In-situ synchrotron X-ray study of shear-induced phase transformation of bismuth using a high-speed rotational diamond anvil cell (HS-RDAC)*

Extreme shear deformation is ubiquitous in the natural world and intentionally employed for engineering unique microstructures in materials. But the dynamic microstructural evolution mechanisms have been predominantly inferred through ex-situ characterizations and computational predictions with no in situ experimental validations. The introduction of the high-speed rotational diamond anvil cell (HS-RDAC) is a breakthrough instrumental development to enable in-situ XRD study of dynamic microstructural evolution at synchrotron x-ray beamlines. We demonstrate in this study the performance of HS-RDAC for bismuth phase transformation under extreme shear conditions. Copper was used together as a pressure marker in a mixed powder form.  [PC1] We observed an early onset of transformation at a high rotational speed (corresponding to xxx /sec shear rate?), which indicates a strain-induced mechanism overcoming or replacing the pressure-induced mechanism for the onset of phase transformation. The apparent pressure as based on hydrostatic Cu-EOS further increases and stabilizes at a stage of constant rotation speed, i.e., a saturation of cumulative strains. With supplementary ex-situ multimodal characterizations, this in-situ result provides new insight into highly dynamic microstructural transformation pathways during extreme shear deformation.