The Role of Hard Layers in Lubricated and Dry Sliding

Abstract

Lubricated and dry experiments on titanium and steel surfaces with and without TiN sputtered coatings of various thicknesses have been conducted. The significance of the layer thickness, interfacial “friction”, magnitudes of normal and tangential surface tractions, and the mechanical properties of the layer and of the substrate (e.g., elastic modulus and hardness) are critically examined. The conditions under which the deformation mode at the solid-solid contacts is elastic or plastic are addressed in light of the experimental evidence and a finite element analysis. It is shown that surfaces with very low friction, especially for unlubricated sliding, and practically zero wear rates can be obtained in both lubricated and dry sliding by coating the surfaces with sufficiently thick TiN layers. Removal of the protective TiN layer resulted in plowing, severe damage, and delamination.