T91和304H锅炉管束用非晶合金涂层制备及性能研究

发布时间：2018-12-08 10:52

【摘要】：Fe基非晶合金具有高硬度和优异的耐蚀性能及较低的成本,采用热喷涂技术可以大面积制备Fe基非晶合金涂层,适合在金属结构件进行防腐处理。本文针对锅炉管束受热面腐蚀失效,依据锅炉管束服役环境设计制备Fe基非晶合金粉末,利用等离子喷涂技术在锅炉管束常用钢304H和T91基体上喷涂制备Fe基非晶合金涂层,研究涂层结构和喷涂工艺及耐蚀性之间规律性关系。通过改变喷涂功率和制备不同厚度涂层获得不同组织结构的非晶合金涂层,研究结果表明:通过不同等离子喷涂工艺,可以制备组织结构均匀一致的Fe基非晶合金涂层,涂层呈波浪状多层结构,涂层与基体之间结合紧密,结合形式以机械结合为主。涂层的XRD衍射峰表现为明显的漫衍射峰和少量的尖锐峰,涂层非晶相含量可达到70%,随喷涂功率增加,涂层非晶相含量降低,涂层厚度增加,涂层非晶相含量升高。此外,随等离子喷涂功率升高和涂层厚度增加,涂层孔隙率下降,显微硬度升高,在喷涂功率为40KW制备的厚度为200μm的非晶合金涂层具有较低的孔隙率和较高的显微硬度,分别为2%和762.4HV。电化学研究表明:非晶合金涂层在0.5mol/LH2SO4溶液和3.5%NaCl溶液中电化学腐蚀行为表现出活性溶解-钝化-过钝化的过程,涂层极化曲线特征表现为在H2SO4溶液中钝化区较宽,在NaCl溶液中腐蚀电流密度较低。随喷涂功率和涂层厚度增加,钝化区明显,腐蚀电位趋于正向移动,腐蚀电流密度降低,表明涂层抗腐蚀性能提高。分析认为,非晶合金涂层组成元素和涂层孔隙率是影响涂层耐蚀性能的主要因素,非晶成分含量略有变化对涂层耐蚀性能影响不大。非晶合金涂层与金属基体相比表现出优异的抗高温氧化和抗高温腐蚀性能。随喷涂功率的升高和涂层厚度增加,孔隙率降低,表现出较好的抗高温氧化和抗高温腐蚀性能。分析认为涂层中Cr元素在高温下与O元素生成结构致密稳定的Cr2O3保护膜层,可以阻碍高温下氧原子的扩散和腐蚀介质的接触,使试样得到充分的保护。此外,喷涂粉末中Mo、P、Ni、Si等元素改善了非晶合金涂层的结构和性能,改善了涂层在高温和腐蚀环境下的抗高温氧化性能和抗高温腐蚀性能。
[Abstract]:Fe based amorphous alloy has high hardness, excellent corrosion resistance and low cost. Thermal spraying technology can be used to prepare Fe based amorphous alloy coating in large area, which is suitable for anticorrosion treatment of metal structural parts. Aiming at the corrosion failure of heating surface of boiler tube bundle, Fe based amorphous alloy powder was prepared according to service environment of boiler tube bundle. Plasma spraying technology was used to prepare Fe based amorphous alloy coating on 304H and T91 substrates of boiler tube bundle. The regular relationship between coating structure, spraying process and corrosion resistance was studied. The amorphous alloy coatings with different microstructure were obtained by changing the spraying power and preparing the coatings with different thickness. The results showed that the amorphous alloy coatings with uniform microstructure and uniform microstructure could be prepared by different plasma spraying processes. The coating is wave-like multilayer structure. The bonding between coating and substrate is close, and mechanical bonding is the main form. The XRD diffraction peak of the coating shows obvious diffuse diffraction peak and a few sharp peak. The amorphous phase content of the coating can reach 70%. With the increase of the spraying power, the amorphous phase content of the coating decreases, the coating thickness increases, and the amorphous phase content of the coating increases. In addition, with the increase of plasma spraying power and coating thickness, the porosity and microhardness of the coating decreased. The amorphous alloy coating with the thickness of 200 渭 m prepared by spraying power 40KW had lower porosity and higher microhardness. 2% and 762.4 HV, respectively. Electrochemical studies show that the electrochemical corrosion behavior of amorphous alloy coatings in 0.5mol/LH2SO4 solution and 3.5%NaCl solution shows the process of active dissolution passivation and over-passivation. The polarization curve of the coating is characterized by a wide passivation zone in H2SO4 solution and a lower corrosion current density in NaCl solution. With the increase of spraying power and coating thickness, the passivation zone is obvious, the corrosion potential tends to move forward, and the corrosion current density decreases, which indicates that the corrosion resistance of the coating is improved. It is considered that the composition of amorphous alloy coating and the porosity of the coating are the main factors affecting the corrosion resistance of the coating, while the minor change of the amorphous composition content has little effect on the corrosion resistance of the coating. The amorphous alloy coating exhibits excellent high temperature oxidation resistance and high temperature corrosion resistance compared with the metal substrate. With the increase of spraying power and coating thickness, the porosity decreases, showing good oxidation resistance and corrosion resistance at high temperature. It is considered that the Cr element in the coating can form a dense and stable Cr2O3 protective film with O element at high temperature, which can hinder the diffusion of oxygen atoms at high temperature and the contact of corrosion medium, so that the sample can be fully protected. In addition, the structure and properties of amorphous alloy coating were improved by Mo,P,Ni,Si and other elements in the sprayed powder, and the oxidation resistance and corrosion resistance of the coating at high temperature and corrosion environment were also improved.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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