Mechanisms of toughening and strengthening in ceramic-based nanocomposites

Toughening and strengthening mechanisms in ceramic-based nanocomposites were explained based on Griffith's energy equilibrium and residual stresses around second-phase nanoparticles dispersed in matrix grains. The residual thermal stresses around a spherical dispersed particle within a concentric sphere of a matrix grain were specifically analyzed to clarify the effects of residual stresses on the toughening mechanism in the frontal process zone involving nanocracking and on the strengthening mechanism caused by nucleation of dislocations. The analytical results revealed that the ratio of the thermal expansion coefficients of the particle and matrix has a marked effect on residual stresses and the estimated residual stresses were of sufficient magnitude to generate lattice defects such as dislocations around the particle even in ceramics, and that the nanosize particle within a matrix can only create dislocations around the particle. The toughening and strengthening mechanisms for nanocomposites were also discussed based on the analytical results and explained schematically. (C) 2002 Elsevier Science Ltd. All rights reserved.