Preparation and vacuum tribological properties of composite coatings fabricated by effective introduction of soft metal Ag into spray-formed YSZ templates

The friction coefficient of thermal sprayed ceramic coatings is relatively high, and the traditional introduction of lubricants will result in the decline of mechanical properties of coatings, which severely limits their applications. Herein, YSZ/Ag self-lubricating coatings were prepared on 316 L stainless steel substrates via thermal spraying technology, vacuum impregnation and in-situ synthesis for the first time. The morphologies, mechanical properties and vacuum tribological performance of composite coatings were studied in detail by comparing with YSZ coatings. Results show that silver particles distribute in the pores, cracks of YSZ coatings, and the filling of defects by silver improves the micro-hardness, fracture toughness and cohesive strength of the coatings. In addition, owing to the formation of lubricating film during the sliding process in vacuum, the friction coefficient of the coating is reduced by about 2 times and the wear rate is reduced by about 600 times after the introduction of silver. At the same time, the addition of the silver lubricant makes the wear of the coupling ball significantly reduced. Since the lubricating film can be continuously replenished and repaired, the YSZ/Ag self-lubricating coating has a relatively long service life (>100,000 sliding cycles).