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Inverse Saltykov analysis for particle-size distributions and their time evolution
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-7656-9733
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.ORCID iD: 0000-0002-4521-6089
2011 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 59, no 3, 874-882 p.Article in journal (Refereed) Published
Abstract [en]

In this work a new method for transforming 2-D to 3-D size distributions is proposed. A representation of the 2-D size distributions is constructed from the data of measured radii with a statistical method called the kernel density estimator. The method yields a smooth density estimation that is more accurate than the classic histogram. The 3-D distribution is optimized from the 2-D density estimate in an iterative manner. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
2011. Vol. 59, no 3, 874-882 p.
Keyword [en]
Grain size, Image analysis, 3-D distribution, Carbides
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-30977DOI: 10.1016/j.actamat.2010.09.046ISI: 000286690100003Scopus ID: 2-s2.0-78650680735OAI: oai:DiVA.org:kth-30977DiVA: diva2:402863
Note
QC 20110310Available from: 2011-03-10 Created: 2011-03-07 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Simulation of Phase Transformations and coarsening: Computational tools for alloy development
Open this publication in new window or tab >>Simulation of Phase Transformations and coarsening: Computational tools for alloy development
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The final properties of an alloy are highly interlaced with its microstructure. It is therefore essential to control the evolution of the microstructure of the material during the fabrication process. Nowadays, materials design involves an increasing part of computational design to complement the traditional experimental trial and error approach. Such simulations of the process can decrease the number of material prototypes and shorten the development time for new alloys.

In this thesis several microstructure models, aimed for process design, have been suggested. The ambition has been to develop physically based models that are capable to represent the evolution of hundreds of grain or particle sizes, where the models should be possible to run on a standard computer with simulation times less than one day. To achieve this goal, simplified approaches have been suggested, which are accurate enough for the growth rate of grains and particles. The microstructure models have all in common that size distributions of grains or particles are simulated with mean-field approaches. Several of the models also utilize composition and temperature dependent thermodynamic and kinetic properties continually throughout the simulations. These properties have been calculated with programming interfaces to Thermo-Calc and DICTRA together with appropriate thermodynamic and kinetic databases. The materials that have been considered in the present thesis are low alloyed steels, aluminium alloys and cemented carbides. The models are however generic in the sense that all materials can be handled if appropriate thermodynamic, kinetic and property databases exist for the alloy.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. iv, 40 p.
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-31454 (URN)978-91-7415-891-5 (ISBN)
Public defence
2011-03-25, F3, Lindstedtsvägen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
QC 20110316Available from: 2011-03-16 Created: 2011-03-16 Last updated: 2011-03-16Bibliographically approved
2. WC grain growth during sintering of cemented carbides: Experiments and simulations
Open this publication in new window or tab >>WC grain growth during sintering of cemented carbides: Experiments and simulations
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cemented carbides are composite materials consisting of a hard carbide and a ductile binder. They are powdermetallurgically manufactured, where liquid-phase sintering is one of the main steps. The most common cemented carbide consists of WC and Co and it is widely used for cutting tools. Two of the most important factors controlling the mechanical properties are the WC grain size and the grain size distribution and thus it is of great interest to understand the grain growth behavior.

In this thesis the grain growth during sintering at 1430 °C is studied both experimentally and through computer simulations. The grain growth behavior in cemented carbides cannot be explained from the classical LSW-theory. The WC grains have a faceted shape necessitating growth by 2-D nucleation of new atomic layers or surface defects. A new model based on 2-D nucleation, long-range diffusion and interface friction is formulated.

Three powders having different average sizes are studied and both experiments and simulations show that a fine-grained powder may grow past a coarse-grained powder, indicating that abnormal grain growth has taken place in the fine-grained powder. Fine-grained powders with various fractions of large grains are also studied and it is seen that a faster growth is obtained with increasing fraction of large grains and that an initially slightly bimodal powder can approach the logaritmic normal distribution after long sintering times.

The grain size measurements are performed on 2-D sections using image analysis on SEM images or EBSD analysis. Since the growth model is based on 3-D size distributions the 2-D size distributions have to be transformed to 3-D, and a new method, Inverse Saltykov, is proposed. The 2-D size distribution is first represented with kernel estimators and the 3-D size distribution is optimized in an iterative manner. In this way both negative values in the 3-D size distribution and modifications of the raw data are avoided.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. vii, 42 p.
Keyword
Cemented carbide, Grain growth, Abnormal grain growth, Image analysis, Modeling, 3-D grain size distribution, Inverse Saltykov
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-32430 (URN)978-91-7415-915-8 (ISBN)
Public defence
2011-05-16, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20110426Available from: 2011-04-26 Created: 2011-04-14 Last updated: 2011-04-26Bibliographically approved

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