Randschicht

Randschicht is a German term that refers to the near-surface region of a material or component in which the composition, microstructure, or properties differ from those of the interior. The concept is used across disciplines such as materials science, surface engineering, and geology to describe layers formed at or near the surface during processing or service.

Formation mechanisms include diffusion-driven redistribution of elements, chemical reactions with the environment, and mechanical or thermal processing. Examples are oxide scales on metals, carburized or nitrided outer zones created by diffusion of light elements into the surface, and work-hardened or tempered surface layers. Such layers can also result from coatings, wear, corrosion, or environmental attack, leading to gradients in hardness, residual stress, grain size, or phase content.

Characteristics and analysis: a randschicht typically has a thickness ranging from a few nanometers to several micrometers or more, depending on the process. It is often identified by changes in composition, phase, microstructure, or mechanical properties from the bulk. Techniques used to study randschichten include optical and electron microscopy, X-ray diffraction, surface analysis methods (XPS, EDS, AES), SIMS, and microhardness testing, as well as profilometry to measure depth profiles.

Significance: the properties of the randschicht influence wear resistance, corrosion behavior, fatigue life, and overall component performance. In engineering practice, controlling the characteristics of the edge layer—through processes like coating, heat treatment, or surface finishing—is essential for achieving desired service performance.