Vladimir A. Esin

Cross Diffusion-Stresses Effects

Three cross diffusion-stresses effects are considered: mobility-stress effect, flux-stress effect and vacancy-stress effect. The value of the migration volume for vacancies in Al is found from atomistic computer simulation. A cross vacancy-stress effect is applied to the process of the pores growth and dissolution in Ni-based superalloys.

Solvent grain boundary diffusion in binary solid solutions: a new approach to evaluate solute grain boundary segregation

A new method to estimate solute grain boundary (GB) segregation from solvent GB diffusion measurements in binary solid solutions is proposed for the systems with restricted solubility and intermediate stoichiometric phases. The method is based on the model of complex formation: solvent atoms (A) interact with solute ones (B) at GB with the formation of AB chemical bond. A description of solvent GB diffusion is then given. Using such an approach, a new equation for the dependence of solvent GB diffusion coefficient on solute bulk concentration is derived for the systems with simple atomic attraction with AB complex formation in GB. Theoretical results predict non-linear dependence of solvent GB diffusion coefficient on solute bulk content, which is in agreement with earlier published experimental data regarding the ease of grain boundary diffusion in alloys of different chemical compositions. More importantly, the equation deduced permits to evaluate, on one hand, the characteristics of solute GB segregation from solvent GB diffusion measurements and, one the other hand, GB diffusion coefficient in pure solvent. Such a numerical data analysis for Fe–Sn system is in agreement with experimental results. In special cases, such an analysis can be done analytically.

About Fe Diffusion in Cu

The temperature dependence of the bulk diffusion coefficient of Fe in Cu is determined by EDX in the temperature range from 923 to 1273 K, , m2/s. These results are different from that obtained earlier by radiotracer technique: activation energy is less by 30 kJ/mol and pre-exponential factor is 50 times smaller. Deviations from ideality of investigated solutions do not explain the differences; consequently, the thermodynamical factor would not responsible for such an effect. Fast grain boundary diffusion of Fe in Cu was not observed in the temperature range from 823 to 1073 K.

Concentration Profiles for Grain Boundary Diffusion in B-Regime with Regard to the Formation of Atomic Complexes in Grain Boundary

Thermodynamics of the atomic complexes formation in a grain boundary (GB) is discussed applying to AB complex. It is shown that the AB complex formation leads to the nonlinearity of segregation isothermes. Consequently, the concentration profiles for GB diffusion are nonlinear. The total (free and bound into complexes) concentration of diffusant B decreases at the given depth as the molar fraction of the complexes increases.

Bulk Diffusion of Iron in Copper

AbstractThe temperature dependence of bulk diffusion coefficient of iron in copper has been determined by electron microprobe analysis (EMA) in the temperature range from 923 to 1273 K to be

Rumpling of nickel aluminide coatings : a reassessment of respective influence of thermal grown oxide and phase transformations

D_{Fe} = 0.03 \times 10^{ - 4} \exp \left( { - \frac{{187 kJ/mol}} {{RT}}} \right)

In situ synchrotron X-ray diffraction and dilatometric study of austenite formation in a multi-component steel: Influence of initial microstructure and heating rate

m2/s. The results obtained differ from the parameters of bulk diffusion determined by the tracer method: the activation energy is less by 30 kJ/mol and the preexponential factor is less by approximately a factor of 50. The deviations of the solutions from the ideality does not explain the discrepancies obtained.

Increase in ductility of Pt-modified nickel aluminide coating with high temperature ageing

During the solidification and the homogenization of single-crystal nickel-base superalloys, pores form which lead to the degradation of the mechanical properties, especially the fatigue lifetime. Hot Isostatic Pressing (HIP) is used for the pores dissolution. In this paper, analytical models for the formation of the homogenization pores and their dissolution during the HIP are developed. The results are compared with experimental data.