Adhesion optimization of DLC thin films through conditioning of steel surfaces by plasma nitriding

类金刚石薄膜（DLC）由于其优异的性能在许多摩擦学应用中是必不可少的。在许多情况下，不令人满意的附着力和机械负载能力限制了它们的应用。一种解决方案，很少使用，直到现在与DLC涂层是预处理等离子氮化。 除了改善的支撑效果之外，还观察到改善的涂层粘附性。以前很少使用这种方法的原因是结果的可重复性差和对它的附着力的知识水平低，本项目的目的是确定，描述和评估等离子体渗氮钢表面DLC膜的附着力标准。初步工作表明，钢表面的等离子渗氮允许DLC涂层具有非常好的附着力，无需进一步详细说明。然而，已经确定，通过适当选择参数对表面进行的改性可以在氮化过程中进行具体调整。这些结果构成了以下工作假设的基础：·DLC涂层附着力的改善是由表面结构的变化引起的，这是等离子体氮化工艺的结果。这些变化包括网格结构、碳的溶解度和扩散速率、反应条件以及相变。·这些变化与涂层附着力之间的相关性在很大程度上仍然未知，但可以通过实验确定。·将特别注意碳的溶解度，这是负责在涂层过程中的扩散过程的增加，因此对涂层的附着力有积极的影响。从这些工作假设中，派生出次级目标，并在下面列出。 深入了解渗氮工艺参数与所得组织和材料性能之间的关系.在等离子渗氮和DLC涂层过程中，考虑到微观组织的扩散过程的模型.解释通过等离子体渗氮得到的表面改性与DLC涂层的附着力之间的联系。确定DLC涂层的适当改性，使其在等离子渗氮表面上具有良好的附着力。为了实现这些目标，选择合适的钢，在工艺参数变化的情况下，分析等离子渗氮及其边缘层成分。然后在规定的条件下在PACVD工艺中对氮化样品进行DLC涂层，并随后检查涂层的附着力。从考试的结果被纳入在材料的氮化过程中发生的过程的建模和模拟。还开发了一个模型的概念，combines各种调查的结果。这使得能够识别和评估渗氮和涂层工艺的影响参数，这些参数对渗氮和涂层工艺具有重要影响。

Diamond-like carbon films (DLC) are essential due to their excellent properties in many tribological applications. In many cases, unsatisfactory adhesion and mechanical load capacity limits their application. One solution, rarely used until now with DLC coatings is pretreatment plasma nitriding. In addition to an improved supportive effect, an improved coating adhesion was also observed. Reasons for the previously seldom use of this approach is the poor reproducibility of results and the low level of knowledge about its adhesion.The aim of this project is the identification, description and assessment of the adhesion criteria of DLC films on plasma-nitrided steel surfaces. Preliminary work has shown that plasma nitriding of steel surfaces allows for a very good adhesion of DLC coatings, without going into further detail. However, it was determined that the modifications of the surface by suitable selection of parameters can be specifically adjusted during the nitriding process. These results form the basis for the following working hypotheses:• The improved adhesion of DLC coatings is caused by changes to the surface structure, which is a result of the plasma nitriding process. These include changes of the grid structure, the solubility and diffusion rate of carbon, the reaction conditions and also phase transformations.• The correlations between these changes and the adhesion of the coatings are still largely unknown, but can be experimentally determined.• Special attention will be paid to the carbon solubility, which is responsible for an increase of diffusion processes during the coating process and therefore has a positive influence on the adhesion of the coating. From these working hypotheses, sub-objectives are derived and listed in the following.1. To reach a deeper understanding of the link between the nitriding parameters and the resulting microstructure and material properties.2. The modeling of diffusion processes during plasma nitriding and DLC coating, taking the micro-structure into account.3. Explanation of the connections between the resulting surface modifications through plasma nitriding and the adhesion of the DLC coatings.4. The identification of suitable modifications of DLC coatings, that allow a good adhesion on plasma-nitrided surfaces.To achieve these objectives, suitable steels are selected, under variation of process parameters, plasma nitrided and their edge layer composition is analyzed. Then the nitrided samples are DLC coated in a PACVD process under defined conditions and the coatings adhesion is examined after-wards. The findings from the examinations are incorporated in the modeling and simulation of the processes taking place during nitriding in the material. Also a model concept is developed that com-bines the results of the various investigations. This allows the identification and evaluation of the influencing parameters of the nitriding and coating processes that have a significant influen