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Adenike Giwa1 Zachary Aitken2 Peter Liaw3 Julia Greer1

1, California Institute of Technology, Pasadena, California, United States
2, Institute of High Performance Computing, Singapore, , Singapore
3, The University of Tennessee, Knoxville, Tennessee, United States

Deformation of micron-sized single crystals of a dual-phase high entropy alloy, Al0.7CoCrFeNi i.e., a face-centered-cubic (FCC) and body-centered-cubic (BCC) structure, has been previously studied and revealed different deformation mechanisms during uniaxial compression. These mechanisms are explained in terms of common nanoplasticity mechanisms: collective dislocation glide and nucleation-governed plasticity in the FCC phase and dislocation crossslip in the BCC phase. In this study, vertically aligned ~ 2 um –diameter pillars made from the same alloy, which contain a single-phase boundary in each sample, were subjected to uniaxial compression. Results reveal that for a high symmetry orientation of FCC [101]/BCC [001] samples, the high symmetry [101] orientation of the FCC phase drives the elastic deformation with a calculated yield stress of 0.5 GPa but the continuous deformation in the plastic regime is a signature that is attributed to the cross slip in the BCC phase. We observed slip transmission through the boundary from FCC to the BCC half-pillar, which suggests dislocation nucleation in the BCC phase at the onset of yield in the FCC phase as well as the dislocation-boundary interaction, which was not observed during the deformation of single crystalline BCC samples of the same orientation [001]. Micro-pillars that contain different crystal orientations (low and high symmetry) were studied; we discuss their deformation mechanisms in the context of different contributions of each phase and orientation to the elastic and plastic deformation of the overall sample. Yield strengths of Nanopillars with high symmetry orientation of BCC half-pillars have a higher yield strength of a factor of 2.5 greater than pillars with high symmetry orientation FCC half-pillars. We show that in addition to strength, the strain-hardening rate also varies with the different orientations and combinations studied.

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