drylubrication

Dry lubrication refers to reducing friction and wear between contacting surfaces using solid lubricants or dry-film coatings, without relying on liquid oils or greases. It is used in environments where liquids fail, such as high temperature, vacuum, contamination-prone, or clean-room conditions.

The effectiveness of dry lubrication relies on boundary lubrication, transfer films, and the formation of low-shear interfaces. Solid lubricants can form layered structures that slide easily under load, or create protective films that separate surfaces. Temperature, humidity, and load influence performance, as some materials react or oxidize under certain conditions.

Common solid lubricants include graphite, molybdenum disulfide (MoS2), tungsten disulfide (WS2), and hexagonal boron nitride (h-BN). Graphite and MoS2 are widely used; MoS2 performs well at moderate temperatures but is susceptible to oxidation, while WS2 offers better high-temperature performance in some environments. Hydrogenated carbon-based coatings such as diamond-like carbon (DLC) and ceramic-like coatings can also serve as dry lubricants or support self-lubricating behavior. In addition, dry lubricants can be embedded in polymers or applied as thin films by physical or chemical vapor deposition, sputtering, or chemical vapor deposition.

Applications include bearings, gears, cams, and sliding interfaces in aerospace, automotive, vacuum systems, space mechanisms, and high-temperature machinery. Advantages include operation in the absence of liquids, reduced leakage, high-temperature tolerance, and resistance to contamination. Limitations involve sensitivity to contaminants, limited load-bearing capacity, potential performance variability with humidity and temperature, and wear of the coating over time. Selection depends on temperature, load, speed, environment, and compatibility with materials.