Phase, hardness, and deformation slip behavior in mixed HfxTa1-xC

Smith, Chase J.; Yu, Xiaoxiang; Guo, Qianying; Weinberger, Christopher R.; Thompson, Gregory B.

doi:10.1016/j.actamat.2017.11.038

Cited by 94 publications

(59 citation statements)

References 34 publications

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“…The measured hardness and Young's modulus of Ta x Hf 1-x C y coatings are reported in Table 5. The measured values are consistent with other values found in the literature on bulk materials [40][41][42][43]-i.e., 23 GPa for hardness and 240 GPa for Young's modulus. Nevertheless, the composition does not influence strongly either the hardness or Young's modulus.…”

Section: Nanoindentationsupporting

confidence: 91%

The Structure, Morphology, and Mechanical Properties of Ta-Hf-C Coatings Deposited by Pulsed Direct Current Reactive Magnetron Sputtering

et al. 2020

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Ta, Hf, TaCx, HfCx, and TaxHf1-xCy coatings were deposited by reactive pulsed Direct Current (DC) magnetron sputtering of Ta or Hf pure metallic targets in Ar plus CH4 gas mixtures. The properties have been investigated as a function of the carbon content, which is tuned via the CH4 flow rate. The discharge was characterized by means of Optical Emission Spectroscopy and, in our conditions, both Ta-C and Hf-C systems seem to be weakly reactive. The structure of the as-deposited pure tantalum film is metastable tetragonal β-Ta. The fcc-MeCx carbide phases (Me = Ta or Hf) are {111} textured at low carbon concentrations and then lose their preferred orientation for higher carbon concentrations. Transmission Electron Microscopy (TEM) analysis has highlighted the presence of an amorphous phase at higher carbon concentrations. When the carbon content increases, the coating’s morphology is first compact-columnar and becomes glassy because of the nano-sized grains and then returns to an open columnar morphology for the higher carbon concentrations. The hardness and Young’s modulus of TaCx coatings reach 36 and 405 GPa, respectively. For HfCx coatings, these values are 29 and 318 GPa. The MeCx coating residual stresses increase with the addition of carbon (from one-hundredth of 1 MPa to 1.5 GPa approximately). Nevertheless, the columnar morphology at a high carbon content allows the residual stresses to decrease. Concerning TaxHf1-xCy coatings, the structure and the microstructure analyses have revealed the creation of a nanostructured coating, with the formation of an fcc superlattice. The hardness is relatively constant independently of the chemical composition (22 GPa). The residual stress was strongly reduced compared to that of binary carbides coatings, due to the rotation of substrates.

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Section: Nanoindentationsupporting

confidence: 91%

The Structure, Morphology, and Mechanical Properties of Ta-Hf-C Coatings Deposited by Pulsed Direct Current Reactive Magnetron Sputtering

et al. 2020

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“…The large number of optical phonon modes arise from the 20 atoms in the primitive unit cell and some of the frequencies obtained are even higher than that of TaC, presumably due to the known contraction of the bond lengths between metal and carbon atoms in the lattice that occurs with the introduction of structural carbon vacancies, which would increase some of the stiffness of the bonds. The flat appearance of the optical modes and the large band gap are a direct result of the large atomic mass discrepancy, a common feature of the transition‐metal carbides . The frequencies along all of the paths are positive, indicating the dynamic stability of the ζ‐Ta 3 C 2 phase.…”

Section: Resultsmentioning

confidence: 97%

A computational search for the zeta phase in the tantalum carbides

Weinberger

Thompson

2018

J Am Ceram Soc

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A systematic electronic structure density functional theory search for the zeta phase in the tantalum carbon system has been conducted, demonstrating that the zeta phase does indeed lie on the convex hull, establishing low‐temperature thermodynamic stability, and is structurally stable. Even though the zeta phase is most oft reported as a R3¯m ζ‐Ta4C3‐x structure, these new computational results reveal that the perfectly ordered zeta phase occurs at the Ta3C2 composition and belongs to the C2/m space group. Furthermore, these results suggest that the R3¯m space group may be a result of an order‐disorder transition and potential deviations from ideal stoichiometry at higher temperatures. The structure of this Ta3C2 compound can be described as ordered strings of carbon vacancies on a single carbon plane, which is also the preferred plane where additional carbon vacancies or interstitials form. These defects have modest formation energies, which provides further explanation for the small homogeneity range in zeta phase.

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“…A transition metal carbide with a B1 (NaCl) structure can be described as an fcc (face centred cubic) lattice of metal atoms with carbon in the octahedral sites. Carbides usually exhibit a mixture of metallic, covalent and ionic bonding [20][21][22][23] and the use of the metallic radius in 12-coordination to calculate lattice distortion is therefore questionable. However, to estimate trends regarding the distortion of the metal fcc lattice we can apply Eq.…”

Section: Contents Lists Available At Sciencedirectmentioning

confidence: 99%