激光熔覆鐵基合金涂層在HCl溶液中的腐蝕行為

激光熔覆鐵基合金涂層在HCl溶液中的腐蝕行為Crrosion Behavior of Fe-based Laser Cladding Coating in Hydrochloric Acid Solutions

采用激光熔覆方法在30CrMo合金鋼表面制備了一種鐵基合金耐腐蝕涂層，利用EIS、極化曲線、浸泡腐蝕實驗等測試方法，結合XPS研究了該涂層在0.5 mol/L HCl溶液中的腐蝕行為，并與304不銹鋼和30CrMo鋼進行對比。電化學結果表明，在0.5 mol/L HCl溶液中，與30CrMo鋼相比，鐵基合金涂層極化曲線出現(xiàn)了明顯的鈍化區(qū)，且具有較低的腐蝕電流密度和較高的自腐蝕電位，熔覆層的耐腐蝕性能顯著提高。與304不銹鋼相比，鐵基合金涂層維鈍電流略微變小，鈍化區(qū)變寬，其耐蝕性與304不銹鋼相當。涂層鈍化膜主要由Cr2O3、FeCr2O4和MoO3組成，涂層具有優(yōu)良耐蝕性能的本質原因是復合氧化膜的鈍化作用對腐蝕介質產生機械阻隔作用。

30CrMo alloy steel has a wide range of applications in the petrochemical industry such as the valve bodies and valve covers of subsea Xmas tree, and oil drilling pipes that working in strong acid environment. Therefore, the methods to improve the corrosion resistance of 30CrMo steel by surface modification techniques have become a hot topic of research. Laser cladding Fe-based coatings are regarded as promising materials, because of their high bonding strength, good hardness and excellent wear and corrosion resistance, and they might replace more expensive Co-based or Ni-based alloys. Additions of Cr, Mo, W, Y, Co and Ni are benefit to improve the corrosion resistance of Fe-based coatings. However, Y, Y, Co and Mo are expensive. With consideration of reduce the materials cost, and at the same time maintain the excellent corrosion resistance, a novel Fe-based alloy without W, Y, and Co and minor Mo content is synthesized. Therefore, in this study, to improve the corrosion resistance of 30CrMo alloy, the novel synthesized Fe-based powder was prepared on the surface by laser cladding. The microstructure, chemical and phase compositions of the fabricated coating were measured systemically by using a scanning electron microscope (SEM) equipment with energy-dispersive (EDS) spectrometer, and X-ray diffraction(XRD). The corrosion behavior of this Fe-based coating in 0.5 mol/L HCl solution were studied by polarization curve and electrochemical impedance spectroscopy (EIS) measurements, combined with immersion tests. The passive film formed on the surface of the alloy after immersion in the 0.5 mol/L HCl solution for 3 d was analyzed by X-ray photoelectron spectroscopy (XPS). The microstructure is mainly composed of dendrites and interdendritic phases, which are confirmed as austenite γ-Fe phase and the eutectics γ-Fe/M23C6. Similar to 304 stainless steel, the Fe-based alloy coating with a very broad passive region, shows positive corrosion potential and less corrosion current density than that of 30CrMo alloy steel. This indicates that the corrosion resistance of the Fe-based coating is superior to 30CrMo alloy steel, and almost the same as 304 stainless steel. The immersion tests show that the corrosion mechanisms of the coating are the combination of anodic dissolution and passive film protection. As for the eutectic region rich in Cr and Mo, the destruction and corrosion of this area in HCl solution are slowed down due to the passivation of Cr and Mo. The passive film is mainly composed of Cr2O3, FeCr2O4 and MoO3. The main reason for the excellent corrosion resistance of the coating is the mechanical barrier effect of the passivation effect of the high density composite oxide film.

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