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A comparative study of microstructural development in the sol-gel derived alumina-mullite nanocomposites using colloidal silica and tetraethyl orthosilicate

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JOURNAL OF SOL-GEL SCIENCE AND TECHNOLOGY 2011年第3期58卷 689-697页

作者： Sedaghat, A. Taheri-Nassaj, E. Soraru, G. D. Ebadzadeh, T. Tarbiat Modares Univ Dept Mat Sci & Engn Tehran Iran Univ Trent Dept Mat Engn & Ind Technol I-38050 Trento Italy Mat & Energy Res Ctr Tehran Iran

This paper compares the microstructure development of two alumina-15 vol% mullite composites during the sintering. The nanopowders of alumina-mullite composite were synthesized by the sol-gel method using aluminum chloride hexahydrate and two different silicon sources (colloidal silica in route 1 and tetraethyl orthosilicate in route 2). The alumina-mullite composites were prepared by pressing and sintering of the nanopowders. Although the intergranular mullites were observed in both routes, there were mullite particles in route 2 formed inside the alumina grains (intragranular mullite). Formation of the intragranular mullite is attributed to the drop in silica solubility, which occurs during the transition from metastable alumina to stable alumina. Compared to route 1, the relative density and the average grain size were increased and accelerated by route 2. The two-stage sintering is not useful for the mullite decomposition.

关键词： Phase evolution microstructure development Alumina Mullite Nanocomposite

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A microstructure model for recrystallisation and phase transformation during the dual-phase steel annealing cycle

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COMPUTATIONAL MATERIALS SCIENCE 2010年第3期48卷 692-699页

作者： Bos, C. Mecozzi, M. G. Sietsma, J. Delft Univ Technol Dept Mat Sci & Engn NL-2628 CD Delft Netherlands Mat Innovat Inst NL-2628 CD Delft Netherlands

A three-dimensional cellular automata model is developed for the description of the relevant metallurgical mechanisms occurring in the annealing stage of dual-phase steels: ferrite recrystallisation, pearlite-to-austenite and ferrite-to-austenite transformation on heating and austenite-to-ferrite transformation on cooling. Based on the local grain-boundary and interface velocity, the latter controlled by both interface mobility and carbon diffusivity, the model is able to simulate the microstructure development throughout the annealing stage. The model also provides information on the carbon gradient in austenite at the end of the cycle, which is relevant for the prediction of martensite formation during the subsequent quenching. The simulated structure thus provides a realistic representation of many microstructural aspects. (C) 2010 Elsevier B.V. All rights reserved.

关键词： Cellular automata model Phase transformation kinetics Mixed-mode kinetics microstructure development

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Fabrication and mechanical properties of high-dispersion-treated carbon nanofiber/alumina composites

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JOURNAL OF THE CERAMIC SOCIETY OF JAPAN 2010年第1381期118卷 847-854页

作者： Ueda, Naoki Yamakami, Tomohiko Yamaguchi, Tomohiro Kitajima, Kunio Usui, Yuki Aoki, Kaoru Nakanishi, Takefumi Miyaji, Fumiaki Endo, Morinobu Saito, Naoto Taruta, Seiichi Shinshu Univ Fac Engn Nagano 3808553 Japan Shinshu Univ Sch Med Nagano 3908621 Japan Japan Med Mat Corp Yodogawa Ku Osaka 5320003 Japan Shinshu Univ Sch Hlth Sci Dept Appl Phys Therapy Nagano 3908621 Japan

High-dispersion-treated carbon nanofibers (CNFs) were used to fabricate uniformly-dispersed CNFs-alumina composites with enhanced mechanical properties. The treatment was effective in obtaining dense and uniform composites. The composites containing 0.4-0.8 wt CNFs were densified to a relative density of more than 99% by vacuum sintering and subsequent hot isostatic pressing, and those containing 1.6-2.5 wt % CNFs were densified to full density by plasma activated sintering. The maximum bending strength of the composites (1050 MPa) was approximately the same as the bending strength of monolithic alumina (1079 MPa). The maximum fracture toughness of the composites was 5.9 MPa.m(0.5), which was a 69% increase compared with the fracture toughness of monolithic alumina (3.5 MPa.m(0.5)). Fracture toughness (Kid increased rapidly with a decrease in alumina grain size (G), and we found that the relationship could be expressed by the following equation: K-IC = (k(1)/G(2)) k(2) (where k(1), and k(2) are constants). (C) 2010 The Ceramic Society of Japan. All rights reserved.

关键词： Carbon nanotube Alumina Composites Sintering microstructure development Mechanical properties

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Effect of Elevated Strip Entry Temperature on the Aluminum Rich Inhibition Layer at the Substrate Coating Interface During Galvanizing

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CANADIAN METALLURGICAL QUARTERLY 2010年第3期49卷 301-309页

作者： Mandal, G. K. Das, S. K. Balasubramaniam, R. Mehrotra, S. P. Natl Met Lab CSIR Jamshedpur 831007 Jharkhand India Indian Inst Technol Kanpur 208016 Uttar Pradesh India

During continuous hot dip galvanizing, the use of higher line speeds and thicker gauge strip often results in the steel strip entering the bath at a temperature significantly higher than that of the zinc bath. Studies on the effect of elevated strip entry temperature on the galvanizing reactions are limited. This investigation evaluates the microstructures of galvanized steel produced in a zinc bath containing 0.2 wt% dissolved aluminum essentially to study the effect of elevated strip entry temperatures on the formation of an aluminum rich inhibition layer at the substrate-coating interface. It is concluded that the inhibition layer consists of the orthorhombic Fe(2)Al(5)Zn(x) (0

关键词： Hot Dip Galvanizing Strip Entry Temperature Aluminium Containing Zinc Bath Inhibition Layer microstructure development

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Fabrication and Piezoelectric Properties of Textured (Bi_1/2K_1/2)TiO₃ Ferroelectric Ceramics

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JAPANESE JOURNAL OF APPLIED PHYSICS 2010年第9期49卷 09MD08-09MD08页

作者： Nagata, Hajime Saitoh, Masahiro Hiruma, Yuji Takenaka, Tadashi Tokyo Univ Sci Dept Elect Engn Fac Sci & Technol Chiba 2788510 Japan

Textured (Bi1/2K1/2)TiO3 (BKT) ceramics were prepared by a reactive templated grain growth (RTGG) method to improve their piezoelectric properties. Also, a hot-pressing (HP) method was modified on the basis of RTGG method to obtain dense ceramics and promote the grain orientation. The textured BKT ceramics prepared by the RTGG and HP methods exhibited a relatively high orientation factor F of 0.82 and a high density ratio of 95-99%. Scanning electron microscopy (SEM) micrographs of the textured HP-BKT indicated a textured and poreless microstructure. In addition, the resistivity of the textured HP-BKT was 1: 73 x 1013 Omega-m. The piezoelectric strain constant d(33) determined by means of resonance and antiresonance method was 125 pC/N for the direction parallel to the sheet-stacking direction of the RTGG process. From the measurement of field-induced stain, the normalized d(33)* (= S-ax/E-max) at 80 kV/cm were 127 and 238 pm/V on the randomly oriented and textured samples (F 0: 82) for the (//) direction, respectively. (C) 2010 The Japan Society of Applied Physics

关键词： TEMPLATED GRAIN-GROWTH TITANATE NA1/2BI1/2TIO3-BATIO3 CERAMICS FIELD-INDUCED STRAIN LEAD-FREE CERAMICS BARIUM-TITANATE ELECTROMECHANICAL PROPERTIES microstructure development ELECTRICAL-PROPERTIES POTASSIUM TITANATE SINGLE-CRYSTALS ELECTROMECHANICAL PROPERTIES electrical properties F Factor Grain orientation Health physics barium titanates single crystals

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Mechanical behavior and microstructure evolution during steady-state dynamic recrystallization in the austenitic steel 800H

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MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES microstructure AND PROCESSING 2009年第1-2期506卷 101-110页

作者： Frommert, M. Gottstein, G. Rhein Westfal TH Aachen Inst Met & Met Phys D-52056 Aachen Germany Max Planck Inst Eisenforsch GmbH D-40237 Dusseldorf Germany

Investigations of steady-state dynamic recrystallization (DRX) were carried out on an austenitic steel alloy BOOK The influence of strain rate and temperature on the mechanical behavior, microstructure development and texture evolution were analyzed. Strain rate and temperature change experiments during steady-state deformation revealed characteristic interdependencies of flow stress, hardening rate, and grain size. The grain size sensitivity of the flow stress was found to scale with the characteristic length scale of the deformed structure. Based on these observations a new model is proposed that relates the process of DRX to an interaction of mobile grain boundaries with deformation-induced subboundaries. (C) 2008 Elsevier B.V. All rights reserved.

关键词： Steady-state dynamic recrystallization Austenitic steel microstructure development Texture evolution Transient deformation conditions

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Phase-field modelling of microstructural evolution in primary crystallization

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JOURNAL OF ALLOYS AND COMPOUNDS 2009年第1-2期483卷 645-649页

作者： Bruna, Pere Pineda, Eloi Rojas, Jose I. Crespo, Daniel Univ Politecn Cataluna Dept Fis Aplicada EPSC ESAB Castelldefels 08860 Spain Univ Politecn Cataluna Dept Fis & Engn Nucl ESAB Castelldefels 08860 Spain Univ Politecn Cataluna Ctr Recerca Nanoengn ES-08034 Barcelona Spain Univ Politecn Cataluna Ctr Recerca Aeronaut & Espai ES-08034 Barcelona Spain

One of the main routes to obtain narrostructured materials is through the primary crystallization of metallic glasses. In such transformations, crystallites with a different composition than the amorphous precursor grow with a diffusion-controlled regime. Particle growth is slowed and eventually halted by the impingement between the concentration gradients of surrounding particles. Primary crystallization kinetics is not well described by the KJMA equation, and this fact was generally ascribed to both the soft-impingement effect and the non-random nucleation. However, recent phase-field simulations showed that the underlying physical reason is the change in the local diffusion properties of the amorphous precursor due to the variation of the composition during the transformation. The kinetics of primary crystallization is thus well described by considering a diffusion coefficient of the slowest diffusing species dependent on the local concentration. The nanostructure developed in such transformations is a key point to explain the macroscopic properties of these materials. In this work the grain size distributions obtained in realistic phase-field simulations of transformations with continuous nucleation and both constant and variable diffusion coefficient are presented. The obtained distributions are analyzed and the physical mechanisms responsible of their different features are recognized. (C) 2008 Elsevier B.V. All rights reserved.

关键词： Nucleation and growth transformations Crystallization kinetics microstructure development Diffusion-controlled growth Phase-field modelling

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NUMERICAL STUDY OF DEFORMATION CHARACTERISTICS IN PLANE STRAIN COMPRESSION TEST (PSCT) VOLUME CERTIFIED FOLLOWING microstructure

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METALURGIJA 2009年第4期48卷 257-261页

作者： Kliber, J. Aksenov, S. Fabik, R. Tech Univ Ostrava Fac Met & Mat Engn Ostrava Czech Republic

Thermal and mechanical parameters of forming and the process of microstructure development should be brought as close to real-world conditions as possible. The plane strain compression test and subsequent computer simulation provided an analysis of the recrystallization kinetics. A study of distribution of deformation characteristics in the sample upon upsetting was performed together with an analysis of microstructure of AN 304 steel during hot forming. The result of the investigation is information on grain size in the sample in relation to applied strain.

关键词： Plane Strain Compression Test (PSCT) finite element method AISI 304 microstructure development fraction softening

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microstructure development in drying latex coatings

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PROGRESS IN ORGANIC COATINGS 2005年第1期52卷 46-62页

作者： Ma, Y Davis, HT Scriven, LE Univ Minnesota Dept Chem Engn & Mat Sci Minneapolis MN 55455 USA

The technical details of high-resolution cryo-scanning electron microscopy (cryo-SEM) in studying latex formation are presented. This technique was used to visualize the microstructure development during drying of monodisperse and bimodal latex coatings. The glass transition temperature of the monodisperse latexes ranged from 100 to - 11degreesC. The film formation process of these latexes, after they were coated onto silicon substrates, was followed. The micrographs showed particle ordering, formation of consolidation fronts, air invasion during drying, particles deformation, film coalescence and skinning phenomena, illuminating important physics that govern the drying process of latex coatings. The bimodal systems consisted of latex blends of large, hard and small, soft particles. Cryo-SEM revealed how porous, permeable structures were created by drying these latex blends. The porous structures were modulated by drying rate, the volume ratio and size ratio of the two kinds of particles. Binder migration phenomenon was observed at higher drying rate. In addition to microstructure investigation, permeability and strength in tension of the porous films were separately measured, illustrating the basic trade-off between integrity and strength on one hand, porosity and permeability on the other. (C) 2004 Published by Elsevier B.V.

关键词： monodisperse latexes microstructure development Cryo-SEM

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microstructure development in drying latex coatings

Microstructure development in drying latex coatings

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29th Conference on Coatings Science and Technology

作者： Ma, Y Davis, HT Scriven, LE Univ Minnesota Dept Chem Engn & Mat Sci Minneapolis MN 55455 USA

关键词： monodisperse latexes microstructure development Cryo-SEM

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