Tribological performance of various coatings in unlubricated sliding for use in small arms action components—A case study

Use of liquid lubricants in dry and dusty environments can lead to malfunction or jamming of small arms weapons. As such, dry or “lubricious” coatings are desired for use on weapons action components to eliminate the need for liquid lubricants. The tribological performance of a variety of coatings was assessed under unlubricated sliding conditions spanning the range of those expected to be found in the action components of small arms. The coating types included in the study covered a broad range of hardness, composition, and deposition methods. Coating types investigated included: hard vapor-deposited PVD TiCN coatings, relatively soft organic PTFE-filled resin-bonded coatings, modified anodized coatings (for aluminum), electroless nickel–cobalt alloy coatings, PTFE-filled electroless nickel coatings, phosphate pre-treatment combined with dry-film burnished MoS2, and a ferritic nitro-carburizing treatment. Substrates included medium carbon steel, D2 tool steel and 6061-T6 aluminum. Tests were run using a cylinder-on-flat geometry, with self-mated coatings in both reciprocating and unidirectional tests under sliding velocities up to 3.6 m/s, at room temperature and 150 °C. These screening tests ranked the tribological performance of the coatings using both the coefficient of friction and the wear coefficient. The best performing samples were tested up to total sliding distances of 3.6 km.