【作者】 张驰；

【导师】 宋光铃；

【作者基本信息】 厦门大学 ， 材料学， 2020， 博士

【摘要】 碳纤维增强高分子复合材料(CFRP)具有潜力巨大的市场推广前景,但其与工程合金的配合使用带来的电偶腐蚀风险和隐患必须引起高度重视,且应得到妥善解决。如何优化CFRP的结构设计与生产工艺、优化铆接的方式及装配件选择,最大程度的避免电偶效应对CFRP/合金的破坏,都是应用中需要特别关注的问题。为此,本文系统地讨论了碳纤维(CF)及其高分子复合材料(CFRP)的电化学行为,以及CFRP与典型常见工程合金之间的电偶腐蚀过程及行为。基于CFRP和工程合金工业实际应用环境条件,进一步讨论了可能对材料服役期间综合性能造成影响的因素及它们的具体失效行为。本研究中使用了由美国通用汽车公司(General Motor)环球研究院提供的PAN基碳纤维(50k)增强的环氧基复合材料(命名为E-CFRP)和尼龙基复合材料(命名为T-CFRP),以及四种工程合金(镀锌高强钢-Zn coated DP590,碳钢-1040steel,铝合金-A16022,镁合金-AZ31)。环境为通用汽车腐蚀标准实验GMW14872所用溶液(0.9wt.%NaCl+0.1wt.%CaCl2+0.075wt.%NaHCO3)和实验室常用盐溶液 3.5wt.%NaCl。使用 Autolab电化学工作站、M470微区电化学显微镜、SU-70/TM-3000扫描电子显微镜、莱卡光学显微镜和Q-lab盐雾箱等仪器设备,进行了样品基本电化学性质测试(如开路电位,极化曲线,电化学阻抗)、样品电化学处理(如恒电位极化,恒电流极化)、样品微区电化学表征、样品宏观微观形貌观察、循环盐雾和全浸泡工程测试等实验。根据所设计的研究方案,首先讨论了 CFRP的微观缺陷对CFRP电化学表观的影响;而后使用电解池长期监测CFRP/合金的电偶电流,进一步提出了 CFRP的微观缺陷模型及影响整个系统电偶进程的“有效缺陷”的概念;在分别研究了阴极CFRP和阳级工程合金的基本电化学性质后,讨论了使用不同类型螺钉铆接时它们的电偶腐蚀行为机理;还分析了阴极材料CFRP实时电化学行为及其内部缺陷分布对电偶腐蚀的影响;最后设计了两种特殊CF微电级,探索了作为CFRP中增强相的CF的横截面和圆柱表面的电化学行为。结果显示两种CFRP的开路电位(OCP)类似于贵金属,与典型工程合金之间的电位差远远高于50 mV,因此在侵蚀性环境中CFRP与合金的偶接会存在引起后者电偶腐蚀的巨大风险;T-CFRP的纤维与基体的结合明显优于E-CFRP,其内部缺陷明显少于E-CFRP,使得T-CFRP在电化学行为上较之E-CFRP会更快到达稳定;由于CFRP中缺陷的存在,在溶液中由于水的渗透带来的电偶过程的变化是具有时间效应的,T-CFRP/合金的起始电流较高,但很快达到稳定,而E-CFRP/合金起始的电流较低,且随时间延长逐渐上升,并最终会超过T-CFRP/合金的电流值。在CFRP与合金铆接之后,除了电偶腐蚀,缝隙腐蚀造成的破坏也非常明显,尤其是在盐雾条件下;并且合金的自腐蚀也需要关注。最令人惊讶的是,研究发现CF在电化学上表现为二维异性,其横截面的电化学活性较之圆柱表面竟高出两个数量级。本博士论文的工作,提出了 CFRP的缺陷性模型,提升了 CFRP电化学行为的认识;深化了 CFRP/金属连接件电偶腐蚀行为的理解;补充了以前被忽视的电偶腐蚀对阴极材料的影响的认知;实践证明了通过不同的铆钉来区分出自腐蚀、电偶腐蚀、缝隙腐蚀对合金整体破坏的技术新思路,深化了人们对工程连接件腐蚀破坏的认识;还初步探索了碳纤维电化学行为的各向异性,为未来的碳纤维研究开辟了新方向。更多还原

【Abstract】 The electrochemical behaviors of carbon fiber(CF)and the reinforced polymers(CFRP)were investigated,and the galvanic corrosion processes between CFRPs and typical engineering alloys were analyzed in this dissertation.All materials used in this research were provided by the General Motor from the United States.The carbon fiber is PAN-based that named 50k.Two kinds of CFRPs(epoxy matrix noted as E-CFRP and nylon matrix noted as T-CFRP)and four alloys(Aluminum 6022,Magnesium AZ31,Zn coated DP590 steel and 1040 steel)were used in the study.Considering the practical application environments,GMW14872 solution(0.9wt.%NaCl+0.1 wt.%CaCl2+0.075wt.%NaHCO3,according to GM worldwide engineering standard)and 3.5wt.%NaCl were used.The basic electrochemical behavior of the CFRPs,as well as the effect of the CFRP microstructure,was systematically studied.The long-term galvanic corrosion currents and corrosion of the CFRP/metal couples were measured.A CFRP microstructural defect model was proposed to understand the electrochemical behavior and the galvanic process.The results show that the open circuit potentials(OCPs)of the two kinds of CFRP are very positive like noble metals Pt and Au.The difference in Ecrr between the CFRP and metals is obviously larger than 50mV.Thus,there will be a big risk of galvanic corrosion in a CFRP/metal couple in the aggressive environment.The number of micro defects inside the E-CFRP body is obviously higher than that in the T-CFRP.Thus,the E-CFRP reaches a relatively stable state relatively more slowly than the T-CFRP in the electrochemical measurements.As the number and distribution of defects in the two CFRPs are very different,their electrochemical behaviors vary differently with time.The galvanic currents of the metal/T-CFRPs started at a relatively high value and then reached stable quickly.The galvanic currents of metal/E-CFRP started at a relatively low value and kept increasing with time.Besides the galvanic corrosion,the effect of crevice corrosion is significant when a metal is coupled with a CFRP in practical applications.Especially in the salt spray environment,the effect of crevice corrosion and self-corrosion can significantly affect the behavior of the galvanic system.The most interesting scientific finding was that carbon fiber is electrochemically anisotropic.The cross-section of the CF is 2 orders of magnitude more active than the cylindrical surface.The study focused more on the cathode than the anode that was overlooked before.A microstructural model was proposed to get a better understanding on the electrochemical behavior of CFRP.The understanding on the corrosion behavior of CFRP/metal couples was improved.The knowledge on the effect of galvanic corrosion on the cathode CFRP was enriched.A new engineering method was proposed by using different kinds of joints to distinguish the contribution of galvanic corrosion,crevice corrosion and self-corrosion in the CFRP/metal couples.To improve the design and manufacture of the composites,to obtain a more reasonable joint,and to reduce corrosion damage,prevent such galvanic corrosion are the hot issues that should be focused in the practical applications.Preliminary investigation was made on the two-dimensional anisotropic electrochemical behavior of CF which provided a new direction on the future research of CF.更多还原