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

LU Jin-tao, DANG Ying-ying, HUANG Jin-yang, ZHOU Yong-li, YANG Zhen, YUAN Yong, GU Yue-feng

Surface Technology ›› 2020, Vol. 49 ›› Issue (11) : 269-276.

PDF(4967 KB)
PDF(4967 KB)
Surface Technology ›› 2020, Vol. 49 ›› Issue (11) : 269-276. DOI: 10.16490/j.cnki.issn.1001-3660.2020.11.031
Surface Failure and Protection

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

  • LU Jin-tao, DANG Ying-ying, HUANG Jin-yang, ZHOU Yong-li, YANG Zhen, YUAN Yong, GU Yue-feng
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Abstract

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 10 000 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 40 μm 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 thin α-Al2O3 film, the thickness of this film was less than 1 μm. 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.

Key words

aluminide coating; boiler tubes; Super304H; steam oxidation; strength; microstructure evolution

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LU Jin-tao, DANG Ying-ying, HUANG Jin-yang, ZHOU Yong-li, YANG Zhen, YUAN Yong, GU Yue-feng. Aluminide Coatings on Inner Wall of Boiler Tubes for Overheater/Reheater of Thermal Power Generating Unit (II):Steam Oxidation, Strength and Microstructure Evolution[J]. Surface Technology. 2020, 49(11): 269-276
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