Residual stress analysis of ceramic coatings

涂层通常用于确保物体表面的功能特性（如腐蚀或磨损保护，传感器）或装饰特征。但在许多情况下，层（涂层）具有制造相关的残余应力，产生不良影响（例如层的开裂和剥落），因此，了解复合材料中的残余应力及其影响是必要的，以便适当地适应涂层工艺。在项目的第一个阶段，基于激光烧蚀过程和耦合数字全息干涉测量，开发并验证了一种用于非接触和微创测量表面残余应力的激光光学方法。基于第一个项目阶段的结果，项目（第二个项目阶段）的目标现在包括通过非接触式在线测量实时原位残余应力（即测量正在进行的过程中的临时应力）。因此，可以获得有关涂层工艺的新知识，以及创建在线过程控制以确保所需涂层性能的可能性。根据获得的信息，并与过程模拟的数据进行比较，通过控制火炬轨迹（运动学）、同步冷却和涂层工艺参数的变化，可以制造具有规定残余应力水平的涂层。方法开发的长期目标是对热喷涂工艺产生的层内残余应力状态的选择性和再生产生进行过程控制。此外，为确定激光烧蚀残余应力而开发的系统应扩展到相对较小的物体（表面边界影响）和圆柱形或自由曲面。

Coatings are commonly applied in order to ensure functional properties (such as corrosion or wear protection, sensors) or decorative features on the surface of an object. But in many cases, layers (coatings) possess manufacturing-related residual stresses that create undesirable effects (e.g. cracking and spalling of layers), and therefore, it is essential to know the residual stresses and their effects in the composite in order to appropriately adapt the coating process. In the 1st project phase, a laser-optical method for contactless and minimally invasive measurement of surface residual stresses, based on a laser ablation process with coupled digital holographic interferometry, has been developed and validated. Based on the results of the 1st project phase, the objective of the project (2nd project phase) now consists of the real-time in-situ determination of residual stresses (i.e. measurement of temporary stresses during the ongoing process) by contactless online measurement. Thereby, new knowledge of the coating process is to be achieved, as well as the possibility to create an in-line process control to ensure the desired coating properties. With the information gained and by comparison with data from process simulation, the manufacturing of coatings with a defined level of residual stresses will be possible by the control of torch trajectory (kinematics), simultaneous cooling and variation of the coating process parameters. The long-term aim of method development is the process control for selective and reproductive generation of residual stress states in layers, which were generated by means of thermal spraying processes. Moreover, the systematics developed for the determination of residual stresses by laser ablation should be extended to comparatively small objects (surface boundary influence) and cylindrical or freeform surfaces.