表面钝化与MoS_(2)涂覆对17-4PH螺栓盐雾环境下力学与腐蚀性能的影响

Effect of Surface Passivation and MoS_(2) Coating on Mechanical and Corrosion Performance of 17-4PH Bolts in Salt Spray Environment

目的 研究钝化处理与MoS_(2)涂层对螺栓盐雾环境下耐腐蚀与力学性能的影响。方法 针对2种不同的表面处理(钝化,MoS_(2)涂覆)的17-4PH螺栓,采用SEM、EDS对腐蚀后螺栓表面涂层进行表征,采用往复摩擦试验获得表面处理后的摩擦因数;对螺栓进行长时盐雾腐蚀实验,对腐蚀后的螺栓进行标准拉伸实验,对腐蚀表面进行显微形貌观察,以获得处理后螺栓抗腐蚀能力。结果 钝化层与MoS_(2)涂层厚度分别为10.7μm和12.5μm,钝化后往复摩擦试验中的平均摩擦因数为0.85,而MoS_(2)涂层平均摩擦因数仅为0.2,对应螺栓摩擦因数则分别为0.081与0.073;在长时盐雾腐蚀过程中,钝化螺栓在192h后螺栓头部与螺纹处出现腐蚀现象,1 800 h后出现严重腐蚀,表面腐蚀但螺栓断裂强度下降并不明显;在0~6 500 h的盐雾腐蚀实验中,涂覆MoS_(2)涂层的螺栓头部与螺纹处均出现明显腐蚀现象,但是螺栓表面开始出现MoS_(2)涂层剥落。结论 与表面钝化相比,表面涂覆MoS_(2)涂层具有更小摩擦因数,且对螺栓盐雾腐蚀防护更有效,能在3 750 h内完全不锈蚀,在6 500 h时发生大面积MoS_(2)涂层剥落,此外,盐雾表面腐蚀对螺栓拉伸断裂强度影响较小。

The indispensability of high-strength bolts in spacecraft systems is indisputable,given their pivotal role in ensuring the seamless operation and structural integrity of the entire system.However,the operational challenges posed by diverse spacecraft environments expose these critical components to corrosion,introducing the potential for component failures that,in turn,pose a significant threat to the overall safety and functionality of the system.Recognizing the severity of this issue,the research embarks on a comprehensive exploration of the performance of distinct surface coatings in a salt spray environment,with meticulous focus on evaluating the corrosion resistance of bolts.This study places particular emphasis on understanding how passivation treatment and MoS_(2) coatings influence the corrosion resistance and mechanical properties of bolts subject to the harsh conditions of a salt spray environment.In initiating this study,the deliberate choice of 17-4PH bolts was based on their widespread use in aerospace applications.By applying two prominent surface treatment methods-passivation and MoS_(2) coatings-it aims to draw nuanced insights into the effectiveness of these treatments under realistic operational conditions.With cutting-edge techniques such as SEM and EDS,the detailed characterization of corroded bolt surface coatings enabled a profound understanding of the underlying properties governing their performance.The subsequent execution of reciprocating friction tests added a crucial layer to the analysis,offering indispensable data on the friction coefficients(cof)of the surface-treated bolts.The extended duration of the salt spray corrosion experiments-spanning intervals of 0,192,580,1000,1800,2600,3750 and 6500 h-allowed for a comprehensive examination of the evolving corrosion patterns on bolt surfaces.Scanning electron microscopy observations,complemented by EDS spectroscopy analysis,provided detailed insights into the structural changes and compositional variations occurring during the corrosion process.Moreover,the incorporation of standard tensile tests post-corrosion provided valuable information on the enduring mechanical integrity of the bolts subject to these challenging conditions.The experimental outcomes revealed significant revelations:the passivation layer exhibited a thickness of 10.7μm,while the MoS_(2) coatings displayed a slightly thicker layer at 12.5μm.The reciprocating friction tests following passivation highlighted an average cof of 0.85,underscoring the inherent challenges of this surface treatment in extreme environments.In stark contrast,the MoS_(2) coatings demonstrated remarkable efficacy,with an average cof of mere 0.2.Correspondingly,the cof for the bolts themselves were measured at 0.081 and 0.073 for passivation and MoS_(2) coatings,respectively.As the salt spray corrosion progressed,passivated bolts exhibited localized corrosion at the head and thread after 192 hours,intensifying into severe corrosion after 1800 hours.Intriguingly,despite surface corrosion,the decline in bolt fracture strength was not pronounced.In sharp contrast,MoS_(2) coatings,while effective in preventing corrosion within the initial 3750 hours,showed significant peeling of the coatings at 6500 h,signaling a limitation in its long-term protective capabilities.In summary,the findings underscore the superiority of MoS_(2) coatings over passivation in terms of a lower cof and more pronounced corrosion protection for bolts in a salt spray environment.The nuanced insights gained from the research contribute significantly to ongoing efforts to optimize bolt surface coatings,enhancing performance in extreme aerospace environments,and fortifying the reliability of spacecraft.This detailed examination not only sheds light on the intricate dynamics of surface treatments but also provides invaluable support for the future design and engineering of spacecraft components,ensuring their resilience and safety in the face of challenging operational conditions.