The effect of nano-inclusions on materials’ strength and toughness had attracted great interest in recent years. It was shown that tuning the morphological and microstructural features of materials could tailor their fracture modes. The existence of a characteristic size of inclusions that favours the fracture mode (i.e. transgranular or intergranular) was experimentally observed but also predicted by a two-dimensional model based upon energetic arguments which related the crack propagation mode to the ratio of the interface area between the crystalline inclusion and the matrix with the area of the crystallite inclusion in a previous work. In the present work, a three-dimensional model was proposed in order to extend the two-dimensional model and take into account the influence of the size of grain boundary zone on the toughening/hardening behaviour of the material as it was observed experimentally in the literature. The model related crack propagation mode to the ratio of the volume of the grain boundary zone between the crystalline inclusion and the matrix with the volume of the nano-inclusion. For a ratio below a critical value, transgranular propagation was favoured while for larger values, intergranular propagation was favoured. It was also demonstrated that the extent of the grain boundary region could significantly affect this critical value. The results of the model were in agreement with published experimental observations related to the toughening/hardening behaviour as a function of the size of crystalline inclusions as well as the width of the grain boundary regions.

Influence of Nano-Inclusions’ Grain Boundaries on Crack Propagation Modes in Materials. T.E.Karakasidis, C.A.Charitidis: Materials Science and Engineering B, 2011, 176[6], 490-3