Séminaire / Seminar – Percolation of grain boundary and triple-junction networks: a test of theory – Ashwin Shahani – 12/10/22

Grain boundaries (GBs) provide fast diffusion pathways in polycrystalline materials due to the excess free volume and enhanced atomic mobility. The distribution and character of GBs have long been known to play a critical role in many intergranular failure events, including corrosion, cracking, and liquid metal embrittlement. Susceptibility towards such failure events is not only dependent upon the crystallographic character of individual GBs, but also the connectivity between them. Here, we investigate the connectivity of more than 10000 grain boundaries in a three-dimensional (3D) microstructure through the lens of bond percolation. Our efforts are made possible by new strides in laboratory-based X-ray diffraction tomography. In the framework of the standard percolation theory, we determine a percolation threshold of high-angle GBs in the thermodynamic limit, above which there exists a continuous pathway of GBs that travels infinitely far. Our results compare well to previous models, when the topological characteristics of the GB network is taken into account. In addition, we investigate the percolation behavior of triple junction lines, which we show to be significantly different from that of GBs. The insights obtained can help guide the design of failure-resistant materials via GB engineering. This talk will introduce the physics of percolation and show how it can be leveraged to investigate the 3D structure of polycrystalline materials.