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，使用环保和节约资源的创新工艺正变得越来越重要。化石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造成的短缺，需要对这些资源进行优化和可持续的利用。这可以通过创新地结合技术产品和机械工程产品的设计和生产过程来实现。在这个研究项目中，滚动接触元件的资源效率是为了达到延长轴承寿命的干式润滑，避免早期故障和减少摩擦损失。本项目的目的是利用钼氧化物作为固体润滑剂，实现可靠的干式润滑。干润滑剂的涂层在基质中提供了坚硬和耐磨的表面和弹性性能。在材料去除的情况下，底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脂润滑轴承进行比较。这项联合研究是由汉诺威莱布尼茨大学三个不同的研究所合作进行的，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)。目的是开发一种自再生固体润滑剂，以确保其在高负荷轧制表面上的可用性。为此，以氧化钼为基础的PVD涂层被用作重负荷轧制表面的干式润滑剂。尤其是三氧化钼(MoO_3)，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到了蓄水层的作用。这些特性将MoO2和MoO3区分为接触辊的可能涂层材料。在轴承运行期间，由于磨损过程，在高负荷滚动接触区发生持续的层退化。同时，从储存层产生固体润滑层。在轴承试验台上对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，还可以得出有关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.