Rolling Contact Performance of a Ti-Containing MoS2 Coating Operating Under Ambient, Vacuum, and Oil-Lubricated Conditions

Abstract

Solid lubricant molybdenum disulfide (MoS2) coatings have been frequently used to lubricate mechanisms operating in environments where oil and grease lubrication are ineffective. This work evaluated the rolling contact performance of a Titanium-containing MoS2 coating under humid ambient, vacuum, and oil-lubricated conditions. Weibull analyses of L50 lifetimes of AISI 52100 steel balls coated with a Ti-MoS2 coating paired with uncoated M50 steel rods were determined to be 3.7, 14.5, and 158.6 million cycles in ambient, vacuum, and oil-lubricated environments, respectively. In the ambient and vacuum tests, failures were determined to be associated with the onset of abrasive wear rather than fatigue or spalling. The L50 lifetimes of tests performed in those environments were found to depend upon the wear rate of the coatings on the balls. That is, the Ti-MoS2 functioned as a barrier to the onset of abrasive wear between the steel alloys until the coating was sufficiently worn away. Under oil-lubricated (boundary lubrication) conditions, L50 was found to depend on the durability and composition of tribofilms formed in-situ on the surfaces of the uncoated M50 rods. The tribofilms were comprised of mixtures of MoS2 crystallites and amorphous hydrocarbon (a-C:H). The crystalline MoS2 in the tribofilm originated from the amorphous Ti-MoS2 coating and likely underwent a thermodynamic phase transition as a result of the applied Hertz stress and frictional heating in the contact. The a-C:H in the tribofilm probably originated from a catalytic scission of the polyalphaolefin (PAO) molecules caused by the d-band character of the Mo or Ti in the coating. Overall, the Ti-MoS2-coated balls were effective at extending the operational lifetimes of M50 rods under ambient, vacuum, and oil-lubricated conditions by an order of magnitude.

A review of physical vapor deposition coatings for rolling bearings

“…Recently, a dense, featureless, and amorphous Ti (∼16 at %) containing MoS 2 coating was developed. 42 The L 50 FL of M50 steel rods was improved by 34.91 times in ambient air, 16.52 times in vacuum, and 2.16 times in an oil-lubricated environment by using Ti–MoS 2 -coated balls.…”

“…Recently, a dense, featureless, and amorphous Ti (∼16 at %) containing MoS 2 coating was developed. 42 The L 50 FL of M50 bearing steel rods was improved by 34.91 times in ambient air, 16.52 times in vacuum, and 2.16 times in an oil-lubricated environment by using Ti–MoS 2 coated balls. It was explained that the abrasive wear between the steel surfaces in the ambient and vacuum environments was mitigated by the Ti–MoS 2 coatings.…”

Study on the Tribological Mechanism of Ultrafine SiO₂/MoS₂ Powders in Complex Calcium Sulfonate Grease

“…Nano-SiO2 powder [7] has the characteristics of high hardness, high pressure resistance [8], and good chemical stability [9]. Ultrafine MoS2 powder is a layered material with a three-sided polyhedral structure [10], which is easy to enter the friction surface [11]. It is easy to form repair layer by adding it to the grease under the action of friction, which has good lubrication property [12].…”