Modeling the Effect of Grain Boundary Segregations on the Fracture Toughness of Nanocrystalline and Ultrafine-Grained Alloys

Abstract

A theoretical two-dimensional (2D) model is proposed that describes the effect of grain boundary (GB) segregations on the fracture toughness of nanocrystalline or ultrafine-grained alloys. It is shown that GB segregations can lead to crack curvature, providing both crack surface roughness and crack deflection near the crack tip. Within the model, the growth of cracks along GBs under the action of a tensile load is considered. The effects of brittle GB segregations on the crack surface roughness and crack deflection near the crack tip are analyzed, and the associated increase in the fracture toughness of the material is calculated. It is shown that toughening can be achieved if segregations are very brittle and occupy a moderate proportion of GBs. In particular, a sufficiently large (up to 50%) fraction of GBs containing very brittle segregations can increase the fracture toughness by 30–35%. The results of the model can be applied to thin nanocrystalline or ultrafine-grained films.

Making Gd2O3 nanofibers flexible by grain-boundary toughening

“…In the process of grain boundary diffusion, grain growth is not obvious but grain boundary migration leads to rapid grain growth, and the activation energy required by grain boundary migration is higher than that required by grain boundary diffusion. 21–23 Therefore, if the sintering process can be designed specifically and the difference between grain boundary diffusion and grain boundary migration dynamics can be used to inhibit grain growth, the grain can be refined and the porosity defects in nanofibers can be reduced, to improve the flexibility and strength of oxide ceramic nanofibers. 24,25…”