Grain boundary migration facilitated by phase transformation and twinning in face-centered cubic metals

B Li and KF Chen, JOURNAL OF MATERIALS SCIENCE, 58, 14740-14757 (2023).

DOI: 10.1007/s10853-023-08863-z

Migration of symmetric tilt grain boundaries (STGBs) in face-centered cubic (FCC) metals under shear loading is investigated in this work. The STGBs have a tilt axis of 110, and the angle theta between the (1 (11) over bar) invariant planes ranges from 8 degrees up to 28 degrees with a 2 degrees increment. Interesting phase transformation and twinning are observed during GB migration in Cu, Ni but not in Al. The results show that for low values of theta, under shear loading, a hexagonal close- packed (HCP) phase is formed along the original GB and the HCP phase grows via shear coupling of one of the two interfaces between the HCP and the FCC grain. As theta increases, both interfaces between the HCP and the grains become mobile and the HCP region traverses and transforms the lattice of one grain into the other. Thus, shear coupling is accomplished and facilitated through FCC -> HCP -> FCC phase transformations. As theta further increases to 18 degrees and greater, instead of FCC -> HCP phase transformation, a 111 twin is formed along the original GB. The twin expands via shear coupling of the new GB between the twin and the FCC grain. Lattice correspondences are carefully analyzed for the phase transformation and twinning. The analyses indicate that the mobility of GBs is predominantly determined by how readily lattice transformation can be accomplished. The lattice correspondence in HCP twinning modes provide key insight on the observed GB migration behavior.

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