Direct observation of intergranular cracks in sintered silicon nitride

Crack propagation along grain boundaries in sintered silicon nitride (Si3N4) was investigated by in-situ straining experiments at room temperature in a transmission electron microscope, using a high-precision microindenter. Using this in-situ technique, cracks introduced were introduced in situ and observed propagating along grain boundaries. High-resolution electron microscopy observation revealed that the propagation of the intergranular crack takes place at an interface between the Si3N4 grains and the intergranular glassy film (IGF). This suggests that the Si3N4/IGF interface has a relatively high excess energy. The result was compared with a theoretical calculation using a molecular dynamics simulation.