tomasz , Marsavina Liviu
Published: January 2010

Two-phase ceramic composite materials, (CMC, e.g. Al2O3/ZrO2), have a non-linear and complex overall response to applied loads due to: different phases, existence of an inital porosity, development of limited plasticity and internal microdefects. All microdefects act as stress concentrators and locally change the state of stress, leading to the development of mesocracks and finally macrocracks. Experimental results show that defects develop mainly inter-granular and cause inhomogeneity and induced anisotropy of the solid. Modelling of such material response is possible by multiscale approach describing different phenomena occuring at different scales: micro- meso- and macro- ones. The paper presents uniaxial tension process of the Al2O3/ZrO2 composite with the gradual degradation of the material properties due to different defects development.
Homogenization of Out-of-Plane Loaded Random Plates
Authors: Sab Karam
Published: January 2010

The homogenization of elastic periodic plates is as follows: The 3D heterogeneous body is replaced by a homogeneous Love-Kirchhoff plate whose stiffness constants are computed by solving an auxiliary boundary problem on a 3D unit cell that generates the plate by periodicity in the in-plane directions. In the present study, a generalization of the above mentioned approach is presented for the random case. The homogenized bending stiffness and the moduli for in-plane deformation of a plate cut from a block of composite material, considered to be a statistically uniform random material in the in-plane directions, are defined in three equivalent manners: a) the first definition considers statistically invariant stress and strain fields in the infinite plate. In the second and third definitions, a finite representative volume element of the plate is submitted to suitable b) kinematically uniform boundary conditions and c) statically uniform boundary conditions. The relationships between these three definitions are studied and bounds are derived.
Modeling of Microstructure Evolution in Process with Severe Plastic Deformation by Cellular Automata
Authors: Svyetlichnyy Dmytro
Published: January 2010

Prediction of microstructure evolution and properties of ultrafine-grained materials is one of the most significant, current problems in materials science. Recently, an interest to apply the cellular automata (CA) to the simulation of different phenomena in materials has been rising constantly. The main asset of the CA is the ability for accurate modeling of the microstructure. Deformation in micro-scale shows anisotropy, which is related with the different crystallographic orientation of the grains in the polycrystalline material. To improve the accuracy of modeling, CA and FEM must be combined with crystal plasticity theory. In present model, deformation in macro-scale is transferred to meso-scale, where a representative element contains several, score or hundreds grains, and then is applied in micro-scale to each grain. Strain and strain rate are decomposed into the crystallographic directions. For each crystallographic direction, development of dislocation and subgrain boundaries are considered. In each grain development of dislocation structure is distinctive because their orientation is unique. Creation of low-angle boundaries and their development into high-angle boundaries are simulated by the cellular automata on the base of calculations using finite element method and crystal plasticity theory. Some algorithms implemented into CA are described in the paper, as well as simulation results.
Microstructure and Texture Evolution in Cold Rolled Interstitial Free (IF) Steel Sheet during Annealing under AC Magnetic Field
Authors: He Chang Shu , Tsurekawa Sadahiro , Kokawa Hiroyuki , Zhao Xiang , Zuo Liang
Published: January 2010

An AC magnetic field (0.5Tesla) is applied with the field direction perpendicular to the rolling direction during annealing of a 76% cold-rolled IF steel sheet. Microstructure and texture evolution in the as-annealed specimens were determined using SEM based OIM technique. It is found that the recrystallization is noticeably retarded by AC magnetic field annealing. At the early stage of recrystallization (annealing at 650°C for 30min), the development of (111) <123> orientations was favored by the AC magnetic field. With progress of recrystallization (annealing at 700°C and 750°C for 30min), the applied AC magnetic field suppressed the development of γ-fiber recrystallization textures to some extent.
Mechanism on Heterogeneous Nucleation of the Primary Al Phase on TiAl3 of a Hot-Dip Zn-11%Al-3%Mg-0.2%Si Coating on Steel Sheet
Authors: Honda Kazuhiko , Ushioda Kohsaku , Yamada Wataru
Published: January 2010

The solidification structure of a hot-dip Zn-11%Al-3%Mg-0.2%Si coating with a Ti addition on a steel substrate was investigated. Steel sheet was coated using a laboratory hot-dip galvanizing simulator. The coating was subsequently characterized via optical and high resolution scanning electron microscopy with EBSD and high temperature X-ray diffractometry. The hot-dip coating consisted of a combination of a Zn/Al/MgZn2 ternary eutectic structure, primary Al phase and MgZn2 phase. TiAl3 acts as a heterogeneous nucleation site for Al, which was shown to have perfect lattice coherency with TiAl3 as epitaxial Al growth from the TiAl3 was found. The growth direction of Al is along <110> and has a random texture, whereas Zn has a rather strong ND//<0001> fiber texture.
Effect of Titanium Addition on Composite L12 Precipitates in Aluminum-Zirconium Alloy
Authors: Maeshima Takashi , Matsuoka Hideaki
Published: January 2010

The particle morphology and composition of nanometer-scale Al3(Zr1-xTix) precipitates formed after aging at 450 °C for 1 h in Al-0.3mol%Zr-0.5mol%Ti alloy were investigated using high resolution electron microscopy (HREM) and three dimensional atom probe tomography (3D-APT). The alloy exhibits an inhomogeneous distribution of solute atoms after casting. After aging, Al3(Zr1-xTix) precipitates with a metastable L12 structure formed within solute-enriched dendrites. The Al3(Zr1-xTix) precipitate particles were spherical with diameters between 3 and 5 nm. The Al3(Zr1-xTix) precipitates were found to be coherent with matrix using HREM. Interfacial segregation of Ti at the matrix/precipitates was also observed in the composite Al3(Zr1-xTix) precipitates. The Zr:Ti atomic ratio in the Al3(Zr1-xTix) precipitates measured by 3D-APT was approximately 7 (x=0.125).
Effect of Deformation Mode on Texture of Ultrafine-Grained Low Carbon Steel Processed by Warm Caliber Rolling
Authors: Inoue Tadanobu , Yin Fu Xing , Kimura Yuuji
Published: January 2010

The evolution of crystallographic texture with equivalent strain, eq, was studied in low carbon steel bars fabricated using multi-pass warm caliber rolling. Finite element analysis was carried out to evaluate eq accumulated and strain components introduced with each pass through the rolled bars. The texture at characteristic deformation sites on the cross section in the bars was analyzed using the electron back-scattered diffraction method. Although the texture in the area around the center was dominated by a strong RD//<101>, in the other two areas, a RD//<101> texture was not produced. It is clarified that this difference results from three deformation modes during rolling. Consequently, the areas around the corners, where eq of over 5.7 is introduced, are filled with ultrafine ferrite grains of below 680 nm, and the texture in the areas is random regardless of the increase of eq.
Phase Alignment Based on Crystal Orientation In Mn-Sb and Al-Ni Alloys Induced by High Magnetic Fields
Authors: Wang Qiang , Liu Tie , Wang Chun Jiang , Wang Kai , Li Guo Jian , He Ji Cheng
Published: January 2010

Those materials with an one dimensional phase-aligned structure have a large amount of potentiality as engineering materials because of their exceptional optical, electrical and anisotropically mechanical properties. Many researchers are now working determinedly to explore the methods for fabricating this kind of material. Recently, high magnetic fields have been used to fabricate non-magnetic materials with textured structure where anisotropic magnetic energy should be strong enough to induce preferred crystal orientation. Based on this mechanism, we developed an in situ process for fabricating phase-aligned composites using high magnetic fields. In this work, hypoeutectic Mn-Sb and hypereutectic Al-Ni alloys were solidified in various magnetic fields. The primary MnSb dendrites in the solidified Mn-Sb alloys were found to be macrostructurally aligned along the field direction, while the primary Al3Ni phases in the Al-Ni alloys were found to be macrostructurally aligned perpendicular to the field direction. The X-ray diffraction (XRD) measurement results suggested that these two phases were also oriented by the magnetic field. It was believed that the above-mentioned alignment is based on the crystal orientation and relevant to the heat flux direction, the preferred growth direction and the concentration field around crystallized crystals.
Effect of Plating Current Density and Frequency on the Crystallographic Texture of Electrodeposited Copper
Authors: Lin Ya Wen , Kuo Jui Chao , Lui Kuan Tai , Chen Delphic
Published: January 2010

For interconnect materials in the microelectronic technology copper has replaced aluminum due to its lower resistivity, higher thermal conductivity and better electromigration resistance. Recently, it was found that nanotwinned copper exhibits ultra high yield strength, ductility and electrical conductivity. Therefore, in this study the effect of plating current density and frequency were investigated on the crystallographic texture of Cu electrodeposited to understand the twin character. Electron backscatter diffraction (EBSD) was used for characterizing the preferred orientation, grain size distribution, and grain boundary character distribution. Three kinds of <110>, <111> and <112> textures were found to be related with the electrodeposited parameters of current density and frequency. Here we will discuss the relationship between the preferred orientation and the electrodeposited parameters.