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Effective diffusion in cemented carbide systems: Geometrical effect of the labyrinth factor
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
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(Engelska)Manuskript (preprint) (Övrigt vetenskapligt)
Abstract [en]

In cemented carbides the effective diffusivities are associated with the carbides acting as obstacles that increase the diffusion distance, thus altering the overall diffusion in the composite. From an industrial point of view, the prediction of the surface gradient formation is important to develop state-of-the-art cemented carbide cutting tools and require an understanding of the liquid binder diffusivities and the effective diffusion reduction at typical sintering temperatures where the binder is molten. Recently, a full description of the diffusivities in the liquid binder has become available and the focus of the present work is thus the effective diffusion reduction. Isotope diffusion couple experiments have been successfully performed to investigate the effective diffusion in a WC-Ni liquid binder-carbide composite material, i.e. a cemented carbide. The 58Ni isotope diffusion profiles have been measured with Secondary Ion Mass Spectroscopy (SIMS) and the results have been compared to DICTRA simulations using an updated kinetic database. The agreement between the experimental and simulated diffusion profiles is excellent showing that the theoretical geometrical limit, simulated with the upper Hashin-Shtrikman bound, is obeyed in simple cemented carbide systems. For complex cemented carbide systems, where gradient sintering is relevant, the effective diffusion is insufficiently explained by the geometrical reduction.

Nationell ämneskategori
Metallurgi och metalliska material
Identifikatorer
URN: urn:nbn:se:kth:diva-214105OAI: oai:DiVA.org:kth-214105DiVA, id: diva2:1140282
Anmärkning

QC 20170919

Tillgänglig från: 2017-09-11 Skapad: 2017-09-11 Senast uppdaterad: 2017-09-19Bibliografiskt granskad
Ingår i avhandling
1. ICME guided development of cemented carbides with alternative binder systems
Öppna denna publikation i ny flik eller fönster >>ICME guided development of cemented carbides with alternative binder systems
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH Royal Institute of Technology, 2017. s. 50
Nyckelord
Cemented carbide, ICME, Materials Design, alternative binder, hardness, AIMD, liquid diffusion, frozen-in solubilities, DICTRA, surface gradients, labyrinth factor
Nationell ämneskategori
Metallurgi och metalliska material
Forskningsämne
Teknisk materialvetenskap
Identifikatorer
urn:nbn:se:kth:diva-214108 (URN)978-91-7729-511-2 (ISBN)
Disputation
2017-10-23, F3, Lindstedsvägen 26, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Anmärkning

QC 20170919

Tillgänglig från: 2017-09-19 Skapad: 2017-09-18 Senast uppdaterad: 2017-09-20Bibliografiskt granskad

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Walbrühl, MartinÅgren, JohnLarsson, Henrik

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