Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《中国腐蚀与防护学报》
Abstract： The electrochemical behavior of three solvent- free epoxy coatings on Q345E carbon steel during corrosion-erosion induced by flowing slurry of simulated sea water with 1% (mass fraction) of sand at 60 ℃ was investigated by means of electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM) and confocal laser scanning microscopy (CLSM), respectively. The results showed that the flowing slurry induced erosion aggravated the deterioration of coatings. The amine-cured epoxy powder coating and phenolic aldehyde amine-cured liquid epoxy coating were cured with slow speed and thus much densified, accordingly, their deterioration process experienced three stages: firstly, the inward migration of corrosive medium; secondly, the corrosion initiation of the substrate metal; thirdly, the corrosion propagation of the substrate metal beneath the coating and finally the failure of coatings. On the contrary, the phenolic aldehyde-cured epoxy powder coating was cured with fast speed and thus much porous, its deterioration process experienced two stages with a shortened second stage. Therefore，the existence of pores in the coating is one of the important factors for inducing failure of coatings during corrosion-erosion.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： Three kind of solvent- free epoxy coatings was prepared on 16Mn (Q345E) steel and then their degradation process in flowing artificial sea water 3.5%NaCl solution was investigated by means of gravimetric method, and the acquired weight gain curves were fitted by Fick model. The effect of the flow velocities on the degradation process of coatings was also studied by open circuit potential method (OCP) and electrochemical impedance spectroscopy (EIS). The results showed that, for the amine- cured epoxy powder coating and the phenolic aldehyde- cured epoxy powder coating within the scope of the test flow velocities and the phenolic aldehyde amine-cured liquid epoxy coating at lower flow velocities, the diffusion of water through the coatings by different flow velocities all agreed well with Fick II diffusion model. However, the phenolic aldehyde amine-cured liquid epoxy coating showed irregular regulation by flow velocity 4 m/s, which may be due to aggravated dissolution, thus the diffusion of water through the coating departed from Fick II diffusion model. As the flow velocity increased, the amount of saturated water uptake of the coatings and the water diffusion coefficient increased simultaneously. The degradation processes of the above mentioned three coatings within the scope of test flow velocities may be differentiated as a process of three stages. The increase of flow velocity could accelerate the degradation of the phe-nolic aldehyde -cured epoxy powder coating and the phenolic aldehyde amine-cured liquid epoxy coating, but had little influence on the amine-cured epoxy powder coating.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： A weld ring with rim of 90/10 cupronickel for marine pipe combination was corroded after 3 years operation. The failure of the ring was analyzed by means of chemical composition analysis, visual examination, metallographic observation of the alloy, as well as characterization of corrosion morphology and corrosion product by SEM/EDS. Results showed that intergranular corrosion was prevalent on the bottom of corrosion pits, in the erosion-corrosion zones and in the thinned region around corrosion perforations. De- nickelification and dissolution occurred in grains which were surrounded by the preferentially attacked boundaries. It was supposed that selective dealloying and dissolution was related with the types of grain boundary and the grain orientations. Sulfide was detected on the surface of the corrosion product and on the facet of emerged grains on the erosion-corrosion zone. Therefore, the failure of the cupronickel ring was the result from the synergistic effect of intergranular corrosion, dealloying corrosion and erosion-corrosion in the sulfide-containing environment.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Amorphous alloy is a new type of material that exhibits exceptional properties or combinations of properties that are often not achievable in conventional crystalline materials. Fe-based amorphous alloys has attracted significant attention over the last few decades because of their low cost and enhanced mechanical performance. However, they are more suitable for the industrial application of coatings due to the fatal disadvantages of poor toughness. High velocity oxygen-fuel (HVOF) spraying is a good way to make amorphous alloy coatings (AMCs), for the individual droplets are cooled at a rate of around 107 K/s which is much higher than the critical cooling rate of the amorphous alloys during the thermal spraying. Fe-based AMCs obtained by using the HVOF spray method are important materials for industrial applications because of high glass- forming ability and exceptional performances, such as excellent corrosion resistance, high hardness, and superior wear resistance. In this work, Fe-CrMoMnWBCSi AMCs were prepared by HVOF thermal spray. The microstructure and amorphous characteristics of AMCs were characterized by SEM and XRD. Electrochemical corrosion behavior of AMCs was investigated in different concentration of NaCl and H2SO4 solutions compared with that of 304 stainless steel and ND steel. The surface film of materials after immersed in two solutions was analysed by XPS. The results indicated that HVOF thermal spraying Fe-based AMCs presented dense layered structure, high amorphous phase content and low porosity. The composite structure of AMCs was formed with some nanocrystallite phases embedded in the amorphous matrix. AMCs exhibited better resistance to pitting corrosion and relatively low uniform corrosion resistance due to the porosity, while the pitting potential of 304 stainless steel was sensitive to NaCl concentration. XPS results revealed that the presence of Cr, Mo and W oxides in the passive film of AMCs may result in the better corrosion resistance. The enrichment of Mo4+ oxides on the surface favored the formation of a more stable and protective layer which could be assumed to be responsible for the observed high stability of passive film. The diminishing or avording pores may be beneficial to further improve the pitting corrosion resistance of AMCs in NaCl solution. In all cases, AMCs showed better resistance to H2SO4 solutions corrosion due to the high stability of passive film. 304 stainless steel and ND steel presented stable passivation behavior only in high concentration of H2SO4 solution. In the lower concentration solution of H2SO4, the amorphous structure of the thinner coatings could facilitate the formation of thicker passivation film and lead to the higher corrosion resistance. The corrosion resistance of AMCs in H2SO4 solution could be enhanced significantly by formation of high amorphous phase.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-07 Cooperative journals: 《中国腐蚀与防护学报》
Abstract：通过电化学阻抗谱（EIS）对两种环氧粉末涂层和一种无溶剂环氧液体涂层在60℃流速为2m/s、含1%wt石英砂的3.5%wt NaCl 溶液中的失效行为进行了研究，并利用扫描电镜（SEM）观察了冲刷后涂层的表面形貌，利用激光共聚焦显微镜（CLSM）观察了涂层/金属的断面形貌。结果表明，和静态浸泡相同温度介质条件下相比，流动含砂条件明显加速了无溶剂涂层的失效。冲刷条件下，1#和3#无溶剂涂层由于结构比较致密，失效过程主要分为三个阶段：腐蚀性介质在涂层中传输阶段、基体金属腐蚀发生阶段和基体金属腐蚀发展与涂层失效阶段；2#无溶剂涂层内部由于孔隙较多，涂层较快形成贯穿孔，没有观察到失效中期阶段；涂层体系内部存在孔隙是加速涂层失效的一个重要因素。
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