多主元合金CoCrFeNiTi0.5耐硫酸盐高温腐蚀行为研究

Corrosion Resistance Behavior to Sulfate of Multi-elements Alloy CoCrFeNiTi0.5 at High Temperature

摘要:

多主元合金因具有良好的热稳定性有望用于制造超超临界锅炉过热器等耐热设备，燃煤气氛下使用时易发生硫酸盐腐蚀。本工作系统分析了表面喷涂碱金属硫酸盐的多主元合金CoCrFeNiTi0.5在750 ℃耐高温腐蚀特性。结果表明：合金CoCrFeNiTi0.5的腐蚀动力学曲线遵循抛物线递增规律；腐蚀过程中有挥发性产物Na4(CrO4)(SO4)、硫化物以及多种氧化物生成；腐蚀初期，氧化膜均匀致密，与基体结合紧密；延长腐蚀时间，氧化膜厚度增加，由致密变得疏松多孔，基体与氧化膜界面产生微孔隙，内氧化和内硫化发生。分析认为，合金CoCrFeNiTi0.5在750 ℃耐硫酸盐高温腐蚀特性归因于：保护性氧化膜的形成以及由低熔点共晶体诱发的Cr2O3在熔融态Na2SO4中的碱性熔融

Abstract:

Multi-elements alloy with good thermal stability is expected to serve as the superheater tube material of ultra-supercritical boiler and may suffer from hot corrosion under the coal-fired atmosphere. In this study, the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 coated with alkali metal sulfate at 750 °C was investigated. The results show the corrosion kinetics curves of the alloy follow parabolic growth rate and the corrosion products, which consist of volatile Na4(CrO4)(SO4), (Fe, Ni) sulfide, Cr/Ti oxide as well as compound oxides with spinel structure, form on the surface and sub-surface of the alloy. The oxide layer is dense and has good adhesion with the matrix at the beginning of corrosion. With the corrosion time increasing, the oxide layer in thickness increases and becomes loose as well as porous. The micro-pores are generated in the interface between the oxide scale and matrix with the formation of the internal oxidation and internal sulfidation. In a word，the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 at 750 °C can be attributed to the formation of the protective oxide layers and to the basic fluxing in molten Na2SO4 induced by low melting point eutectic.