UC Merced

NiTi alloys are highly resistant to corrosion 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. Previous studies suggested castor oil as a natural lubricant for NiTi and reported friction coefficients less than 0.01, i.e. superlubricity, when sliding steel against 60NiTi (60wt.% Ni, 40 wt.% Ti). Here we explore the robustness of those findings by characterizing the change in friction coefficient as a function of contact pressure and surface roughness. It is found that friction is extremely sensitive to surface roughness, such that ultra-low friction could only be achieved with surfaces having roughness less than tens of nanometers, conditions which may not be achievable in some practical bearing applications.