A review on the fatigue cracking of twin boundaries: Crystallographic orientation and stacking fault energy

Twin boundaries (TBs) are ubiquitous interfaces with specific structure in metallic materials. They possess special interactions with dislocations and the fatigue cracking behaviors are distinctive from that of conventional high-angle grain boundaries. A profound understanding on the fatigue cracking mechanisms of various TBs achieved over past decades is reviewed here for the first time. The dislocation slips in the matrix and twin grains determined by grain orientations are closely related to the inclinations of coherent and incoherent TBs. The variable TB-dislocation interactions generate tunable fatigue cracking behaviors of TBs. Besides the grain orientations, the stacking fault energy (SFE) also alters the piling-up of dislocations at TBs by influencing dislocation dissociation. Both factors synergistically affect the fatigue cracking behaviors of TBs with a linear relationship between the difference in Schmid factors and SFE at the threshold of TB cracking. Moreover, the TBs produced by deformation twins in face-centered cubic metals are strong to resist fatigue cracking by promoting deformation homogeneity while those linked with deformation twins in hexagonal-close-packed or body-centered-cubic metals are preferential sites for fatigue cracking with strain localization and stress concentration. These fundamental knowledges of TB fatigue cracking provide important guidance in interfacial design to enhance materials fatigue performance.