A low friction coefficient is a guarantee of improving energy efficiency. At high temperature, many tribo-components require low friction coefficient to save energy or retain mobility, such as sliding bearings, forming moulds, cannon bores. On the basis of the classical theory of adhesion and solid lubrication, if chemical reaction film or physical adsorption film with low shear stress covers on the contact surface, it can achieve a low friction coefficient in boundary lubrication. During high temperature friction, the solid-lubricating film generated on the worn surface by physical or chemical reaction can effectively reduce the friction. The ideal design for achieving a low friction coefficient is to have an elastically stiff and hard substrate to support the normal load and keep the contact area small, while the surface lubricating film provides shear accommodation and reduces adhesive strength. High temperature solid-lubricating material mainly serves in extremely harsh conditions, such as atmosphere and vacuum under high temperature, high temperature corrosion environment, high speed, and heavy load conditions. Most of the thermal machinery needs to experience a low temperature startup stage or low/high temperature cycling during the operation, such as foil bearing working at a wide temperature range from cryogenic to over 650 °C. From the perspective of the whole service conditions, mechanical system must go through the low temperature stage during startup and shutdown periods, thus the high temperature refers to the wide temperature range from the initial environmental temperature to high temperature operation stage. From the engineering technology, high temperature solid-lubricating material has abilities of continuous lubrication function and satisfactory wear resistance at wide environmental range. Besides of solid lubricant being suitable for diverse environments, environmental durability should be also in consideration for design of solid-lubricating materials. Some solid-lubricating materials need to only survive a few seconds (forging dies) or minutes (re-entry flight vehicle) while others must endure for years (aircraft engine parts). The lifetime of some solid-lubricating materials involve over 108 cycles (satellite parts) or several cycles (space docking mechanism). Tribological behaviors are not intrinsic properties of material relying on physical and mechanical properties; instead, they are systems’properties involving interactions within pairs of contacting surfaces and between them and the environment. This dictates a need for high temperature solid-lubricating material to provide favorable friction and wear in a broad range of operating environments.
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