| 1. |
- Lamelas, Victor, et al.
(författare)
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Broadening of the carbon window and the appearance of core-rim carbides inWC-Fe/Ni cemented carbides.
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Among several separate challenges, the major one for replacing cobalt in cemented carbides is the difficulty to obtain alternative binder materials witha C-window broad enough to be robustly processed under conventional industrial control on the C content. The C-window is defined as the C contentrange for which phases that are detrimental to the mechanical properties are avoided. The present paper has two main objectives: first, to show that theprocessing C-window of Fe-Ni based systems is in fact wider than what thermodynamic equilibrium calculations predict, and that its width can becontrolled moderately by tweaking the initial WC grain size and the cooling rate used in the material’s processing. Secondly, in case those detrimentalphases are not avoided, this work gives insight on how to make their appearance less detrimental for the mechanical properties. The morphology,volume fraction and particle size distribution of the detrimental phases, specifically η-carbides at low C contents, are investigated to explore desirablecombination of hardness and toughness of alternative binder cemented carbides.During this study it was also discovered that in samples with carbon contents below the low-C limit of the C window a carbide with hexagonallattice known as κ, not commonly seen in cemented carbides, appeared and formed the core of a core-rim structure together with the more common η-phase. It is believed that the κ-carbide form due to local high concentrations of tungsten during solid state sintering and that it has an impact on theprecipitation characteristics of the η-phase.
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| 2. |
- Lamelas, Victor, et al.
(författare)
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Microstructural stability of cemented carbides at high temperatures: modelingthe effect on the hot hardness
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- There are several semi-empirical models available in literature that correlate the intrinsic hardness of cemented carbides’ constitutive phases and certainmicrostructural parameters, such as mean WC grain size and Co volume fraction, with the hardness of the cemented carbide. Nonetheless, suchempirical relations fall short on predicting the behavior of materials other than WC-Co which they were fitted to, limiting their applicability on materialswith diverse particle size distributions, alternative binder systems or with additional carbides (γ-carbides). Additionally, current models are limited tothe prediction of room temperature hardness. Framed in an Integrated Computational Materials Engineering (ICME) approach, this work proposesseveral models to be integrated into an already validated semi-empirical approach to describe the hardness of cemented carbides as a function oftemperature. First, new microstructural descriptors on the particle and binder size distributions are proposed to enable a better understanding of theinfluence of polydispersity and of the addition of γ-carbides on the hard-to-soft phase reinforcement. Second, a validated Peierls-Nabarro-based modelis used to describe the intrinsic softening of the hard phases with temperature. And finally, the importance of the microstructural changes happeningunder stress at high temperatures is highlighted and its effect on hot hardness is introduced into the model. These upgrades increase the theoretical andphysical base of the modelling tool providing a physical meaning to all the modeling parameters, lowering the need for numerical fitting, making themodel more generic and bringing additional information into the micromechanics involved in the softening of cemented carbides.
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| 3. |
- Linder, David, et al.
(författare)
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An energy release rate approach to cemented carbide fracture toughness for computational materials design
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- Linder, David, et al.
(författare)
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Indentation behavior of highly confined elasto-plastic materials
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Linder, David, et al.
(författare)
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Indentation behavior of highly confined elasto-plastic materials
- 2020
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Ingår i: International Journal of Solids and Structures. - : Elsevier. - 0020-7683 .- 1879-2146. ; 193-194, s. 69-78
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Linder, David, et al.
(författare)
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Martensite transformation in cemented carbides with alternative binders
- 2016
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Ingår i: World PM 2016 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA). - 9781899072484
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Konferensbidrag (refereegranskat)abstract
- The recent interest in substitution of cobalt in cemented carbides has led to renewed efforts into finding alternative binders. Promising candidates are Fe and Ni-based systems which generally can be divided into austenitic (fcc) and martensitic (bct) binders. The martensitic transformation may drastically change the properties, thus, when designing an alternative binder it is important to know at what temperature and composition the martensitic transformation takes place. Furthermore, it is of interest to understand how the transformation is affected by the binder mean free path and the stresses in the binder introduced by the carbide grains. Another aspect, that is important for high temperature properties, is the tempering of martensite as well as reversion to austenite. The effect of these processes is here investigated along with how they influence the behavior of the cemented carbides at different temperatures, thereby determining their application range.
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| 7. |
- Linder, David, et al.
(författare)
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Modeling confined ductile fracture – a void-growth and coalescence approach
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 8. |
- Linder, David, et al.
(författare)
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Modeling confined ductile fracture - A void-growth and coalescence approach
- 2020
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Ingår i: International Journal of Solids and Structures. - : Elsevier BV. - 0020-7683 .- 1879-2146. ; 202, s. 454-462
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Pinomaa, T., et al.
(författare)
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The significance of spatial length scales and solute segregation in strengthening rapid solidification microstructures of 316L stainless steel
- 2020
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Ingår i: Acta Materialia. - : Acta Materialia Inc. - 1359-6454 .- 1873-2453. ; 184, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser melting (SLM) can produce outstanding mechanical properties in 316L stainless steel. Nonetheless, the technique can lead to considerable variation in quality. This reflects an incomplete understanding and control of the process-structure-properties linkage. This paper demonstrates how length-scale informed micromechanical behavior can be linked to solidification microstructures and how these structures depend on SLM process conditions. This linkage is produced by sequential phase field and crystal plasticity simulations. Rapid solidification is described with a recent quantitative phase field model with solute trapping kinetics, where a range of process conditions are considered in terms of thermal gradients and pulling speeds. The predicted morphological transitions (dendritic-cellular-planar) are consistent with experiments, including segregation-free microstructures, which emerge in planar growth conditions. The predicted cell spacing vs. cooling rate data are also consistent with experiments. The simulated cellular structures produced through phase field modeling are then analyzed with a Cosserat crystal plasticity model with calibrated length-scale and hardening effects and with a solid solution strengthening description that depends on the local microsegregation. It is found that the length scale characteristics and solute segregation greatly influence the overall hardening behavior and affect plastic localization and the evolution of geometrically necessary dislocation (GND) type hardening. Our results suggest that the material strength of SLM 316L steel is more sensitive to cell spacing (microstructural length scale) than to the magnitude of solute segregation. Pulling speed (solidification velocity) is identified as the main process condition determining the material micromechanical behavior. Further analysis of idealized polycrystalline structures demonstrated that plastic incompatibilities and subgrain cell interactions with grain boundaries lead to notable strengthening. The presented sequential phase field-crystal plasticity modeling scheme is a proof-of-concept for systematically investigating and discovering new compositions, process conditions and microstructures for SLM.
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| 10. |
- Walbrühl, Martin, et al.
(författare)
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A new hardness model for materials design in cemented carbides
- 2018
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Ingår i: International journal of refractory metals & hard materials. - : Elsevier. - 0263-4368. ; 75, s. 94-100
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Tidskriftsartikel (refereegranskat)abstract
- The Materials Design approach offers new possibilities towards property-oriented materials development. The performance of cemented carbides is significantly influenced by properties like the hardness and fracture toughness. Fundamentally based phenomenological models, which allow for prediction of the properties of interest, make it possible to tailor the properties of the material based on the required performance. None of the previously available models are suitable to actively design the cemented carbide hardness because they are valid only for Co binders and do not allow alternative binder phases. The hardness is greatly influenced by the chemistry, binder volume fraction and carbide grain size. Only the chemistry, specifically the binder composition, leaves the possibility to optimize the binder hardness and to exceed classical WC-Co cemented carbides. Specifically focusing on the design of the binder phase, a new binder hardness description is implemented in a modified Engqvist hardness model and allows description of a wider range of conventional and alternative systems. The model was validated for various published cemented carbide systems and is able to predict their hardness within a 10% error. The assessed systems contain classical Co binders as well as alternative, austenitic binders based on Fe, Ni and Co.
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