Structure and properties of PVD-coatings by means of impact tester

Abstract Machine parts like rolling bearings or gears are stressed during operation in a changing mechanical strain. This causes wear by impacts and wear by rolling which is marked by the so-called surface ruin. The appearance of surface fatigue is based upon structural transformation, cracking and cracking-growth processes and ends with the separation of debris particles caused by the above-mentioned permanent changing strain [K.-H. Habig, Verschleis und Harte von Werkstoffen, Carl Hanser Verlag Munchen Wien, S. 203ff, 1980]. The final stage, which is equivalent to the component failure, is the so-called ‘pitting’ on the technical surface, which is characteristically named ‘surface fatigue’. The impact tester is used for detailed research on failure mechanisms of thin films. Statements about the adherence of hard material coatings under dynamic compressive stress can be made using this test method, due to the possibility of simulating some effects of rolling strain. Therefore, a hard metal ball strikes with a frequency of up to 50 Hz on to the surface. The altitude stress can be varied to obtain a detailed evaluation of fatigue strength under reversal strain. Selected hard material coatings were analyzed after testing with the described method applying an impact force of 300 N, 500 N and 700 N. In the framework of this presentation, MSIP (Magnetron Sputter Ion Plating) coatings on titanium- and chromium basis were used. The fatigue defects and the results of this study will be discussed relative to structure and morphology of thin films.