火电机组过/再热器锅炉管内壁铝化物涂层研究(Ⅱ):蒸汽氧化、强度及组织演化

Aluminide Coatings on Inner Wall of Boiler Tubes for Overheater/Reheater of Thermal Power Generating Unit(Ⅱ):Steam Oxidation,Strength and Microstructure Evolution

目的分析表征锅炉管内壁铝化物涂层的综合性能。方法通过动态高温蒸汽氧化实验、高温拉伸试验、高温持久试验和650℃/10000 h热暴露实验,分别评价Super304H锅炉管内壁铝化物涂层的抗蒸汽氧化性能、高温强度、高温持久性能和涂层组织时效稳定性,并通过X射线仪、电子显微镜和能谱技术分析涂层结构与物相、氧化产物和断口特征。结果采用料浆法可在Super304H锅炉管内壁制备厚度约40μm的铝化物涂层,涂层以FeAl相为主,且与母材呈冶金结合。在650℃、1000 h饱和蒸汽氧化过程中,涂层表面生长极薄的α-Al2O3,氧化膜厚度小于1μm,抗氧化能力优于表面喷丸Super304H及更高Cr含量的HR3C合金。在650℃高温,涂层Super304H合金的强度与断裂韧性与母材相当,持久寿命与母材持平,蠕变断裂位置未发生在涂层一侧。650℃长时热暴露过程中,涂层由FeAl相向Fe3Al相退化。结论涂层制备过程未对合金母材组织有显著影响,铝化物涂层显著提高了Super304H合金650℃饱和蒸汽氧化性能,对合金的高温力学性能无显著影响。长时热暴露后,涂层与基体互扩散造成组织退化。

The work aims to analyze and characterize the overall performance of aluminide coating on the inner wall of boiler tube.Through dynamic steam oxidation experiment,tension test and endurance test at high temperature and heat exposure experiment at 650℃for 10000 h,the steam oxidation resistance,high-temperature strength,high-temperature endurance property and aging stability of coating microstructure of aluminide coating on the inner wall of boiler tube were evaluated respectively.The structure,phase,oxidation product and fracture characteristics of the coating were analyzed through X-ray,electron microscope and energy spectrum technique.The results showed that the aluminide coating with a thickness of about 40μm can be prepared on the inner wall of the Super304H boiler tube.The coating was mainly FeAl and metallurgical combined with the base metal.The aluminide coating significantly improved the oxidation performance of the Super304H alloy in the saturated steam at 650℃for 1000 h.The coatings grew very thinα-Al2O3 film,the thickness of this film was less than 1μm.The oxidation resistance of the coating samples was better than that of the Super304H with the surface peening and the HR3C alloy.At 650℃,the strength and the breaking tenacity of the coating Super304H alloy were equal to the base metal.The creep fracture did not occur on the coating side.During the long time exposure at 650℃,the coating degenerated from FeAl phase to Fe3Al phase.The preparation process of coating has significant effect on the base metal of the alloy.The aluminide coating significantly improves the saturated steam oxidation performance of Super304H ally at 650℃.It has no significant influence on the high temperature mechanical properties of alloy.After long time exposure,counterdiffusion of coating and substrate would result in microstructure degradation.