Improvement of the dynamic strength of thermally sprayed coatings by means of machining surface conditioning

通过喷砂活化表面，通过涂层颗粒的机械夹持改善了基材和涂层之间的界面结合。粗糙化的表面形貌诱导残余压应力，这通常导致在过渡的一个基板的动态负载能力的增加。然而，最近对热喷涂复合材料的疲劳行为的研究证实了用精加工工艺代替喷砂工艺的潜力。在本项目的范围内，表面形貌的具体调整以及基体材料的过渡区中的残余应力状态应该有助于确定涂层的界面结合和基体的加工过程之间的功能依赖性。残余应力是通过车削工艺引起的，并且根据材料的硬度和车削工艺的参数而变化。工件的过渡区，从车削过程中产生的，是由随后的珩磨过程中去除和具有可变的材料比的表面形貌产生的珩磨过程的参数依赖。在珩磨过程中，待去除的材料去除量会受到影响，因此，在精加工后的表面上可以发现工件中更深处的残余压应力状态。此外，进一步的可能性，以调整由热喷涂工艺引起的残余应力将被仔细检查。这涉及到通过改变高速氧气燃料喷涂过程中的气体成分以及控制喷枪的处理参数来对残余应力进行特定的调整。此外，这些改变后的残余应力对涂层性能，特别是对附着到基板上的效果将密切调查。在项目结束时，将对替代表面活化的潜力进行科学评估，并在旋转弯曲测试中对过渡区的质量和表面形貌进行综合调整。随后的涂层处理也将通过珩磨工艺进行分析。结构化表面在摩擦学载荷下比非结构化表面表现出更高的耐磨性。型材槽的特殊插入会产生空隙，作为润滑剂的储存。然而，在动态载荷下，这些凹槽会导致缺口效应，这会对动态强度产生负面影响。因此，还需要分析特别引入的表面形貌结构与动态疲劳行为之间的函数依赖性。

activation of the surface by blasting improves the interfacial binding between the substrate and coating by means of mechanical clamping of the coating particles. The roughening of the surface topography induces residual compressive stresses, which normally lead to an increase of the dynamic loading capacity in the transition one of the substrate. Recent studies on the fatigue behavior of thermally sprayed composite materials, however, verify the potential of substituting the grit blasting process with a fine machining process. Within the scope of this project, specific adjustments of the surface topography as well as the residual stress state in the transition zone of the substrate material are supposed to help determine the functional dependency between the interfacial binding of the coating and the machining process of the substrate. The residual stresses are induced by means of a turning process and vary, depending on the hardness of the material and the parameters of the turning process. The transition zone of the workpiece, resulting from the turning process, is removed by a subsequent honing process and a surface topography with varia-ble material ratio is generated in dependency of the parameters of the honing process. The stock removal to be removed can be influenced during the honing process and thus, the residual com-pressive stress states deeper in the workpiece can be found on the surface after fine machining. Additionally, further possibilities to adjust residual stresses induced by the thermal spraying pro-cess will be scrutinized. This involves a specific adaptation of the residual stresses by varying the gas composition during High Velocity Oxygen Fuel spraying as well as the handling parameters to control the spray gun. Furthermore, the effect of these altered residual stresses on the coating properties, especially on the adhesion onto the substrate will be closely investigated. The potential of an alternative surface activation will be scientifically evaluated towards the end of the project with the combined adjustment of the quality of the transition zone and the surface topography in rotation bending tests. The subsequent coating treatment will be analyzed by means of a honing process as well. Structured surfaces exhibit a higher wear resistance under tribological loads than non-structured surfaces. The specific insertion of profile grooves creates voids, which serve as storages for lubricants. However, under dynamic load, these grooves can lead to notch effects, which can negatively affect the dynamic strength. Therefore, the functional dependence between a specifically introduced structuring of the surface topography and the dynamic fatigue behavior needs to be analyzed as well.