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[en] The solute enhancement factor B was calculated for b.c.c. alloys containing small concentrations of solute (<2at%). Only the second term in the equation D2(c) = D2(0) [1 + B1c + B2c2 +..] was taken into consideration. D2(c) and D2(0) are the solution diffusion coefficients in the alloy and in the pure solvent, respectively. It is shown that if the absolute value of B1 > 5 the other terms in the above equation cannot be neglected if the convergence of the series is to be maintained. Experimental values for B are considered and are compared with theoretical estimations. (orig.)
[en] 1. Introduction; 2. Concentration of vacancies and interstitials in thermal equilibrium; 3. Jump frequencies of point defects; 4. Random-walk theory; 5. The thermodynamics of irreversible processes; 6, Annealing of vacancies in dilute alloys; 7. Epilogue. (author)
[en] Magnetoresistance dependence on temperature was measured (a) for dilute alloys of Al with Zn and Ge, (b) for dilute alloys of Cu with Au, and (c) for pure Al and Cu with different RRR. A maximum in this magnetoresistance dependence is observed in the case of pure samples, known as anomalous behavior, due to the anisotropic scattering, which is suppressed with the presence of foreign atoms which is caused by the isotropization of the scattering process. (orig.)
[en] The free energy functional is derived for a system of free electrons interacting with randomly distributed magnetic impurities (Kondo system). This is done by starting with the microscopical, quantum mechanical description of the system. Instead of postulating, as usual, the form of the functional, we are able this way to obtain quantities and correctly take into account quantum effects. This derivation is the object of the next section; section 3 is devoted to the expansion of the free energy up to the fourth order in the fluctuating fields; section 4 contains the study of the stationary points of the GLW effective hamiltonian in the mean field approximation. In the last section we study the profile of the GLW surface in the case of the static, homogeneous approximation. (author)
[en] The migration of vacancy-type point defects in pure metals and dilute alloys is investigated within the framework of the pseudopotential method. The total lattice energy can be separated into volume-dependent and structure-dependent energies. If only the structural energy is considered under the condition of constant volume, the migration energy of a point defect can be obtained by comparing the structural energy of an activated configuration with that of a normal configuration. (Auth.)
[en] Classical and quantum calculations were performed in characterizing the interstitials transport parameters in the bulk of a diluted FeCr alloy and, in the symmetric tilt grain boundary (GB) structure. For the bulk, in the same line of ideas as the multi-frequency model, we obtain the relevant transport parameters, namely: i) the involved jump frequencies in the associated multi-frequency model, ii) the full set of phenomenological Onsager coefficients, iii) the interstitial wind parameter, as well as, iv) the tracer self- and solute diffusion coefficients. Our calculations include the effects of entropy and ferromagnetic transition in the activation energy. We compare present calculations with available experimental data. As is expected, we have found in the bulk that Fe and Cr diffuse mainly via a vacancy mechanism, while diffusion by interstitials is several orders of magnitudes slower. For the GB, our calculations are in accordance with experimental data and show that diffusion is almost two orders of magnitude higher than in the bulk. Also, contrary to the bulk Cr diffuses slower than Fe in the GB. Present results show that both, interstitial and vacancy mechanisms, are important in studying diffusion in the GB.
[en] In this first-principles study, we investigate the effect of many kinds of substitutional solute species on screw dislocation motion in bcc-Fe, dominating the strength of dilute Fe alloys. Most of the solute species show a significant interaction with the dislocation core, while only several solute species among them, such as Si, P, and Cu, significantly lower the Peierls potential of the screw dislocation motion. A first-principles interaction energy with the “Easy-core” structure excellently correlates with the change in the γ-surface caused by solute atoms (i.e., chemical misfit). Based on the interaction energy, we predicted the effect of each species on macroscopic critical resolved shear stress (CRSS) of the dilute Fe alloy. The CRSS at low and high temperature for various alloys basically agree with experiment CRSS. These results provide a novel understanding of the interaction between a screw dislocation and solute species from the first-principles.