【摘要】：Fe基非晶合金具有高硬度和優(yōu)異的耐蝕性能及較低的成本,采用熱噴涂技術可以大面積制備Fe基非晶合金涂層,適合在金屬結構件進行防腐處理。本文針對鍋爐管束受熱面腐蝕失效,依據鍋爐管束服役環(huán)境設計制備Fe基非晶合金粉末,利用等離子噴涂技術在鍋爐管束常用鋼304H和T91基體上噴涂制備Fe基非晶合金涂層,研究涂層結構和噴涂工藝及耐蝕性之間規(guī)律性關系。通過改變噴涂功率和制備不同厚度涂層獲得不同組織結構的非晶合金涂層,研究結果表明:通過不同等離子噴涂工藝,可以制備組織結構均勻一致的Fe基非晶合金涂層,涂層呈波浪狀多層結構,涂層與基體之間結合緊密,結合形式以機械結合為主。涂層的XRD衍射峰表現(xiàn)為明顯的漫衍射峰和少量的尖銳峰,涂層非晶相含量可達到70%,隨噴涂功率增加,涂層非晶相含量降低,涂層厚度增加,涂層非晶相含量升高。此外,隨等離子噴涂功率升高和涂層厚度增加,涂層孔隙率下降,顯微硬度升高,在噴涂功率為40KW制備的厚度為200μm的非晶合金涂層具有較低的孔隙率和較高的顯微硬度,分別為2%和762.4HV。電化學研究表明:非晶合金涂層在0.5mol/LH2SO4溶液和3.5%NaCl溶液中電化學腐蝕行為表現(xiàn)出活性溶解-鈍化-過鈍化的過程,涂層極化曲線特征表現(xiàn)為在H2SO4溶液中鈍化區(qū)較寬,在NaCl溶液中腐蝕電流密度較低。隨噴涂功率和涂層厚度增加,鈍化區(qū)明顯,腐蝕電位趨于正向移動,腐蝕電流密度降低,表明涂層抗腐蝕性能提高。分析認為,非晶合金涂層組成元素和涂層孔隙率是影響涂層耐蝕性能的主要因素,非晶成分含量略有變化對涂層耐蝕性能影響不大。非晶合金涂層與金屬基體相比表現(xiàn)出優(yōu)異的抗高溫氧化和抗高溫腐蝕性能。隨噴涂功率的升高和涂層厚度增加,孔隙率降低,表現(xiàn)出較好的抗高溫氧化和抗高溫腐蝕性能。分析認為涂層中Cr元素在高溫下與O元素生成結構致密穩(wěn)定的Cr2O3保護膜層,可以阻礙高溫下氧原子的擴散和腐蝕介質的接觸,使試樣得到充分的保護。此外,噴涂粉末中Mo、P、Ni、Si等元素改善了非晶合金涂層的結構和性能,改善了涂層在高溫和腐蝕環(huán)境下的抗高溫氧化性能和抗高溫腐蝕性能。
[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.
【學位授予單位】：長安大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TG174.4

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