Theory of ultrathin films at metal–ceramic interfaces

Johansson, Sven; Wahnström, Göran

doi:10.1080/09500831003800863

Cited by 23 publications

(18 citation statements)

References 35 publications

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“…14) They also determined that this ultrathin layer would hinder W diffusion into or out of the WC grains. If such an ultrathin layer were to exist stably at the WC(0001) surface, it is believed that the WC grain growth would then be strongly inhibited compared with the other surface.…”

Section: Discussionmentioning

confidence: 99%

“…7,13) The slight variation in concentration seen between the two different cooling rates for the solid-state-sintered specimen does, however, suggest the presence of a segregation layer at 1473 K. The minimal grain growth during solid-state sintering could be caused by a strong restriction of the dissolution-reprecipitation of the WC phase due to the existence of the (V,W,Cr)C x segregation layer formed under increasing temperature. Based on a thermodynamic calculation by Johansson and Wahnström,14) the (V,W,Cr)C x phase would be expected to dissolve in the Co phase. Moreover, the fact that the WC grain size of the liquid-state-sintered specimen was larger than that of the solid-state-sintered specimen suggests that grain growth during liquid-state sintering is made possible by dissolution of the (V,W,Cr)C x layer on the WC surface formed under increasing temperatures, in addition to an increase in the sintering temperature.…”

Section: Discussionmentioning

confidence: 99%

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Segregation of Dopants at WC/Co and WC/WC Interfaces in Solid-State-Sintered WC-VC-Cr3C2-Co Cemented Carbides

Kawakami

Kitamura

2015

Mater. Trans.

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The segregation of V and Cr at WC/Co and WC/WC interfaces in ultrafine-grained WC-0.7VC-1.4Cr 3 C 2 -10Co (mass%) cemented carbides produced through solid-state sintering and semi-sintering was investigated. This segregation was compared against that of a liquid-statesintered specimen to elucidate the mechanism by which WC grain growth is inhibited by V and Cr. The V and Cr were found to segregate at the WC/Co and WC/WC interfaces during solid-state sintering and semi-sintering, but no differences were observed in the V and Cr concentrations at the interfaces among the liquid-state-sintered, solid-state-sintered and semi-sintered specimens. Furthermore, these concentrations were unchanged by quenching of the solid-state-sintered specimen. From these results, it was concluded that (V,W,Cr)C x segregation layers are stably formed at the WC/Co and WC/WC interfaces at a temperature below the solidus of the Co phase, but almost dissolve in the liquid Co phase once the temperature exceeds its liquidus. Thus, the (V,W,Cr)C x segregation layers observed at the WC/Co and WC/WC interfaces at room temperature are formed during the cooling that follows the liquid-state sintering. This supports the finding that WC grain growth is inhibited by the adsorption of dopant atoms onto steps/kinks on the WC surface during liquid-state sintering, as well as by the segregation layers formed on the WC surface during solid-state sintering.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Segregation of Dopants at WC/Co and WC/WC Interfaces in Solid-State-Sintered WC-VC-Cr3C2-Co Cemented Carbides

Kawakami

Kitamura

2015

Mater. Trans.

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“…69) Recently the existence of the (W,V)C X layers during liquid-phase sintering is confirmed by ab-initio calculations. 70) …”

Section: Interface Structural Change Induced By Dopant Segregationmentioning

confidence: 99%

Nano/sub-nano analysis based on high resolution transmission electron microscopy for ceramic materials

Yamamoto

2011

J. Ceram. Soc. Japan

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Grain boundaries, interfaces and surfaces are very attractive areas from the viewpoint of lattice discontinuity. Doped elements and point defects often segregate there, which largely changes bulk properties such as microstructure, mechanical strength, electrical conductivity. To understand the details of the dopant effects, it is necessary to use nano-scale analysis techniques based on transmission electron microscopy with energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy with nano/sub-nano electron probe. This review contains some nano-scale analysis studies performed in our research group for the grain size control of BaTiO 3 polycrystals, electrical properties across single grain boundaries of n-type BaTiO 3 , SrTiO 3 and ZnO, interface structural change of WCCo based cemented carbides and the preparation of novel dislocation nano-wires.Grain boundaries in BaTiO 3 sinters were revealed to exhibit grain boundary faceting by doping a very small amount of excess TiO 2 . The formation of the facets due to extra TiO 2 bonding is closely related to abnormal grain growth, which is often observed in TiO 2 -excess BaTiO 3 sinters. A similar faceting feature is also observed in VC-doped WCCo cemented carbides. Doped VC strongly segregates to WC/Co interfaces to form micro facets. The formation of the micro facets resulted in WC grain size reduction. In ZnO boundaries, doped Pr was revealed to segregate at the grain boundary. The segregated Pr ions are situated in specific atomic columns. Further, electron energy-loss spectroscopy has revealed that the valence of the segregated Pr ions is 3+, which means that they are not acceptors but donors to ZnO. The improvement of varistic effect observed in Pr-doped ZnO is closely related to Zn vacancies enhanced by Pr doping. Meanwhile, dislocations are a kind of one-dimensional lattice defect including extra half planes. By pipe-diffusion of dopants at dislocation cores, we can successfully develop conducting nano-wires in insulating sapphire crystals.

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“…For modeling of interfaces with complex bonding, DFT has proved its usefulness, 23,24 and the WC/Co interface has been previously studied by us with same method. 3,[25][26][27] In this paper, our previous modeling is extended by also including configuration free energies into an interface model which we explicitly couple with thermodynamic modeling of the W-C-Co-M system. Configuration free energies at finite temperatures are obtained from Monte Carlo (MC) simulations with interactions based on the cluster expansion (CE) method.…”

Section: Introductionmentioning

confidence: 99%

“…It has been well established that the appearance of certain interfacial "phases" different from those of the adjoining bulk phases (e.g., segregation structures, amorphous wetting films, etc.) can be understood from thermodynamic considerations; [1][2][3][4][5][6] the disparate interfacial phases are equilibrium states stabilized by the interface. The term "complexion" has been suggested to separate these interfacial phases from ordinary bulk phases.…”

Section: Introductionmentioning

confidence: 99%

First-principles study of an interfacial phase diagram in the V-doped WC-Co system

Johansson

Wahnström

2012

Phys. Rev. B

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We present a method of determining an interfacial phase diagram using density functional theory calculations for interface energetics. Cluster expansions based on these calculations are used in Monte Carlo simulations to obtain configurational free energies. The method is applied to study the segregation of V to the WC(0001)/Co interface and to construct the corresponding interface diagram, a "complexion" phase diagram. By CALPHADtype analysis for the adjoining bulk phases, a connection with real materials is made. We find that, in equilibrium, the interface contains a thin V-rich film for a wide range of temperatures and chemical potentials of V corresponding to V additions below the (V,W)C x solubility limit. The results are compared with available experimental data, and implications of the strong segregation of V for the sintering process of V-doped WC-Co are discussed.

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Theory of ultrathin films at metal–ceramic interfaces

Cited by 23 publications

References 35 publications

Segregation of Dopants at WC/Co and WC/WC Interfaces in Solid-State-Sintered WC-VC-Cr<sub>3</sub>C<sub>2</sub>-Co Cemented Carbides

Segregation of Dopants at WC/Co and WC/WC Interfaces in Solid-State-Sintered WC-VC-Cr<sub>3</sub>C<sub>2</sub>-Co Cemented Carbides

Nano/sub-nano analysis based on high resolution transmission electron microscopy for ceramic materials

First-principles study of an interfacial phase diagram in the V-doped WC-Co system

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