bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical Modeling of Behaviour a Liquid Steel Flow and a Non-Metallic Inclusions in the One Strand Wedge Type Tundish with a Subflux Turbulence Controller and a Low Dam
Authors: Cwudziński Adam , Jowsa Jan
Published: January 2012

The numerical modelling technique is successfully used for simulation of liquid metal movement and behaviour of non-metallic inclusions in the continuous casting devices. The CFD (Computational Fluid Dynamic) method allows information on physical, chemical and hydrodynamic phenomenon in the metallurgical processes to be obtained. In the continuous steel casting process, where the tundish performs the function of a device batching steel to the mould, the monitoring especially of non-metallic inclusions is very essential because a quantity of non-metallic inclusions in the liquid steel limit the quality of final steel product. The paper presents the results of computing simulation of behaviour a liquid steel flow and non-metallic inclusions in the one-strand tundish with stopper rod system. The subject of simulation was a one-strand tundish of a nominal capacity of 30 tons. The tundish is used in the polish steel mill to process of continuous casting slabs. In the paper authors analysed two tundish i.e. tundish with a low dam and tundish with a subflux turbulence controller and a low dam. The Ansys-Fluent® program was used for solved mathematical model of casting process. The computer simulations were performed for unsteady and nonisothermal conditions. The population balance model was used to description of non-metallic inclusions growth process. As a result of computations, fields of liquid steel flow, fields of secondary phase volume fraction, fields of volume fraction for particular bins and non-metallic inclusions growth curve were obtained.
Numerical Modeling of Nonmetallic Inclusions Flowing Out during Solidification of Continuous Cast Steel Billets in Mould Zone
Authors: Derda Wlodzimierz , Staniewski Ireneusz
Published: January 2012

Developing the metallurgical purity of steel products requires, among other things, the understanding of the behavior of non-metallic inclusions (NMI) in the bulk of liquid steel in the mould zone within the forming skin of a concast billet. The identification of the mode of NMI distribution with different values of casting parameters influencing the state of the metal in the mould, including electromagnetic stirring intensity, may be of key importance to developing the metallurgical purity of concast billets being cast. The present article discusses the analysis of the results of simulation of NMI flowing out from the liquid steel volume in the mould zone of the steel continuous casting machine (CCM). As the investigation object, two different types of square cross-section mould were chosen, while for carrying out computations for two selected steel grades, a hydrodynamic module (HDM) being an extension of the FLUENT® program was employed. The use of this module made it possible to take consideration of the influence of the EMS-M type electromagnetic stirrer on the conditions of NMI flotation and distribution in the metal volume within the mould for defined thermal – dynamical conditions.
The Influence of the Initial State on the Softening and Precipitation Kinetics in Hot Metal Forming
Authors: Hagemann Philipp , Kawalla Rudolf , Korpala Grzegorz , Schmidtchen Matthias
Published: January 2012

Energy-efficient production in today’s metal industry includes the usage of casting heat to allow hot deformation directly after solidification for saving time and cost of expensive reheating processes. Due to the different initial state this processing route also leads to differences in deformation behavior (strain, flow stress) and softening and precipitation kinetics compared to a reheated material. This is caused by the different microstructures in the material directly after solidification, showing a much more coarsed grain structure and a higher amount of dissolved microalloying elements. Therefore, a material directly deformed after solidification usually shows a retarded softening behavior accompanied by precipitation processes. The different behaviour of a reheated material and a material directly deformed after solidification is shown in this work. The different modes of action for micro-alloying elements in different initial states are compared at the example of steels with different chemical compositions. Differences in deformation behaviour were simulated with semi-empirical models including specific coefficients to consider the processing parameters strain, strain rate, temperature, and chemical composition. The models are capable of describing the retarded softening caused by a superimposed precipitation kinetic leading to a typical plateau. The results of these models are compared with established physical models.
Predicting Solid-State Phase Transformations during Welding of Ferritic Steels
Authors: Hamelin Cory J. , Muránsky Ondrej , Bendeich Philip , Short Ken , Edwards Lyndon
Published: January 2012

The current work presents the numerical analysis of solid-state transformation kinetics relating to conventional welding of ferritic steels, with the aim of predicting the constituent phases in both the fusion zone and the heat affected zone (HAZ) of the weldment. The analysis begins with predictions of isothermal transformation kinetics using thermodynamic principles, such that the chemical composition of the parent metal is the sole user-defined input. The data is then converted to anisothermal transformation kinetics using the Scheil-Avrami additive rule, including the effects of peak temperature and austenite grain growth. Subroutines developed for the Abaqus finite element package use the semi-empirical approach described to predict phase transformations in SA508 Gr.3 Cl.1 steel. To study the effect of the cooling rates and the ability of the current model to predict the final microstructure, two weld samples were subjected to autogenous beam TIG welds under a fast (TG5-F, 5.00 mm/s) and slow (TG5-S, 1.25 mm/s) torch speed. Model validation is carried out by direct comparison with microstructural observations and hardness measurements (via nanoindentation) of the fusion and heat affected zones in both welds. Excellent agreement between the measured and predicted hardness has been found for both weld samples. Additionally, it is shown that the correct identification of the partial austenisation region is a crucial input parameter.
Determining the No-Recrystallization Conditions for Industrial Hot Strip Rolling of Steels Using Laboratory Simulations
Authors: Herman Gwenola , Poliak Evgueni I.
Published: January 2012

Avoiding recrystallization of austenite in hot strip rolling of steels is highly important for enhancing mechanical properties of hot rolled products, as well as for the products undergoing cold rolling and annealing or coating. Recrystallization can only be avoided if its incubation time is longer that the time intervals characteristic for a particular hot rolling process. The present work focuses on computation of incubation time tinc for static recrystallization using laboratory hot deformation data and on extrapolation the results to industrial conditions. The computations are done based on application of critical conditions for initiation of dynamic recrystallization to the static case. No-recrystallization temperature in hot strip rolling is determined by setting tinc equal to interpass time. Simulations allow for prediction of the onset of austenite static or metadynamic recrystallization after individual rolling passes during industrial hot rolling and evaluation of the effects of strip thickness, rolling speeds, etc.
Effect of Water Temperature on Wetting Front Kinematics during Forced Convective Quenching
Authors: Hernández-Morales Bernie , González-López Juan Ramón , Solorio-Díaz Gildardo , Vergara-Hernández Héctor Javier
Published: January 2012

The kinematics of the wetting front, i.e., the history of the locus of the boundary between the vapor blanket and the nucleate boiling area is of outmost importance in quenching operations. In this investigation, the effect of water temperature on the wetting front kinematics was studied in forced convective quenching experiments of conical-end cylindrical probes. Three values of water temperature (30, 45 and 60 °C) were studied for a free-stream water velocity of 0.2 m/s. The wetting front kinematics was characterized from: 1) the measured thermal response at three longitudinal positions inside the probe, near the probe surface, and 2) high-speed video-recordings of the events that took place at the probe surface upon quenching. From the video-recordings, the position of the wetting front as a function of time was determined to estimate the wetting front velocity from a linear regression. The wetting front velocity was constant for a given experiment and increased as the water temperature decreased. The bubble size decreased and the frequency of bubble formation increased as the water temperature decreased. Using the measured thermal responses, the surface heat flux history was estimated, solving the corresponding inverse heat conduction problem. A regression analysis was applied to relate the maximum (critical) surface heat flux and the water temperature as a first step towards modeling the surface heat flux history as a function of water temperature.
Modelling of Strip Shape and Profile during Cold Rolling of Ultra Thin Strip
Authors: Jiang Zheng Yi , Cheng Xiao Wei , Du Xiao Zhong , Wei Dong Bin , He Xiao Feng
Published: January 2012

In this paper, finite element models of the strip shape during cold rolling of ultra thin strip in both symmetrical and asymmetrical rolling cases have been successfully developed, and the strip shape such as the thickness distribution along the strip width has been obtained. The strip shape and edge drop are discussed under both symmetrical and asymmetrical rolling conditions. Simulation results show that the asymmetrical rolling can reduce strip edge drop dramatically. The work roll edge curve also affects strip shape significantly. The developed finite element model has been verified with the experimental values.
Numerical Simulation of Solidification of Thick-Wall Stainless Steel Pipe in Horizontal Centrifugal Casting Process
Authors: Guo En Yu , Zheng Qiwei , Jing Tao
Published: January 2012

A mathematical model of the horizontal centrifugal casting process based on the cast cylindrical coordinates for stainless steel pipe has been developed. Thermal boundary conditions, including the radiative and convective heat transfer conditions, have been taken into consideration. The model equation was solved numerically using non-uniform cylindrical grids and the finite differential method (FDM). Several parameters of casting process such as melt superheat, preheating temperature of mold, thermal conductivity of coating and flux powder, which affect the temperature distributions in both cast pipe and mold and the changed positions of melt solidifying at last are investigated. In order to verify the results of simulation, calculated temperatures were compared with the experimental data.
Influences of Cracking of Coated Layer on Critical Current in Coated Composite Superconductor
Authors: Ochiai S. , Okuda H. , Toda Akihiro , Nagano Shinji , Sugano M. , Osamua Kozo , Prusseit Werner
Published: January 2012

Influences of cracking of the coated DyBa2Cu3Ȯ˽δ˰superconducting layer in composite superconductor under applied tensile strain on V(voltage)-I(current) curve, critical current and n-value were studied experimentally and analytically. The measured variations of V-I curve and critical current with increasing applied strain were described well by the modeling analysis. Also, the variations of shunting current with increasing imposed current and also with extension of cracks were revealed, from which the influences of shunting current on the variation of n-value with current were elucidated.
Result Mining in Numerical Simulation of Casting and Heat Treatment Processes
Authors: Kang Jin Wu , Huang Tian You
Published: January 2012

Tons of numerical simulation results are obtained by numerical simulation of casting and heat treatment process. However, these results are not utilized sufficiently, most are wasted. The aim, to predict defects of castings, such as shrinkage, hot tearing, deformation and etc, need further processing of the simulated results. Therefore, the criteria should be established on the processing of the directly simulated results. What kind of more results can be acquired from these calculated data This is an interesting question. In this paper, schematic analysis is carried out for further processing of results, result mining (RM) is proposed and its meaning is explained. Meanwhile, some case studies are presented.
Analysis of the Asymmetric Plate Rolling Process
Authors: Kawałek Anna , Dyja Henryk , Sołtysiak Ł. , Mróz Sebastian , Szota Piotr
Published: January 2012

The paper presents the results of the theoretical analysis of the asymmetric plate rolling process conducted in the plate finishing mill. The purpose of the work was to determine the influence of working rolls velocity asymmetry on the value and direction of the bending radius of strip flowing out from the deformation zone. The variable parameters of the process were: rotational speed asymmetry factor, av ; strip shape factor, h0/D; and cross-sectional area reduction ε. For the theoretical study, a commercial computer program, FORGE 2008®, was employed. Working rolls of a diameter of 1100 mm and a constant lower working roll rotational speed of n = 80 rpm were assumed for the study. The asymmetric rolling process was achieved by varying the rotational speed of the upper roll, which was lower than that of the lower roll. The range of variation of the roll rotational speed asymmetry factor, av, was 1.01÷1.20. On the basis of the conducted theoretical analysis, the influence of the speed asymmetry factor (av = 1.00÷1.20) on plate curvature upon exit from the deformation zone was determined, and the distributions of strip velocity.
Algorithm for Controlling Mechanical Properties of Hot Rolled Steels Using Bayesian Network Model
Authors: Khlybov Oleg S. , Dubinin Igor V.
Published: January 2012

The work presents a control method for on-line adjustment of mechanical properties of as rolled steels produced at hot strip mills. The key idea of the method is a probabilistic causal (Bayesian) network which represents in a form of a directed acyclic graph the joint probability distribution of mechanical properties, chemical composition and temperature–strain parameters acting during hot rolling. As a slab moves along the mill the distribution is used for continuous recalculating the posterior probability of all mechanical properties conditioned by chemical composition and all other process parameters which become known to the moment of recalculating. Finally, when a strip is just before the finishing group we evaluate the probability distribution of finishing rolling temperature and coil temperature given the strip has the target mechanical properties. It generates new setups for these temperatures A pilot version of the method has been just implemented at CSP–line at Vyksa, Russia, United Metallurgical Company’s steel production site The adjustment is realized through appropriate correction of finish rolling temperature or/and coiling temperature setups of the mill automatic control system after the last chemical analysis of the current heat is made at the start of casting. Only “cautious” corrections of the temperatures are permissible so far (deviation from predefined level not more than ±30 degrees for each temperature) and the main aim of them is to set off the influence of chemistry variations on mechanical properties scatter of a given steel grade. The results of using the algorithm show that even these limited but interconnected actions reduce approximately twice the standard deviation of the mechanical properties inside a steel grade.
From TRB and LP Plate to Variable Gauge Rolling: Technology, Theory, Simulation and Experiment
Authors: Liu Xianghua , Wu Zhi Qiang , Fang Zhi , Zhang Guang Ji , Zhi Ying
Published: January 2012

Tailor Rolled Blank (TRB) and Longitudinal Profile plate (LP plate) are both new products for materials saving. TRB produced by cold rolling can partially substitute for Tailor Welded Blank (TWB) achieving lightweight in vehicles. LP plate produced by hot rolling can be utilized in shipbuilding, bridge manufacturing and constructions, realizing structures lightweight. This paper stressed the common point of TRB and LP plate: Variable Gauge Rolling (VGR). Basic equations of VGR were deduced, a velocity relationship which assures the shape and dimension of transition region was provided, a FEM simulation of VGR was performed, VGR experiments were carried out and TRB samples with a thickness ratio 1:2 were obtained. All above achievements have established a foundation for VGR’s industrial application.
Parabolic and Hyperbolic Two-Temperature Models of Microscopic Heat Transfer. Comparison of Numerical Solutions
Authors: Majchrzak Ewa
Published: January 2012

The paper deals with the microscale heat transfer problems. In particular, the ultrafast laser heating of thin metal film is considered. The problem is described by so-called two-temperature models consisting of two equations concerning the electron and lattice temperatures. Energy equations are supplemented by two additional ones determining the dependencies between electrons (phonons) heat flux and electrons (phonons) temperature gradient. According to the form of above dependencies one obtains the parabolic or hyperbolic heat transfer models discussed here. The problems have been solved using the finite difference method. In the final part of the paper the results of computations and the comparison of solutions obtained are presented.
Numerical Model of Thermal Processes in Domain of Thin Film Subjected to a Cyclic External Heat Flux
Authors: Mochnacki Bohdan , Ciesielski Mariusz
Published: January 2012

Thermal processes in a thin metal film subjected to a cyclic external short-pulse heating are considered (axially-symmetrical 3D problem). The heat transfer proceeding in domain analyzed is here described by the dual phase lag model (DPLM). According to the newest opinions the DPLM constitutes a very good description of real heat transfer processes proceeding in the micro-scale domains subjected to the strong external heat flux. The base of DPLM formulation is a generalized form of Fourier law (GFL) in which two times τq, τT appear (the relaxation time and thermalization one, respectively). The acceptation of GFL leads to DPLM equation [1, 2]. Thermal processes proceeding in a thin metal film subjected to a cyclic external short-pulse heating are considered (axially symmetrical 3D problem). In the paper the thermal interactions between cyclic external heat source qb and cylindrical micro-domain are analyzed. The external heat source is the function dependent on spatial co-ordinates and time. On the remaining parts of the boundary the no-flux conditions are assumed. It should be pointed out that the DPL model requires the adequate transformation of boundary conditions which appear in the typical macro heat conduction models. The initial conditions are also known (initial temperature of domain and initial heating rate). Numerical model of the process discussed bases on a certain variant of finite differences method and in the final part of the paper the examples of computations are shown.
First-Principles Study of H2O Adsorption on Oxygen-Covered Fe Surface
Authors: Nunomura Norio , Sunada Satoshi
Published: January 2012

We present the results from first principle calculations of H2O adsorption on oxygen-covered Fe (100) surface. The calculations are based on a density-functional theory, surface modeling which uses supercell slab models. As a surface oxygen coverage increases, the surface is not activated, which makes the adsorption of water molecules on Fe surface unfavorable. It has been found that the surface covered oxygen exerts an influence on the adsorption of H2O molecule on Fe surface.
Austenite-Bainite Transformation Kinetic Model for the Powder-Metallurgical Steel Astaloy 85 Mo
Authors: Nusskern Philipp , Hoffmeister Jürgen , Schulze Volker
Published: January 2012

A new approach for case hardening of powder metallurgical steels is surface densification prior to heat treatment, hence avoiding hardening to the core caused by open porosity. With regard to this process chain a porosity and carbon dependent model of the transformation kinetics is essential. In powder metallurgical materials the transformation behavior is mainly influenced by the chemical composition, homogeneity and porosity. Using a prealloyed powder, e.g. Astaloy 85 Mo, a homogeneous distribution of alloying elements after sintering can be assumed and the transformation behaviour is mainly determined by pores and the carbon profile caused by case hardening. The effect of carbon is widely known but up to now, only a few details about the effect of porosity on the transformation can be found in literature. It is reported that a decreasing relative density causes a reduction of incubation and overall isothermal transformation time. In the present study, the transformation kinetics of a powder metallurgical steel based on Astaloy 85 Mo were investigated for the carbon levels 0.5 and 0.8 wt% as well as the relative densities 6.8, 7.2 and 7.8 g/cm³. The investigations were carried out using a high-speed quenching dilatometer. The isothermal time temperature transformation diagrams for this powder-metallurgical alloy are presented and Avrami-type equations are fitted to the measured data. A good correlation can be found for the transformation model and the experimental results verifying the used modeling approach showing the potential to be applied within case hardening simulations.
New Methodology to Model Simultaneous and Sequential Reactions: Main Results and Applications
Authors: Rios Paulo Rangel , Villa Elena , de Oliveira Simone C.
Published: January 2012

In a recent work, the present authors developed a new formal kinetics methodology suitablefor the situation in which transformations take place simultaneously or sequentially. In this work themain results of such a methodology are briefly presented in a simplified form. It is shown here howthis new methodology may be used for obtaining expressions for simultaneous or sequential reactionsfrom models of the kinetics of each reaction in isolation. It is also shown how one may extract theo-retical information from the experimentally measured quantities. Moreover, the methodology is usedto analyse published data on the recrystallization kinetics of IF steels.
The Physical and Numerical Modeling of Heat Treatment the Experimental Complex-Phase (CP) Steel
Authors: Rapalska J. , Dyja Henryk , Koczurkiewicz Bartosz
Published: January 2012

The fast development of automotive industry effects significantly on aspirations of designers and constructors to reduces the mass-produced cars, affecting meaningly on fuel consumption and gas emition. From the standpoint of automotive industry materials for modern car-body sheets should have high mechanical properties (primarily high tensil strenght) and very good cupping. The required high mechanical and plastic properties steels used in produce of car bodies are dependent on the type of the obtaining structure, witch be shaped by an appropriate heat and thermo-plastic treatment. The modern steels used in automotive industry are multi-phase steels e.g. dual-phase (DP), complex-phase (CP) and transformation induced plasticity (TRIP) steels. In this paper are presented the results of physical and numerical modeling of heat treatment the experimental complex-phase steel, witch be conducted in the Institute of Modeling and Automation of Plastic Working Processing on Częstochowa University of Technology. The numerical modellig of heat treatment were carried with using the commercial programe TTSteel. Based on the results of computer simulation the changes of steel microstructure during continuous cooling were analyzed and the characteristics temperature and CCT diagram was constructed. Numerical research have been verified by the physical simulation of heat treatment by the dilatometer DIL805. The characteristic temperature of investigated steel and the size of initial austenite grains were determined. On the samples was also metallographic examination and Vickers hardness testing conducted. The obtained results were used to build a real CCT diagram of steel.
3D FEM Modelling and Experimental Verification of the Rolls Wear during the Bar Rolling Process
Authors: Szota Piotr , Mróz Sebastian , Dyja Henryk , Kawałek Anna
Published: January 2012

Numerical modelling of the round bar rolling process, while considering the wear of the passes depending on their shape, was carried out within the present work. For the theoretical study of the rolling process, the Forge2008® was employed, which is finite element method-relying software that enables the thermomechanical simulation of rolling processes in a triaxial strain state. The wear model implemented in the Forge2008® permits no quantitative evaluation, but only comparative analysis of the wear of rolls. In order to use the results of simulation employing the simplified Archard model for the quantitative evaluation of roll wear, it is necessary to define the wear factor and hardness of the tool as a function of temperature. The paper present a methodology for the determination of the quantitative wear of rolls based on the results of computer simulations performed using the Forge2008® software for a selected round pass during rolling of round bars.
Aluminum Hydride Clusters as Hydrogen Storage Materials and their Electronic Stress Tensor Analysis
Authors: Ichikawa Kazuhide , Ikeda Yuji , Terashima Ryo , Tachibana Akitomo
Published: January 2012

We study the chemical bonds of small Al clusters (Aln, n=2-8) and hydrogenated Al clusters (AlnHm , n=1-8 and m=1,2) using electronic stress tensor. We calculate the bond order based on energy density for these clusters. We also study the electronic structure under the presence of electronic current by the electronic stress tensor for AlH3 molecule.
Atomistic Simulation of Stress-Induced Grain Boundary Diffusion: For Tin-Whisker Problem
Authors: Umeno Yoshitaka , Negami Jun
Published: January 2012

The problem of whisker formation in tin (Sn) wiring in small electronic devices has become an important issue with the requirement of lead-free wiring, because doping of Pb to reduce whisker formation cannot be applied. It is therefore urged to better understand stress migration in tin, which is suspected to play a key role in whisker growth. We aim to study grain boundary diffusion in tin by atomistic simulation. After constructing an efficient interatomic potential suitable for diffusion of atoms using the genetic algorithm (GA), we perform molecular dynamics (MD) simulation of grain boundary diffusion in Sn under stress. We find that the magnitude of stress effect on diffusion depends on the boundary structure. Moreover, we examine the effect of impurities on vacancy migration by ab initio calculation to find atom doping that has potential to suppress diffusion.
Fracture Laws for Simulating Compressive Fracture in Lattice-Type Models
Authors: van Mier Jan G.M.
Published: January 2012

The paper explores possible fracture laws that can be used in meso-level lattice-typemodels for simulating the behaviour of cohesive frictional materials like concrete and rock. A newfailure criterion is proposed, which includes three possible mechanisms that appear to explain thefracture of these materials at the macro-level.
Modeling of the Steel Flow and Non-Metallic Inclusion Separation due to Flotation in a Six-Strand cc Tundish
Authors: Warzecha Marek
Published: January 2012

Constantly increasing customers’ demands for the production of high and very high-quality steels, promote the intensive technological development of their production. Today, the dominating method of global steel production is continuous casting. A continuous casting plant includes the ladle turret, several steel ladles, a tundish, and a mold followed by a framework of rolls to support the strip. The tundish has become a very important metallurgical unit in the continuous casting process. Nowadays its role is not only to guaranty the link between the process of secondary metallurgy and the continuous casting process in the mould but it becomes an active metallurgical reactor. Therefore in recent years a lot of researches were done to establish a better understanding of the physical phenomena accompanying the steel flow through the tundish and non-metallic inclusion separation into the top slag cover. The article presents computational studies of the three-dimensional turbulent steel flow and non-metallic inclusions separation in a multi-strand tundish for steady-state casting conditions. Simulations of the steel flow in the tundish are performed with boundary conditions that are derived from the real casting process. The mathematical model used for simulations, was partly validated with experimental measurements. Numerical calculations are carried out by the finite-volume code Fluent using k-ε standard turbulence model. With the calculated flow field, micro-inclusions removal due to flotation to the coving slag is investigated numerically. For the particle separation at the interface a modified boundary condition is implemented.
Some Aspects Regarding Microstructural Heterogeneities during Steel Processing
Authors: Rodriguez-Ibabe J.M. , Uranga Pello , López Beatriz
Published: January 2012

The microstructural heterogeneities in steels may have different origins. The tendency in industry to decrease the total amount of reduction during hot working decreases the possibilities of applying approaches based on “thermo-mechanical homogenization”. In this situation, alternative approaches need to be evaluated to reduce the heterogeneities present in the initial microstructure and, simultaneously, to avoid the possibility of inducing additional heterogeneities during processing. This paper analyzes the relevance of several processing parameters in different cases.
The Solute Drag Model to Calculate Grain Growth Rate at High Temperatures in Carbon Steels
Authors: Yogo Yasu , Tanaka K. , Ikehata Hideaki , Iwata Noritoshi , Nakanishi Kou , Ishikawa T.
Published: January 2012

Based on the solute drag model, a practical model incorporating the segregation effect is proposed to calculate grain growth rates in carbon steels. The segregation effect is modeled using two factors: the difference in atomic diameter between a solvent and a substitutional element, and the solubility of a substitutional element. By including the segregation energy, the proposed model enables the simulated retardation of grain growth by the addition of microalloying elements. The calculated grain growth rate by the proposed model shows reasonable correspondence between grain growth rates for experimental and calculated results. The temperature dependence of the grain growth rate is also well simulated.
Carbo-Nitride Precipitation in Tempered Martensite - Computer Simulation and Experiment
Authors: Zamberger Sabine , Kozeschnik Ernst
Published: January 2012

In the present work, the precipitation behavior of a V-microalloyed, quenched and tempered steel with 0.3wt % C is investigated experimentally and by computer simulation. The specimens are analyzed by means of transmission electron microscopy using selected area diffraction (SAD) and energy dispersive x-ray spectroscopy (EDX). The analysis is done on electropolished foils and on extraction replica. The numerical simulation is performed with the thermokinetic software package MatCalc, where the precipitation kinetics is examined for the experimentally applied thermo-mechanical cycles. Good agreement between experiment and simulation is obtained and the experimentally observed precipitate microstructure can be well explained on the basis of these simulations.
Internal Stresses in Nanocrystalline Nickel and Nickel-Iron Alloys
Authors: Giallonardo J.D. , Erb Uwe , Palumbo G. , Botton G.A. , Andrei C.
Published: January 2012

Nanocrystalline metals are often produced in a state of stress which can adversely affect certain properties, e.g. corrosion resistance, wear, fatigue strength, etc. This stress is referred to as internal or “intrinsic” stress since it is not directly caused by applied loads. The structural causes of these stresses in nanocrystalline materials are not fully understood and are therefore an area of particular interest. The internal stresses of nanocrystalline Ni and Ni-16wt%Fe were measured and found to increase with the addition of iron. Characterization using HR-TEM revealed no signs of porosity, second phase particles, or a high density of dislocations. Both materials possessed well defined high-angle grain boundaries. The main structural difference between the two materials was found to be grain size and correspondingly, a decrease in grain size resulted in an increase in internal stress which supports the applicability of the coalescence theory. The current study also provides evidence to rule out the effect of voids (or porosity), dislocations, and second phases as possible causes of internal stress.
Crystallographic Features of the C-Type Orbital-Ordered, and Charge- and Orbital-Ordered States in the Simple Perovskite Manganite Ca1-xLaxMnO3
Authors: Inoue Yasuhide , Arao Masazumi , Shiga Daisuke , Koyama Yasumasa
Published: January 2012

The C-type orbital-ordered (CTOO), and charge-and orbital-ordered (COO) states are present in the simple perovskite manganite Ca1-xLaxMnO3, which has a three-dimensional highly-correlated electronic system. In this study, the crystallographic features of the CTOO and COO states have been investigated mainly by transmission electron microscopy to understand responses of a lattice system to these orderings. Of these two states, the cooling from the disordered orthorhombic Pnma (DO) state around x = 0.20 resulted in the CTOO state with the monoclinic P21/m symmetry. As a result of the monoclinic distortion as a response of the lattice system, the CTOO state consisted of a banded structure that was characterized by an alternating array of two monoclinic domains with different β values. In 0.30 < x < 0.50, on the other hand, the appearance of the COO state from the DO state on cooling accompanied a transverse lattice modulation with q = []DO as a response to orbital ordering in the COO state. The subsequent cooling in the COO state led to the antiferromagnetic ordering with a large lattice dilatation. In other words, no change in the crystal symmetry occurs in the appearance of the antiferromagnetic ordering.
Electrodeposited Nanocrystalline Ni-Fe with Banded Structure
Authors: Klement Uta , Shahabi-Navid Mehrdad , Hibbard Glenn D.
Published: January 2012

The microstructure of a Ni–18 wt.% Fe electrodeposits having a banded structure is described in detail. The aim is to investigate the influence of the banded structure on grain growth behaviour and texture and to elucidate if there are other mechanisms operative in the stabilization of nanocrystalline electrodeposits. Spectroscopy techniques have been used to characterize the variations in alloy/impurity concentration perpendicular to the growth direction. The influence of these chemical variations on the microstructural evolution has been monitored by in-situ annealing treatments in the TEM. Local texture of the annealed material has been determined by use of the electron backscatter diffraction (EBSD) technique. SEM and TEM investigations have shown that the banded structure is not related to phase changes and that grain growth is not affected by the banded structure, i.e. there is no preferred growth along bands. The first grown grains have <100>, <112> and <111> orientations with the growth direction and upon further grain growth a <111> fibre texture with respect to the growth direction of the electrodeposits is formed. The banded structure seems not to affect the general behaviour of nanocrystalline electrodeposits.
Obtaining Ultrafine and Nanocrystalline Structure by Hot and Warm Deformation in Microalloyed Steel X90
Authors: Ringinen Dmitry , Kolbasnikov N.G. , Zotov Oleg G. , Rudskoi Andrey
Published: January 2012

In this paper we have investigated the possibility of increasing the complex mechanical properties of steel strength category X90 by refinement the structure of hot and warm deformation. Were carried out tests to determine the critical points of recrystallization and built thermokinetic curves of austenite decomposition. After that, for produce disperse ferrite in samples has been applied to the processing mode, which is exactly the same mode of controlled rolling, then, to obtain nanoscale state of the metal deformed at temperatures of bainite transformation with varying degrees of deformation at different temperatures. It was shown that the dispersion and morphology of the structure and, consequently, the mechanical properties vary depending on temperature and strain, and samples show satisfactory ductility at high strength.
Nanostructured Superhydrophobic Silver Surfaces
Authors: Sarkar Dilip K.
Published: January 2012

Inspired by “lotus-effect”, a superhydrophobic surface, in general, is prepared via two steps: (i) creating a surface roughness and then (ii) lowering the surface energy via a self-assembly of organic molecules or via low surface energy coatings. Superhydrophobicity cannot result if one of these two essential factors does not coexist. In the present work, it has been shown that superhydrophobic properties can be achieved on silver surfaces both via two-steps and a novel and simple one-step process. In the two step-processes a fractal-structured silver film deposited on copper surface by galvanic exchange reactions was passivated using stearic acid organic molecules to reduce the surface energy resulting in the superhydrophobicity. In the one-step process, however, the copper substrates were simply immersed in the silver nitrate solution containing fluoroalkylsilane (FAS-17) molecules resulting in superhydrophobicity. The silver films prepared both via two-steps and one-step processes were found to be highly water repellant with the water drops rolling off those surfaces. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were utilized to understand the morphology, molecular bonding, and chemical properties of the superhydrophobic silver surfaces.
Synthesis and Fabrication of Aligned Conjugated Polymer Thin Films
Authors: Hirahara Takashi , Yoshizawa-Fujita Masahiro , Takeoka Yuko , Rikukawa Masahiro
Published: January 2012

Fluorene-thiophene copolymers having chiral and azobenzene substituents, PAzB4-T, were synthesized by the Pd-catalyzed Suzuki coupling method. We studied the aligning organization of the main chain of PAzB4-T with the activation of the attached functional groups by thermal annealing and photo-annealing processes. Circular dichroism (CD) measurements revealed that the thermally annealed PAzB4-T spin-coated films exhibited bisignate Cotton effects over the absorption regions of the polymer main chains and the azobenzene side chains due to the formation of chiral assemblies. After the photo-annealing process, which means linearly polarized light irradiation accompanied by thermal annealing, the PAzB4-T spin-coated films showed linear dichroism over the absorption region of the main chains, due to the alignment of azobenzene side chains against the electric field of the linearly polarized light. These results suggested that rigid conjugated polymers were successfully aligned by the alignment of functional groups with the external stimuli.
Characterization of Magnetic Properties of Nanocrystalline Ni and Ni-15%Fe Alloy
Authors: Arabi S. , Avramovic-Cingara G. , Palumbo G. , Erb Uwe , Niewczas Marek
Published: January 2012

Magnetic properties of nanocrystalline Ni and Ni-Fe alloys produced by electrodeposition have been studied at 2K and at 298K. Ni and Ni-15%Fe alloy deposits show nano-grain structure with the average grain size of 23 nm and 12 nm, respectively. Both materials exhibit soft magnetic properties. Nanocrystalline Ni at 2K shows saturation magnetization, coercive force, and remanent magnetization of 57 emu/gr, 101 Oe, and 16 emu/gr respectively. Nanocrystalline Ni-15%Fe alloy exhibits superior soft magnetic properties than Ni with corresponding saturation magnetization, coercive force, and remanent magnetization at 2K of 96 emu/gr, 6 Oe, and 4 emu/gr respectively. The magnetic properties and their dependence upon temperature data are interpreted in terms of the Herzer random anisotropy model for nanocrystalline materials.
X-Ray Measurement of Residual Stress Distribution in Sputtered Cu Thin Films
Authors: Akiniwa Yoshiaki , Sakaue Taku
Published: January 2012

Three kinds of copper thin films were fabricated by RF-magnetron sputtering. The target power was selected to be 10 and 150 W to change the properties of the films. Thin glass sheet was used as a substrate. For the target power of 150 W, the deposition time was selected to be 7 and 40 min. The thickness was 0.6 μm and 2.9 μm, and the grain size measured was 243 nm and 450 nm, respectively. The grain size of thicker film was larger than that of thinner one. On the other hand, for the target power of 10 W, the thickness and grain size were 2.4 μm and 54 nm, respectively. The grain size depends on the target power. The residual stress distribution in the films was measured by X-ray method. Several methods such as the grazing incidence X-ray diffraction method, the constant penetration depth method and the conventional sin2ψ method were adopted. The measured weighted average stress increased with increasing depth. After taking the maximum value at about 0.3 μm from the surface, the value decreased with increasing depth. The stress distribution near the surface in the films deposited at 150 W was almost identical irrespective of thickness. On the other hand, for the target power of 10 W, the stress distribution shifted to compression side. The reason could be explained by the effect of the thermal residual stress. The real stress distribution was estimated by using the optimization technique. The stress took the maximum value at 0.5 μm from the surface, and was compressive near the substrate. .
EDXRD Setup for Real Time Observation of a Gas Tungsten Arc (GTA) Welding Process
Authors: Altenkirch Jens , Gibmeier Jens , Buslaps Thomas , Honkimäki V.
Published: January 2012

Residual stresses in welds are of major concern for the structure integrity assessment in industrial components. The stresses in the final weld can be determined relatively simple using well established destructive or non-destructive techniques. However, such measurements reflect only the final condition and it remains unclear how stresses built up during the welding process. In order to optimise the final residual stresses in the weld, it is important to monitor the formation of residual strain and stress during the welding process and as such to gain insight into the mechanisms of stress development. In this work non-destructive high energy dispersive synchrotron X-ray diffraction at a high count rate is applied in order to dissolve the welding process in-situ in time and temperature. However, the achievable time resolution at commonly used instruments is restricted by either a limited photon flux or the read out electronics of the detector system resulting in counting times usually much longer than 1sec. We present an energy dispersive detector and read-out-electronics setup realized at the high flux and energy beam line ID15A at the ESRF. The setup allowed for monitoring the strain evolution in two perpendicular directions simultaneously at a sampling rate of 5Hz, resulting in sufficient time and temperature resolution. The change in detector dead time is accounted for by a correction function, which was specifically determined for the detector setup as used for this in-situ experiment.
Effect of Coating with Hydroxyapatite on the Bonding of Bone to Implant
Authors: Benmarouane Abdelilah , Millet Pierre , Buslaps Thomas , Lodini Alain , Honkimäki Veijo
Published: January 2012

The aim of the present study was to study the interface implant-bone by synchrotron radiation, the implant has two faces the first one coated with hydroxyapatite and the second uncoated. In orthopaedic surgery, Titanium (Ti-Al-4V) implants are currently coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2, in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface, the new bone reconstituted after two months of implantation must have the same properties like the natural bone in order to accept the implant. Therefore we studied the texture of the reconstituted bone crystals at the interface applying non destructive x-ray diffraction. The required high spatial resolution was achieved utilizing high-energy synchrotron radiation on ID15 at ESRF in Grenoble, France.
Macro to Micro Stress and Strain Conversion in Porous Ceramics
Authors: Levandovskiy A.N. , Efremov Alexander M. , Bruno G.
Published: January 2012

In this work, we propose an analytical model, capable of distinguishing the contribution of porosity, pore morphology and solid domain properties to the macroscopic elasticity of a porous ceramic material. A practical method is shown for the evaluation of the dense material elastic properties in porous (and microcracked) polycrystalline materials, making use of in-situ neutron diffraction experiments. By this method, axial and transverse microstrains measurements can reveal the average values for Young’s modulus and Poisson’s ratio of the dense material, as well as the value of pore morphology at known porosity. The approach has been validated on porous SiC. Finite Element Modeling is shown to allow calculating the three-dimensional strain and stress state under applied uniaxial stress, highlighting that small but finite shear stresses arise. Stress-strain curves of porous and microcracked materials have been generated, which correlate qualitatively well with the measured properties and can be used for quantitative numerical simulation of the materials strength. Predictions of FEM coincide very well with analytical calculations, thus corroborating the validity of the analytical method proposed.
Residual Stress Analysis of Textured Materials by X-Ray Diffraction Method
Authors: Ejiri Shouichi , Sasaki Toshihiko , Hirose Yukio
Published: January 2012

The residual stress measurement by the conventional X-ray diffraction was formulated on the assumption that a specimen from polycrystalline materials was quasi-isotropic and homogeneous, and the stress was biaxial and almost constant within the X-ray penetration depth. Therefore, it was not available to analyze the stress state of the textured materials by the conventional measurement as a general rule. In resent years, advanced methods have been proposed for the X-ray stress measurement of textured materials. In some methods, it is assumed that the X-ray elastic constant is derived from the crystallite orientation distribution function of textured materials for solving the first anisotropic problem. However, there is a nonlinear problem in the stress analysis from the measured lattice strain. In present study, the X-ray elastic constants were averaged as the expected value around the normal direction of the X-ray diffraction in a similar way. A stress analysis was proposed by differential calculus of the X-ray elastic constant in order to the avoidance of nonlinear problem. The stress analysis was applied to residual stress measurements of a titanium carbide coating film with preferred orientation and a cold-rolled steel with texture. The calculated values of the X-ray elastic constants showed the linearity on some condition for the film. The X-ray stress determination was carried out by the fitting the gradients of the measured lattice strain.