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

喷砂表面的活化通过机械夹持涂层颗粒改善了基材和涂层之间的界面结合。表面形貌的粗化会产生残余压应力，而残余压应力通常会导致基材过渡区的动载荷力增加。然而，最近对热喷涂复合材料疲劳行为的研究证实了用精细机械加工过程取代磨粒喷射过程的潜力。在本项目的范围内，特定的表面形貌调整以及衬底材料过渡区的残余应力状态被认为有助于确定涂层的界面结合与衬底的加工过程之间的函数依赖关系。残余应力是通过车削过程产生的，并随材料的硬度和车削工艺参数的不同而变化。由车削过程产生的工件的过渡区被随后的研磨过程去除，并根据研磨过程的参数产生具有可变材料比的表面形貌。在研磨过程中，会影响要去除的残留物的去除，因此，在精加工后的表面上，可以发现较深处的残余压应力状态。此外，还将仔细研究调整热喷涂过程中产生的残余应力的进一步可能性。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操作参数来具体适应残余应力。此外，这些变化的残余应力对涂层性能的影响，特别是对基材附着力的影响将被密切研究。在项目接近尾声时，将结合旋转弯曲试验中对过渡区质量和表面形貌的综合调整，对替代表面活化的潜力进行科学评估。后续的涂层处理也将通过珩磨工艺进行分析。在摩擦学载荷作用下，结构表面表现出比非结构表面更高的耐磨性。异形槽的特定插入会产生空隙，作为润滑剂的储存库。然而，在动态载荷下，这些凹槽会导致缺口效应，从而对动态强度产生负面影响。因此，还需要分析特殊引入的表面形貌结构与动态疲劳行为之间的函数依赖关系。

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.