Diffusion‐Controlled Processes and Plasticity of Submicrocrystalline Materials

The influence of interstitial impurities on true grain-boundary sliding of titanium in coarse-grained and submicrocrystalline states

“…A similar relation between the activation energy of internal grain-boundary friction and the activation energies of volume and grain-boundary (for imperfect boundaries) selfdiffusion is also observed in submicrocrystalline structure. According to the available experimental data and theoretical estimates [2,5,8,9], the activation energy of grain-boundary diffusion is substantially decreased as the boundary structure becomes less perfect. As shown in [26], the activation energy of grain-boundary diffusion in cobalt in the course of transition from coarse-grained to submicrocrystalline structure decreased from 91 ± 15 to 56 ± 10 kJ/mol.…”

Surface impurity diffusion-induced recrystallization of ultrafine-grained molybdenum

“…The activated recrystallization process is brought about by the transition of the grain-boundaries to the nonequilibrium state under the action of grain-boundary diffusion fluxes of impurity atoms from the surface of the specimen [4]. Hence it follows that the decrease in the activated recrystallization start temperature for UFG molybdenum as compared to the material subjected to diffusion annealing for the same period of time is due to the change in the state of the molybdenum grain boundaries during severe plastic deformation and to the increased grain-boundary diffusion permeability.…”

“…Activated recrystallization of metals was traced to the presence of uncompensated diffusion fluxes of impurity atoms along grain boundaries that cause stresses to appear there, thus carrying the grain boundaries to a high-energy nonequilibrium state. As a result the mobility of grain boundaries is increased [4]. Activated recrystallization is controlled by diffusion.…”

“…Activated recrystallization is shown to occur for a nonstationary grain-boundary diffusion regime of the C type [4] according to the classification developed in [5] or for a closely corresponding B 1 -regime. The C-regime is characterized by grain-boundary diffusion without nickel penetration into the bulk of the grains, whereas the B 1 -regime is identified with the onset of penetration of the impurities into the bulk, minimal as it is.…”

“…The C-regime is characterized by grain-boundary diffusion without nickel penetration into the bulk of the grains, whereas the B 1 -regime is identified with the onset of penetration of the impurities into the bulk, minimal as it is. The motion of the activated recrystallization front is controlled by grain-boundary diffusion and is determined by the depth of the diffusant penetration into the metal [4]. According to the model put forward by Fischer [6], the impurity concentration C (x, y, z) in a grain boundary at a depth x can be found from the following equation:…”