Cooperative Grain Boundary Sliding and Migration Process in Nanocrystalline Solids

Abstract

A new physical mechanism or mode of plastic deformation in nanocrystalline metals and ceramics is suggested and theoretically described. The mode represents the cooperative grain boundary (GB) sliding and stress-driven GB migration process. It is theoretically revealed that the new deformation mode is more energetically favorable than "pure" GB sliding and enhances the ductility of nanocrystalline solids in wide ranges of their structural parameters.

Micromechanics of fracturing in nanoceramics

“…For illustrative purposes, let us briefly consider the most effective toughening micromechanisms related to nanoscale plastic flow, namely the cooperative GB sliding and migration process [36,37]. The geometry of this process is schematically presented in figure 4.…”

“…Within the approach [36,37], GB sliding occurs under the applied shear stress and transforms the initial configuration I of GBs (figure 4b) into configuration II (figure 4c). In doing so, according to [36,37], GB sliding results in the formation of a dipole of wedge disclinations (rotational defects) A and C in configuration II (figure 4c) characterized by strengths ±ω, whose magnitude ω is equal to the tilt misorientation of the GB AB. The distance between the disclinations A and C is equal to the magnitude x of the relative displacement of grains (figure 4c).…”

“…These micromechanisms typically involve plastic deformation processes mediated by grain and interphase boundaries [30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Such interfacial deformation processes are dominant in nanocrystalline ceramics, for two reasons.…”

“…reviews [1,2,4], book [3] and original papers [8][9][10][11][12][13]19]). These experimental data are logically explained within the concept that (i) conventional toughening micromechanisms (that dominate in microcrystalline-matrix ceramics) operate in specific, inherent to nanostructures, ways in nanocrystalline ceramics where they effectively hamper crack growth and (ii) new, special (inherent to nanocrystallinity) toughening micromechanisms come into play in nanocrystalline ceramics [30][31][32][33][34][35][36][37][38][39][40][41][42][43]. The new toughening micromechanisms are often related to specific deformation modes that operate in nanomaterials (e.g.…”

“…The specific toughening micromechanisms include the GB sliding [30], the stress-driven migration of GBs [36,43], the nanoscale twin deformation carried by partials emitted from GBs [31], the creep deformation conducted by GB processes (Ashby-Verall creep carried by GB sliding accommodated by GB diffusion and grain rotations [32,33]), the cooperative GB sliding and migration process [36,37], stress-driven GB rotations [39,41], slow and fast nanoscale rotational deformation modes [35,38,40].…”