The effect of additives on the wear behavior of bearing steels with RfO(CF2O)x(CF2CF2O)y(CF2CF2CF2O)zRf perfluoropolyalkylether fluids

In previous research, high wear of M-50 bearing steel in low humidity air environments was observed for RfO(CF2O)(x) (CF2CF2O)(y)(CF2CF2CF2O)(z)R-f base fluid in a reciprocating tribometer. In this work, the effect of humidity on wear was observed with a four-ball tribometer using the same base fluid in an oxygen-deficient environment with 52100 bearing steel. In low humidity atmospheres, air was found to decrease wear compared to nitrogen in the four-ball wear tribometer. Next, the effects of additives soluble in the base fluid on the wear behavior of M-50 and 52100 steel were studied at low humidity using both a reciprocating tribometer as well as a four-ball tribometer. An attempt was made to adjust conditions of the four-ball test to allow its use for routine screening of additives; however, under the conditions attempted, the four-ball tribometer, whit improved in repeatability for perfluoropolyalkylethers, was not as discriminating as the reciprocating tribometer. All of the additives were found to be effective as antiwear agents using the reciprocating tribometer, but not the four-ball tribometer. The four-ball tribometer results did not correlate well with the reciprocating tribometer results, likely because of higher Hertzian stress In the four-ball tribometer. Analysis of the reciprocating tribometer specimen surfaces by grazing angle microscope Fourier transform infrared spectroscopy provided insight into the additives' mechanisms. Results are presented along with proposed explanations for the behavior of the additives in the base fluid.