bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical and Magnetic Properties of Hg1-xMnxSe Alloys
Authors: Jovanović Dj. , Milivojević D. , Romčević M.J. , Babić-Stojić B. , Romčević N.Ž
Published: March 2009

In this paper we used X-ray, far-infrared reflectivity and electron paramagnetic resonance measurements to investigate the optical and magnetic properties of Hg1-xMnxSe (x£0.26) alloys. Also, we used different models to describe magnetic and phonon structure.
Influence of Additive Type on Densification and Phase Transformation of Seeded Si3N4
Authors: Vučković A. , Matović B. , Bošković Snezana
Published: March 2009

This paper deals with densification and a®b phase transformation of Si3N4, with a constant b-Si3N4 seeds concentration regarding sintering temperature and different additive types. The seeds of b-Si3N4 were obtained by sintering of silicon nitride in a-form and additive mixture consisting of Y2O3 and SiO2. Two different Si3N4/additive mixtures (Y2O3 + Al2O3 and CeO2) containing constant amount of seeds were prepared and tested. Characterization of sintered samples involved phase analysis by X−ray diffraction and density measurements. The results indicated that in the presence of yttria-alumina mixture both the phase transformation and the densification were enhanced as compared to samples containing only CeO2 as a sintering additive. The reasons for observed behavior are discussed in detail.
Nanotribological Properties of UHMWPE/Quartz Composites
Authors: Tang Chak Yin , Uskoković P.S. , Tsui Chi Pong , Chan K.C. , Lo S.C.L. , Xie Xiao Lin
Published: March 2009

Wear of ultra-high molecular weight polyethylene (UHMWPE) and its composites is one of the main obstacles that limit the longevity of total joint replacements. Compression molded UHMWPE/quartz composites with organosiloxane as a cross-linking agent for UHMWPE matrix, were tested in nanoindentation and nanowear. The nanomechanical properties of the composite were examined in the light of nanoindentation experiments performed with a diamond tip of nominal radius of curvature of about 150 nm under conditions of various contact loads. Results from nanowear tests show that, in addition to the nanohardness and elastic modulus, the crosslinking procedure has the most pronounced effect on the tribological properties and at 0.5 phr organosiloxane, composites reache their maximum nanowear resistance. These findings are in agreement with the results of conventional mechanical and wear tests performed on these materials.
Low Energy Impact Damage Detection in Laminar Thermoplastic Composite Materials by Means of Embedded Optical Fibers
Authors: Kojović A. , Živković I. , Brajović Lj. , Mitraković D. , Aleksić R.
Published: March 2009

The possibility of applying optical fibers as sensors for investigation of real time low
energy impact damage in laminar thermoplastic composite materials has been studied. For that purpose intensity based optical fibers were embedded in composite material specimens. Kevlar 129 (DuPont’s registered trade-mark for poly (p-phenylene terephthalamide)) woven fabric was used as reinforcement. Impact toughness testing by the Charpy impact pendulum was conducted in order to investigate low energy impacts. Transient intensity of optical signal during the impact, were compared with material crack initiation energy and crack propagation energy. Following this approach, development of damage in material was monitored. Obtained results show that intensity based optical fibers could be used as detectors for material damage appearance, and also, for level evaluation of its degradation caused by low energy impacts.
Biodegradable and Bioactive Polymer/Bioglass® Composite Foams for Tissue Engineering Scaffolds
Authors: Boccaccini Aldo Roberto , Blaker J.J. , Maquet V. , Jerome R. , Blacher S. , Roether Judith A.
Published: March 2009

Porous bioresorbable and bioactive composite materials designed for applications as
scaffolds in tissue engineering are discussed. The systems fabricated by thermally induced phase separation method and based on poly(D,L-lactide) (PDLLA) or poly(lactic acid-co-glycolic acid) (PLGA) with additions of bioactive glass particles (45S5 Bioglass®) are described in detail. The scaffolds exhibit a well-defined, oriented and interconnected porosity. The porosity structure of foams with and without Bioglass® was characterised by scanning electron microscopy. The in vitro bioactivity and degradability of the composite foams were investigated in contact with phosphate buffer saline (PBS) and simulated body fluid (SBF). High chemical reactivity of scaffolds in SBF, which leads to the prompt formation of bonelike hydroxyapatite crystals on the material surfaces, indicates an enhanced bioactive character of the composites and therefore their potential for use as bone tissue engineering scaffolds.
Biphasic Calcium Phosphate/Poly-(DL-Lactide-Co-Glycolide) Biocomposite as Filler and Blocks for Reparation of Bone Tissue
Authors: Ignjatović N. , Ninkov P. , Ajduković Z. , Konstantinović V. , Uskokovic Dragan P.
Published: March 2009

Composite biomaterials, like calciumphosphate/bioresorbable polymer, offer excellent
potential for reconstruction and reparation of bone tissue defects induced by different sources. In this paper synthesis of calciumphosphate/poly-DL-lactide-co-glycolide (BCP/DLPLG) composite biomaterial formed as filler and blocks was studied. BCP/DLPLG composite biomaterial was produced in the form of spherical granules of BCP covered by a DLPLG layer, average diameter of 150-250 µm. By cold and hot pressing of granules at up to 10000 kg/cm2, blocks with fine distribution of phases and porosity up to 3% were obtained. Characterization was performed by
wide-angle X-ray structural analysis (WAXS), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), infrared spectroscopy (IR), and mechanical properties by defining the compressive strength. In vitro citotoxicity research was carried out on cellular cultures of fibroblasts of human (MRC5) and mouse (L929). In vivo research was performed in two steps. Reparatory ability of BCP/DLPLG in mice was examined in the first step, and then bone tissue
reconstruction possibilities on 10 patients in the next step. In vitro tests showed very good fibroblast adhesion and non-citotoxicity of the composite. A material is considered non-cytotoxic if the cell survival is above 50 %, and in our case it was 90%. In vivo research on mice indicated high level of reparatory ability of this composite with formation of new bone and vascular tissue six weeks after reparation. Application of this composite for healing infrabone defects of patients showed a high level of osseous regeneration.
Structural, Doped, Radiation Defects and Properties of Non-Stoichiometrical Solids
Authors: Kulagin N.
Published: March 2009

The paper includes experimental and theoretical data on spectral properties of oxide single crystals doped with ions of the iron group elements, as well as on the stability of ions oxidation state under irradiation. Experimental data resulting from the investigation of radiation-induced defects into pure and doped single crystals, such as sapphire (α-Al2O3) and garnets (Y3Al5O12, Gd3Ga2Sc3O12, Gd3Sc2Al3O12), are presented. The main conditions of creation of irradiation-induced color centers and point defects, including theoretical analysis, are considered too.
Latent Hardening in Copper and Copper Alloys
Authors: Boyle K.P.
Published: March 2009

A new phenomenological latent hardening model is developed for rate-dependent single crystal plasticity. The model quantitatively predicts the latent hardening evolution and latent hardening material dependence for f.c.c. single crystals. Increased overshoot, typically observed in copper alloys as opposed to copper, is rationalized based on the history dependence of latent hardening.
Shear Banding in Twinned Structures and Their Influence on Brass-Type Texture
Authors: Paul Henryk , Morawiec Adam , Bouzy Emmanuel , Fundenberger Jean-Jacques , Piątkowski Andrzej
Published: March 2009

The local crystallography within shear bands (SB) has been examined in a single crystal of {112}<111> orientation of pure copper deformed at 77K by channel-die compression to strains of about 1. Setting up a system for making high-resolution orientation maps using transmission electron microscopy (TEM) has opened new advantageous circumstances for the analysis of orientation changes within SB. This method with spatial resolution higher than 10nm allows the examination of microstructure images composed of nanoscale subcells forming SB. It has been
found that for well-developed shear bands, a crystal lattice rotation about <112> direction tends to dominate and this process is usually accompanied by activation of new slip systems. The present work shows that despite the plane strain deformation mode, the mechanism of lattice rotation within emerging SBs may lead to Goss and Brass texture components.
Effect of Hexagonal Crystal Structure Anisotropy on the Selective Grain Boundary Mobility during Texture Formation and Secondary Recrystallization in Zn
Authors: Sursaeva Vera G.
Published: March 2009

Texture formation during secondary recrystallization depends on the nature of secondary recrystallization process itself. So microstructure evolution and texture development during secondary recrystallization should be discussed concurrently. The main goal of the paper is studying of the effect of internal stresses on grain boundary motion or, more generally, the interaction of grain boundaries with stress fields and the effect of deformation inhomogeniety on grain boundary mobility during secondary recrystallization. Considering transformation from normal grain growth to secondary recrystallization, the attempt was made to characterize the microstructure and to relate it to the processes of nucleation and growth of new rains. The nucleation process is heterogeneous. The data allow us to assume that the nuclei are strain free grains.
Influence of Thermo-Mechanical Treatments on the Stored Energy Simulated by FEM for Two Low Carbon Steels
Authors: Baudin Thierry , Etter Anne Laure , Gerber Ph. , Samet-Meziou Amel , Penelle Richard , Rey Cristian
Published: March 2009

The stored energy of two cold rolled IF-Ti steels is calculated using finite element
method from an EBSD microstructure. Because the thermo-mechanical treatments are different for the two materials, the parameters of the behaviour law used in the simulation and identified using a polycrystalline model and an inverse method from experimental results are also different. Their variation is due to the number of experimental tests taken into account for their identification and obviously to the thermo-mechanical path. The stored energy is mainly influenced by Lu which represents the mean free path of the mobile dislocations gliding on the system u and which is expressed as a function of a K material parameter. Using one tension test, the experimental stored energy values estimated from neutron diffraction measurements can be reproduced only for a material parameter K fixed.
YBCO Coated Conductor Applications - A Texture Problem
Authors: Obst B. , Nast Rainer , Kotzyba G. , Goldacker Wilfried
Published: March 2009

YBa2Cu3O7-δ ("YBCO") is a high-temperature ceramic superconductor. Due to its complex layered structure, a strong biaxial texture of the YBCO grains is necessary to achieve technically relevant currents. In this paper, we describe the development of flexible metallic tapes with strong cube texture, providing a lattice-matched template for buffer and YBCO coatings in proper orientation. Texture analysis was performed using electron backscatter diffraction (EBSD).
Quantification of Texture Inhomogeneity
Authors: Bonarski Jan T.
Published: March 2009

In the paper some aspects of analysis of crystallographic texture concerned to evaluation^of its inhomogeneity have been described. The introduced classification and quantitative measure of texture inhomogeneity have been applied in microstructure characterization of cold rolled Cu-sheet and of electrodeposited Cu-layer with a depth-graded structure.
Toughness Anisotropy in Intercritically Rolled Steel Plates
Authors: Petrov Roumen H. , Kestens Leo , Houbaert Yvan
Published: March 2009

The toughness anisotropy in steel plates (0.08%C, 1.52%Mn, 0.3%Si, 0.055%Nb and 0.078%V) was studied in relation to the crystallographic texture and microstructural anisotropy of the material. The plates, with a ferrite –pearlite microstructure, were obtained by hot rolling in a laboratory reversible rolling mill to 66% reduction with the final rolling pass in the two-phase (g/a) domain followed by accelerated cooling to 570°C and subsequent slow cooling to room temperature (coiling simulation). Standard size Charpy samples with their long axis oriented at 0, 22.5, 45, 67.5 and 90° with respect to the rolling direction of the plate were tested at different temperatures varying from +20°C to –80°C. Microstructures and textures of the plates were studied by means of orientation scanning electron microscopy and XRD. A specific toughness anisotropy profile was observed which could not be correlated to the crystallographic texture of the plates, which all displayed very weak, almost random transformation type textures with a maximum intensity of approximately 2x random. Therefore, it was investigated whether the toughness anisotropy might be related to the microstructural anisotropy rather than to the crystallographic texture. The study of the grain size distribution in differently oriented sections together with the distribution of the pearlite zones in these sections revealed that the directional changes in the toughness could be successfully associated to these parameters. A significant increase in the absorbed impact energy from 140J to 270J, together with a remarkable decrease of the toughness anisotropy at room temperature, was observed after annealing the hot rolled samples at an intercritical temperature followed by an isothermal treatment in the low bainite region. The observed effect was explained by the replacement of the pearlite constituents by lower bainite in the grain boundary regions which produced a local strengthening of grain boundaries.
Effects of Texture and Anisotropy on Intergranular Stress Development in Zirconium
Authors: Oliver E.C. , Daymond Mark R. , Withers Philip J.
Published: March 2009

The influence of texture and anisotropy on the generation of intergranular stresses in clock-rolled zirconium is investigated using neutron diffraction and elastoplastic self-consistent modelling. Comparison between experimental data and model calculations indicates that the operation mainly of prismatic and basal slip explains the trends in intergranular stress evolution during in-plane tensile and through-thickness compressive deformation, whilst twinning plays a significant role during in-plane compression.
Measurement and Calculation of Elastic Properties in Low Carbon Steel Sheet
Authors: Luzin Vladimir , Banovic S. , Gnäupel-Herold Thomas , Prask Henry , Ricker R.E.
Published: March 2009

Low carbon steel (usually in sheet form) has found a wide range of applications in industry due to its high formability. The inner and outer panels of a car body are good examples of such an implementation. While low carbon steel has been used in this application for many decades, a reliable predictive capability of the forming process and “springback” has still not been achieved. NIST has been involved in addressing this and other formability problems for several years. In this paper, texture produced by the in-plane straining and its relationship to springback is reported. Low carbon steel sheet was examined in the as-received condition and after balanced biaxial straining to 25%. This was performed using the Marciniak in-plane stretching test. Both experimental measurements and numerical calculations have been utilized to evaluate anisotropy and evolution of the elastic properties during forming. We employ several techniques for elastic property measurements (dynamic mechanical analysis, static four point bending, mechanical resonance frequency measurements), and several calculation schemes (orientation distribution function averaging, finite element analysis) which are based on texture measurements (neutron diffraction, electron back scattering diffraction). The following objectives are pursued: a) To test a range of different experimental techniques for elastic property measurements in sheet metals; b) To validate numerical calculation methods of the elastic properties by experiments; c) To evaluate elastic property changes (and texture development) during biaxial straining. On the basis of the investigation, recommendations are made for the evaluation of elastic properties in textured sheet metal.
Determination of Morphological Textures of the Fibres in Composite Materials Made from Textiles of Carbon Fibres
Authors: Langelaan G. , Deprez S. , Verpoest Ignaas , van Houtte Paul
Published: March 2009

The orientation distribution of fibres (morphological texture) in a composite is very important in determining the properties of the material. Therefore, methods which can provide quantitative descriptions of the morphological texture are essential. One approach to determining the morphological texture function (MTF) is to measure the orientation distribution of the crystals in the fibres. Since many types of reinforcing fibres are crystalline and textured (i.e. carbon fibres, whiskers, etc.) this approach may be interesting for commercial/industrial applications. For this technique to be applied, the crystallographic texture intrinsic to the fibres must be determined and subsequently measurements of the crystallographic texture should be made in the composite. The morphological texture can then be calculated by a deconvolution of the composite texture with the fibre’s intrinsic texture. In this paper, morphological textures are determined in woven fabrics made from carbon fibres embedded in a polymer matrix. Straight fibres removed from the fabric serve as the reference material for the deconvolution. It is demonstrated that this technique is applicable and can resolve the orientation distribution to an accuracy greater than is needed for determining the elastic properties.
Texture Evolution during Roll-Cladding of a Composite of Five Plies of Ferritic Stainless Steel and Aluminium Sheets
Authors: Kim Jong-Kook , Huh Moo Young , Jee Kwang Koo , Engler Olaf
Published: March 2009

A clad composite of five plies of STS/Al/Al/Al/STS was produced by roll-cladding at 350°C from ferritic stainless steel (STS) and aluminum (Al) sheets. In order to clarify the strain state during roll-cladding, the evolution of textures at different through-thickness layers in the roll-clad composite was investigated. Because the deformation mainly occurred in the Al sheets during roll-cladding, the present investigation was focused on the Al sheets. In the STS/Al/Al/Al/STS composite, the mid Al sheets between STS and center Al displayed pronounced texture gradients with shear textures and plane strain rolling textures, while the center Al sheet depicted a plane strain texture throughout the whole sheet thickness. Simulations with the finite element method (FEM) disclosed that a large variation of shear strain rate during roll-cladding led to the formation of these texture gradients.
Extension of Orientation Mapping to the Transmission Electron Microscope
Authors: Dingley David J.
Published: March 2009

This paper describes progress in improving the spatial resolution of the well-established Orientation Imaging Microscopy technique, OIM, by developing an analogous procedure for the transmission electron microscope. The transmission orientation micrographs are obtained by recording a large series of dark field micrographs taken from the chosen area in the specimen. This area is selected so that it contains all of the grains of interest and is imaged at sufficiently high magnification to yield the spatial resolution required. The changing intensity of each pixel in different dark field micrographs permits the equivalent of a diffraction pattern for that pixel to be constructed. This enables determination of the lattice orientation of small volumes in the sample corresponding to that imaged in each individual pixel. Experimentation has shown that problems arise however, that decrease the fraction of correctly measured points due to ambiguities in determining the index of higher order reflections, especially when the total number of reflections observed is small. The solution has been to both modify the indexing procedure and to sum the
diffraction vectors observed within a single grain. The paper concentrates on a detailed analysis of a heavily deformed aluminium sample, chosen because of the fragmentation of the structure.
Effect of Initial Texture on the Evolution of Texture and Stored Energy during Recrystallization of Interstitial Free Steel
Authors: Lee Kyoo Young , Kim Gyo Sung , Kestens Leo
Published: March 2009

By applying a double cold rolling and annealing treatment, the evolution of the α and γ
fiber components differed from the ones observed in conventional processing. This is attributed to the difference of the initial texture. An increased reduction of stored energy of the {111}<112> component was found by monitoring the change of the stored energy during annealing, indicating that the onset of the nucleation stage of recrystallization by relaxation and annihilation of dislocations occurred mainly on the {111}<112> component with its higher stored energy. The detailed texture evolution of the double cold rolled specimen during 2nd annealing is described by coupling the theory of oriented nucleation and orientation pinning, which is experimentally confirmed by OIM scan.
Cube Texture Formed in Biaxially Rolled Low-Carbon Steel
Authors: Yin Fu Xing , Inoue Tadanobu , Nagai Kotobu
Published: March 2009

Cube texture ({001}<100>) influences extensively the plastic anisotropy and physical properties of materials. Researches on cube texture have been concentrated in f.c.c structured metals only since the scarce observation of the texture in b.c.c. metals. In the present work, the cube texture was found to be developed in low-carbon steel under the biaxial rolling mode (ND and TD rolling
alternatively). Cube texture and {112}-{111}<110> partially concentrated a-fiber texture were observed in biaxially rolled samples instead of the typical a-fiber and g-fiber texture formed in the normal flat-rolling. At 923K rolling where recrystallization occurred, highly developed {001}<110> recrystallization texture with some g-fiber texture was observed in the flat rolled sample. In contrast a quite intensified cube texture and {hkl}<110> texture were observed in the biaxially rolled sample. EBSD measurement showed the fraction of grains belonging to the two orientations was 0.35 and 0.55, respectively. Elongated along RD, grains in cube texture showed both the near-equiaxial and diagonally elongated shapes when observed from RD in the 923K rolled samples. Those grains containing lighter plastic strain had an average grain size (~1.5µm) which was 2 times larger than
the grains in the RD//<110> texture. Meanwhile, the cube oriented grains were characteristic of only low-angle grain boundaries (<15o), but showed a specific misorientation (S17b, <110> 86.6o) with the grains in the RD//<110> texture. Besides rolling deformation produced cube oriented grains, preferential growth of cube oriented recrystallization nuclei, and the transformation of the {001}<110> recrystallization grains were considered to cause the development of cube texture
during the 923K biaxial rolling.
Influence of Starting Microstructure on Texture Development in Cold Rolled and Annealed Low Carbon Steel Strip
Authors: Xu Wan Qiang , Ferry Michael
Published: March 2009

The effect of initial microstructure on the recrystallization behaviour and texture development of low carbon (LC) steel was investigated. Steel strip samples (0.05 wt.% C) of 2 mm in thickness were heat treated to produce a microstructure consisting predominantly of either polygonal ferrite or acicular ferrite. Samples were cold rolled 50, 70 and 90% reduction then annealed for various times in the temperature range 580-640 oC. The microstructures and textures produced by deformation and annealing were studied by optical microscopy and electron backscatter diffraction in the SEM. The initial microstructure was found to have a substantial influence on the rate of recrystallization and final texture. It was found that polygonal ferrite recrystallizes more rapidly than acicular ferrite with the former generating the strongest <111>//ND recrystallization texture. The results are examined within the framework of improving the formability of LC steel produced by direct strip casting whereby controlled thermal and mechanical processing prior to cold rolling and annealing can generate the same types of initial microstructures, as studied in this work.
Crystallographic Control on the Development of Texture in Precipitated Quartz Grains
Authors: Lagoeiro Leonardo , Ferreira Paola , Castro Cristiane
Published: March 2009

In this study we analysed microstructures and determined [c]-axis textures of quartz
crystals in veins formed parallel to composition banding in naturally deformed iron oxide-quartz rocks. Only veins of few millimeters thick were sampled. These veins were formed in a regime of non-coaxial deformation under temperature of ~300°C. We made thin sections from rock slabs cut perpendicular to shear plane and parallel to shear direction. In thin sections veins are composed of large single quartz crystals of lens or rhomb-shaped blocks similar to s-porphyroclast systems. Lattice distortion (i.e. undulose extinction, gradual lattice banding and subgrain boundaries) occurs in single crystals as revealed by optical microscopy. Distortion was caused by slip of dislocations preferentially on basal planes. These are also planes along which microcracks developed. Distinct types of microcracks are individualized based on size, orientation and distribution of voids. Microcracrack voids are filled by polycrystalline quartz aggregates. In contrast to single crystals,
these aggregates do not have any optical microstructure that might be related to crystal plastic process. Moreover grain size distribution are quite different from those related to dynamic recrystallized aggregates. Despite of that, polycrystalline quartz aggregates have strong [c]-axis preferred orientations. These orientations are similar to those of single crystals close to the microfracture walls. In large spaced voids c-axes orientation of quartz in polycrystalline aggregate have significant misorientation angles with respect to the single crystal [c]-axis orientation, reaching values up to 45° to the foliation plane (XY section of the finite strain). Based on microstructural and textural data we propose a mode for quartz [c]-axis texture development in both single crystals and polycrystalline aggregates that fill microcrack voids.
Texture Control in Silver
Authors: Liu Dan Min , Liu Wei Peng , Liu Xing , Zhou Mei Ling
Published: March 2009

The influence of the oxygen-content, the rolling method, the annealing method and the annealing temperature on the texture in silver have been studied. The results show that low oxygen-content in original material, annealing at a temperature higher than 700ı and annealing in an atmosphere such as inert gas, air or pure oxygen are beneficial to obtain the {110}<110> component. Textured Ag substrate in which the main components is {110}<110> has been obtained. The mechanism of texture-forming is studied using electron back-scattered diffraction (EBSD) method.
A Study of the Early Stages of Recovery in Cold Rolled {110}<001> Oriented Copper Single Crystals
Authors: Ferry Michael , Humphreys John F.
Published: March 2009

Copper single crystals of {110}<001> crystallographic orientation were cold rolled to a true strain of 1.4. Specimens were cut from the as-deformed crystals with all surfaces mechanically ground and deep-etched in concentrated nitric acid to minimise the likelihood of surface nucleation of recrystallized grains during subsequent annealing. The early stages of static recovery were studied by annealing specimens at 300 oC. The crystallographic features of the deformed and annealed microstructures were determined by high resolution electron backscatter diffraction. It was observed that deformation was homogeneous with the microstructure in ND-RD plane exhibiting two complementary sets of intersecting bands at ~+ 35o to ND. Along these bands and in the microstructure, in general, there was an overall spread in orientation about ND towards {110}<112>. However, the orientation spread along these bands was cyclic, that is, sinusoidal orientation gradients were generated about ND with amplitude of up to 20o and wavelength 5-10 µm. Annealing resulted in the preferred growth of cells that have orientations at the edge of the orientation spread of the deformation substructure. This localized coarsening of the microstructure is similar to the discontinuous subgrain growth observed in {110}<001> oriented Al single crystals and indicates that discontinuous subgrain (cellular) growth can also occur in metals of lower stacking fault energy.
Orientation Fragmentation in Copper, Nickel and Aluminum: A Comparative Study of the Nucleation Process
Authors: Seefeldt Marc , van Houtte Paul
Published: March 2009

An attempt to model the nucleation of fragment boundaries during cold plastic deformation of f.c.c. metals is presented. The paper focuses on intrinsic nucleation in the grain interior due to elementary processes on the dislocation level. Since orientation fragmentation seems to be linked to slip banding and the underlying mechanisms should be the same, the model is based on the elementary process of double cross-slip. Simulations were carried out for Cu, Ni and Al. Fragment boundary spacings and misorientations could be predicted in reasonable agreement with experiment for Cu. For Ni, comparable results were obtained, when a stacking fault energy at the lower end of the range of literature data was chosen. The resulting rate equation for the generation of partial disclinations as carriers of orientation fragmentation can be implemented into an earlier model for the coupled substructure and texture development during cold plastic deformation.
Processing Path Model to Describe Texture Evolution during Mechanical Processing
Authors: Li Dong Sheng , Bouhattate J. , Garmestani Hamid
Published: March 2009

Using a processing path model based on the conservation principle in the orientation space explicit solutions can be formed linking any final (desired) microstructure to a given initial state for polycrystalline materials. The model uses texture coefficients in spherical harmonics expansion to as materials descriptors to represent the texture state of polycrystalline materials. In this work, the effect of increasing the maximum number of texture coefficients used in the series expansion (represented by Lmax) on the prediction of texture and its accuracy is fully studied.
Compressive Creep of Hot-Pressed Si3N4 Ceramics Using CRE2O3-Al2O3 or CRE2O3-AlN Additive Mixtures
Authors: dos Santos Claudinei , Strecker Kurt , Barboza M.J.R. , Baldacim Sandro Aparecido , Neto Francisco Piorino , Silva Olivério Moreira Macedo , Silva Cosme Roberto Moreira
Published: March 2009

The creep behavior of hot-pressed Si3N4 ceramics was investigated. The proposal of this work is to investigate the use of yttrium-rare earth oxide mixture, CRE2O3, produced at FAENQUIL, as sintering additive, since the cost of production of this material is 80% inferior to Y2O3. These ceramics were obtained by uniaxial hotpressing using different additive contents and mixtures (CRE2O3-Al2O3 or CRE2O3- AlN). Compressive creep tests were carried out at 13000C and 300 MPa, in air. The Si3N4-CRE2O3-Al2O3 ceramics demonstrated that the creep resistance is inversely proportional to the additive content. Mixtures with high intergranular phase content presented low creep resistance due to high oxidation and more pronounced softening of the intergranular phase. Si3N4-CRE2O3-AlN ceramics demonstrated better creep resistance with a steady-state creep rate of 7 x 10-8 s-1. This behavior is related to the a-SiAlON content, a solid solution of Si3N4 that incorporates a great fraction of intergranular phase, decreasing the amount of intergranular phase.
The Nitriding of Ferrous Powder Alloys - Mathematical Modelling and Simulation
Authors: Politano R. , Rossi J.L.
Published: March 2009

Mathematical modelling has been developed to improve processes control and has helped theories about complex systems to be written. Nitriding is a multivariable system that needs the convergence of efforts to allow its improvement. Computer simulation is an important tool to give a simultaneous evaluation of all variables and respective effects in the result of the process. Surface conditions have an important effect in the interaction between gases and metals. Its influence can only be studied under two-dimensional and 3-D simulations. The presence of oxides and other barrier have a critical influence on the kinetic and on the result of the process. Secondary reactions such as precipitation and nitride layer formation also affect the process. Particularly, porosities can have an important effect by enhancing the gas permeation inside the sintered material. Depending on the variables that might be deleterious to the process, the simulations give some indications how to proceed and how to control these process variables. This work show, through simulation tools, how variables such as gas atmosphere, temperature, powder surface conditions, porosity and alloy composition will affect the final result of the nitriding process of sintered and non-sintered powders. A methodology was developed using numerical methods and systemic algorithms.
Use of Impedance Spectroscopy in the Study of the Effect of Cr Concentration on the Electrical Properties of SnO2-Based Ceramics
Authors: Leite Daniela Russo , Las W.C. , Brankovic G. , Zaghete M.A. , Cilense M. , Varela José Arana
Published: March 2009

This paper reports a study of influence of Cr concentration on the electrical properties and microstructure of SnO2-based powders doped with Mn and Nb, prepared by an organic route (Pechini method). All the samples were compacted into discs and sintered at 1300°C for 3h, resulting in ceramics with relative density varying between 78% and 98%. The powders were characterized by X-ray diffraction analysis. Impedance spectroscopy characterization indicated that the conductivity decreases as Cr concentration increases, probably due to Cr segregation at grain boundaries, which reduces grain size, increasing the number of resistive boundaries.
Ceramic Composites Derived from Nb/Al2O3-Filled Polysilsesquioxane
Authors: Schiavon Marco Antônio , Yoshida I.V.P. , Silva A.C. , Acchar Wilson
Published: March 2009

Ceramic matrix composites (CMC) were prepared by the active-filler-controlled polymer pyrolysis process (AFCOP) using a polysilsesquioxane resin filled with metallic niobium and alumina powders. Samples containing 60 wt% of polysilsesquioxane and 40 wt% of metallic niobium and alumina powders mixtures were homogenized, uniaxially pressed and pyrolysed in an alumina tube furnace up to 1400 °C, under argon flow. The ceramic products were characterized by X-ray diffraction (XRD), thermogravimetry (TGA), differential thermal analysis (DTA), Fourier transform infrared (FTIR) and energy-dispersive (EDS) spectroscopies. XRD analysis of the products showed the presence of crystalline phases such as NbC, Nb3Si, Nb5Si3, SiC, crystoballite and mullite. Thermogravimetry data of the composites presented low weight losses at 1000 °C. DTA curves showed an endothermic peak at 1350 °C, which was associated to the beginning of carbothermic reduction and/or the formation of silicon oxide and carbide. In addition, an exothermic peak at 1400 °C was associated to the formation of the mullite phase.
Densification Study of SiC:Al2O3:Y2O3 with Polymer Additions
Authors: Godoy Ana Lúcia Exner , Bressiani José Carlos , Bressiani Ana Helena A.
Published: March 2009

The influence of polymer precursor additions on liquid phase sintering of SiC:Al2O3:Y2O3 has been evaluated. Two polymer precursors were used: polymethylhydrogensiloxane and D4Vi (1,3,5,7-tetramethyl-1,3,5,7-tetraviniylcyclotetrasiloxane). The ceramic phase had the following composition in wt%: 91.6 SiC, 4.2 Al2O3 and 4.2 Y2O3. The composites were prepared using the following ceramic phase to polymer ratios in wt%: 82.7: 17.3; 74.0: 26.0 and 71.5: 28.5. Density measurements were carried out using a helium picnometry and the Archimedes method. The crystalline phases were identified by X-ray diffraction analysis and the microstructures were observed by optical and scanning electron microscopy.
Anelastic Spectroscopy in Al2O3
Authors: Grandini Carlos Roberto , Oliveira R.L.N. , Mota Rogério Pinto , Santos F.P. , de Campos Élson
Published: March 2009

Engineering ceramics have found use in many applications, such as engine parts, ball bearings, artificial bone and hip replacements and gyroscopes, because of their good chemical inertness, hardness, high temperature stability and excellent wear resistance. Oxide ceramic may meet these demands. Alumina (Al2O3) ceramics offer a high potential for many engineering applications, such as wear- and/or corrosion-resistant components, and as material for substrates or housings in microelectronic devices. Alumina is used among other things for seal ring, draw-cones, guides, water mixing tapes, bearing parts, medical prostheses and cutting tools. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature can distinguish among the different atomic jumps, which occurs in the various phases or at different local ordering. In this paper, it is reported anelastic relaxation measurements in Al2O3 samples using commercial starch. These measurements were carried out in a torsion pendulum operating in frequencies around 40 Hz. The results shown strongly influence of the type of forming in the elastic modulus obtained by anelastic relaxation measurements.
Oxidation Behavior of Hot-Pressed Si3 N4 Ceramics Using CRE2 O3 -AlN and CRE2 O3 -Al2 O3 as Sintering Additives
Authors: dos Santos Claudinei , Strecker Kurt , Neto Francisco Piorino , Lanna M.A. , Silva Olivério Moreira Macedo , Silva Cosme Roberto Moreira
Published: March 2009

In this work, an yttrium and rare-earth oxides mixture, CRE2O3, produced at DEMAR-FAENQUIL, was used as sintering additive for silicon nitride (Si3N4) ceramics. Samples were produced by uniaxial hot-pressing, using mixtures of CRE2O3- Al2O3 or CRE2O3-AlN as additives. Four kind of hot-pressed Si3N4 were used as oxidation samples: Si3N4+ 5vol% or 20vol.% of CRE2O3-Al2O3 (forming only β-Si3N4 as crystalline phase), Si3N4+ 5vol.%CRE2O3-AlN (α-SiAlON+β) and Si3N4+ 20vol.%CRE2O3-AlN (only α-SiAlON). The oxidation behavior was evaluated at 13500C, in air up to 160 hours. The oxidation rate of Si3N4 ceramics increased with increasing CRE2O3/Al2O3 content, and oxidation kinetics obeyed the usual parabolic law. Pure α-SiAlONs (Si3N4 +20 vol.% CRE2O3-AlN) were high oxidation resistant with weight gain, after 160 hours, of 0.1 mg.cm-2, while β-Si3N4+20vol.%CRE2O3- Al2O3 showed a weight gain of 1.4 mg.cm-2 after only 10 hours. The oxidation behavior of these ceramics was comparable with ceramics sintered with Y2O3. This result confirms the possibility of the fabrication of high oxidation resistance Si3N4 ceramics using the low cost sintering additive CRE2O3.
Anelastic Spectroscopy in Superconducting Oxides
Authors: de Albuquerque Gimenez Juliana Maria , Grandini Carlos Roberto , dos Santos Dayse Iara , Cunha Alfredo Gonçalves da
Published: March 2009

Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the "step" in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and O5 of the lattice.
Molybdenum Silicides as a Bonding Phase in Diamond Composites
Authors: Jaworska L. , Morgiel Jerzy , Stobierski Ludosław , Lis Jerzy , Krolicka B. , Maziarz W.
Published: March 2009

Molybdenum silicides were obtained by the self-propagating synthesis (SHS) method. Diamond composites containing 30 mass% of MoSi2 or Mo5Si3 bonding phase had been prepared using HT-HP Bridgman type apparatus. Sintering of the diamond composites were carried out at 2073±50 K and 8±0.2 GPa. The interactions in diamond-silicide composites were studied by means of X-ray diffractometry and transmission electron microscopy (TEM). Results of both
mechanical properties and thermal resistance measurements are reported. Hardness HV1 for the composite with the predominantly MoSi2 bonding phase was found to be around 42 GPa. After heat treatment in 1200 °C for 30 min. in vacuum HV1 decreases to 29 GPa. In the second composite containing the Mo5Si3 bonding phase the HV1 of 28.0 GPa after thermal exposure changes to 21.0 GPa.
Doped Tin Oxide Nanometric Films for Environment Monitoring
Authors: Falla P. Hidalgo , Peres H.E.M. , Gouvêa Douglas , Ramirez-Fernandez F.J.
Published: March 2009

In this work tin dioxide (SnO2) doped with nickel is studied with the aim of develop integrated gas sensors for some important pollution gases into environment, principally sulphur dioxide (SO2). SnO2 powders doped with Nickel were prepared by Pechini`s method [1] and characterized morphologically by X-Ray diffraction, measurement of specific surface area (SBET) and transmission electron microscopy (TEM), which revealed grain sizes around 5 to 10 nm. Gas sensors were fabricated by spin-coating deposition of Ni doped SnO2 films over alumina substrate with gold contacts. Electrical resistance of such device is characterized, at room temperature, as function of SO2 concentration into environment, showing a sensitivity around 0.0058 ppm-1 for relative resistance variation, with good linearity for SO2 concentrations up to 30 ppm. Also, FTIR analysis shows the desorption of SO2 from SnO2 surface, after cleaning into fresh air.
Organophilization of Four Differents Bentonitic Clays with a Quaternary Ammonium Salt
Authors: Andrade Daniela de Lourdes A.C.S. , Freire Wildemberg A. , Araújo Sueila S. , Vieira Lucianna G.F. , de Melo Costa Ana Cristina Figueiredo , de Carvalho Laura H. , Gomes Ailton S. , Silva Suédina Maria L.
Published: March 2009

Organophilic Bentonities clays are widely used for industrial purposes, as components of petroleum drilling fluids as well as in cosmetics, lubricants adhesives and paints. Most recent they have been used as fillers in polymer nanocomposites. In this work, three organophilic bentonitic clays from the distric of Boa Vista and one from Campina Grande, PB, Brazil, were synthesized and characterized. The four clays were treated with a quaternary chloride ammonium salt- dimethyl benzyl ammonium alkyl chloride (Dodigen 1611) provided by Chemco. The cation exchange and swelling capacities of the modified clays were determined and the clays were characterized by FTIR, Thermal Analysis (DTA, TGA) and X-ray diffraction. The results showed the modification of all four clays by the quaternary ammonium salt to be successful.
An Investigation on the Corrosion Behaviour of Nd-Fe-B Magnets in a Chloride Solution
Authors: Costa Isolda , Oliveira M.C.L. , De Melo Hercílio G. , de Faria Jr. Rubens Nunes
Published: March 2009

In this study, the corrosion behaviour of a sintered commercial Nd-Fe-B magnet has been investigated in naturally aerated and deaerated 3.5 (m/v)% sodium chloride solutions. Magnetized specimens were used in this investigation. The corrosion behaviour of the specimens was monitored at increasing test times by means of electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization curves and surface observation by scanning electron microscopy (SEM), were also carried out after 30 days of immersion in the test solutions. Experimental results indicated that the corrosion resistance was affected by aeration of the solution. The corrosive attack penetrates deeply into the specimens and, consequently, the magnetic properties decreased with immersion time. The magnetic properties most influenced by corrosion were the remanence (Br) and the maximum energy product (BHmax), both presenting a reduction corresponding to 6%, after 30 days of immersion.
Strain Induced Precipitation in Model and Conventional Microalloyed Steels during Thermomechanical Processing
Authors: Poths R.M. , Rainforth Mark W. , Palmiere Eric J.
Published: March 2009

The finishing rolling of microalloyed steels was simulated by double-deformation plane strain compression testing of both model and conventional steels microalloyed with Nb. The flow behavior following interpass delay times of 1-100s was related to the deformed microstructure, the deformation substructure and the strain-induced precipitation. Fe-30wt%Ni is clearly a good model alloy for conventional microalloyed steels, as similar results are observed for both materials. In addition, the location of fine strain-induced precipitates in relation to the deformation substructure can be determined directly using transmission electron microscopy.
Application of Nb-O Affinity in Clean Steel
Authors: Imagumbai Masana , Kajioka Hiroyuki , Takechi Hiroshi
Published: March 2009

This report introduces a new deoxidation process that starts with a vacuum degassing followed by the addition of ferro-niobium in the same vacuum facility. The addition of strong deoxidation substance like aluminum and/or silicon is not adopted. Owing to the degassing in vacuum, which in reality reacts as deoxidation with C in molten steel, the solute oxygen in molten steel (O) is stabilized by niobium, which generates an ample number of fine oxide particles composed of (Nb, Mn)2O3-phase. Provided the carbon-degassing is conducted so as to reach the O prior to the FeNb addition would be around 100ppm and less, these oxide-inclusions do not agglomerate before and during solidification, because of the weak cohesivity of niobium-based oxides in molten steel, which would enable defect-free cast products as well as clogging-less casting operation. Also, the steel containing these fine (Nb, Mn)2O3-particles but no Al, exhibits so-called intra-granular acicular ferrite transformation and good toughness of weld heat affected zone (HAZ).
Application of Coercive Field Measurements to the Evaluation of Recovery and Recrystallization in Cold Rolled Interstitial Free (IF) Steel
Authors: Martínez-de-Guereñu Ane , Oyarzabal M. , Arizti F. , Gutiérrez Isabel
Published: March 2009

The recovery and recrystallization kinetics of a cold rolled interstitial free (IF) steel were studied during isothermal annealing. Magnetic methods based on coercive field measurements, hardness tests and metallography were applied so as to follow the kinetics experimentally. The coercive field measurement technique reveals a higher degree of resolution for monitoring recovery than conventional hardness determination and also allows the recrystallization progress to be monitored. The results obtained are compared to those previously determined for a non-stabilized extra low carbon (ELC) steel. The observed differences are discussed in terms of the presence of microalloying elements, Ti and Nb, which slow down recovery and delay recrystallization.