Finely grained nanometric and submicrometric coatings by thermal spraying: A review

Technology, microstructure and properties of nanostructured coatings obtained using different feedstock including: (i) powders composed of agglomerated nanocrystals; (ii) solutions; and (iii) suspensions are discussed. The methods of nanostructured coarse powders manufacturing are reviewed together with the problems related to formulation of solutions and suspensions. A particular attention is paid to the key problem at liquid feedstock spraying, namely to their delivery and injection into jets or flames. The physical and chemical phenomena occurring at flight of injected liquid droplet of solution and suspension are shown and related to the formation of coatings and their microstructure. Some microstructural, chemical, mechanical and electrical properties of coatings are collected and related to the operational processing parameters by regression equations derived from the design of spray experiments. Finally, the possible applications of nanostructured coatings are briefly discussed.