Advanced thermal spray coatings for tribological applications

Thermal spray coating is one of the most common procedures to improve the tribological properties of materials. Ceramic and cermet coatings, especially those based on oxides (alumina, chromium oxide, etc.) and carbides, are widely used for wear protection. Improvements under investigations are related to the possible use of nanostructured coatings and to the potential application of hybrid techniques. As a possible alternative, solid lubrication is proposed as integration or replacement of the traditional liquid lubrication in the case of severe operative conditions when there is the possibility of a lack of lubricant or when environmental problems can arise from waste disposal. In the present paper, results from experimental activities on different types of abrasion-resistant thermal spray coatings are presented: graded coating systems, specifically designed for titanium-based alloys, obtained by reactive plasma spraying and physical vapour deposition of titanium nitrides; nanostructured WC-Co coatings deposited by high velocity oxy-fuel; plasma-sprayed ceramic coatings based on oxides containing nanophases either from nanostructured precursors or postprecipitated by purposely designed thermal treatments; self-lubricant coatings deposited by plasma spray with the inclusion of graphite.