Diffusion phase transformations in nanocrystalline alloys under severe plastic deformation

Modeling Enhanced Diffusion Mass Transfer in Metals during Mechanical Alloying

“…Similar deformation mechanisms operate at superplastic deformation of micron and submicron grained alloys at elevated temperatures where accommodation of grains takes place via grain boundary diffusion (Kaibyshev, 2002) and vacancies arising in the boundary may penetrate into grains. However, as noted in (Shtremel', 2007), a mechanism via which disclinations can generate vacancies is not described in , and estimates for the vacancy generation rate are not presented in (Gapontsev et al, 2000;Gapontsev et al, 2002;Gapontsev et al, 2003). Besides, the interaction of vacancy flux in a grain with edge dislocations, which can substantially reduce the vacancy concentration, is not considered, i.e.…”

“…Thus, models Gapontsev et al, 2000;Gapontsev et al, 2002;Gapontsev et al, 2003) can be considered as incomplete and relating to a distant stage of MA where nanorgains of a solid solution or intermetallic compound have already been formed via a certain physical mechanism which was not considered in these works. An idea of solid solution formation during MA by the "shear-drift diffusion" (Foct, 2004) or "trans-phase dislocation shuffling" (Raabe et al, 2009; has been proposed, which the authors of these works base upon the certain outcomes of atomistic simulations (Bellon & Averback, 1995).…”

“…It should be noted that cyclic process of formation and decomposition of an amorphous or intermetallic phase was observed during prolonged ball milling in certain systems (El-Eskandarany et al, 1997;Courtney & Lee, 2005). In these models, grain boundaries (Gapontsev et al, 2000;Gapontsev et al, 2002;Gapontsev et al, 2003) or disclinations (triple grain junctions) can act as vacancy sources when the deformation proceeds via grain boundary sliding and rotational modes. This corresponds to a situation when the size of grains in the particle has reduced to nanometric.…”

“…However, this term was not analyzed in detail. Models for diffusion demixing of a solid solution or intermetallic compound in the course of MA have been developed Gapontsev et al, 2000;Gapontsev et al, 2002;Gapontsev et al, 2003) which consider the formation of non-equilibrium vacancies in grain boundaries and their diffusion into grains. The vacancy flux directed into grains brings about an oppositely directed diffusion flux of solute atoms, which ultimately results in demixing of this stable or metastable phase.…”

Forming and deformation behavior of the ultrafine-grained Zr-1Nb alloy

“…Ɉɞɧɚɤɨ ɩɪɨɱɧɨɫɬɧɵɟ ɯɚɪɚɤɬɟɪɢɫɬɢɤɢ ɍɆɁ ɫɩɥɚɜɨɜ ɫɭɳɟɫɬɜɟɧ-ɧɨ ɡɚɜɢɫɹɬ ɧɟ ɬɨɥɶɤɨ ɨɬ ɪɚɡɦɟɪɨɜ ɷɥɟɦɟɧɬɨɜ ɫɬɪɭɤɬɭɪɵ, ɧɨ ɢ ɨɬ ɮɚɡɨɜɨɝɨ ɫɨɫɬɚɜɚ. Ʉ ɧɚɫɬɨɹɳɟɦɭ ɜɪɟɦɟɧɢ ɭɫɬɚ-ɧɨɜɥɟɧɨ [5,6], ɱɬɨ ɂɉȾ ɦɨɠɟɬ ɩɪɢɜɨɞɢɬɶ ɤ ɪɚɡɜɢɬɢɸ ɜ ɫɩɥɚɜɚɯ ɬɚɤɢɯ ɩɪɨɰɟɫɫɨɜ, ɤɚɤ ɮɚɡɨɜɵɟ ɩɪɟɜɪɚɳɟɧɢɹ, ɪɚɫɩɚɞ ɜɬɨɪɵɯ ɮɚɡ, ɨɛɪɚɡɨɜɚɧɢɟ ɩɟɪɟɫɵɳɟɧɧɵɯ ɬɜɟɪ-ɞɵɯ ɪɚɫɬɜɨɪɨɜ. ɉɪɢ ɷɬɨɦ ɪɚɡɜɢɬɢɟ ɭɤɚɡɚɧɧɵɯ ɩɪɨɰɟɫ-ɫɨɜ ɡɚɜɢɫɢɬ ɤɚɤ ɨɬ ɯɚɪɚɤɬɟɪɢɫɬɢɤ ɫɩɥɚɜɚ (ɪɚɫɬɜɨɪɢɦɨɫ-ɬɢ ɥɟɝɢɪɭɸɳɢɯ ɷɥɟɦɟɧɬɨɜ, ɷɧɟɪɝɢɢ ɞɟɮɟɤɬɚ ɭɩɚɤɨɜɤɢ, ɜɨɡɦɨɠɧɨɫɬɢ ɪɚɡɜɢɬɢɹ ɞɜɨɣɧɢɤɨɜɚɧɢɹ ɢɥɢ ɮɚɡɨɜɵɯ ɩɪɟɜɪɚɳɟɧɢɣ, ɞɪ.…”