The phase stability and mechanical properties of Nb–C system: Using first-principles calculations and nano-indentation

Wu, Lailei; Wang, Yachun; Yan, Zhigang; Zhang, Jingwu; Xiao, Furen; Liao, Bo

doi:10.1016/j.jallcom.2013.01.200

Cited by 69 publications

(19 citation statements)

References 46 publications

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“…The low‐temperature orthorhombic phase, ξ‐Nb 2 C, has been suggested to be stabilized by impurities . The review authors are doubtful of this argument since its stability has been demonstrated with DFT simulations . Collectively, these results suggest that the low‐temperature phase should have the ξ‐Nb 2 C structure.…”

Section: Experimental Observations Of Specific Crystal Structuresmentioning

confidence: 80%

“…However, when the error in the formation energy of graphite was accounted for, the B1 NbC was found to be either on the convex hull or very close such that it is within the error of the DFT calculations. The discrepancy in the identified vacancy‐ordered B1 structured Nb 4 C 3 phase between the 2 aforementioned study arises because it was not included in trial structures used by Wu et al . This again demonstrates the limitations of only resorting to known structures and the advantage of evolutionary algorithms in the determination of stable phases.…”

Section: Phase Stability Predictionsmentioning

confidence: 92%

“…In contradiction, Yu et al found 3 phases that lie on the convex hull—the Pnma Nb 2 C and the Nb 6 C 5 (with essentially the same degenerate structures as the V‐C system above) and now the vacancy‐ordered C2/c Nb 4 C 3 . As with Wu et al, the rocksalt phase was not on the convex hull. However, when the error in the formation energy of graphite was accounted for, the B1 NbC was found to be either on the convex hull or very close such that it is within the error of the DFT calculations.…”

Section: Phase Stability Predictionsmentioning

confidence: 94%

“…In the Nb‐C system, only one study has been conducted using an evolutionary algorithm and one study that used already known structures . Wu et al used known Nb‐C phases to populate their calculations and construct a convex hull.…”

Section: Phase Stability Predictionsmentioning

confidence: 99%

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Review of phase stability in the group IVB and VB transition‐metal carbides

Weinberger

Thompson

2018

J Am Ceram Soc

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This review summarizes the phase stability in the group IVB (Ti‐C; Zr‐C; Hf‐C) and group VB (V‐C; Nb‐C; Ta‐C) transition‐metal carbides. The order parameter functional (OPF) method and density functional theory (DFT) method have been used to predict phase equilibria in these systems. Extensive experimental investigations have attempted to determine both phase stability as a function of composition as well the crystal structures present using X‐ray diffraction, neutron diffraction, electron backscatter detection, and selected area electron diffraction. These investigations have demonstrated that the structures that form are based on the close‐packing of the metal atoms and the arrangement of the carbon atoms in the octahedral interstices. In general, the rocksalt B1 phase is stable for all of the transition‐metal carbides, with their substoichiometry tolerance increasing with temperature; vanadium carbide is the exception due to its negative vacancy formation energy. Vacancy‐ordered M6C5 phases have been predicted and experimentally confirmed in both groups of carbides; however, kinetic limitations often inhibit the formation of vacancy‐ordered phases, which has contributed to controversy in phase identification. The vacancy‐ordered M4C3 phase has been predicted for select carbides and has only been observed in zirconium carbide. In contrast, the stacking fault phase ζ‐M4C3−x has been readily reported in the group VB carbides (but not in the group IVB carbides). The vacancy‐ordered M3C2 has been predicted by DFT for the group IVB carbides but not in the group VB carbides, whereas OPF predicts its stability in both carbides. Vacancy‐ordered M3C2 phases have been experimentally observed in the Ti‐C and Hf‐C systems. Finally, the M2C phase has been predicted in both group carbides, except for hafnium carbide, with an order‐disorder transition with temperature. These factors result in phase diagrams that are similar among all the carbides, but each phase diagram is unique due to subtle differences in bonding that result in slight differences in thermodynamically stable phases.

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Section: Experimental Observations Of Specific Crystal Structuresmentioning

confidence: 80%

Section: Phase Stability Predictionsmentioning

confidence: 92%

Section: Phase Stability Predictionsmentioning

confidence: 94%

Section: Phase Stability Predictionsmentioning

confidence: 99%

See 2 more Smart Citations

Review of phase stability in the group IVB and VB transition‐metal carbides

Weinberger

Thompson

2018

J Am Ceram Soc

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“…Typically, activation energy for vacancy migration and thus self‐diffusion needed for a sintering process would be expected to scale with melting point. But long‐range vacancy order and subsequent transformation to Nb 6 C 5 can be achieved by relatively short annealing times, and studies have confirmed that the formation enthalpies of Nb 6 C 5 and Nb 8 C 7 are extremely close to NbC 1‐x relative to the same stoichiometries in ZrC . This explains why sintering of NbC is observed at lower temperatures compared with other UHTCs such as TiC and ZrC .…”

Section: Discussionmentioning

confidence: 90%

Niobium carbide as a technology demonstrator of ultra‐high temperature ceramics for fully ceramic microencapsulated fuels

Ang

Snead

Benensky

2019

Int J Ceramic Engine & Sci

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The consolidation of Fully Ceramic Microencapsulated (FCM) fuels has been extended from matrices based on SiC to ultra-high temperature ceramics (UHTCs). Specifically, sintering conditions of NbC 1-x were compatible with hosting of microencapsulated fuel. NbC powder in as-received, chemically treated, and composite forms was consolidated. Elemental analysis, shrinkage of powder compacts, contents of ejected vapor, density, microstructure, and NbC lattice constants were analyzed. As-received NbC showed more shrinkage due to the presence of a liquid phase compared with the chemically treated powder. Removal of impurity metals was observed from chemical treatment and during sintering of as-received powders. An increase in true density during sintering was attributed to removal of compounds with lower density than NbC.Chemically treated powder showed reduced densification rate and absence of a liquid phase after sintering. Smaller grain sizes were observed in the NbC composite. The implications for NbC and other binary carbides as matrices for FCM fuels are discussed. K E Y W O R D Scarbides, niobium/niobium compounds, nuclear thermal propulsion, sinter/sintering, spark plasma sintering

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Niobium Carbides

Shabalin¹

2019

Ultra-High Temperature Materials II

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The phase stability and mechanical properties of Nb–C system: Using first-principles calculations and nano-indentation

Cited by 69 publications

References 46 publications

Review of phase stability in the group IVB and VB transition‐metal carbides

Review of phase stability in the group IVB and VB transition‐metal carbides

Niobium carbide as a technology demonstrator of ultra‐high temperature ceramics for fully ceramic microencapsulated fuels

Niobium Carbides

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