电化学方法研究环氧涂层/基体在3.5%NaCl溶液中的腐蚀行为

采用电化学方法研究了两种常用涂层-环氧沥青涂层和环氧铝粉涂层在3.5%NaCl溶液中的腐蚀行为.腐蚀电位-时间结果表明,两种涂层的自腐蚀电位都比基体的更正,都能起到屏蔽作用保护基体,浸泡中电位向负方向移动说明活化腐蚀过程在继续.电化学阻抗结果表明,腐蚀介质能够较快的渗入涂层到达界面,使涂层的屏蔽作用降低,生成的腐蚀产物可在一定程度上抑制腐蚀的发展.并提出了两种涂层的等效电路模型,对阻抗结果进行了拟合.表明在浸泡初期涂层电阻随浸泡时间延长迅速降低,随后趋于稳定.指出电化学方法能获得与涂层性能有关的定量数据,非常适合于研究涂层/基体的性能.     

环氧粉末涂层在1.5mol/LNaCl溶液中的失效行为

通过电化学阻抗谱(EIS)对两种环氧粉末涂层在1.5 mol/LNaCl溶液中的失效行为进行了研究,利用扫描电子显微镜(SEM)和能谱仪(EDS)对涂层底部金属表面的腐蚀产物进行了分析,探讨了环氧粉末涂层在1.5 mol/L NaCl溶液中的失效机理。结果表明,在1.5 mol/L NaCl溶液中,Cl-等腐蚀介质能在涂层中形成传输通道渗透到涂层与金属界面,并参与界面的腐蚀反应,腐蚀产物主要为Fe的氧化物和氯化物。     

Zn粉含量及表面沾污对环氧富Zn漆电化学行为的影响

采用腐蚀电位、电化学阻抗谱(EIS)评价了Zn粉含量以及涂层／基体界面污染程度对环氧富Zn涂层的防腐蚀性能的影响并探索了富Zn涂层的失效机制。实验结果表明，当涂层中Zn含量较少时，Zn粉没有有效的阻挡作用。通过对可能的阻抗模型的分析，认为富Zn涂层的电化学阻抗谱的低频段是由Zn^2 从金属表面穿过腐蚀产物的扩散控制。涂层／基体界面污染不仅影响了环氧富Zn涂层的防腐蚀性能的发挥，也加速了钢铁基体的腐蚀。     

不同体系中缺陷大小对有机涂层失效形貌的影响

分别在刷涂于铁基体、Al电弧喷涂层和Zn-Al-Mg-RE电弧喷涂层表面的有机涂层中制备了大小不同的人工缺陷,观察了各体系进行电化学交流阻抗(EIS)测试后有机涂层的失效形貌及缺陷处腐蚀产物的微观结构,并分析了各体系的失效机制.结果表明,对于在铁基体和Al电弧喷涂层表面刷涂有机涂层体系,缺陷尺寸越小,有机涂层失效越严重,主要是因为缺陷大小影响腐蚀产物向腐蚀介质中的扩散造成的;对于在Zn-Al-Mg-RE电弧喷涂层表面刷涂有机涂层的体系,缺陷尺寸大小对有机涂层失效形貌的影响不大,主要是因为在人工孔隙中生成了微观结构致密的腐蚀产物造成的.     

深海压力-流速耦合环境对环氧玻璃鳞片涂层失效行为的影响

采用吸水率测试EIS、附着力测试SEM、FT-IR等方法,对比研究常压-静态环境(0.1 MPa-0 m/s)、流体流动环境(0.1 MPa-4 m/s)、高静水压力环境(10 MPa-0 m/s)和压力-流速耦合环境(10 MPa-4 m/s)下环氧玻璃鳞片涂层的失效行为和机制。实验结果表明,耦合环境下,填料与涂层基体间的界面结合被显著削弱,涂层的物理结构发生严重破环,腐蚀介质在涂层中加速扩散,并在涂层缺陷和涂层/金属界面处大量聚集,导致涂层吸水率大幅上升,力学性能显著下降,附着力迅速丧失,发生大面积鼓泡,快速失效。     

无溶剂环氧防腐涂层在不同流速模拟海水冲刷条件下的失效行为

通过OCP和EIS对3种无溶剂环氧防腐涂层在60℃不同流速(2,4和6 m/s)下,含1%(质量分数)石英砂的模拟海水环境中的失效行为进行了研究,并利用CLSM观察了冲刷后涂层的表面形貌,利用SEM和EDS对涂层底部Q345E钢表面的腐蚀产物进行了分析,探讨了无溶剂环氧防腐涂层在模拟海水冲刷条件下的失效机理。结果表明,冲刷条件下,3种涂层的失效过程大大缩短,流速对水在涂层中的传输速率影响不明显,涂层加速失效的原因主要有两点:一方面,砂粒对涂层的磨损作用导致涂层表面产生凹坑或孔洞,缩短了腐蚀介质扩散到达涂层/金属界面的距离;另一方面,流速加速了Cl-在涂层中的传输从而使涂层失效加速。     

硅烷处理对涂层/金属体系耐蚀性能的影响

采用电化学阻抗研究了输电塔架用Q345钢基体上环氧富锌涂层的失效过程,分析了硅烷处理对涂层/金属体的耐腐蚀性能的影响。结果表明,环氧富锌涂层/未表面处理金属体系经过240h的浸泡腐蚀后涂层失去保护作用;而环氧富锌涂层/硅烷处理金属体系经过408 h的浸泡腐蚀后涂层失去保护作用。经阻抗谱和孔隙率与吸水率分析表明,Q345钢经硅烷表面处理后延缓了腐蚀性介质侵入涂层,较大地提高了体系的抗腐蚀能力。     

静水压力下Q235钢环氧涂层在3.5%NaCl溶液中的失效过程

利用电化学阻抗谱（EIS）研究了一种适用于深海环境的重防护环氧涂料在3.5%NaCl溶液中常压以及3.5 MPa下的破坏机制,探讨了静水压力对涂< 层失效过程的影响。结果表明,静水压力加速了电解质溶液在涂层中的渗透,对涂层的失效过程有着明显的影响。与常压下相比,静水压力下涂层电阻更小,涂层的失效过程更快;涂层/金属界面的电荷转移电阻更小,界面处金属腐蚀反应更快,涂层下金属基体更容易发生腐蚀,涂层的防护性能变差。     

承载作用下铁红环氧脂底漆失效过程的电化学响应特征

采用局部电化学阻抗(LEIS)技术和电化学阻抗(EIS)技术研究了不同承载条件下,海水介质中铁红环氧脂底漆失效过程的电化学响应特征。结果表明:在不同的承载力作用下,铁红环氧脂底漆的失效过程呈阶段性变化,且应力加载过程加速了涂层的失效。在300 MPa屈服应力作用下,腐蚀介质可以沿着细小的裂缝快速渗透涂层,与基体接触,缩短涂层的失效时间。涂层失效后,整体阻抗值明显降低,同时试样表面随机分布的高阻抗点数量有所减少,涂层防护性能明显下降,基材发生腐蚀。     

有机覆膜对热烧结锌铝涂层耐腐蚀性能的影响

为提高热烧结锌铝涂层（简称锌铝涂层）的耐蚀性,在涂层表面涂覆一层环氧富铝膜,形成复合涂层。采用十字划格法测试锌铝涂层和复合涂层的附着强度,并用扫描电镜（SEM）分析涂层微观形貌;用海水全浸实验和中性盐雾实验评价涂层的耐蚀性能;采用动电位极化曲线和电化学阻抗谱（EIS）研究涂层的电化学性能。结果表明,复合涂层表面更为完整致密,防水性能优于锌铝涂层;环氧富铝膜层能够有效的阻挡腐蚀介质的入侵,复合涂层耐蚀性比锌铝涂层高。复合涂层腐蚀初期主要为扩散控制,随着腐蚀介质的不断渗入,环氧膜层中的Al粉发生活化反应,起到了一定的牺牲阳极保护作用。有机覆膜提高了锌铝涂层在海洋环境中的适用能力。     

超音速火焰喷涂316L不锈钢涂层性能研究

采用超音速火焰喷涂技术(HVOF)在高强钢表面制备了316L不锈钢涂层,利用扫描电镜、显微硬度仪、电化学测试系统等设备对涂层金相组织、硬度、结合性能和抗腐蚀性能等进行了测试,并分析了WC-CoCr中间层对316L不锈钢粉末涂层结合强度及涂层界面的影响。结果表明:超音速火焰喷涂316L不锈钢粉末颗粒在喷涂中变形充分,形成较致密的涂层,并具有超过400 HV0.1的显微硬度;涂层具有较高自腐蚀电位,耐蚀性优于高强钢;涂层结合强度随着涂层厚度的减小、基体硬度的增加而提高;WC-CoCr底层可改善涂层界面结合,从而改善316L不锈钢涂层的结合性能。     

磁控溅射制备的Cr/CrN和Cr/CrN/CrAlN涂层耐腐蚀性能对比研究

目的比较Cr/CrN/CrAlN涂层和Cr/CrN交替涂层的耐腐蚀性能。方法利用电化学极化曲线、阻抗谱和中性盐雾试验进行测量,结合扫描电子显微镜(SEM)和原子力显微镜(AFM)表征微观形貌,分析两种涂层耐腐蚀性能的差异。同时,为研究涂层在服役中的损伤工况,分析了预制划痕对Cr/CrN/CrAlN涂层耐腐蚀性能的影响。结果Cr/CrN/CrAlN涂层的自腐蚀电流密度较Cr/CrN交替涂层和TC4基体低2个数量级,腐蚀速率较小。无损伤的Cr/CrN/CrAlN涂层的极化电阻Rp为868.7 kΩ·cm^2,预制1条损伤划痕涂层的极化电阻为792.0 kΩ·cm^2,而带有5条损伤划痕涂层的极化电阻Rp仅为77.2 kΩ·cm^2,减小至原始涂层的8%。Cr/CrN/CrAlN涂层经288 h连续盐雾腐蚀后增重仅为0.1 mg/cm^2,远小于CrN涂层和TC4基体,且增重速率趋于平缓。CrN涂层在连续盐雾腐蚀24 h后,腐蚀增重速率明显增加。结论由于Cr/CrN/CrAlN涂层结构增加了微裂纹和位错运动的界面阻塞,避免孔隙的连通,阻碍了腐蚀介质进入基体,因此涂层的耐腐蚀性能提高。对于表面预制划痕的Cr/CrN/CrAlN涂层,首先发生涂层的局部腐蚀,通过阴极极化加速后,腐蚀凹坑延伸到涂层/基体界面,加剧涂层的局部剥离。     

镀锌钢表面硅烷掺杂电泳漆涂层的腐蚀电化学行为研究

将γ-(2,3环氧丙氧) 丙基三甲氧基硅烷 (GPTMS) 掺杂到不含颜料的水性环氧树脂中,通过一步电泳法在镀锌钢表面构建得到硅烷掺杂的电泳漆涂层。采用电化学阻抗谱和扫描电化学显微镜技术研究了涂层体系的防护性能,并结合其它手段开展了机理研究。结果表明,有机硅烷的加入能够显著提高环氧电泳漆涂层在腐蚀介质中的防护性能,硅烷掺杂抑制环氧涂层的吸水和溶胀。提出了硅烷掺杂电泳漆涂层的如下防护机理：一方面,GPTMS的掺杂增加了涂层的交联程度;另一方面,电泳过程中促进GPTMS组分在金属与涂层界面的优先沉积形成富集层,从而提高了基体与涂层间的结合力。     

Stepwise Depletion of Coating Elements as a Result of Hot Corrosion of NiCrAlY Coatings

Present investigation deals with the hot corrosion behaviour of the NiCrAlY coatings deposited by HVOF technique on Superni76 under cyclic conditions at 900  °C in the presence of Na₂SO₄ + 60% V₂O₅ salt. The weight change behaviour of the coatings was followed with time up to 200 cycles and K _p value was calculated for the hot corrosion process. Surface and cross-section of the corroded samples were examined by FESEM/EDS and XRD to follow the progress of corrosion up to 200 cycles. In earlier cycles, the corrosive species oxidised top surface of the coatings. With increasing number of cycles, oxidation of the coatings occurred up to 40-μm depth. A Cr-depleted band was seen below the oxide scale. Further increase in number of cycles led to migration and oxidation of Al to form Al₂O₃ sublayer at coating/scale interface, thereby leading to formation of Al-depleted zone in the coating below the Al₂O₃ sublayer. The corrosion resistance of the NiCrAlY coatings is attributed to the formation of the continuous and dense Al₂O₃ sublayer at the coating/scale interface, which acts as barrier to the migration of Cr to the surface. The appearance of Al₃Y after 100 and 200 cycles also contributes to the increased corrosion resistance of coatings after 100 and 200 cycles.     

Corrosion properties of in situ laser remelted NiCrBSi coatings comparison with hard chromium coatings

This study aims at evaluating the effect of an in situ laser remelting treatment of NiCrBSi coatings, deposited by plasma spraying. Life Cycle Assessment (LCA) method was used to estimate the environmental impacts of coating processes. It was demonstrated with this LCA that the in situ remelting process was clean. Microstructural results were also evaluated. A good metallurgical bond was formed at the remelted coating interface. Scanning electron microscopy observation revealed also that laser treatment induces a change of the microstructure from lamellar to columnar dendritic. The dependence between the microstructure of NiCrBSi coatings, which was modified by laser treatment, and corrosion resistance has been evaluated by potentiodynamic polarization curves. Results show that, the corrosion resistance was increased because of a finer structure and higher densities of the coatings, but corrosion mechanisms occurring in all cases were different. From the electrochemical experiments in NaCl solution it can be deduced that laser remelting of as-sprayed coatings does not affect their corrosion rate. Corrosion evolves due to a progressive penetration of the electrolyte through the disturbed structure of the as-sprayed samples, whereas the substrate surface of remelted coating is not reached, because of a higher density. But ClMO intermediate species were formed on the surface, because Cl⁻ can destroy the protective film on the coating. The hybrid plasma/laser process was cleaner than hard chromium plating and its corrosion behavior is superior too.     

掺杂镍对镁合金表面冷喷涂锌基涂层性能的影响

目的研究镍添加对冷喷涂锌基涂层耐蚀性的影响,为镁合金提供有效的防护涂层。方法采用低压冷喷涂技术在镁合金基体表面分别制备锌基和锌/镍基复合涂层,通过微观观察、摩擦磨损实验、电化学极化法和电化学阻抗谱测试及全浸泡腐蚀试验,研究镁合金表面冷喷涂涂层的结构、摩擦磨损行为和耐蚀性。结果镁合金表面冷喷涂锌基涂层后,其硬度和耐磨性得到显著提高,掺镍后的锌/镍基涂层具有更高的硬度和耐磨性。锌基和锌/镍基涂层均能为镁合金提供腐蚀防护,锌/镍基涂层比锌基涂层具有更好的耐蚀性。相对镁合金来说,锌基涂层和锌/镍基涂层的自腐蚀电位分别正移了260 mV和560 mV;长期腐蚀后锌/镍基涂层形成了更致密的腐蚀产物膜,腐蚀电阻显著高于锌基涂层。结论冷喷涂锌基和锌/镍复合涂层均能对镁合金提供防护作用,掺杂镍后的锌/镍基复合涂层具有更高的硬度、耐磨性和耐蚀性。     

Failure mechanism of MCrAlY coating at the coating‐substrate interface under type I hot corrosion

MCrAlY coatings are widely used to provide protection of hot component in modern gas turbine engines against high‐temperature oxidation and hot corrosion. Coating‐substrate interface, where the substrate is only partially covered by the ?coatings, is vulnerable to the hot corrosion attack. The accelerated degradation at the coating‐substrate interface can cause fast spallation of the coating, leading to the early failure of the gas turbine components. In this paper, MCrAlY powder was deposited on IN792 disks by high‐velocity oxygen‐fuel spraying. The hot corrosion behavior of the coated sample was investigated using (0.8Na, 0.2K)₂SO ₄ salt deposition at 900°C in lab air. Results showed a minor attack in the coating center, however, an accelerated corrosion attack at the coating‐substrate interface. The fast growth of corrosion products from substrate caused large local volume expansions at the coating‐substrate interface, resulting in an early coating spallation.     

废气再循环单向阀阀片失效分析及腐蚀防护

目的 明确废气再循环(Exhaust Gas Recirculation,EGR)单向阀阀片的腐蚀失效机理及防护涂层的失效过程,提高其服役寿命和可靠性。方法 利用电火花直读光谱仪、金相显微镜、体视显微镜、扫描电子显微镜和能谱仪等对EGR单向阀阀片断裂件进行失效分析,表征其化学成分、宏观腐蚀形貌、微观腐蚀形貌及腐蚀产物的元素分布,明确失效机制。采用电化学测试方法和浸泡试验对比研究了3种涂层防护的有效性,包括聚四氟乙烯(Polytetrafluoroethylene,PTFE)、淬火–抛光–淬火(Quench-Polish-Quench,QPQ)+PTFE和聚酰胺酰亚胺涂层,揭示EGR单向阀阀片的腐蚀失效机理及防护涂层的失效过程。结果 EGR单向阀阀片表面及断口腐蚀严重。随着浸泡时间的延长,3种涂层的吸水率增加。涂层电容增大而电荷转移电阻减小,涂层的防护性能降低。30 d的浸泡试验结果显示,聚酰胺酰亚胺涂层的耐蚀性最好,涂层剥落少,其次是PTFE涂层,而QPQ+PTFE涂层的耐蚀性最差,涂层大面积脱落且划痕处和阀片边缘出现了明显的腐蚀产物。结论 EGR单向阀阀片断裂的主要原因是腐蚀降低了单向阀阀片的承载能力,在应力作用下发生断裂而失效;受涂层厚度限制,3种涂层在浸泡24 h后均发生溶液渗入涂层到达涂层/金属基体界面的过程,涂层的耐渗水性能低。聚酰胺酰亚胺涂层和PTFE涂层可以作为防护涂层,能在一定程度上提高单向阀的服役寿命。