| 1. |
- Fors, Dan, 1982, et al.
(författare)
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Theoretical investigation of moderate misfit and interface energetics in the Fe/VN system
- 2010
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Ingår i: Computational Materials Science. - : Elsevier BV. - 0927-0256. ; 50:2, s. 550-559
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Tidskriftsartikel (refereegranskat)abstract
- In this study an ab initio based approach to determine the effect of moderate misfit on energies and structures for interfaces is presented and applied to the Fe(0 0 1)/VN(0 0 1) system. The interface energetics of the coherent and semicoherent structures of thin VN films in Fe is investigated in order to determine how the misfit is taken up. The coherent interface is directly treated with ab initio calculations, whereas the semicoherent interface energy is accessed by using a Peierls-Nabarro framework, in which ab initio data for chemical interactions across the interface is combined with a continuum description to account for the elastic distortions. The continuum treatment is here extended to thoroughly account for the anisotropy in the materials. Our approach shows that the elastic contribution to the total interface energy dominates for both the coherent and semicoherent structure and must therefore be accurately accounted for in the interface description. Further, the Peierls-Nabarro framework for the semicoherent interface is evaluated by comparing a full scale two-dimensional solution to one-dimensional approximations. We show that the one-dimensional treatment is sufficient in the present case for accurate results, and consequently interactions at dislocation intersections at the interface do not have to be considered. © 2010 Elsevier B.V. All rights reserved.
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| 2. |
- Johansson, Sven, 1981, et al.
(författare)
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A computational study of special grain boundaries in WC–Co cemented carbides
- 2015
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Ingår i: Computational Materials Science. - : Elsevier BV. - 0927-0256. ; 98, s. 345-353
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we model Sigma = 2 and Sigma = 1 {10 (1) over bar0}parallel to{10 (1) over bar0} WC/WC boundaries in WC-Co using density functional theory (DFT). In particular, the misfit structure of the Sigma = 2 twist boundary is modeled explicitly with a previously developed Peierls-Nabarro model for misfit dislocations. The grain boundary energy of the twist boundary is found to be 0.7 J/m(2), which is small in comparison with energies of general WC/WC boundaries. The misfit structure can be described as a square network of screw dislocations with Burgers vectors 1/6 . Our calculations show that Co will not segregate to the Sigma = 2 twist boundary, which contrasts with predictions for other WC/WC boundaries that typically give half a monolayer of segregated Co.
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| 3. |
- Petisme, Martin, 1981, et al.
(författare)
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A computational study of interfaces in WC-Co cemented carbides
- 2015
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Ingår i: Modelling and Simulation in Materials Science and Engineering. - : IOP Publishing. - 1361-651X .- 0965-0393. ; 23:4, s. 045001-
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Tidskriftsartikel (refereegranskat)abstract
- Interfaces in WC-Co cemented carbides have been investigated using the density functional theory (DFT). Six different model WC/WC grain boundaries are considered, together with the corresponding WC surfaces and WC/Co phase boundaries. The contribution to the grain boundary energies arising from misfit is estimated using an analytical bond order potential (ABOP) and the effect of magnetism is investigated using spinpolarized and non-spinpolarized calculations. A systematic study of adsorption of Co to WC surfaces, Co segregation to WC/WC grain boundaries and Co substitution at WC/Co phase boundaries has been carried out. Adsorption of Co to most WC surfaces is predicted, and result in a monolayer coverage of Co and sometimes a mixed Co/W or Co/W monolayer. The WC surfaces will become prewetted with Co as soon as the atoms become mobile at finite temperatures. Co substitutional segregation is predicted to all model WC/WC grain boundaries in 0.5 monolayer proportion. The segregation of Co to grain boundaries stabilizes the continuous skeleton network of hard WC grains in cemented carbides. Using the obtained interfacial energies, the wetting and the driving force for cobalt grain boundary infiltration are discussed. A dependence on the wetting efficiency on the carbon chemical potential is predicted, which could be an explanation for the better wetting observed experimentally under W-rich conditions.
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| 4. |
- Petisme, Martin, 1981, et al.
(författare)
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Molecular dynamics simulation of WC/WC grain boundary sliding resistance in WC–Co cemented carbides at high temperature
- 2015
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Ingår i: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 49:1, s. 75-80
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Tidskriftsartikel (refereegranskat)abstract
- Grain boundary sliding is thought to be an important deformation mechanism in WC-Co based cemented carbides at high temperature. It has been assumed that when the WC skeleton breaks up and grain boundaries are infiltrated by Co, sliding is facilitated. In this work, molecular dynamics simulations with classical interatomic potentials were used to perform simulations of grain boundary sliding at two model WC/WC grain boundaries. Shear stresses were calculated for different numbers of Co layers in the grain boundary at the constant sliding velocity 10 m/s for T = 500 K, 1000 K, 1500 K, and 2000 K. It was found that in all considered cases, about 6 layers of Co in the grain boundary were sufficient to significantly facilitate sliding. The shear stresses that were obtained are an order of magnitude lower with a Co film (>= 6 layers) compared to the most stable configurations containing half a monolayer of Co for T
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| 5. |
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| 6. |
- Petisme, Martin, 1981
(författare)
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Atomistic modeling of interfaces in WC-Co cemented carbides
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Grain and phase boundaries are crucial in understanding the properties of real materials. In this thesis, interfaces in WC–Co cemented carbide are modeled atomistically using density functional theory (DFT) and analytic interatomic potentials. WC-Co is a strong and tough material of great technological importance, which is used for metal cutting, rock drilling, and various other applications. e material consists of the refractory carbide WC cemented in a ductile Co binder and is produced by liquid phase sintering of milled powders.Special and general WC/WC grain boundaries in cemented carbides are studied using DFT. The special Sigma = 2 twist grain boundary, the most frequently observed grain boundary, is studied in detail using a Peierls-Nabarro model combining DFT with elasticity theory. is grain boundary is predicted to have a low energy of about 0.7 J/m2 and be free from Co segregation, in agreement with experimental observations.For models of more general grain boundaries, DFT calculations predict larger grain boundary energies, on average 2.3 J/m2. e grain boundaries are also predicted to contain 0.5 monolayers of Co, in accord with atom probe measurements. WC and Co surfaces and WC/Co phase boundaries are also considered, and it is found that most WC surfaces should become pre-wetted with a full Co monolayer or a mixed Co/C or Co/W monolayer. e calculated interface energies are used to discuss the wetting of WC by Co, and a dependence on the carbon chemical potential is predicted, which is a potential explanation for the better wetting observed experimentally under W-rich conditions.Segregation of Mn, Fe, Co, Ni, Ti, V, Cr, Zr, Nb, and Ta, to WC/WC grain boundaries is further investigated. Fe, which is used as a binder phase in cemented carbides, is found to segregate in 0.5 monolayer proportion and have a strengthening effect on grain boundaries similar to Co. It is predicted that Ti and V may segregate to grain boundaries as monolayer thick cubic TiC and VC films of NaCl structure, and VC film segregation is found to have a potentially embrittling effect on grain boundaries.Lastly, WC/WC grain boundary sliding, which is believed to be an important high-temperature deformation mechanism in WC-Co, is investigated. An analytic interatomic potential describing WC-Co is developed and sliding simulations of two model grain boundaries show that the Co infiltration of grain boundaries lowers the required stresses by an order of magnitude in the solid state.
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