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Surface gradients in cemented carbides from first-principles-based multiscale modeling: Atomic diffusion in liquid Co
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0002-9920-5393
2017 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 66, 174-179 p.Article in journal (Refereed) Published
Abstract [en]

The kinetic modeling of cemented carbides, where Co is used as binder element, requires a detailed diffusion description. Up to now, no experimental self- or impurity diffusion data for the liquid Co system have been available. Here we use the fundamental approach based on ab initio molecular dynamics simulations to assess diffusion coefficients for the liquid Co system, including six solute elements. Our calculated Co self-diffusion coefficients show good agreement with the estimates that have been obtained using scaling laws from the available literature data. To validate the modeling method, we performed one set of calculations for liquid Ni self-diffusion, where experimental data are available, showing good agreement between theory and experiments. The computed diffusion data were used in subsequent DICTRA simulations to model the gradient formation in cemented carbide systems. The results based on the new diffusion data allows for correct predictions of the gradient thickness.

Place, publisher, year, edition, pages
Elsevier Ltd , 2017. Vol. 66, 174-179 p.
Keyword [en]
Ab initio molecular dynamics, Cemented carbides, DICTRA, Diffusion, ICME, Liquid co, Calculations, Carbide tools, Carbides, Diffusion in liquids, Diffusion in solids, Liquids, Molecular dynamics
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-207284DOI: 10.1016/j.ijrmhm.2017.03.016Scopus ID: 2-s2.0-85016489381OAI: oai:DiVA.org:kth-207284DiVA: diva2:1111852
Note

QC 20170619

Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2017-09-18Bibliographically approved
In thesis
1. ICME guided development of cemented carbides with alternative binder systems
Open this publication in new window or tab >>ICME guided development of cemented carbides with alternative binder systems
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The development of alternative binder systems for tungsten carbide (WC) based cemented carbides has again become of relevance due to possible changes in EU regulations regarding the use of Cobalt (Co). A framework for the ICME (Integrated Computational Materials Engineering) based Materials Design is presented to accelerate the development of alternative binder systems.

Part one of this work deals with the design of the cemented carbide composite hardness. It has been shown that the intrinsic binder hardness is comparable to a bulk metal alloy and that based on the binder solubilities a solid solution strengthening model developed in this work can be employed. Using a method presented in this work the non-equilibrium, frozen-in binder solubilities can be obtained. Both the design of the binder phase and composite hardness is presented based on a general Materials Design approach.

Part two deals with a multiscale approach to model the surface gradient formation. The experimentally missing data on liquid binder diffusion has been calculated using AIMD (Ab initio Molecular Dynamics). The diffusion through the liquid cemented carbide binder has to be reduced to an effective diffusion value due to the solid carbides acting as obstacles that increase the diffusion path. The geometrical reduction of the diffusion has been investigated experimentally using the SIMS (secondary ion mass spectroscopy) technique in WC-Nickel-58Nickel diffusion couples. The geometrical contribution of the so-called labyrinth factor has been proven by the combination of the experiments and in conjunction with DICTRA simulations using the precise liquid AIMD diffusivities. Unfortunately, despite the improved kinetic database and the geometrical diffusion reduction, the surface gradient formation cannot be explained satisfactory in complex cemented carbide grades. Additional, but so far unidentified, contributions have to be considered to predict the surface gradient thickness.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 50 p.
Keyword
Cemented carbide, ICME, Materials Design, alternative binder, hardness, AIMD, liquid diffusion, frozen-in solubilities, DICTRA, surface gradients, labyrinth factor
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-214108 (URN)978-91-7729-511-2 (ISBN)
Public defence
2017-10-23, F3, Lindstedsvägen 26, Stockholm, 10:00 (English)
Opponent
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Note

QC 20170919

Available from: 2017-09-19 Created: 2017-09-18 Last updated: 2017-09-20Bibliographically approved

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Korzhavyi, Pavel A.

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