Dry lubrication of rolling contacts by self-regenerating molybdenum-oxide coatings

由于全球经济和生态环境的变化，使用创新的环境友好型和资源节约型工艺变得越来越重要。矿物燃料和稀有合金元素等资源的短缺，例如由于中国和印度等新兴工业国家的出现，需要对这些资源进行最佳和可持续的利用。这可以通过技术产品以及机械工程产品的设计和生产过程的创新组合来实现。在本研究项目中，为了延长轴承寿命，避免早期失效，减少摩擦损失，在干润滑中实现滚动接触元件的资源效率。本课题的目的是利用具有自再生特性的氧化钼作为固体润滑剂，实现可靠的干式润滑。干润滑剂的涂层在基体中提供了坚硬耐磨的表面和弹性特性。在材料去除的情况下，下层与大气中的氧气发生反应，从而再生耐磨表面。需要研究涂层的应用范围，并将其性能与传统的油脂润滑轴承进行比较。这项联合研究是由莱布尼茨Universität汉诺威大学的三个不同研究所合作进行的，即材料科学研究所（IW）、机械设计与摩擦学研究所（IMKT）和成形技术与机械研究所（IFUM）。目标是开发一种可自我再生的固体润滑剂，以确保其可用于高负载的滚动表面。为此，基于氧化钼的PVD涂层被用作重载轧制表面的干润滑剂。特别是三氧化钼（MoO3），由于其层状结构，适合作为固体润滑剂。二氧化钼（MoO2）在滚动轴承钢和功能表面之间起着储层作用。这些特性使MoO2和MoO3成为接触轧辊的可能涂层材料。在轴承运行期间，由于磨损过程，在高负荷滚动接触区发生连续层退化。同时，由储层生成固体润滑层。对轴承试验台滚动接触过程进行了分析。磨损过程必须通过有限元模型和数值磨损计算相结合的方法进行深入研究。这项研究工作将有助于更好地理解涂层的磨损行为。此外，它将有可能得出关于涂层在运行中的耐磨性的结论。

Due to the changing global economical and ecological scenarios, the use of innovative environmental friendly and resource-saving processes is becoming increasingly important. The shortage of resources, such as fossil fuels and rare alloying elements, e.g. because of the emerging industrial nations such as China and India, requires an optimal and sustainable use of these resources. This can be achieved by an innovative combination of the design and the production processes for technical goods as well as mechanical engineering products. In this research project, the resource efficiency of rolling contact elements is to be achieved for dry lubrication regarding extended bearing life, avoiding early failures and a reduction of frictional losses. The aim of this project is to realize a reliable dry lubrication applying molybdenum-oxides as solid lubricants with self-regenerating properties. The coating of the dry lubricant offers a hard and wear-resistant surface and elastic properties in the matrix. In case of material removal, the underlying layer reacts with the atmospheric oxygen hence regenerates the wear-resistant surface. The application limits of the coatings needs to be investigated and their performance will be compared with the conventional grease-lubricated bearings. This joint research is performed as collaboration between three different institutes of the Leibniz Universität Hannover namely the Institute of Materials Science (IW), the Institute of Machine Design and Tribology (IMKT), and the Institute of Forming Technology and Machines (IFUM). The goal is to develop a self-regenerating solid lubricant that ensures its availability for highly loaded rolling surfaces.For this purpose, PVD coatings based on molybdenum oxide are used as a dry lubricant on the heavily loaded rolling surfaces. Particularly, molybdenum-tri-oxide (MoO3) is suitable as a solid lubricant due to its layer structure. Molybdenum-di-oxide (MoO2) serves as a reservoir between the rolling bearing steel and the functional surface. These properties distinguish MoO2 and MoO3 as possible coating materials for rolls in contact. During the operation of the bearings, a continuously layer degradation takes place in the highly loaded rolling contact zone, due to wear processes. At the same time, the solid lubricant layer is generated from the reservoir layer. The processes in the rolling contact are analysed in bearing test rigs. The wear processes have to be investigated in-depth by means of an FE model in combination with a numerical wear calculation. This research work will allow for a better comprehension of the wear behaviour of the coatings. In addition, it will be possible to draw conclusions about the wear resistance of the coatings in operation.