Special rotational deformation as a toughening mechanism in nanocrystalline solids

Micromechanics of fracturing in nanoceramics

“…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.…”

“…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.…”

“…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].…”

Grain growth rate for coupled grain boundary migration and grain rotation in nanocrystalline materials

“…Grain rotation at these smaller length scales allows accommodation of plastic deformation which could play an important role in improving ductility [17]. Such grain rotation has been attributed as a cause of notch insensitive failure in small-scale specimens [18] and as a toughening mechanism in NC specimens [19][20][21].…”

Strong crack blunting by shear-coupled migration of grain boundaries in nanocrystalline materials

“…(3) is introduced to account for the effect of a local plastic flow, i.e., the shear-coupled migration of GB "AB" and the slip of the dislocations emitted from the crack tip, on crack growth. By modifying a mode I brittle crack growth criterion, which is based on the balance between the energy release rate and the energy needed by a new free surface formation [21,30,31], the effective stress intensity factor can be expressed as…”