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- Bonvalet, M., et al.
(author)
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Modelling of prismatic grain growth in cemented carbides
- 2019
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In: International journal of refractory metals & hard materials. - : ELSEVIER SCI LTD. - 0263-4368. ; 78, s. 310-319
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Journal article (peer-reviewed)abstract
- A mean-field model dealing with prismatic grain growth during liquid phase sintering of cemented carbides with a Co-rich binder is presented. The evolution of the size of an assembly of non-spherical grains is obtained using a Kampmann-Wagner approach and by introducing a constant shape factor between the characteristic lengths of prisms. This factor is a function of interfacial energies of the two kind of facets, basal and prismatic, considered. The growth model is based on three different mechanisms, that can be rate limiting, taking place in series: 2D nucleation of a new atomic layer, mass transfer across the interface and long-range diffusion. The driving force for coarsening is distributed between the different facets. These equations are solved numerically, and the simulation results reveal that the specific abnormal grain growth phenomena experimentally observed in cemented carbides may be reproduced with this new more realistic description of the grain shape contrary to the spherical approach developed in the past. It is also shown that the initial powder size distribution, and more specifically its shape has a strong influence on the distribution of the driving force between the different rate limiting mechanisms and thus on the occurrence of abnormal grain growth. In that case, the self-similarity of the normalized grain size distribution over time is not achieved.
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- Gaisina, Vladilena, et al.
(author)
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An experimental investigation of the mechanical behavior of sintered Astaloy™ 85 Mo
- 2020
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In: Proceedings - Euro PM2020 Congress and Exhibition. - : European Powder Metallurgy Association (EPMA).
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Conference paper (peer-reviewed)abstract
- To examine the mechanical behavior of a sintered steel, Astaloy™ 85 Mo, an experimental investigation was conducted using uniaxial tensile testing. The samples analyzed were processed to varying amounts of porosity, as well as at different sintering times and temperatures. Test data is used to determine constitutive parameters and strength. The influence of porosity on these properties is discussed. In an ongoing effort to formulate constitutive models of the sintered material, additional testing (in particular uniaxial compressive and indentation testing) to determine, for example, the compressive yield behavior, is planned.
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| 6. |
- Lamelas, Victor, et al.
(author)
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Broadening of the carbon window and the appearance of core-rim carbides in WC-Fe/Ni cemented carbides
- 2024
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 999
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Journal article (peer-reviewed)abstract
- Among several separate challenges, the major one for replacing cobalt in cemented carbides is the difficulty to obtain alternative binder materials with a C-window broad enough to be robustly processed under conventional industrial control on the C content. The C-window is defined as the C content range for which phases that are detrimental to the mechanical properties are avoided. The present paper has two main objectives: first, to show that the processing C-window of Fe-Ni based systems is in fact wider than what thermodynamic equilibrium calculations predict, and that its width can be controlled moderately by tweaking the initial WC grain size and the cooling rate used in the material's processing. Secondly, in case those detrimental phases 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 η6-carbides at low C contents, are investigated to explore desirable combination 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 hexagonal lattice known as κ, not commonly seen in cemented carbides, appeared and formed the core of a core-rim structure together with the more common η6-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 the precipitation characteristics of the η6-phase.
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| 7. |
- Lamelas, Victor, et al.
(author)
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Microstructural stability of cemented carbides at high temperatures : Modeling the effect on the hot hardness
- 2024
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In: International journal of refractory metals & hard materials. - : Elsevier BV. - 0263-4368. ; 124
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Research review (peer-reviewed)abstract
- There are several semi-empirical models available in literature that correlate the intrinsic hardness of cemented carbides' constitutive phases and certain microstructural parameters, such as mean WC grain size and Co volume fraction, with the hardness of the cemented carbide. Nonetheless, such empirical relations fall short on predicting the behavior of materials other than WC-Co which they were fitted to, limiting their applicability on materials with diverse particle size distributions, alternative binder systems or with additional carbides (γ-carbides). Additionally, current models are limited to the prediction of room temperature hardness. Framed in an Integrated Computational Materials Engineering (ICME) approach, this work proposes several models to be integrated into an already validated semi-empirical approach to describe the hardness of cemented carbides as a function of temperature. First, new microstructural descriptors on the particle and binder size distributions are proposed to enable a better understanding of the influence of polydispersity and of the addition of γ-carbides on the hard-to-soft phase reinforcement. Second, a validated Peierls-Nabarro-based model is used to describe the intrinsic softening of the hard phases with temperature. And finally, the importance of the microstructural changes happening under stress at high temperatures is highlighted and its effect on hot hardness is introduced into the model. These upgrades increase the theoretical and physical base of the modeling tool providing a physical meaning to all the modeling parameters, lowering the need for numerical fitting, making the model more generic and bringing additional information into the micromechanics involved in the softening of cemented carbides.
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| 8. |
- Lamelas, Victor, et al.
(author)
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Modeling of the intrinsic softening of γ-carbides in cemented carbides
- 2023
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In: Materials Today Communications. - : Elsevier BV. - 2352-4928. ; 37
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Journal article (peer-reviewed)abstract
- Cemented carbides are widely used materials in industrial applications due to their remarkable combination of hardness and toughness. However, they are exposed to high temperatures during service leading to a reduction of their hardness. A common practice to damp this softening is to incorporate transition metal carbides in cemented carbide compositions, which keeps the hardness relatively higher when temperature increases. Understanding the underlying mechanisms of this softening is crucial for the development of cemented carbides with optimal properties. In this work, atomic-scale mechanisms taking place during plastic deformation are analyzed and linked to the effect that they have on the intrinsic macro-scale softening of the most common TMC used in cemented carbides grades (TiC, ZrC, HfC, VC, NbC and TaC). The proposed model uses the generalized stacking fault energy obtained from density functional theory calculations as an input to Peierls-Nabarro analytical models to obtain the critically resolved shear stress needed for deformation to occur in different slip systems. Subsequently, this information is used to predict the hardness variation across the temperature service range experienced by cemented carbides in wear applications. In addition to the prediction of hot-hardness for TMC, the obtained results also offer valuable insights into the intrinsic mechanisms governing TMCs deformation. The results facilitate the identification of dominant dislocation types influencing plasticity within distinct temperature regimes, define energetically favorable slip systems, and predict the brittle-ductile transition temperature in these materials. For instance, for group IV carbides at low temperatures, the slip system with a lower GSFE is {110}<11̅0> and around 30% of their melting temperature, the GSFE of partial slip in {111}<12̅1> becomes lower, changing the dominant slip mechanism and characterizing the Brittle-Ductile transition.
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| 9. |
- Lamelas, Victor, et al.
(author)
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Modelling of detrimental phases appearance in cemented carbides
- 2021
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In: Euro PM2021 Congress Proceedings. - : European Powder Metallurgy Association (EPMA).
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Conference paper (peer-reviewed)abstract
- Integrated Computational Materials Engineering (ICME) has proved to be an efficient tool for understanding the process-structure-properties relationships and help us design materials. In the case of cemented carbides, ICME can be used to study how well-established relationships are affected by new industry challenges, like the replacement of Co by alternative binder materials. The C-window is one of the most critical parameters in cemented carbides and is defined as the range in C-content for which phases detrimental to the mechanical properties are avoided. For alternative binder materials, the processing window may become very narrow, and a good understanding of its limits becomes crucial. The low-C side of the C-window is limited by the precipitation of η-carbides (M6C/M12C). Here, a systematic and integrated study on the formation of η-carbides as a function of binder chemical composition, cooling rate and microstructure is presented.
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| 10. |
- Lamelas, Victor, et al.
(author)
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Modelling the formation of detrimental phases in cemented carbides
- 2023
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In: Materials & design. - : Elsevier BV. - 0264-1275 .- 1873-4197. ; 228, s. 111823-
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Journal article (peer-reviewed)abstract
- Integrated Computational Materials Engineering (ICME) has proved to be an efficient tool for understand-ing the process-structure-property relationships and helping us to design materials. For instance, in cemented carbides manufacturing, one of the most critical parameters is the C-window. It is defined as the C content range for which phases detrimental to the mechanical properties are avoided. This pro-cessing window has been traditionally defined using applied thermodynamics methods. However, the deviation between equilibrium calculations and real manufacturing conditions requires big additional empirical efforts to precisely define the C-window. In this work, an ICME-based approach is proposed to redefine the processability limits of cemented carbides taking the cooling rate and the material's initial powder size into consideration. The method relies on the interactive coupling of several adapted models and tools, to not only set the processability boundaries, but also to study the complex mechanisms inter-play happening along microstructural evolution. A better understanding of these underlaying mecha-nisms leads to new inputs that can be used in the design of cemented carbides. In this regard, it is observed that faster cooling rates or coarser WC grades could be effectively used to prevent nucleation of the detrimental phases enlarging the C-window towards lower C contents.
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