Fundamental Considerations for Future Solid Lubricants

Report Number: AFML-TR-70-127 p. 40
Author(s): Johnson, R. L., Sliney, H. E.
Corporate Author(s): Lewis Research Center, National Aeronautics and Space Administration
Laboratory: Air Force Materials Laboratory
Date of Publication: 1970-07
Pages: 27
Contract: AF33(615)-5278
DoD Project: 7343
DoD Task:

Abstract:
There are many properties important to the perfomance of solids as lubricants. Those properties include shear characteristics, coherence between particles resistance to cold flow, adherence to the substrate, applicable chemical thermodynamics and kinetics of materials and environments , polymorphism, rheology. Several of the above properties are discussed with the intent of stimulating more general concern for fundamentals in the study, selection, and application of solids as lubricants. Chemical thermodynamics and kinetics have been used effectively to predict stability and thereby to guide the application and use of solid lubricants. Those in the forefront of lubrication cannot afford to disregard this available technology. Low shear strength can most generally be anticipated based on bonding force criteria which is reflected in crystal structure. Intercalation compounding and radiation exposure are means to expand critical lattice spacings and achieve reduced friction. Rheology of constituents and formulations such as effects of high pressure and shear rates on shear force as well as viscoelasticity to enhance life merit careful attention. Adherence and mobility of films can be enhanced by use of surface energy (wetting) relationships and materials or methods that provide chemical bonding. Vacuum deposition by sputtering gives very adherent films. The nonstoichiometric intercalation compound graphite fluoride has good adherence in varied environments as well as useful shear properties and stability.