Unusual macroscopic shearing patterns observed in metals processed by high-pressure torsion
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A duplex stainless steel was processed by high-pressure torsion (HPT) and then examined by optical microscopy. The results reveal unusual flow patterns including double-swirl strains, shear vortices, and the presence of significant local turbulence. Similar flow behavior was also visible in disks of high-purity aluminum and a Zn–22%Al eutectoid alloy. These complex flow patterns and the presence of double-swirls are consistent with the presence of a Kelvin–Helmholtz instability during HPT processing where this may arise if there are local shear velocity gradients between adjacent positions within the HPT disks.
KeywordsShear Strain Friction Stir Welding Duplex Stainless Steel Helmholtz Instability Strain Gradient Plasticity
The authors express their great appreciation to the scientific and technical input and support from the Australian Microscopy & Microanalysis Research Facility node at the University of Sydney. This project was supported by the Australian Research Council [Grant No. DP0772880 (Y.C., Y.B.W., and X.Z.L.)], the U.S. DOE IPP program (Y.T.Z.), and the National Science Foundation of the United States [Grant No. DMR-0855009 (M.K. and T.G.L.)].
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