Barrier layer of a component in which the content of one or several elements has been changed compared to the original composition of the component. This mixed-crystal layer may additionally contain depositions produced during slow cool-down. This coat is also referred to a deposition layer. If inter-metal phases occur between the element diffusing into the base metal and the base metal itself, layers of these inter-metal phases may also be generated, so-called connection layers at the surface. The barrier layer area below the connection layer is referred to as diffusion layer. In contrast to the connection layer, the diffusion layer may have a thickness of several tenths of a millimetre. In surface engineering, the diffusion layer is a layer on metal components generated by the diffusion of chemical substances into the base metal.