Metals can deform thanks to the introduction and movement of trillions of line defects (dislocations) in the crystalline lattice. It is well known that the dislocations interact to form nearly perfect cells surrounded by boundaries with very high concentrations of dislocations.
However, the underlying physical mechanisms have been elusive: until recently materials models were incapable of even simulating the cell formation. Supported by two ERC grants, the group of Henning Friis Poulsen and Grethe Winther has pursued the vision of visualising the formation and evolution of such cells in-situ, deep within mm sized crystals, using Dark Field X-ray Microscopy. As a first result, we report on the development of 40,000 cells.
We discovered that the cells form in a stochastic, isotropic and uncorrelated manner already at 1% strain. The excellent population statistics implied that we can state that the cell size is consistent with log-normal distributions, while distributions compliant with existing theories of formation and refinement of cells can be ruled out.
Moreover, the distributions exhibit scaling with the external strain – in physics this is typically a sign of universal behavior – while maintaining a fixed volume ratio between cell interior and cell boundary. This insight leads to an interpretation of the formation and evolution steps in terms of universal stochastic multiplicative processes – a type of models well known e.g. from populations models.
A. Zelenika, A.A.W. Cretton, F. Frankus, S. Borgi, F. B. Grumsen, C. Yildirim, C. Detlefs, G. Winther, H.F. Poulsen Sci. Rep.15, 8655 (2025). https://doi.org/10.1038/s41598-025-88262-3
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