Smoother TiAlN is characterized by lower friction coefficients of 0.06−0.0043 for SAE 15W40 and from 0.076 to 0.0044 for SAE 5W30 and SAE 0W20 accordingly. This explains the impact of the surface roughness through the roughness parameter (ζκσ) and asperity slope (σ/κ) in the mixed...