Boundary Lubrication RCF Performance of 4 cSt Gas Turbine Engine Oils at 204 °C

The rolling contact fatigue (RCF) and wear performance of three qualified formulations of MIL-L-7808K (4 cSt at 100 °C) were evaluated using AISI VIM-VAR M50 steel. The RCF tester differentiated the fatigue life and wear performance of gas turbine engine lubricants in boundary lubrication regime. Tests were conducted using a ball-on-rod type RCF tester at a maximum Hertzian stress of 4.8 GPa and temperature of 204 °C. Although all the three lubricants meet the military specification, the RCF results suggest that life and wear in the boundary lubrication regime are significantly affected by the formulation. Changes in physical and chemical properties of post test lubricants such as viscosity, acid number and additive concentration were minimal. However, the lowest Fe concentration and COBRA reading, which is a measure of the electrical property of the lubricant, correlated with the highest RCF life and lowest wear.