Importance of Substrate in Surface Engineering

Abstract

The substrate plays an important role in the application of surface engineering processes. It provides mechanical support for the surface layer in components and may also interact with a surface layer during processing. The term ‘subsurface engineering’ has been coined to describe the deliberate selection or alteration of substrates to satisfy engineering and processing requirements economically. ’Passive’ subsurface engineering describes the conscious selection of a core material and its initial constitution to match it to a proposed surface engineering process. The materials engineering involved in selecting core materials for traditional thermochemical processes is well established. This is not generally so for new processes, or when older processes are applied to other types of substrate, as is illustrated with respect to the plasma nitriding of SG cast iron. ‘Active’ subsurface engineering entails the production of an intermediate layer on the core material. Often, the materials engineering requires account to be taken of the interaction of this subsurface layer with the surface layer created during processing, and this is illustrated by reference to some experiments on the CVD production of a TiC coating on a precarburised steel. Some mechanical requirements of a subsurface layer are illustrated by reference to the stress systems present in bending, in rolling contact, and in gears.