Various high temperature solid-lubricating materials have been developed to meet different requirement. According to the composition, high temperature solid-lubricating material is divided into metal matrix, intermetallic matrix and ceramic matrix high temperature solid lubricating material. According to the usable form, high temperature solid-lubricating material is divided into high temperature solid-lubricating coating/film and high temperature solid-lubricating composite/ bulk. There has been considerable progress in the development of high temperature solid-lubricating coatings. Initially, high temperature solid-lubricating coatings consist of single solid lubricant or a monolithic component. However, at elevated temperatures, it is very difficult for single solid lubricant coatings to maintain low friction and wear simultaneously. Consequently, multiphase high temperature solid-lubricating coatings have been extensively and intensively investigated. Recently, on the basis of self-adaption mechanism, adaptive high temperature solid-lubricating coatings are explored, which are endowed with favorable tribological properties at a wide environment range. The monolithic high temperature solid-lubricating coatings include transitional metal disulfides coatings, noble metal coatings, Cs-compounds coating, and sulfate coatings. Table 1 lists tribological properties of Cs-compounds and sulfates solid-lubricating coatings. Cscompounds coatings were reported to be very promising for lubricating Si-based ceramic components at high temperatures. Cs-compound provides Si3N4 with a good lubrication from room temperature to 750 °C, especially with an average value of 0.03 at 600 °C. During sliding at high temperature, a mixed oxide layer consisting of Cs2O and SiO2 is believed to be responsible for low friction. Additionally, sulfates coatings like CaSO4, BaSO4, and SrSO4 also provide quite low friction coefficient of about 0.15 at high temperature of 600 °C. Tribological and mechanical properties of monolithic solid-lubricating coatings mainly depend on those of solid lubricants. Due to the sensitive nature of solid lubricant to environment atmosphere and ambient temperature, the monolithic high temperature solid-lubricating coatings are routinely applied under simple and specific service conditions.
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