Lubrication of Intermetallic Nickel Titanium Bearing Materials
- Author(s): Walters, Nicholas Alexander
- Advisor(s): Martini, Ashlie
- et al.
60NiTi (60wt.\% Ni, 40 wt.\% Ti) is a highly resilient and corrosion resistant intermetallic alloy with hardness and elasticity properties suitable for bearing applications. However, lubrication of this material is still being explored since many commercial lubricants are designed to function through chemical and physical interactions with steel surfaces. Titanium rich alloys are known to have poor tribological performance and to be chemically aggressive toward lubricants. Since 60NiTi is a titanium rich alloy, and components made from 60NiTi will likely operate with a lubricant, it is vital to study how to properly lubricate 60NiTi contacts. The goal of this research is to characterize the performance of 60NiTi sliding contacts with different lubricants at a range of operating conditions. First, previous studies suggested castor oil as a natural lubricant for 60NiTi, and reported friction coefficients less than 0.01, i.e. superlubricity, when sliding against steel. Here, the robustness of those findings was explored by characterizing the friction coefficient as a function of contact pressure and surface roughness. It was found that friction under castor oil lubrication is highly sensitive to surface roughness, and that friction coefficients approaching the superlubricity regime are only achievable with very smooth surfaces, which may not be realistic in practical engineering applications. Second, a series of tests were performed to characterize the wear and friction of self-mated 60NiTi contacts lubricated by different greases in low sliding speed contacts. It was found that polytetrafluoroethylene (PTFE) thickened perfluoropolyether (PFPE) greases significantly reduced wear compared to the other greases tested by mitigating adhesive wear modes. These results provide valuable information to guide the selection of grease for 60NiTi contacts. Overall, this work lays the groundwork for future development of new greases and lubricants specifically designed for 60NiTi contacts.