Molten Salt Corrosion Behaviors and Mechanisms of Ytterbium Silicate Environmental Barrier Coating

doi:10.15541/jim20220265

Abstract

Abstract:

Environmental barrier coating (EBC) is essential for protection of ceramic matrix composite hot-sections in future gas turbine engines with high thrust-to-weight ratio. Rare-earth silicates, such as Yb₂SiO₅ and Yb₂Si₂O₇, have been developed for potential application as EBC. However, the corrosion behaviors and mechanisms of EBC in molten salt environment such as Na₂SO₄ at high temperature are not clear. In this work, the Yb₂SiO₅/Yb₂Si₂O₇/Si coating was prepared by vacuum plasma spraying (VPS). The molten salt (Na₂SO₄+25% NaCl, in mass) corrosion behaviors and mechanisms of the coating at 900 ℃ for 60-240 h were investigated. Results showed that the Yb₂SiO₅/Yb₂Si₂O₇/Si coating exhibited dense structure with good bonding between the triple ceramic layers. The molten salt of Na₂SO₄+25% NaCl penetrated the Yb₂SiO₅ top layer and enriched in the Yb₂Si₂O₇ interlayer, while the interfacial bonding between the coating and substrate still remained good after corrosion for 240 h. The Yb₂SiO₅ phase in the top layer exhibited good stability, while the second phase of the Yb₂O₃ reacted with molten salt. The content of the Yb₂O₃ decreased with the increase of corrosion time. The Yb₂Si₂O₇ phase in the interlayer reacted with molten salt to form apatite phase of NaYb₉Si₆O₂₆ and sodium silicate as well as volatile species such as Cl₂ and SO₂, which might shorten the service life of the coating. Moreover, there was almost no molten salt in the silicon bond layer, which remained intact. The Yb₂SiO₅/Yb₂Si₂O₇/Si coating exhibited good resistance to molten salt corrosion.

Key words: environmental barrier coating, ytterbium silicate, Na₂SO₄+25% NaCl molten salt, corrosion mechanism

CLC Number:

TQ174

LIU Pingping, ZHONG Xin, ZHANG Le, LI Hong, NIU Yaran, ZHANG Xiangyu, LI Qilian, ZHENG Xuebin. Molten Salt Corrosion Behaviors and Mechanisms of Ytterbium Silicate Environmental Barrier Coating[J]. Journal of Inorganic Materials, 2022, 37(12): 1267-1274.

Figures/Tables 11

Table 1 Operating parameters used for vacuum plasma spraying

	Yb₂SiO₅	Yb₂Si₂O₇	Si
Primary Ar/(L·min^-1)	46	53	52
Secondary H₂/(L·min^-1)	14	10	13
Carrier Ar/(L·min^-1)	2.3	2.3	2.0
Spray distance/mm	220	220	290

Fig. 1 XRD patterns and SEM morphologies of as-sprayed Yb2SiO5/Yb2Si2O7/Si coating (a) XRD patterns; (b) Surface morphology; (c-e) Cross-sectional morphologies

Fig. 2 Macro-photographs of Yb2SiO5/Yb2Si2O7/Si coating after molten salt corrosion for different time (a) As-sprayed; (b) 60 h; (c)100 h; (d) 240 h

Fig. 3 XRD patterns of Yb2SiO5/Yb2Si2O7/Si coating after molten salt corrosion for different time

Fig. 4 Surface morphologies of Yb2SiO5/Yb2Si2O7/Si coating after molten salt corrosion for different time and correponding EDS analyses of different areas (a-c) Low magnification; (d-f) High magnification

Fig. 5 Cross-sectional morphologies and corresponding element analyses of Yb2SiO5 top layer after molten salt corrosion for different time

Fig. 6 Cross-sectional morphologies and corresponding EDS element mappings of Yb2SiO5/Yb2Si2O7/Si EBCs after molten salt corrosion for different time Colorful figures are available on website

Fig. 7 High-magnification cross-sectional morphologies and corresponding EDS mappings of infiltration zone in Yb2Si2O7 interlayer after molten salt corrosion for different time Colorful figures are available on website

Table 2 EDS elemental compositions of the marked regions in Fig. 7/%(in atom)

Position	Yb	Si	Na	O
1	21.69	14.27	1.98	62.06
2	24.91	12.57	-	62.52
3	18.29	18.09	-	63.62
4	10.15	18.67	2.41	58.77
5	22.50	13.75	1.67	62.08
6	24.92	12.57	-	62.51
7	18.03	18.31	-	63.66
8	8.95	19.25	13.25	58.55
9	22.93	13.20	2.04	61.82
10	24.45	12.96	-	62.59
11	17.82	18.04	-	63.25
12	8.91	19.21	13.39	58.49

Fig. 8 Schematic diagrams of Yb2SiO5/Yb2Si2O7/Si coating under Na2SO4+25% NaCl molten salt corrosion at 900 ℃

Fig. 9 EPR spectra of Yb2SiO5 and Yb2Si2O7 coating

References 35

[1]	PADTURE N P. Advanced structural ceramics in aerospace propulsion. Nature Materials, 2016, 15(8): 804-809. DOI PMID
[2]	LEE K N, FOX D S, ELDRIDGE J I, et al. Advanced environmental barrier coatings developed for SiC/SiC composite vanes (2022-06-01). https://ntrs.nasa.gov/search.jsp?R=20050214693.
[3]	EATON H E, LINSEY G D. Accelerated oxidation of SiC CMC's by water vapor and protection via environmental barrier coating approach. Journal of the European Ceramic Society, 2002, 22(14/15): 2741-2747. DOI URL
[4]	RICHARDS B T, WADLEY H N G. Plasma spray deposition of tri-layer environmental barrier coatings. Journal of the European Ceramic Society, 2014, 34(12): 3069-3083. DOI URL
[5]	TIAN Z L, ZHENG L Y, WANG J M, et al. Theoretical and experimental determination of the major thermo-mechanical properties of RE₂SiO₅ (RE=Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y) for environmental and thermal barrier coating applications. Journal of the European Ceramic Society, 2016, 36(1): 189-202. DOI URL
[6]	LIU J, ZHANG L T, LIU Q M, et al. Calcium-magnesium- aluminosilicate corrosion behaviors of rare-earth disilicates at 1400 ℃. Journal of the European Ceramic Society, 2013, 33(15/16): 3419-3428. DOI URL
[7]	JIANG F R, CHENG L F, WANG Y G. Hot corrosion of RE₂SiO₅ with different cation substitution under calcium-magnesium- aluminosilicate attack. Ceramics International, 2017, 43(12): 9019-9023. DOI URL
[8]	DONG Y, REN K, LU Y H, et al. High-entropy environmental barrier coating for the ceramic matrix composites. Journal of the European Ceramic Society, 2019, 39(7): 2574-2579. DOI URL
[9]	SUN L C, REN X M, DU T F, et al. High entropy engineering: new strategy for the critical property optimizations of rare earth silicates. Journal of Inorganic Materials, 2021, 36(4): 339-346. DOI
[10]	ZHONG X, NIU Y R, LI H, et al. Thermal shock resistance of tri-layer Yb₂SiO₅/Yb₂Si₂O₇/Si coating for SiC and SiC-matrix composites. Journal of the American Ceramic Society, 2018, 101(10): 4743-4752. DOI URL
[11]	ZHU T, NIU Y R, ZHONG X, et al. Influence of phase composition on microstructure and thermal properties of ytterbium silicate coatings deposited by atmospheric plasma spray. Journal of the European Ceramic Society, 2018, 38(11): 3974-3985. DOI URL
[12]	ZHONG X, NIU Y R, LI HONG, et al. Microstructure evolution and thermomechanical properties of plasma-sprayed Yb₂SiO₅ coating during thermal aging. Journal of the American Ceramic Society, 2017, 100(5): 1896-1906. DOI URL
[13]	ZHONG X, WANG Y W, NIU Y R, et al. Corrosion behaviors and mechanisms of ytterbium silicate environmental barrier coatings by molten calcium-magnesium-alumino-silicate melts. Corrosion Science, 2021, 191: 109718. DOI URL
[14]	WANG Y W, NIU Y R, ZHONG X, et al. Water vapor corrosion behaviors of plasma sprayed RE₂SiO₅ (RE=Gd, Y, Er) coatings. Corrosion Science, 2020, 167: 108529. DOI URL
[15]	ZHONG X, ZHU T, NIU Y R, et al. Effect of microstructure evolution and crystal structure on thermal properties for plasma- sprayed RE₂SiO₅ (RE=Gd, Y, Er) environmental barrier coatings. Journal of Materials Science & Technology, 2021, 85: 141-151.
[16]	LI G, QIN L, CAO X Q, et al. Water vapor corrosion resistance and failure mechanism of SiC_f/SiC composites completely coated with plasma sprayed tri-layer EBCs. Ceramics International, 2022, 48(5): 7082-7092. DOI URL
[17]	LEE K N, FOX D S, BANSAL N P. Rare earth silicate environmental barrier coatings for SiC/SiC composites and Si₃N₄ ceramics. Journal of the European Ceramic Society, 2005, 25(10): 1705-1715. DOI URL
[18]	ZHANG X F, ZHOU K S, LIU M, et al. Preparation of Si/mullite/ Yb₂SiO₅ environment barrier coating (EBC) by plasma spray- physical vapor deposition (PS-PVD). Journal of Inorganic Materials, 2018, 33(3): 325-330. DOI URL
[19]	WANG C, ZHANG X F, ZHOU K S, et al. Nano-composite structured environmental barrier coat-ings prepared by plasma spray- physical vapor deposition and their thermal cycle performance. Rare Metal Materials and Engineering, 2019, 48(11): 3455-3462
[20]	ZHANG X F, SONG J B, DENG Z Q, et al. Interface evolution of Si/Mullite/Yb₂SiO₅ PS-PVD environmental barrier coatings under high temperature. Journal of the European Ceramic Society, 2020, 40(4): 1478-1487. DOI URL
[21]	ZHANG X F, ZHOU K S, LIU M, et al. Oxidation and thermal shock resistant properties of Al-modified environmental barrier coating on SiC_f/SiC composites. Ceramics International, 2017, 43(16): 13075-13082. DOI URL
[22]	HU X X, XU F F, LI K W, et al. Water vapor corrosion behavior and failure mechanism of plasma sprayed mullite/Lu₂Si₂O₇-Lu₂SiO₅ coatings. Ceramics International, 2018, 44(12): 14177-14185. DOI URL
[23]	LIU P P, ZHONG X, NIU Y R, et al. Reaction behaviors and mechanisms of tri-layer Yb₂SiO₅/Yb₂Si₂O₇/Si environmental barrier coatings with molten calcium-magnesium-alumino-silicate. Corrosion Science, 2022: 110069.
[24]	WU S J, CHENG L F, ZHANG L T, et al. Corrosion of SiC/SiC composite in Na₂SO₄ vapor environments from 1000 ℃ to 1500 ℃. Composites Part A: Applied Science and Manufacturing, 2006, 37(9): 1396-1401. DOI URL
[25]	KOSIENIAK E, BIESIADA K, KACZOROWSKI J, et al. Corrosion failures in gas turbine hot components. Journal of Failure Analysis and Prevention, 2012, 12(3): 330-337. DOI URL
[26]	JACOBSON N S. Kinetics and mechanism of corrosion of SiC by molten salts. Journal of the American Ceramic Society, 1986, 69(1): 74-82. DOI URL
[27]	HERWEYER L A, OPILA E J. High-temperature Na₂SO₄ interaction with air plasma sprayed Yb₂Si₂O₇+Si EBC system: Topcoat behavior. Journal of the American Ceramic Society, 2021, 104(12): 6496-6507. DOI URL
[28]	LI L, LU J, LIU X Z, et al. Al_xCoCrFeNi high entropy alloys with superior hot corrosion resistance to Na₂SO₄+25% NaCl at 900 ℃. Corrosion Science, 2021, 187: 109479. DOI URL
[29]	HAGAN J M, OPILA E J. High-temperature Na₂SO₄ deposit- assisted corrosion of silicon carbide-I: temperature and time dependence. Journal of the American Ceramic Society, 2015, 98(4): 1275-1284. DOI URL
[30]	SUN Z Q, LI M S, ZHOU Y C. Kinetics and mechanism of hot corrosion of γ-Y₂Si₂O₇ in thin-film Na₂SO₄ molten salt. Journal of the American Ceramic Society, 2008, 91(7): 2236-2242. DOI URL
[31]	FAN X Y, SUN R J, DONG J, et al. Effects of sintering additives on hot corrosion behavior of γ-Y₂Si₂O₇ ceramics in Na₂SO₄+V₂O₅ molten salt. Journal of the European Ceramic Society, 2021, 41(1): 517-525. DOI URL
[32]	LATSHAW A M, YEON J, SMITH M D, et al. Synthesis, structure, and polymorphism of A₃LnSi₂O₇ (A=Na, K; Ln=Sm, Ho, Yb). Journal of Solid State Chemistry, 2016, 235: 100-106. DOI URL
[33]	LATSHAW A M, WILKINS B O, CHANCE W M, et al. Influence of rare earth cation size on the crystal structure in rare earth silicates, Na₂RESiO₄ (OH) (RE=Sc, Yb) and NaRESiO₄ (RE=La, Yb). Solid State Sciences, 2016, 51: 59-65. DOI URL
[34]	JONNALAGADDA K P, MAHADE S, KRAMER S, et al. Failure of multilayer suspension plasma sprayed thermal barrier coatings in the presence of Na₂SO₄ and NaCl at 900 ℃. Journal of Thermal Spray Technology, 2019, 28(1): 212-222. DOI URL
[35]	蒋凤瑞. B_1-_xS_xAS及稀土硅酸盐环境障碍涂层热腐蚀性能研究. 西安: 西北工业大学博士学位论文, 2017.