Room-temperature plastic deformation of single crystals of high-purity β-silicon nitride investigated by micropillar compression

The room-temperature plastic deformation behavior of single crystals of high-purity β-silicon nitride has been investigated by micropillar compression tests as a function of loading-axis orientation and specimen size. Prism < c > slip ({01$\overline{1}$0}[0001] slip) is identified to be the only operative slip system under uniaxial compression at room temperature. The critical resolved shear stress (CRSS) value for prism < c > slip does not depend much on the specimen size and loading-axis orientation, with the average CRSS value of 1.66 ± 0.22 GPa. The [0001] dislocations on the prism slip planes exhibit a strong tendency to align along their screw orientation, indicating the existence of a high Peierls barrier for the [0001] dislocation in the screw orientation. The generalized stacking fault energy calculations by first-principles density functional theory indicate that the [0001] dislocations prefer to glide as undissociated dislocations on the prism slip plane with the largest interplanar spacing, where the large empty channels (imaged as regular hexagons in the [0001] projection) are not cut. The values of fracture toughness K_IC are evaluated to be 2.0–2.3 MPa·m^1/2 without apparent orientation dependence by single-cantilever bend tests of chevron-notched single-crystal specimens. In addition, grain boundary sliding is found to occur at a relatively low shear stress of about 0.9–3.3 GPa during compression tests on micropillar specimens unintentionally containing a grain boundary.