Cooperative grain boundary sliding and nanograin nucleation process in nanocrystalline, ultrafine-grained, and polycrystalline solids

Abstract

A special physical mode of plastic deformation in nanocrystalline, ultrafine-grained, and polycrystalline solids is suggested and theoretically described. The mode represents the cooperative grain boundary (GB) sliding and nanoscale grain nucleation (occurring through stress-driven splitting and migration of GBs) process. It is theoretically revealed that, in certain ranges of parameters of the defect structure under consideration, the special deformation mode is more energetically favorable than both "pure" GB sliding and the previously examined [Bobylev et al., Phys. Rev. Lett. 105, 055504 (2010)] cooperative GB sliding and migration process. In addition, the special deformation mode enhances ductility of nanocrystalline and ultrafine-grained solids, and this enhancing effect is more pronounced compared to that of the cooperative GB sliding and migration process.

Stress-driven migration of deformation-distorted grain boundaries in nanomaterials

“…2d). The splitting processes do not have their analogs in the previously examined [3,5,7,10,11,[18][19][20][21][22][23] situations with conventional, non-distorted GBs and lead to formation of new nanoscale (sub)-grains in nanomaterials. With these theoretical results, one can conclude that, in parallel with previously examined grain refinement mechanisms such as (i) continuous dislocation ensemble evolution resulting in sequential formation of dislocation subboundaries, cells and high-angle GBs [43][44][45], (ii) formation and intersection of elongated laminate structures and microbands [46], and (iii) re-arrangements of GB disclination structures [47,48], the stress-driven splitting of deformation-distorted GBs (Fig.…”

“…This process is new for science of stress-driven migration of GBs in nanomaterials. The splitting process has no analogs in the previously examined [3,5,7,10,11,[18][19][20][21][22][23] situations with stress-driven migration of conventional, non-distorted GBs.…”

“…It has been revealed that stress-driven migration of GBs plays a significant role in grain growth, plastic deformation and fracture processes in nanomaterials and thereby essentially influences the outstanding mechanical properties of these materials having a huge potential for technological applications. The previous theoretical examinations and computer simulations [3,5,7,10,11,[18][19][20][21][22][23] of stress-driven migration were focused on conventional GBs having equilibrium structures. At the same time, real GB structures are intensively distorted by deformation processes in nanomaterials during their plastic deformation.…”

Effect of cooperative grain boundary sliding and migration on emission of dislocations from a crack tip in nanocrystalline materials

“…In most of them, intergrain sliding, grain boundary migration, triple junction diffusional creep, Coble creep, rotational deformation and nanoscale deformation twinning have been theoretically described as specific deformation modes in nanocrystalline materials. And the specific toughening mechanisms are attributed to specific deformation modes in nanocrystalline materials [20][21][22][23][24][25].…”

On shear-coupled migration of grain boundaries in nanocrystalline materials

“…Recently, GB migrations attract intensive scientific interests because they have been found to be closely related to grain growth in NC materials and their exceptional ductility and toughness. [7][8][9][10][11] The normal GB migration was usually accompanied by a tangential translation parallel to the GB plane for both low-angle and high-angle boundaries, which would then produce shear deformation of the lattice traversed by the GB when an external stress field was applied at room temperature or 0 K, as revealed by some molecular dynamics (MD) and quasi-continuum studies for both bicrystals 6,12-18 and nano-polycrystallines. [19][20][21][22] This phenomenon was also observed in many experiments for bicrystals [23][24][25][26] and nanocrystalline materials.…”