General Procedure for Selecting and Testing Materials and Coatings in Response to a Tribological Problem

In general, there is no available tool which can help engineers and researchers to choose optimal materials for friction pairs. This article proposes a dual approach for the choice of materials and coatings. First, in order to select the initial materials, a selection matrix helps to rank a reduced number of solutions to a tribological problem with the aim of building the most credible and viable experimental campaign. Then, this experimental phase is necessary for final selection taking into account tribological properties. The final step involves experimental validation on a prototype and on the real device. This methodology was applied on the complex geometry of an air compressor under severe friction conditions. Technical specifications are defined by a functional analysis of the tribological system. Then, the selection matrix is created on the basis of empirical rules and bibliographic data, including predetermined material/coating properties, process considerations, and tribological features, in accordance with the functional analysis. As an example, four potential solutions were tested: diamondlike carbon (DLC) and polytetrafluoroethylene (PTFE) coatings on 15-5PH stainless steel and two composites, reinforced PTFE and polyetheretherketone (PEEK). Experimental results were then compared to expected values from the specifications. The performance of each solution was highlighted by a graphic radar representation. The selection matrix gave the DLC coatings as one of the best solutions, and experimental tests confirmed this choice while allowing to refine the preselected solutions. This result shows that the selection matrix gives a reliable choice of optimal solutions.