Friction of molybdenum disulfide–titanium films under cryogenic vacuum conditions

The tribological behavior of steel and sapphire sliding on a sputtered MoS2+Ti coating was studied in ultra-high vacuum as a function of temperature over the range of 4–300 K. The coefficient of kinetic friction for the steel/moly interface was determined to be approximately 0.05 from room temperature to 240 K, and increased monotonically to 0.125 at 4 K. The sapphire/moly friction coefficient was measured to be 0.15±0.05 at room temperature and increased monotonically to 0.25 at 4 K. We also analyze in detail the flash temperature due to frictional heating at the sliding contacts. Flash heating is a particularly strong effect at cryogenic temperatures.