Durability evaluation of selected solid lubricating films

An investigation was conducted to examine the coefficients of friction, wear rates, and durability of bonded molybdenum disulfide (MoS2), magnetron-sputtered MoS2 (MS MoS2), ion-plated silver, ion-plated lead, magnetron-sputtered diamond-like carbon (MS DLC), and plasma-assisted chemical-vapor-deposited DLC (PACVD DLC) films in sliding contact with 6 mm-diameter AISI 440C stainless steel balls. Unidirectional ball-on-disk sliding friction experiments were conducted with a load of 5.9 N and a sliding velocity of 0.2 m/s at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7×10−7 Pa), humid air (relative humidity, ∼20%), and dry nitrogen (relative humidity, <1%). The main criteria for judging the performance of the solid lubricating films were coefficient of friction and wear rate, which had to be <0.3 and on the order of 10−6 mm3/N m or less, respectively. The bonded MoS2 and MS MoS2 films met the criteria in all three environments. The ion-plated lead and silver films met the criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen. The MS DLC and PACVD DLC films met the requirements in humid air and dry nitrogen but failed in ultrahigh vacuum.