Fatigue and adhesion characterization of DLC coatings on steel substrates by perpendicular and inclined impact tests

During the Future Advanced Rotorcraft Drive System (FARDS) program, the Aviation Development Directorate (ADD), Aviation Applied Technology Directorate (AATD), Bell Helicopter Textron Inc., University of Toledo and the Aristotle University of Thessaloniki worked together to perform bearing coating tests. The mechanical properties of the DLC coating and its steel substrate were determined via nano-indentations and a FEM supported evaluation of the obtained results. The coating fatigue and adhesion were quantified by perpendicular and inclined impact tests respectively, coupled with appropriate finite element method (FEM) calculations. The inclined impact tests were conducted under lubricated conditions for avoiding abrasion caused by sliding friction on the coated surfaces. In this way, the coating fatigue failure during this test was mainly affected by the impact load, the material's properties and the film adhesion. The effects of these factors on the coating fatigue failure were described via an iterative FEM supported method. Using this method, the coating adhesion was estimated taking into account the exercised impact loads and the determined material properties.