Experimental and simulative investigations on the fatigue behavior of compounds, consisted of Cr-based nitride hard coatings on steel substrate under cyclic impact loads and bending stresses“ (Fatigue)

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PVD (physical vapor deposition) coated tools are subject to cyclic impact forces and superimposed bending loads during their operating time in tribological applications, e.g. in forward cold forging. Impact tests and 4-point bending tests are among the established methods for investigations on the fatigue behavior of PVD coated tools. While tools in technical applications are usually subjected to both stresses, in the literature either the cyclic impact stresses or the bending forces are considered. Furthermore, there are contradictory reports in the literature regarding the influence of PVD coatings on the fatigue strength of the coated tools, since the failure mechanisms under mentioned loadings have not yet been sufficiently investigated. The overall objective of this research project is thus the experimental and simulative investigation of the fatigue behavior of compounds, consisted of (Cr,Al)N hard coatings and steel substrate HS6-5-2C, under both cyclic impact loads and bending stresses. A fundamental contribution to the description of failure mechanisms will be provided in dependence upon the coating properties thickness, morphology, chemical composition and elastic-plastic properties as well as depth-dependent properties indentation hardness, indentation modulus and residual stresses. For this purpose, the coating systems (Cr1-xAlx)N, with x = 0.20; 0.40; 0.60, will be deposited on steel substrate 1.3343 by means of HPPMS (high power pulsed magnetron sputtering). Impact tests will be carried out to investigate the material behavior under cyclic impact forces. 4 point bending tests will be used for cyclic bending loads. The coated steel specimens will be compared with uncoated samples with respect to the fatigue strength under cyclic loading. The fatigue behavior of all variants will be investigated, taking into account the depth dependent properties, by both experimental works at Surface Engineering Institute (IOT), RWTH Aachen University, and simulative studies at Institute for Materials Testing, Materials Science and Strength of Materials (IMWF), University of Stuttgart. A major part of this research project is the analysis of the fatigue behavior and the failure modes of the test specimens after cyclic loading tests. For this purpose, fundamental analyzes will be carried out by means of scanning (SEM) and transmission electron microscopy (TEM). Thus, on the one hand, it will be clarified how the considered coated and uncoated test specimens behave mechanically in the impact and in the 4 point bending tests. On the other hand, the influence of the hard (Cr1-xAlx)N coatings on the fatigue strength of the compound will be investigated. A verification and extension of the findings for further coating systems is planned for a possible third research year.