Rolling contact fatigue life of AISI 52100 steel balls with mineral and synthetic polyester lubricants with PTFE nanoparticle powder as an additive

This work evaluates the rolling contact fatigue life of AISI 52100 steel bearing balls with mineral and synthetic oil, with and without additive, using a four-ball tester. IP 300/87 was applied with a total load of 600 kg (corresponding to a maximum Hertz stress of 8.709 MPa). SN-350 (a neutral mineral solvent) and TMP-05 (an environment friendly synthetic polyester) of the same viscosity were additivated with PTFE nanoparticle powder in different percentages. The total test time for each specimen was recorded and processed on Weibull probability plots. L10 and L50 are given for pure base oils and oils additivated with 1, 3 and 5 wt.% of PTFE powder. The results point to an increase in the fatigue life when additive-containing oils were used. In order to provide some understanding of the protection mechanism of the additive, the contact angle and the influence of the surface wettability on the lubricant unctuosity were analysed. Scanning electron microscopy and LINK techniques were used to study pitting, crack propagation, the chemical influence of additive and fluorine content.