Connectivity between plasticity and brittle fracture: An overview from nanoindentation studies

Nanoindentation and scanning probe microscopy techniques applied to deforming thin films, nanospheres, nanowires, and nanocrystalline structures have uncovered new mechanical property phenomena dependent on size scale. This overview addresses several segments — those associated with measurement by nanoindentation, as well as the resulting properties of elasticity and plasticity, and fracture toughness of semi-brittle crystals. Specific to volumes in indentation or compression, it is shown that both pressure and scale effects can become dominant for both elasticity and plasticity at sizes less than 100nm. A strong inverse relationship between yield strength and activation volume for both single crystal and nanocrystalline structures is reviewed. Equally strong is a relationship between fracture toughness, the number of shielding dislocations accommodating indentation prior to fracture, and the basic mechanical and physical properties of semi-brittle solids. The link between fracture toughness and plasticity in these semi-brittle materials is shown to be the activation volume for dislocation nucleation in these strong solids.