Coated Metal : Structure and Properties of Metal-Coating Compositions

Saving in metal, corrosion and wear control of machine parts are the problems of increasing priority. Conventional constructional materials are unable to provide re­ liability and durability of equipment under conditions of increased working speeds and loads, aggressive medium attacks and elevated temperatures. Solution to these problems involves change in properties of the surface layers of products, in the first instance, by means of depositing functional coatings on machine parts. Rela­ tive simplicity of the process and. practically unlimited possibilities of varying properties of coatings have resulted in their wide usage in machine building and transport industry, instrument engineering, radio electronics and other industries. Coating provides means for enhancing constructional strength of steels and al­ loysl. It makes possible a combined method when one group of dislocation mechanisms is used for bulk hardening (grain refining, creation of stable sub­ granular dislocation structures), while the working surface is hardened through other mechanisms (dislocation density increase, separation of excess phases, etc). Combined hardening saves valuable alloying components and provides reduction in metal consumption of machines and constructions. Coating allows manufacturing new composites that combine high durability (fatigue resistance, wear resistance) with sufficient reliability (fracture toughness); enhancement of operational stability of machine parts and tools as compared to stability attainable using conventional heat treatment methods; restoration of worn surfaces and, consequently, reduction in demand for spare parts.