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This review appeared in the January 2022 edition of the Nanomechanical Testing Journal Club — a monthly email brief highlighting leading-edge research and the latest discoveries supported by Bruker nanomechanical testing technology.
In this open-access Nature Communications article featuring precision in situ TEM experiments that take a detailed look at the interaction between defects to develop new mechanistic insights. Specifically, this is the interaction between coherent twin boundaries (CTB) and single-arm dislocations sources in nickel. This is interesting because of reported enhancements to both strength and ductility at the bulk scale when high densities of grown-in twins are present. The results of this study are important data for modelling and the development of future structural materials.
The authors utilized Bruker’s Hysitron PI 95 in situ TEM mechanical testing system to perform tensile tests on Ni bi-crystals mounted on the Push-to-Pull (PTP) sample mounts. As exemplified by this study, the PI 95 and PTP testing configuration offers stable and detailed mechanical and microscopy data. During the tensile test, two distinct single-arm sources are observed to activate and nucleate dislocations, which interact with a nearby coherent twin boundary. Using systematic contrast analysis, the dislocations were characterized, which allowed stress levels associated with each of these processes to be estimated based upon the load-displacement data and Schmid factors. Initially, the screw dislocations are transmitted across the CTB, but the mechanism switches to absorption and subsequent CTB sliding after some plasticity occurs. The authors also made other interesting observations, such as reflection of a non-screw dislocation from the CTB and the formation of constriction nodes in the CTB. These constriction nodes were found to have an important role in determining whether dislocations were transmitted or absorbed at the CTB, which was also supported by molecular dynamics simulations.