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Towards computational materials design and upscaling of alternative binder cemented carbides
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.ORCID iD: 0000-0003-2754-6196
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing demands on economic, social and environmental sustainability throughout society is putting pressure on the development of new and improved materials for resource efficiency, improved component life-time and substitution of toxic or rare elements. For the cemented carbide industry, as a major provider of tools for e.g. mining and metal cutting which are integral parts of many production chains, this may require complete or partial substitution of cobalt. Cobalt ore is primarily mined in conflict regions and cobalt powder has been shown to be carcinogenic upon inhalation. Substitution of this element could therefore have significant impact on several aspects of society. However, it is far from trivial to substitute this critical element in cemented carbide production. Nearly a century of materials and product development has made state-of-the-art cemented carbides with cobalt binder phase one of the most successful engineering materials. Over the years, accumulated investments throughout the supply chain has made these materials indispensable in industrial production. When envisioning cobalt substitution, it is therefore critical to generate new methods for accelerated materials development and standardised materials qualification. This will enable faster and more reliable development of new materials with the potential to substitute cobalt throughout the industry.

The present thesis is focused on the continued development of an integrated computational materials engineering framework for materials design as well as the development of quality control methods for alternative binder cemented carbides. The existing computational framework is here extended with a model for fracture toughness which allows for property trade-off between hardness and toughness. The extended framework is shown to replicate experimentally well-established property combinations and is thereby applicable for computational design of cemented carbides for specific applications. Furthermore, conventional quality control methods based on magnetic properties are evaluated and further developed for alternative binder cemented carbides. Combining these results on computational materials design and the steps towards standardised quality control has the potential to greatly accelerate future development of cemented carbides, both for cobalt substitution and for improved component life-time.

Abstract [sv]

Ökande krav på ekonomisk, social och miljömässig hållbarhet i samhället sätter press på utvecklingen av nya och förbättrade material för resurseffektivitet, ökad komponentlivslängd och substitution av toxiska ämnen. Inom hårdmetallindustrin, som producerar verktyg till exempelvis gruvbrytning och metallbearbetning vilket är centrala delar av många produktionskedjor, kan detta kräva total eller partiell substitution av kobolt. Koboltmineral utvinns huvudsakligen i konfliktregioner och koboltpulver har visats vara cancerogent vid inhalering. Koboltsubstitution kan därför ha betydande effekt på flera aspekter av samhället. Det är däremot långt ifrån trivialt att ersätta en så central komponent i hårdmetallproduktion. Närmare ett århundrande av material- och produktutveckling har gjort modern hårdmetall med kobolt som bindefas till ett av de mest framgångsrika materialen. Genom åren har ackumulerade investeringar genom hela leverantörskedjan gjort dessa material oumbärliga inom industriell produktion. I samband med visionen om koboltsubstituton är det därför kritsikt att generera nya metoder för accelererad materialutveckling och standardiserad materialkvalificering. Detta skulle medföra snabbare och mer tillförlitlig utveckling och introduktion av nya material med potential att ersätta kobolt genomgående i industrin. 

Den här avhandlingen fokuserar på fortsatt utvekling av ett beräkningsbaserat ramverk för materialdesign enligt konceptet ”Integrated Computational Materials Engineering” samt utvecklingen av metoder för kvalitetskontroll av hårdmetall med alternativa bindefaser. Den existerande beräkningsplattformen utvecklas vidare med en modell för brottseghet. Detta medför möjligheten att med hjälp av beräkningar göra avvägningar mellan hårdhet och seghet genom design av mikrostrukturen. Det utökade ramverket påvisas upprepa empiriskt väletablerade samband mellan mikrostruktur och mekansika egenskaper och kan därmed tillämpas för beräkningsbaserad materialdesign av hårdmetall för specifika tillämpningar. Utöver detta utvärderas tillämpbarheten av konventionella metoder för kvalitetskontroll, baserade på magnetiska egenskaper, för hårdmetall med alternativa bindefaser. En kombination av resultaten kring beräkningsbaserad materialdesign och stegen mot standardiserad kvalitetskontroll har potential att accelerera framtida utveckling av hårdmetall, både för koboltsubstitution och förbättrad materiallivslängd.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. , p. 160
Series
TRITA-ITM-AVL ; 2020:5
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-266818ISBN: 978-91-7873-433-7 (print)OAI: oai:DiVA.org:kth-266818DiVA, id: diva2:1388274
Public defence
2020-02-21, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2020-01-31 Created: 2020-01-24 Last updated: 2020-01-31Bibliographically approved
List of papers
1. Indentation behavior of highly confined elasto-plastic materials
Open this publication in new window or tab >>Indentation behavior of highly confined elasto-plastic materials
(English)In: Article in journal (Refereed) Accepted
Abstract [en]

The effect of geometric confinement is well-known from hardness measurements of thin films on stiff substrates and has been modeled both phenomenologically and using e.g. Finite Element Analysis. However, these models are mainly focused on a specific experiment or a certain material family. In the present work, Finite Element Analysis is used to gain a better understanding of the interplay between geometric constraints in various microstructures and a wide range of materials properties. It is shown that a very simple model can be used to replicate thin film hardness data where the film is softer than the substrate as well as how materials properties alter the indentation behavior of materials confined in one to three dimensions. It is shown that qualitative agreement with nanoindentation of the metallic binder phase in the complex 3D-microstructure of a cemented carbide is achieved using an axisymmetric “pill-box” model with classical plasticity. It is also shown that the effect of higher-order confinement can be described by the Korsunsky thin film hardness model by re-optimizing the fitting parameters. 

Keywords
Nanoindentation; Hardness; Composite; Finite Element Analysis; Complex microstructure;
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-266817 (URN)
Note

QC 20200124

Available from: 2020-01-24 Created: 2020-01-24 Last updated: 2020-01-24Bibliographically approved
2. Modeling confined ductile fracture – a void-growth and coalescence approach
Open this publication in new window or tab >>Modeling confined ductile fracture – a void-growth and coalescence approach
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

In a composite material a soft, ductile matrix can be confined by a hard, brittle phase, altering its deformation and fracture behavior. Increasing confinement leads to embrittlement of the matrix and, in turn, also the composite. From a materials design perspective, it is usually desired to avoid brittle fracture without compromising the hardness of the material. Understanding confined ductile fracture is therefore critical for modeling the mechanical response of composite materials with fine microstructure. The present work is focused on confined ductile fracture of a thin ductile film, with elasto-plastic power-law hardening behavior, sandwiched between ideal linear elastic substrates. Fracture of the ductile layer is modeled by growth and coalescence of prescribed voids in 2D. Influences of material properties, initial void volume fraction, geometric constraints and elastic mismatch are investigated. The results show a loss of ductility with decreasing film thickness that is accompanied by a severe decrease in fracture initiation toughness as well as an increased stress at the interface. The influence of materials properties is significant in all cases while the effect of initial void volume fraction is comparatively less critical for highly confined materials than for bulk materials. Increasing confinement also results in increasing normal stress at the phase interface, promoting interface decohesion prior to ductile fracture of the film. The present approach and results are a step towards more detailed prediction of composite fracture toughness and crack-growth resistance.

Keywords
Confined ductile fracture; Void-growth and coalescence; Composite material; Fracture toughness; Finite element modeling;
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-266815 (URN)
Note

QC 20200129

Available from: 2020-01-24 Created: 2020-01-24 Last updated: 2020-01-29Bibliographically approved
3. An energy release rate approach to cemented carbide fracture toughness for computational materials design
Open this publication in new window or tab >>An energy release rate approach to cemented carbide fracture toughness for computational materials design
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Integrated computational materials engineering and computational materials design have the potential to greatly accelerate materials development at reduced cost compared to conventional experimentally-based methods. These methodologies, however, require physically-based property models to be truly predictive. Fracture toughness is a critical material property of cemented carbides for high-performance mining and metal cutting tools. In the present work, a fracture toughness model framework based on the energy release rate formalism is presented and applied to conventional and alternative-binder cemented carbides. The framework is physically-based and designed to be modular, where each sub-model can be independently modified or replaced without disturbing the calculation-flow of the overall framework. In the presented examples, the sub-models are based on e.g. finite element simulations and atomistic calculations as well as limited calibration to experimental data. The model framework is intended for integration with previously developed computational tools and models, such as a composite hardness model and a grain growth model, for computational design of novel and improved cemented carbides with the aim to potentially substitute cobalt as the dominating binder phase in cemented carbides.

Keywords
Fracture toughness; Energy release rate; Composite; Computational materials design; Cemented carbide;
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-266816 (URN)
Note

QC 20200129

Available from: 2020-01-24 Created: 2020-01-24 Last updated: 2020-01-29Bibliographically approved
4. Effect of carbon content on the Curie temperature of WC-NiFe cemented carbides
Open this publication in new window or tab >>Effect of carbon content on the Curie temperature of WC-NiFe cemented carbides
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2019 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 78, p. 27-31Article in journal (Refereed) Published
Abstract [en]

We have investigated the effect of the carbon content on the Curie temperature of a cemented carbide composite material with a Ni-Fe alloy as the binder phase and WC as the hard phase. In the carbon concentration range from 5.72 to 5.83 wt% carbon, which covers the interval where WC coexists with fcc Ni-Fe without other phases (the ‘carbon window’), the Curie temperature rises from 200 to 527 °C. This result indicates the possibility to use the Curie temperature to determine the carbon balance in the system. With thermodynamic calculations and kinetic simulations we can quantitatively establish the correlation between the carbon and tungsten content of the binder phase and the Curie temperature. This strong compositional effect on the Curie temperature is quantitatively very different from the conventional Co-based cemented carbides, with Curie temperatures of about 950–1050 °C.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Alternative binder, Carbon window, Cemented carbide, Curie temperature, Hard metals, Binary alloys, Binders, Carbide tools, Carbides, Cobalt compounds, Iron alloys, Nickel alloys, Carbon concentrations, Cemented carbide composites, Cemented carbides, Compositional effects, Effect of carbons, Kinetic simulation, Thermodynamic calculations, Temperature
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-236334 (URN)10.1016/j.ijrmhm.2018.08.010 (DOI)000451489300003 ()2-s2.0-85052282006 (Scopus ID)
Note

QC 20181109

Available from: 2018-11-09 Created: 2018-11-09 Last updated: 2020-01-24Bibliographically approved
5. A comparative study of microstructure and magnetic properties of a Ni–Fe cemented carbide: Influence of carbon content
Open this publication in new window or tab >>A comparative study of microstructure and magnetic properties of a Ni–Fe cemented carbide: Influence of carbon content
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2019 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 80, p. 181-187Article in journal (Refereed) Published
Abstract [en]

Due to the renewed interest in alternative binders for cemented carbides it is important to understand how the binder composition influences not only mechanical properties but also the microstructure and related measurements for quality control. Microstructure and chemical composition of WC-Co is often evaluated by magnetic measurements. However, when the binder composition deviates significantly from conventional Co-based binders it should not be assumed that the standard measurements can be used to directly evaluate the same parameters. In this paper we investigate the influence of relative C-content on the microstructure and magnetic properties of an alternative binder cemented carbide. It is shown that the saturation magnetization is related to the relative C-content and the magnetic coercivity is related to the microstructure, more specifically to the binder phase distribution, but could not be directly linked to the carbide grain size in the same manner as for standard WC-Co. Furthermore, a direct correlation between Curie temperature and saturation magnetization is observed for this system which means that the Curie temperature potentially could be used for calibration of empirical relations or as a method to accurately determine the binder volume fraction.

Place, publisher, year, edition, pages
Elsevier Ltd, 2019
Keywords
Alternative binder, Cemented carbide, Cermet, Cobalt substitution, Magnetic properties, Metal-matrix composite, Microstructure
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-246465 (URN)10.1016/j.ijrmhm.2019.01.014 (DOI)000460992100018 ()2-s2.0-85060087544 (Scopus ID)
Note

QC 20190326

Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2020-01-24Bibliographically approved

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