超低温高速重载自润滑轴承制造关键技术与长寿命设计

For the bearings used in liquid-hydrogen turbo-pumps of large launch rocket engines, the operational dn value has increased from 1×10^6 to 2.1×10^6 mm·r/min at present, and will soon come up to the advanced world standard of about 3×10^6 mm·r/min. Under the extreme operational conditions, i.e., ultra-low temperature, high speed, heavy load and the solid lubrication by transfer films, the angular contact ball bearings used in hydrogen turbo-pumps are facing several critical issues, such as the thermal instability due to poor lubrication, the structural strength of the cage and the thermal shocks of the ceramic balls because of the alternating impacts of both the loads and the temperatures, as well as the low-cycle fatigue under heavy loads and high shear stress. However, the range in the design parameters for the bearings used in turbo-pumps is limited. The current trial-and-error development method takes a high consumption of time, cost and energy. This project aims to reveal mechanism of the following issues, i.e., the formation of transfer film lubrication, the development of the friction and wear at the contact interfaces, the generation and propagation of thermal-shock-induced cracks on the surfaces of ceramic ball bearings, the property control of surface layer and the low-cycle fatigue. The high-strength laminate PTFE-composite cages reinforced with carbon-fiber will be fabricated. The microstructures and stress-control method of ceramic ball surfaces will be developed. The surface modification of the stainless bearing steel will be conducted. The boundary parameters for the domain of the competitive failure modes will be obtained, which can provide a constraint function for the targeted optimization design of the bearings with high dn values. Through this project, the detailed design and property-controlled manufacture of ultra-low-temperature high-speed heavy-load bearings can be achieved, meeting the needs of sustainable development of space exploration.

大运载火箭用氢氧发动机氢涡轮泵用轴承的工作转速dn值（mm.r/min）已从早期100万发展到目前210万，并即将突破国际先进水平300万，轴承已成为核心和瓶颈技术。氢涡轮泵用角接触球轴承在超低温高速重载工况和依赖固体转移膜润滑的条件下，面临着润滑不良热失稳、温度与载荷交变冲击下保持架薄壁结构强度和陶瓷球热震强度、重载高剪切低周疲劳等多重风险，轴承设计参数窗口十分狭窄，试错式研制方法耗时耗钱耗力。项目立足于揭示转移膜润滑形成和界面摩擦磨损发展规律、氮化硅陶瓷球表面热震裂纹形成与发展机理、不锈轴承钢表层控制和快速疲劳机制；发展高强度碳纤维布层压增强PTFE复合材料保持架、陶瓷球表面显微结构和应力控制、轴承钢表面强化工艺方法；获取不同失效模式竞争性发展的参数作用边界域，为高dn值轴承的目标裁剪性综合优化设计提供约束函数，实现该苛刻工况轴承的精细化设计与控性制造，满足空间探索的可持续发展需求。

项目以我国重型推力液体火箭发动机氢涡轮泵轴承可靠服役和寿命延长为主要目标，围绕液氢介质中高速重载自润滑陶瓷球轴承服役过程主要矛盾和技术瓶颈开展失效机理，设计方法和复合材料、陶瓷球、不锈轴承钢的制造工艺研究。项目发明了碳纤维布/聚四氟乙烯层压管轴承保持架复合材料，突破了同心绕制成型工艺技术，解决了碳纤维布与聚四氟乙烯树脂之间界面结合强度弱、径向分层、复合材料耐磨性差和抗蠕变性能差等问题；研制的碳纤维布/聚四氟乙烯层压管的常温和低温径向抗拉强度为均超过100MPa，且表现出优异的低温摩擦稳定性和抗磨损性能，可满足超低温高速涡轮泵轴承的使用要求。开展了C30高氮不锈轴承钢的性能测试，其额定疲劳寿命约为普通9Cr18不锈钢的36倍。C30钢相较于9Cr18钢具有更小的摩擦系数，其滑滚摩擦瞬时温升更低，可提高表面抗胶合能力30%以上，表面固体润滑薄膜能够进一步提升C30钢在重载干摩擦条件下的减摩抗磨能力。研究发现了氮化硅陶瓷球承压时接触区边缘首先出现环形裂纹，后产生径向裂纹，最终瓣状碎裂的演化规律，其压溃强度超过20GPa。氮化硅陶瓷球接触微区的耦合分析结果表明，随着摩擦系数和热应力增加，瞬时力热作用下接触浅表层的后沿拉伸主应力会超过材料断裂强度并萌生裂纹，但热影响区深度在几微米量级，接触宽度远大于接触深度，这是陶瓷球热震表面网状裂纹出现的原因。裂纹扩展与裂纹深度关系较大，当裂纹深度小于2μm时其重复受载影响基本可以忽略不计。结合轴承钢和陶瓷球的失效判据，提出了超低温高速重载涡轮泵轴承的极限设计方法，构建了面向具体工况需求参数的轴承结构优化模型，核算了轴承保持架的冲击强度，研制了适用于型号需求的7207自润滑角接触陶瓷球轴承，初步形成了面向新一代运载需求的自润滑陶瓷球轴承自主研制保障能力。项目形成的超低温自润滑轴承极限设计方法对航空、航天苛刻工况轴承设计具有指导意义，轴承零件制造和表面工艺技术可推广应用于众多高端轴承领域。