Stacking Faults in a Non‐Stoichiometric Face‐Centred Cubic TaC

Martin, J.L.; Jouffrey, B.; Costa, P.

doi:10.1002/pssb.19670220202

Cited by 20 publications

(10 citation statements)

References 10 publications

(2 reference statements)

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“…1. This carbon-depleted fault notation concept is important as faults are often observed in these materials (Martin et al, 1967;Rowcliffe & Thomas, 1975;Lewis et al, 1972;Morris et al, 2012Morris et al, , 2013Yu, Guziewski et al, 2016; and it establishes the often-used -M 4 C 3 notation for this phase. Yvon and Parthé found substantial deviations from this ideal chemistry as the vanadium carbide zeta phase was near VC 0.67 , and consequently the phase is more often denoted -M 4 C 3Àx to indicate the off-stoichiometry of the zeta phase.…”

Section: Introductionmentioning

confidence: 99%

The crystal structure and phase stability of the zeta phase in the group VB transition metal carbides: a computational investigation

Weinberger

Thompson

2019

Acta Crystallogr Sect B

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The crystal structure and composition of the zeta phase in the group VB transition metal carbides are not completely understood despite decades of experimental studies. As such, the phase rarely appears on phase diagrams of the group VB transition metal carbides. There is currently renewed interest in this phase, as tantalum carbide composites exhibit high fracture toughness in the presence of this phase. This work extends the initial computational study using density functional theory of the phase stability of the zeta phase in the tantalum carbide system, where the tantalum carbide zeta‐phase crystal structure and stability were determined, to the niobium and vanadium carbides. It is shown that the zeta phases in the three systems share the same crystal structure and it is an equilibrium phase at low temperatures. The carbon atom ordering in the three different phases is explored and it is demonstrated that the zeta phase in the tantalum carbides prefers to order carbon atoms differently than in the niobium and vanadium carbide zeta phases. Finally, the properties of this crystal are computed, including elastic constants, electronic densities of states and phonon dispersion curves, to illustrate that this crystal structure is similar to other transition metal carbides.

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Section: Introductionmentioning

confidence: 99%

The crystal structure and phase stability of the zeta phase in the group VB transition metal carbides: a computational investigation

Weinberger

Thompson

2019

Acta Crystallogr Sect B

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“…tPresent address: Brunswick Corp, Needham Laboratories, Needham, Mass, USA. TaC0.v5 which show the existence of a second phase associated with intrinsic stacking faults [8,9].…”

Section: Introductionmentioning

confidence: 99%

Structure and properties of tantalum carbide crystals

Rowcliffe¹,

Warren²

1970

J Mater Sci

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Single crystals of tantalum carbide, up to 2 mm in size have been grown from solution in a bath of molten iron. The slip plane was found to be {1 11} using a two-surface analysis on etch-pitted crystals deformed by microindentation at room temperature. Observations of etch-pit patterns around inclusions suggest that slip occurs on other planes at elevated temperatures. Maximum microhardness values between 3800 and 5200 Knoop (100 gm load) were found at a composition TaC0.83• In regions of crystals with a carbon content less than TaC0.83 a phase transformation was seen close to microhardness indentations in samples decarburised below 2200 ~ C. The mechanical behaviour of tantalum carbide is discussed with reference to a general model for the electronic structure of carbides. IntroductionLike the other monocarbides of the Group IVA and VA transition metals, tantalum carbide possesses the rock salt structure and exists over a wide range of substoichiometry. The most recent phase diagram [1] indicates the composition limits for single-phase tantalum carbide as TaCo.75 to TaC0.9s below about 1500 ~ C. A maximum melting point of 3983 ~ C occurs at TaC0.98. Storms [2] has suggested that the maximum melting point might lie at TaC0.s but he also points out that the actual values of composition and temperature are subject to some uncertainty due to the experimental difficulties in making the measurements [3]. A number of authors have reported a zeta-phase tantalum carbide [4-6] which might be a metastable compound [2,4,5]. Its composition has been determined as TaCo.75 [5] or TaC0.r4 [6], but it also appears to exist over a range of substoichiometry [7]. Yvon and Parth6 [7] have recently shown that the structure of the zeta-phase consists of an arrangement of twelve close-packed metal atoms in a unit cell, with the carbon atoms in octahedral interstices. The arrangement of the metal atoms can be regarded as alternate layers of hcp and fcc stacking, i.e. a close-packed structure containing 50~ stacking faults. Such a structure with a high density of faults is in accord with recent electron microscope studies of *Present address:

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“…Such circular formation of ζ-Ta 4 C 3 nuclei has been noted to occur in TaC-Ta reaction diffusion couples [10]. Alternatively, these faults could nucleate through the preferential binding of carbon vacancies to dislocation cores, creating wide stacking faults also observed in experiments [34,35] and eventually creating complete carbon depleted stacking faults. In this proposed scenario, the carbon likely diffuses through the dislocation cores leaving a carbon depleted stacking fault in its wake ultimately extending the carbon depleted fault.…”

Section: Model Parameter Estimationmentioning

confidence: 99%

“…It is also possible to postulate the existence of other related SFPs such as a M 7 X 6 phase, M 8 X 7 phase and so on. In the limit of the largest index, these SFP converge on a single isolated plane that is depleted of non-metal atoms and sheared by a Shockely partial dislocation, a process quite important for moderate temperature slip in some of these materials [34,35,36].…”

Section: Introductionmentioning

confidence: 99%

A model for understanding the formation energies of nanolamellar phases in transition metal carbides and nitrides

Guziewski

Thompson

et al. 2016

Modelling Simul. Mater. Sci. Eng.

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Abstract. In this paper we introduce a stacking-fault based model to understand the energetics of formation of the nanolamellar-based metal carbide and nitride structures. The model is able to reproduce the cohesive energies of the stacking fault phases from Density Functional Theory calculations by fitting the energy of different stacking sequences of metal layers. The model demonstrates that the first and second nearest metal-metal neighbor interactions and the nearest metal-carbon/nitrogen interaction are the dominant terms in determining the cohesive energy of these structures. The model further demonstrates that above a metal to non-metal ratio of 75%, there is no energetic favorability for the stacking faults to form a long-range ordered structure. The model's applicability is demonstrated using the Ta-C system as its case study from which we report that the interfacial energy between ζ-Ta 4 C 3 and TaC or Ta 2 C is negligible. Our results suggest that the closed packed planes of these phases should be aligned and that precipitated phases should be thin, which is in agreement with experiments.

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Stacking Faults in a Non‐Stoichiometric Face‐Centred Cubic TaC

Cited by 20 publications

References 10 publications

The crystal structure and phase stability of the zeta phase in the group VB transition metal carbides: a computational investigation

The crystal structure and phase stability of the zeta phase in the group VB transition metal carbides: a computational investigation

Structure and properties of tantalum carbide crystals

A model for understanding the formation energies of nanolamellar phases in transition metal carbides and nitrides

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