المحاضرة 8

Lec.8
Thermal Coating Processes
Introduction
In modern mechanical engineering, components are generally subject to both a high strength requirement and high requirements of the surface properties, e.g. corrosion and/or wear resistance. Further, functional characteristics must often be fulfilled at the surface. The entire requirement profile may not be met by one material alone. Only by a functional separation of the tasks of the component surface and inside, which is technically realized by applying coatings onto a structural
component, can the entire requirement complexity be fulfilled. A large range of procedures can be used in principle to manufacture coatings.
Besides physical (PVD) and chemical (CVD) vapor deposition, galvanic and external currentless chemical deposition, a hot-dipping process, thick-film coatings of thermal spraying and cladding welding have been utilized. Thick-film coatings are characterized by high deposition rates and short process times for manufacturing material composites. In these, partial multilayered coatings are used to ensure the stability of the composite layer. Both the substrates, which determine the component strength, and the coatings can be composite materials.
Thermal spraying and cladding procedures, which in particular find their application in protective coatings against wear and corrosion of highly stressed components, are of high economic importance and are described in detail in the following, where their applications will be discussed with examples. The economic loss as a consequence of wear and corrosion amounts to at least 8 billion Euros in the Federal Republic of Germany, so that a high value is attached to these applications.
Such layers can be important to reduce friction as well as to provide thermal or electrical isolation. Finally, functional coatings with special magnetic, thermoelectric or chemical characteristics are becoming increasingly important.