Localization of deformation in shear bands is widely observed preceding intense damage and fracture in ductile or granular materials. However, mechanisms about how shear bands form are generally not known. Here, we show that nanocrystalline ceramic (NCC) nanopillars of ZrN fracture by shear banding under compression. The microstructure evolution of entire shear banding process was in situ monitored by electron imaging and diffraction. Results show that the nanopillars deform through a series of granular activities due to intermittent nucleation and propagation of dislocations. The stress drops associated with the dislocation activities are relatively small since dislocation avalanches are restricted in NCCs because of the effect of nanograin size. Localized and cooperative granular activities, as well as nanocracks, are discovered in the regions where shear bands form. A model about shear band and nanocrack formation is proposed. These findings thus demonstrate for the first time of spatial and temporal nature of intermittent granular activities, leading to shear band formation in NCCs.
ASJC Scopus subject areas
- Materials Science(all)
- Physics and Astronomy (miscellaneous)