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A team of international scientists headed by Prof. Marco Salvalaglio from TUD–Dresden University of Technology has found out that internal stresses—not just interface energy—play a key role in shaping the microstructure of crystalline materials. These findings challenge classical theories and could improve how we design materials for engineering and technology. The results have recently been in the Proceedings of the National Academy of Sciences.

Polycrystalline materials are made up of many tiny crystals called grains and are found everywhere, from rocks in nature to metals and ceramics in engineering. The way these grains are arranged and how they change over time has a big impact on important properties like strength, flexibility, and electrical conductivity. Understanding what drives these changes, especially the role of internal stresses inside the material, is key to explaining how materials behave and to designing better ones for specific uses.

Using advanced computer simulations and theoretical modeling, Salvalaglio and his team demonstrate that shear deformations and internal mechanical stresses—emerging as grain boundaries move—play a crucial role in how microstructures evolve. Such a mechanism, known as "shear coupling," can strongly influence the shape and behavior of grains, making their growth deviate from classical theories.

This discovery helps explain why real polycrystals often behave differently than predicted and could lead to better ways of designing materials for specific uses, from stronger metals to more efficient electronics. It also further highlights what sets crystalline materials apart from other systems like foams or emulsions: they are capable of sustaining deformations.

"Exploring the role of internal stresses in the evolution of microstructures in polycrystalline materials has been the focus of a research line initiated a few years ago, starting with the formulation of a dedicated continuum model and preliminary investigation of grain boundary migration. It has been particularly exciting to realize that this work helps reconcile previously unexplained experimental observations and offers a fundamental revision and update of classical theories.

"Until now, our work has primarily focused on stresses generated by interface motion in single-component polycrystalline systems. With this groundwork in place, the next step is to address the interplay with other mechanisms, such as plastic relaxation within grains, and to investigate analogous phenomena in multicomponent materials," states Salvalaglio.