The origins of roughness

The researchers found out that surfaces made of different materials, which show distinct mechanisms of plastic deformation, always develop surface roughness with identical statistical properties.

"Roughness on these smallest scales is important because it controls the area of intimate atomic contact when two surfaces are pressed together and thus adhesion, conductivity and other functional properties of surfaces in contact."

In collaboration with colleagues from the Karlsruhe Institute of Technology, the École Polytechnique Fédérale de Lausanne/Switzerland, and the Sandia National Laboratories/USA, and funded by the European Research Council (ERC), Pastewka and his group were able to simulate the surface topography for three reference material systems at the JUQUEEN and JUWELS supercomputers at the Jülich Supercomputing Centre, which included monocrystalline gold, a high entropy alloy of nickel, iron and titanium, and the metallic glass copper-zirconium, in which the atoms do not form ordered structures but an irregular pattern.

The scientists now investigated the mechanism of the deformation and the resulting changes in the atomic scale both within the solid and on its surface.

Pastewka, who is also a member of the Cluster of Excellence Living, Adaptive and Energy-autonomous Material Systems (livMatS), and his team found that despite their different structures and material properties, all three systems, when compressed, develop rough surfaces with a so-called self-affined topography.