Tracking the evolution of intergranular corrosion through twin-related domains in grain boundary networks

Tailoring the grain boundary network is desired to improve grain boundary-dependent phenomena such as intergranular corrosion. An important grain boundary network descriptor in heavily twinned microstructures is the twin-related domain, a cluster of twin-related grains. We indicate the advantages of using twin-related domains and subsequent statistics to provide new insight into how a grain boundary networks respond to intergranular corrosion in a heavily twinned grain boundary engineered 316L stainless steel. The results highlight that intergranular corrosion is typically arrested inside twin-related domains at coherent twins or low-angle grain boundaries. Isolated scenarios exist, however, where intergranular corrosion propagation persists in the grain boundary network through higher-order twin-related boundaries. Clustered twin grain boundaries in stainless steel can stop intergranular corrosion, but only if they are coherent. A team led by Mitra Taheri at Drexel University in the USA analyzed microstructural regions in a 316 stainless steel where all grain boundaries were twinned and found that, when the twins in these clusters were coherent or had a low misorientation angle, they arrested interganular corrosion. They emphasized this effect by engineering more coherent and low-angle grain boundaries with thermomechanical processing, leading to larger twin-related domains. In contrast, twinned clusters with high-angle grain boundaries consistently failed at resisting corrosion, a similar manner to the rest of steel. Twin-related domains may therefore be a good predictor of intergranular corrosion and may help us mitigate metal damage.