Friction and Wear Characteristics of Advanced Space Lubricants

The performance of a variety of space lubricants was compared under boundary lubrication at ground level. The types of lubricants studied were the two synthetic base oils PFPE 815Z and MAC 2001A and the two greases 601EF and R2000. High-pressure rheological tests were performed in order to characterize the behavior of each base oil as a function of pressure and temperature. The effect of base oils and greases on friction and wear was studied using Soda-type four-ball tribometer. The highest wear scar was found for 815Z, but it showed the lowest coefficient of friction, whereas 601EF (containing a rust and corrosion inhibitor blended with base oil 815Z), base oil 2001A, and grease R2000 blended with base oil 2001A showed lower wear scars, but produced higher friction coefficients. This unique phenomenon of 815Z was investigated from the phase diagram of 815Z. Investigating these phenomena, the authors found that the decomposition of base oil 815Z containing the acetal group (-OCF2O-) occurred by mechanical shear at high shear rates in the elastic-plastic solid. Hydrogen fluoride is released from the decomposition of acetal groups within the fluoropolymer. As a result, the generation of hydrogen fluoride increased the wear rate of the 815Z base oil. Grease 600EF (formulated without the rust and corrosion inhibitor) and 602EF (containing a molybdenum disulfide) blended with base oil 815Z were also studied.