Thermal spraying of thick film systems - process optimization by means of residual stress and residual stress stability

涂层系统中，特别是界面处的残余应力分布对涂层部件的疲劳和失效行为至关重要。通过调整涂层参数，可以优化涂层过程引起的RS分布，使其符合部件的工艺要求。在本课题第一期资助期内，提出了一种基于增量钻孔法分析厚膜系统局部残余应力深度分布的实用测量与评价策略。随后，该方法成功应用于固体氧化物燃料电池（SOFC）应用的热喷涂YSZ热障涂层和MCF铬蒸气保护层。在研究项目继续进行的过程中，测量和评估策略将被调整和扩展(a)到功能梯度材料（FGM）和(b)到冷喷涂材料。在下文中，残余应力结果将用于涂层工艺参数的调整。对于FGM，含钨层将沉积在eurofer钢衬底上，而钨含量将通过粉末混合物的供应逐渐增加，直到顶层达到纯钨。这种FGM层的可能应用是用于核聚变反应堆的材料，其中钨被用作铁素体-马氏体- europofer钢的保护涂层。在这里，关于残余应力的知识对于评估分层构件的机械完整性和寿命至关重要。将使用相同的分析探针分析的另一个应用是冷喷涂层，这将用于修复局部损坏的高温部件（例如涡轮叶片）。第一次成功的初步试验进行了冷祈祷镍基衬底。对于局部损伤部件的修复，了解修复过程中产生的残余应力分布是至关重要的。增量钻孔法的应用可直接应用于热喷涂部件。此外，除了在第一个资助期对热喷涂ysz涂层进行的残余应力分析外，还将评估已经在FRM II （Garching）的应力分析仪上进行的中子衍射分析数据。在此基础上，对残余应力结果进行综合评价。由于进行了所谓的“穿透表面扫描”，因此数据评估非常复杂，并且需要对发生在非常表面以及层状结构界面的表面效应进行校正。

The residual stress (RS) distribution in coating systems in particular atthe interfaces is essential for the fatigue and failure behavior ofcoated components. The RS distribution induced by the coatingprocess can be optimized to fit the technical requirements of thecomponents by adapting the coating parameters. Within the scope ofthe first funding period of the research project a practicable measuringand evaluation strategy based on the incremental hole drilling methodfor analysis of local residual stress depth distributions for thick filmsystems was developed and provided. Subsequently, this methodicalapproach was successfully applied to thermally sprayed YSZ thermalbarrier coatings and MCF chromium vapor protective layers for solidoxide fuel cell (SOFC) applications. In the course of the continuationof the research project the measuring and evaluation strategy will beadapted and extended (a) to functional graded materials (FGM) and(b) to cold sprayed materials. In the following, the residual stressresults will be used for adjustment of the coating process parameters.For the FGM tungsten containing layers will be deposited onEUROFER steel substrates, while the tungsten content will begradually increased by the supply of the powder mixtures until puretungsten will be achieved for the top layer. Possible applications ofsuch FGM layers are e.g. materials for application in fusion reactors,where tungsten is used as protective coating of the ferritic-martensiticEURPOFER steel. Here, knowledge about residual stresses isessential for the assessment of the mechanical integrity and the lifetimeof layered components. A further application that will be analyzedusing the same analysis probe is on cold sprayed layers, which will beused for the repair of localized damaged high temperature parts (e.g.turbine blades). First successful preliminary test were performed forcold prayed nickel-base substrates. For the repair of localizeddamaged components knowledge about the residual stressdistribution induced by the repair process is of crucial importance.Application of the incremental hole drilling method can directly beapplied at the thermally sprayed component. Furthermore, in additionto residual stress analyses on thermal sprayed YSZ-coatingsperformed in the first funding period data of neutronographicdiffraction analyses, which are already carried out at the instrumentStressSpec at FRM II (Garching), will be evaluated. Based on thisevaluation a holistic assessment of the residual stress results will bemade. Since, so called ´through-surface-scans´ were performed, thedata evaluation is very elaborate und requires inter alia the correctionof surface effects which occur at the very surface as well as at theinterfaces of the layered structure.