Effect of tip size and experimental conditions on nano-scale friction testing

Abstract

Assessment of nano-tribological properties (friction and wear) on polymer surface helps to understand their scratch, mar and wear properties. More polymers are used now for automotive, electronics, appliances, and building and constructions industries due to aesthetics and design freedom. Owing to their lower mechanical properties, polymers are vulnerable to surface damage and deteriorate their morphology, functionality, and aesthetics with time. In this study, nano-indenter was used for measuring friction and wear properties varying test parameters and indenter tips. A Berkovich tip (B-tip) with radius of ∼50 nm and a conical tip (C-tip) with 60° cone angle and tip radius of 1000 nm were used. Polyoxy methylene (POM) with additives were chosen for friction testing. Higher coefficient of friction (COF) for C-tip was observed compared to B-tip and this explained based on the higher tip-material interactional area for C-tip. COF was decreased with higher additive concentration and same trend was followed for wear depth for the B-tip. For C-tip, COF was increased with the testing loads and corresponding wear depth were higher for higher load. Change of COF with test velocity was not showing any specific trend. Shallow wear depth using B-tip compared to C-tip may be better for probing top surface of the materials. Nano-scale tribo-mechanical evaluation techniques are uniquely suited for fundamental understanding and screening many additives quickly. Observed wear properties not only depend on the additives added to the formulation, but may also be influenced by the geometry of the tip.