水润滑轴承材料表面微观形貌的摩擦学性能及其评价方法研究

Driven by the growing pressure on marine environment and regional marine protection regulations, applying the marine propulsion system based on water lubrication technology and improving the corresponding tribological performance of water-lubricated bearings have increasingly become a focus of worldwide study. Based on the concept of improving the properties of friction reduction and lubrication through reasonable design of surface texture, this project is proposed to study the effects and the underlying mechanism of surface micro-/nano-structures of water-lubricated bearing materials on the tribological performance. The micro-/nano-structured surfaces of ultra-high molecular weight polyethylene (UHMWPE) and its metallic counterpart will be manufactured by the laser surface texturing or the conventional machining methods. Then, the synergistic enhancement effects of surface micro-textures and surface roughness on the tribological properties will be carefully investigated by the friction and wear experiments. By synthesizing the assessment parameters including the geometric parameters of micro-texture, surface roughness, surface waviness, fractal dimension and hydrophobic properties, the synthetic evaluation method on tribological properties will be proposed in order to optimize the surface micro-/nano-topographies and forecast the corresponding tribological properties on rough surface. By applying various simulation methods under different scales, the cavitation effect and hydrodynamic lubrication effect induced by surface micro-/nano-morphologies, as well as the corresponding influence on tribological properties, will be studied. Moreover, the wear process and the friction reduction mechanism, will be investigated at the molecular scale. The results will provide theoretical and experimental support for the design of UHMWPE-based water-lubricated bearings and the evaluation of the tribological performance.

在海洋环境压力和地区海洋保护法规的推动下，应用基于水润滑的船舶推进系统并提高水润滑轴承的摩擦学性能，已成为国内外研究焦点。基于表面织构化设计增强材料减摩润滑性能的理念，本项目研究水润滑轴承材料表面的微纳结构特征对其摩擦学性能的影响规律及作用机理。借助激光造型技术或常规机械加工方法在超高分子量聚乙烯（UHMWPE）及其摩擦对偶件表面制备微纳结构，通过摩擦磨损实验分析表面微织构和粗糙度协同增强水润滑轴承材料表面摩擦学性能的作用规律；基于微织构几何参数、粗糙度、波纹度、分形维数和疏水性等评定参数，提出表面微观形貌摩擦学性能的评价方法，实现表面微观形貌的优化设计和对摩擦学性能的预测；采用多种尺度的模拟方法，研究微纳结构产生的空化效应和动压润滑效应，并从分子角度揭示织构化表面的磨损过程及减摩作用机理。本项目的研究成果能为UHMWPE水润滑轴承的设计及其摩擦学性能的评价提供理论和实验支持。

设计和制备基于水润滑的船舶推进系统，同时提高水润滑轴承的摩擦学性能，已成为缓解海洋环境压力和适应地区海洋保护法规的关键内容。基于表面织构化设计增强材料减摩润滑性能的理念，本项目研究了水润滑轴承材料表面微织构的摩擦学性能，并对水润滑摩擦副表面微观形貌的减摩机理进行了深入研究。建立了有序微织构（光滑织构）表面和计入随机粗糙度的表面织构模型，借助流体动力学计算方法分析了表面微织构和粗糙度协同增强水润滑摩擦副表面摩擦学性能的作用规律。借助飞秒激光加工工艺和铣削工艺制备了不同形式的表面微纳结构及其复合结构，获得了微结构尺寸参数和铣削轮廓参数（如粗糙度、刀痕高度和宽度）对润滑特性的影响规律。结果表明合理的粗糙表面能够提升摩擦副的润滑效果，且在最优的铣削加工表面在引入织构后摩擦系数较光滑织构表面摩擦系数进一步降低。通过球-盘摩擦实验，研究了不同摩擦条件下金属对偶件表面UHMWPE转移膜的形成规律，发现干摩擦条件下钢球表面始终难以形成较为稳定的转移膜；而在水润滑条件下，钢球表面可形成均匀且连续的UHMWPE转移膜。借助基于反应力场的分子模拟方法，研究了UHMWPE转移膜形成的机理。在摩擦过程中UHMWPE经历剪切变形，此时靠近摩擦界面的聚乙烯发生断裂并粘附在金属表面，不断堆积而最终形成转移膜。借助经典分子动力学模拟方法建立了UHMWPE的分子摩擦模型，分析了非晶态UHMWPE基底的摩擦剪切变形过程，发现摩擦过程中UHMWPE基底逐渐发生解缠结，并伴随着结晶度不断提高。在水润滑条件下，摩擦界面的水分子在摩擦过程中将逐渐扩散到UHMWPE中，界面水分子在扩散过程中更倾向于聚集成单独的团簇，并破坏相邻PE链之间的分子间吸引力，进而加剧UHMWPE基底的磨损。本项目的研究成果将为UHMWPE水润滑轴承的设计及其摩擦学性能的评价提供理论和实验支持。