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3種熱噴涂涂層在模擬氣氛/煤灰環境下的熱腐蝕及失效行為

2021-05-19 14:32:36 作者：熊義來源：中國腐蝕與防護學報分享至：

摘要

采用超音速火焰噴涂技術在T91鋼表面制備了45CT、NiCr/Cr3C2和NiCrAlY 3種涂層。在T91鋼和3種涂層表面涂覆37.5%Na2SO4+37.5%K2SO4+15%Fe2O3+10%SiO2的合成煤灰后通入模擬煙氣在750 ℃下進行腐蝕，獲得腐蝕動力學曲線，腐蝕200 h后觀察涂層腐蝕前后厚度變化。采用XRD、SEM、EDS對高溫腐蝕產物成分、結構、形貌進行分析。結果表明，T91鋼腐蝕非常嚴重，腐蝕產物大量剝落。3種涂層在腐蝕前期均表現為增重，而在腐蝕后期均存在失重現象。經過200 h腐蝕后，45CT、NiCr/Cr3C2和NiCrAlY涂層分別減薄25、112.7和93.1 μm。T91鋼腐蝕后表面殘留的腐蝕產物主要為Fe2O3。45CT涂層表面主要的腐蝕產物相為Cr2O3，而NiCr/Cr3C2和NiCrAlY的腐蝕產物為Cr2O3和NiCr2O4。所有樣品表層腐蝕產物中不同程度均嵌入了煤灰粒子。腐蝕介質會通過涂層擴散到涂層/基體界面導致基體一側發生腐蝕。45CT、NiCr/Cr3C2涂層樣品基體處腐蝕嚴重導致涂層/基體開裂，而NiCrAlY涂層由于孔隙率較低，以及稀土效應，界面的基體側腐蝕輕微，未出現裂紋。

關鍵詞： 45CT ; NiCr/Cr3C2 ; NiCrAlY ; 熱噴涂涂層 ; 熱腐蝕

Abstract

Three coatings of 45CT, NiCr/Cr3C2 and NiCrAlY were prepared on the surface of T91 steel by high velocity oxygen fuel spray. The hot corrosion behavior of the coated steel was examined in a simulated flue gas at 750 ℃ for the prepared samples enveloped with a layer of synthetic coal ash of 37.5%Na2SO4+37.5%K2SO4+15%Fe2O3+10%SiO2. The sample was weighed at a certain interval to obtain the corrosion kinetic curve. The thickness changes of the coatings before and after 200 h corrosion were measured. The composition, structure and morphology of high temperature corrosion products were characterized by means of XRD, SEM and EDS. The results show that the bare T91 steel suffered from serious corrosion with corrosion products peeled off in large quantities. Mass gain in the early corrosion stage and then mass loss in the late corrosion stage was observed for the three coatings. After 200 h corrosion, the thinning amount of the three coatings 45CT, NiCr/Cr3C2 and NiCrAlY was about 25, 112.7 and 93.1 μm, respectively. The corrosion products remaining on the surface of T91 steel after corrosion were identified as mainly Fe2O3. The main corrosion products on the surface of 45CT coating was Cr2O3. However, the corrosion products of NiCr/Cr3C2 and NiCrAlY were Cr2O3 and NiCr2O4. Some coal ash particles were embedded in the corrosion products. For three coatings, corrosion media would diffuse through the coating to the coating/substrate interface during the test, which would lead to substrate corrosion. The substrate of beneath coatings of 45CT and NiCr/Cr3C2 suffered from serious corrosion, which led to cracks formation at the interface of coating and substrate. However, the substrate of beneath NiCrAlY coating showed slight corrosion, which may be ascribed to the low porosity and reactive element effect of rare earth of the coating.

Keywords： 45CT ; NiCr/Cr3C2 ; NiCrAlY ; thermal spraying coating ; hot corrosion