Identification of crack path fractures in sintered silicon of inter- and transgranular nitride by in situ TEM

Inter- and/or transgranular crack paths in sintercd silicon nitride (Si(3)N(4)) during fracture were investigated by in situ straining experiments in a transmission electron microscope at room temperature, using a high-precision micro-indenter. By this technique, cracks introduced in an in situ manner were observed to propagate in the grain interior and along grain boundaries. High-resolution electron microscopy (HREM) observation revealed that the crack propagation takes place at an interface between Si(3)N(4) grains and an intergranular glassy film (IGF) in the case of intergranular fractures. According to the results by previous molecular dynamics simulations, a number of dangling bonds are present at the Si(3)N(4)/IGF interface, which should result in the observed fracture behavior at the interface. On the other hand, the crack path introduced during transgranular fracture of Si(3)N(4) grains was found to be sharp and straight. The observed crack propagated towards [(11) over bar 20] inside the Si(3)N(4) grain with the crack surface parallel to the (1 (1) over bar 00) plane. The HREM observations of crack walls revealed them to be atomically flat. The atomic termination of the crack walls was identified in combination with image simulations based on atomic models of the cleaved crack walls.