A methodology to determine surface durability in multifunctional coatings applied to soft substrates

The tribological characterization, in particular the surface durability of multifunctional layers applied to soft, non-magnetic materials, due to their important differences in mechanical and tribological properties, constitutes, by itself, an important challenge to the tribologist. These multifunctional layers consist of a solid lubricant coating on top of a hard, wear resistant and high load-supporting layer. The use of low severity conditions, which are necessary to discriminate between solid lubricants, induce unnecessary and unduly long test times. The use of high severity conditions, which are more adequate to analyse the hard. high load supporting layers, produce shorter tests but are not able to discriminate among the solid lubricant deposits. In this paper, a new methodology allowing short test time with good discrimination between multifunctional layers is proposed. The test protocol is based on a method of incremental loading. By increasing the normal load in increments at a constant time interval the surface durability of both the hard layer and the solid lubricant coating was determined. The suitability, reliability and reproducibility of the proposed methodology were determined by testing commercially available solid lubricants (DLC, Teflon (R), MoS2 dispersed in an inorganic binder and MoS2 dispersed in an organic binder) coated on commercial aluminium (as received and as anodised). (c) 2005 Elsevier Ltd. All rights reserved.