Alloykerros

Alloykerros is a term used in metallurgy to describe a surface layer in which the near-surface region of a material has been modified to form an alloy with a composition differing from the bulk substrate. The layer can form by diffusion between materials, or by deposition or chemical reaction during processing.

Formation of an alloykerros occurs through several mechanisms. Diffusion-based processes such as carburizing, nitriding, aluminizing, or chromizing introduce alloying elements into a base metal, creating a modified layer with new phases. Cladding, welding, and chemical vapor or physical vapor deposition can also produce a surface alloy, sometimes with a graded transition between substrate and coating.

The alloykerros typically exhibits a composition gradient and a thickness that can range from a few micrometers to several tens of micrometers or more. Its phases and properties—such as hardness, wear resistance, corrosion resistance, and thermal stability—depend on the elements involved and the processing conditions. In some cases, the layer may be brittle or bear residual stresses.

Characterization of an alloykerros employs microscopy with chemical analysis (for example, SEM/EDS or EPMA) and phase identification (XRD). Depth profiling techniques (GD-OES, SIMS) can determine how composition changes with depth.

Applications of alloykerros include improving the surface performance of gears, bearings, cutting tools, turbine blades, and corrosion-resistant vessels. The concept underpins diffusion-hardened steels and protective coatings designed to extend service life under demanding conditions.