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)

在摩擦学应用中，PVD（物理气相沉积）涂层工具在运行期间会受到循环冲击力和叠加弯曲载荷的影响，例如在前向冷锻造中。冲击试验和四点弯曲试验是研究PVD涂层刀具疲劳行为的常用方法。虽然技术应用中的工具通常受到这两种应力，但在文献中，要么考虑循环冲击应力，要么考虑弯曲力。此外，关于PVD涂层对涂层工具疲劳强度的影响，文献中有相互矛盾的报道，因为上述载荷下的失效机制尚未得到充分研究。因此，本研究项目的总体目标是对由（Cr,Al）N硬涂层和钢基体HS6-5-2C组成的化合物在循环冲击载荷和弯曲应力下的疲劳行为进行实验和模拟研究。对失效机制描述的基本贡献将取决于涂层性能，厚度，形态，化学成分和弹塑性性能以及与深度相关的性能，压痕硬度，压痕模量和残余应力。为此，涂层体系为（Cr1-xAlx）N, x = 0.20；0.40;通过HPPMS（高功率脉冲磁控溅射）将0.60镀层沉积在1.3343钢基体上。将进行冲击试验，以研究材料在循环冲击力下的性能。4点弯曲试验将用于循环弯曲载荷。将涂覆钢试样与未涂覆钢试样在循环荷载下的疲劳强度进行比较。亚琛工业大学表面工程研究所（IOT）的实验工作和斯图加特大学材料测试、材料科学和材料强度研究所（IMWF）的模拟研究将对所有变体的疲劳行为进行研究，并考虑到深度相关特性。本课题研究的主要内容是对试件在循环加载后的疲劳行为和破坏模式进行分析。为此，将通过扫描（SEM）和透射电子显微镜（TEM）进行基本分析。因此，一方面，将澄清所考虑的涂覆和未涂覆试样在冲击和4点弯曲试验中的机械行为。另一方面，研究了硬质（Cr1-xAlx）N涂层对复合材料疲劳强度的影响。计划在可能的第三个研究年度对进一步涂层系统的研究结果进行验证和扩展。

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.