【摘要】：我國電站鍋爐在實際運行過程中,受煤種變化等因素的影響,實際的排煙溫度常常比設計值高,這會大幅度地降低鍋爐的熱效率,為提高電站的運行效率應有效地回收煙氣余熱。煤炭中含有一定量的硫元素,在鍋爐的尾部煙道中,煙氣中的水蒸氣和硫酸蒸汽進入溫度較低的受熱面時,與金屬壁面接觸,可能發(fā)生冷凝而對金屬壁面造成低溫腐蝕,從而影響設備的安全運行,縮短其使用壽命,因此,要突破金屬材料腐蝕的限制以充分利用煙氣余熱。非晶合金是一種高強度、高硬度和耐腐蝕的新型材料,在原有的金屬材料上鍍上非晶合金,可作為低溫煙氣腐蝕問題的解決方法。本文開展非晶合金在低溫煙氣環(huán)境下的腐蝕研究。通過調研選取合適的工藝參數(shù),采用激光熔覆技術制備單層和雙層鐵基非晶涂層,隨后進行了金相分析、SEM觀察、X射線衍射分析、能譜分析和維氏硬度表征,結果表明:制備的非晶涂層結構致密均勻,表面裂紋較少,冶金結合良好,出現(xiàn)了明顯的分層現(xiàn)象,非晶顆粒中夾雜著少量的納米晶顆粒,非晶/納米晶的復合結構使基體的硬度提升了2~3倍;然后,進行摩爾濃度為0.5mol/l的硫酸和質量濃度為3.5%的氯化鈉電化學實驗,得出試樣的Tafel極化曲線顯示:非晶涂層的自腐蝕電位明顯高于基體,自腐蝕電位分別提高了0.1V~0.2V,表明涂層能很好地適應電站強酸等腐蝕環(huán)境;最后,模擬煙氣腐蝕實驗結果表明:單層非晶涂層的耐腐蝕速率約為基體的2倍,雙層非晶涂層的耐腐蝕速率約為基體的3倍,主要原因是涂層自身的復合結構性能優(yōu)異,同時,鉬、鉻等微量元素在表面形成鈍化膜,可阻止煙氣腐蝕的繼續(xù)深入。綜合分析,在基體上用激光熔覆技術鍍上非晶涂層,可以有效地改善基體的耐腐蝕性能。研究成果將為低溫煙氣腐蝕環(huán)境下的金屬材料優(yōu)化提供指導,有助于推動煙氣余熱利用由理論分析走向工程實踐。
[Abstract]:In the actual operation process of power station boilers in our country, affected by the change of coal type and other factors, the actual smoke exhaust temperature is often higher than the design value, which will greatly reduce the thermal efficiency of the boiler. In order to improve the operation efficiency of the power station, the waste heat of flue gas should be effectively recovered. Coal contains a certain amount of sulfur. In the tail flue of the boiler, when the steam and sulfuric acid steam in the flue gas enter the heating surface with low temperature, the condensation may occur and cause low temperature corrosion to the metal wall, thus affecting the safe operation of the equipment and shortening its service life. Therefore, it is necessary to break through the limitation of metal material corrosion to make full use of the waste heat of the flue gas. Amorphous alloy is a new type of material with high strength, high hardness and corrosion resistance. Coating amorphous alloy on the original metal material can be used as a solution to the corrosion problem of low temperature flue gas. In this paper, the corrosion of amorphous alloys in low temperature flue gas environment is studied. Through investigation and selection of suitable process parameters, single-layer and double-layer iron-based amorphous coatings were prepared by laser cladding technology. Metallographic analysis, SEM observation, X-ray diffraction analysis, energy spectrum analysis and Vickers hardness characterization were carried out. the results show that the amorphous coatings have dense and uniform structure, few surface cracks, good metallurgical bonding and obvious delamination, and a small amount of nanocrystal particles are mixed in the amorphous particles. The hardness of the matrix is increased by 2 times as much as that of the matrix by the composite structure of amorphous / nanocrystal. Then, the electrochemical experiments of sulfuric acid with molar concentration of 0.5mol/l and sodium chloride with mass concentration of 3.5% were carried out. The Tafel polarization curves of the samples showed that the self-corrosion potential of the amorphous coating was significantly higher than that of the substrate, and the self-corrosion potential of the amorphous coating was increased by 0.1 V 鈮，

本文編號：2504279