Unveiling grain boundary Brownian ratchets: a 4D investigation of grain boundary dynamics under cyclic annealing

Grain boundaries (GBs) are conventionally assumed to migrate with equal mobility regardless of direction. This fundamental assumption has been challenged by recent theoretical work suggesting that GBs can act as Brownian ratchets, exhibiting direction-dependent mobilities and unidirectional motion under cyclic thermal annealing. This proposal aims to validate the GB Brownian ratchet effect experimentally in bulk polycrystalline aluminum alloys. Utilizing various diffraction techniques at beamline ID11, we will capture microstructure evolution in two Al alloys (with and without pinning particles) during in situ annealing with temperature oscillations to detect potential unidirectional GB motion and quantify differences in GB migration rates. This will provide insights into the validity of the Brownian ratchet model in real, bulk polycrystals—with significant implications for understanding and controlling the microstructure of materials.