Activation energy of gas interstitials in BCC metals (original) (raw)
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Lattice distortion due to gas interstitials in bcc metals
Journal of Physics F: Metal Physics, 1973
The static lattice distortion and relaxation energy for nitrogen and oxygen interstitials at octahedral and tetrahedral sites in niobium, tantalum and vanadium have been calculated by using the Green function method for lattice statics. The forces responsible for the lattice distortion have been obtained from the measured values of the dipole tensor, which avoids the need for a priori knowledge of the gas-host potential. However. simple functions for the 'effective' gas-host interaction have been fitted to the calculated values of the atomic displacements which should be useful for further calculations on these systems.
The non-Arrhenius migration of interstitial defects in bcc transition metals
Comptes Rendus Physique, 2008
Thermally activated migration of defects drives microstructural evolution of materials under irradiation. In the case of vacancies, the activation energy for migration is many times the absolute temperature, and the dependence of the diffusion coefficient on temperature is well approximated by the Arrhenius law. On the other hand the activation energy for the migration of self-interstitial defects, and particularly self-interstitial atom clusters, is very low. In this case a trajectory of a defect performing Brownian motion at or above room temperature does not follow the Arrhenius-like pattern of migration involving infrequent hops separated by the relatively long intervals of time during which a defect resides at a certain point in the crystal lattice. This article reviews recent atomistic simulations of migration of individual interstitial defects, as well as clusters of interstitial defects, and rationalizes the results of simulations on the basis of solutions of the multistring Frenkel-Kontorova model. The treatment developed in the paper shows that the origin of the non-Arrhenius migration of interstitial defects and interstitial defect clusters is associated with the interaction between a defect and the classical field of thermal phonons. To cite this article: S.L. Dudarev, C. R. Physique 9 (2008). Crown
Journal of Alloys and Compounds, 2020
Solubility and diffusivity of interstitials in Ni is of prime importance to understand and quantify reactivity of Ni-base structural alloysat high temperature. We thus present a first-principles study of the insertion and diffusivity of interstitial species in nickel. We put an emphasis on carbon, nitrogen and oxygen atoms and compare our results with those found for hydrogen and in the literature. The interactions with the metal and the relative stability of sites are discussed in detail in terms of phonon, electronic, elastic, magnetic properties and charge transfers. As a result, we identified one new stable interstitial position for C and N atoms, and we also showed that the tetrahedral site can be considered as unstable from an elastic standpoint for carbon. In the light of these new results, diffusion mechanisms were reviewed and diffusion coefficients were calculated. The effects of temperature on enthalpy and migration energies were investigated. We thus showed that C and N atoms on one hand, H and O atoms on the other hand, show the same behavior.
2021
Plasticity in body centered cubic (bcc) refractory metals are largely due to the stress tensor induced either by solute or thermal activation. The mechanism of the solute atom(s) residence causes instability in such metals. Earlier research have considered the mechanism of oxygen (O) or carbon (C) in tungsten (W), even though the major component of the environment is nitrogen (N). In this article, the density functional theory (DFT) was employed to investigate the thermodynamic stable site for an interstitial solute (N or O) in the bcc refractory metals (Mo and Nb) by calculating the equilibrium and structural parameters, dissolution energetics and volumetric strain. The dissolution mechanism of all the relaxed solid solution structures were predicted to be an exothermic reaction from the supersaturated cell to the low concentration (1.82 at.%) except for Mo-N solid solution. Convergence of volumetric strain was observed at the low concentration of the solute. At this point, the sol...
Materials Research, 2006
Mechanical spectroscopy measurements have been extensively used in the last decades to obtain information about many aspects of the behavior of solutes in metallic materials. Metals of body-centered cubic lattice that contain heavy interstitial elements (oxygen, nitrogen and carbon) in solid solution, present anelastic relaxation peaks when submitted to cyclic tensions, due to process know stress-induced ordering. Internal friction and frequency as a function of temperature were performed between 300 K and 650 K in a polycrystalline sample of Nb, for three distinct conditions, using a torsion pendulum inverted Kê-type operating in a frequency oscillation between 1Hz and 10 Hz range, with a heating rate of 1 K/min and pressure lower than 2 x 10-5 mbar. The experimental spectra obtained for each condition of the sample, were decomposed by the successive subtraction method in elementary Debye peaks. The following metal-interstitial interactions were identified: Nb-O and Nb-N for all conditions of the sample. From the anelastic relaxation parameters obtained (relaxation strength, peak temperature, activation energy and relaxation time) and lattice parameter (obtained from x ray diffraction), the determination of the oxygen and nitrogen interstitial diffusion coefficient in Nb was possible, for each condition of the sample.
Interdiffusion in niobium-vanadium alloys
Journal of the Less Common Metals, 1965
A determination of the variation of interdiffusion coefficient with composition for Nb-V alloys has been made for diffusion temperatures of 1404', 1505", 1630" and 1750°C. Three types of doubly infinite couples were employed: Nb/V, Nb/alloy and V/alloy, where the alloy was 50 at.% Nb. Compositions in the diffusion zone were * N.S.F. Postdoctoral Fellow, University of Birmingham.
Transactions of the Japan Institute of Metals, 1972
The hardness profile was correlated with the concentration of nitrogen in niobium. It was found that the diffusion kinetics in this temperature range could be represented by a single Arrhenius type rate equation. The activation energy and the pre-exponential factor were found to be 24.9kcal/mol and 0.0023cm2/sec, respectively. The analysis of available experimental data for diffusion of nitrogen in niobium shows that the apparent activation energy decreases with increasing temperature.. An explanation can be formulated in terms of a temperature dependence of the motion enthalpy Hm of interstitial nitrogen atoms. Hm is found to decrease from 38.6kcal/mol to 24.7kcal/mol between
In this work, we have successfully applied one of the most effective semi-empirical interatomic potentials called embedded atom method EAM to calculate some thermodynamics properties of refractory metals (Nb, Ta, Mo and W). Our theoretical calculated values for mono-vacancy formation energy are in excellent agreement with the available experimental values. Among these metals, the highest f v E 1 is obtained for W. It is well known that the value of the mono-vacancy formation energy of each metal is directly proportional to its cohesive energy. i.e. the lower the cohesive energy is, the lower the mono-vacancy formation energy and vice versa. The trend exhibited by these metals whose mono-vacancy migration energies were computed revealed that migration energies are small but cannot be negative. The mono-vacancy activation energy was obtained by summing the mono-vacancy formation energy and mono-vacancy migration energy together. For all the metals considered, W has the largest values for mono-vacancy formation energy, mono-vacancy migration energy and mono-vacancy activation energy followed by Mo and then Ta. This could be as a result of parameter β used in the calculation. We used 8 as β for both W and Mo, while β = 6 for all other metals. The values for di-vacancy formation energy are larger than their corresponding mono-vacancy formation energy but still lower than corresponding cohesive energy of each metal. The binding energies were computed from mono-vacancy formation and di-vacancy formation energies. The obtained values for Nb and Ta metals are in good agreement with Zhang et al but there are no experimental values for these two metals. Experimental values are highly needed before conclusion can be drawn.
First-principles theory of the energetics of He defects in bcc transition metals
Physical Review B, 2008
Helium defect properties in V, Nb, Ta, Mo, and W were studied using first-principles electronic structure calculations. The most stable position for the He in all bcc metals is a substitutional site; the tetrahedral interstitial position is more favorable than the octahedral position. The formation energy of He substitutional defect is nearly the same for all the metals, while the formation energy of He interstitial defect strongly depends on the electronic structure of the host and insignificantly on its atomic size. The obtained He formation energies were used to calculate He binding energy to the vacancy. For V, Nb, and Ta He-vacancy binding energy is about one-half of the vacancy formation energy; for Mo and W it is about 40% higher than the vacancy formation energy. Both pair potentials and effective-medium theory fall to reproduce the preference order or the relationship between the formation energies. Calculated He formation energies and He-vacancy binding energies improve understanding of He behavior and diffusion mechanisms in metals.