Microstructure Evolution, High Temperature Oxidation and Molten Salt Corrosion Behavior of EB-PVD Prepared Al2O3 Protective Layer

MU Rende; DING Ning; LIU Guanxi; SHEN Zaoyu

doi:10.16490/j.cnki.issn.1001-3660.2026.03.008

PDF(19940 KB)

Surface Technology ›› 2026, Vol. 55 ›› Issue (3) : 84-95. DOI: 10.16490/j.cnki.issn.1001-3660.2026.03.008

Special Topic—High-temperature Protective Coatings for Advanced Engines

Microstructure Evolution, High Temperature Oxidation and Molten Salt Corrosion Behavior of EB-PVD Prepared Al₂O₃ Protective Layer

MU Rende^1,*, DING Ning², LIU Guanxi¹, SHEN Zaoyu¹

Author information +

History +

Abstract

In the high-temperature service environment of aircraft engine turbine blades, which are continuously subject to intense impact from high-temperature gases, exceptional resistance to both elevated temperature and corrosion is required. MCrAlY metallic coatings, as a well-established high-temperature protective coating system, are widely applied on the surface of turbine blades to withstand oxidation and corrosion under such demanding conditions. While material modifications to the MCrAlY coating system, such as adjustments in composition or the incorporation of reactive elements like Hf, can enhance its oxidation and corrosion resistance to some extent. A primary limitation is their inherent inability to completely block direct contact between the coating and external corrosive agents, such as molten sulfate salts. Alumina (Al₂O₃) coatings have long been recognized as a promising candidate for high-temperature protection due to their high melting point, excellent thermochemical stability, and superior resistance to high-temperature oxidation. However, its low coefficient of thermal expansion and low fracture toughness often lead to stress concentration and spallation under high temperature service condition. Electron beam physical vapor deposition (EB-PVD) is characterized by its ability to generate a unique columnar microstructure. This specific architecture can provide exceptional strain tolerance, allowing the coating to accommodate thermal expansion mismatch and thereby enhancing the coatings durability. The application of EB-PVD to the as-deposited Al₂O₃ coating presented a strategic approach to mitigate its brittleness. To address the aforementioned challenges, the EB-PVD technique is employed to deposit an Al₂O₃ protective layer onto a NiCoCrAlYHf metallic coating. The high-temperature performance of this Al₂O₃/NiCoCrAlYHf coating system is systematically evaluated through oxidation tests and molten salt corrosion experiments. The degradation mechanisms are elucidated via detailed analysis of microstructural evolution and compositional changes. The as-deposited Al₂O₃ coating is found to consist of a single α-phase structure, exhibiting morphology of fine columnar grains with distinct microscopic intercolumnar gaps and a clear, sharp interface with the underlying NiCoCrAlYHf coating, without observable elemental interdiffusion. During high-temperature oxidation testing, the microscopic gaps within the Al₂O₃ layer act as diffusion pathways for oxygen atoms. This ingress of oxygen prompts the selective oxidation of the NiCoCrAlYHf coating, leading to the formation of a continuous TGO layer at the interface. The subsequent growth of this TGO layer, combined with the internal stresses generated within the Al₂O₃ overlay due to sintering at high temperature, induces the formation of vertical cracks within the Al₂O₃ layer. These cracks, in turn, create additional and more direct pathways, further accelerating the inward diffusion of oxygen. Consequently, under the tested oxidation conditions, the EB-PVD Al₂O₃ coating is unable to effectively block oxygen penetration and thus does not confer a significant improvement in oxidation resistance. In contrast, the behavior during high-temperature molten salt corrosion is markedly different. In the corrosion tests, the molten salt is observed to penetrate through the Al₂O₃ layer via its inherent gaps and reach the NiCoCrAlYHf coating. There, it reacts predominantly with the Cr content within the metallic coating, leading to the dissolution of protective oxides and degradation of the coating's internal structure. Al₂O₃ material itself demonstrates excellent chemical stability and inertness in the aggressive molten salt environment. The columnar structure of the Al₂O₃ overlay effectively acts as a substantial barrier, significantly hindering the adherence and inward diffusion of the molten salt to the metal surface. This barrier effect reduces the kinetics of the corrosion reaction, thereby significantly enhancing the overall resistance of the coating system to hot corrosion attack.

Key words

Al₂O₃ / EB-PVD / NiCoCrAlYHf / high temperature oxidation / molten salt corrosion

Cite this article

EndNote

Ris (Procite)

Bibtex

Download Citations

MU Rende, DING Ning, LIU Guanxi, SHEN Zaoyu. Microstructure Evolution, High Temperature Oxidation and Molten Salt Corrosion Behavior of EB-PVD Prepared Al₂O₃ Protective Layer[J]. Surface Technology. 2026, 55(3): 84-95

References

[1] 刘大响. 一代新材料, 一代新型发动机: 航空发动机的发展趋势及其对材料的需求[J]. 材料工程, 2017, 45(10): 1-5.
LIU D X.One Generation of New Material, One Generation of New Type Engine: Development Trend of Aero-Engine and Its Requirements for Materials[J]. Journal of Materials Engineering, 2017, 45(10): 1-5.
[2] PADTURE N P, GELL M, JORDAN E H.Thermal Barrier Coatings for Gas-Turbine Engine Applications[J]. Science, 2002, 296(5566): 280-284.
[3] 徐惠彬, 宫声凯, 刘福顺. 航空发动机热障涂层材料体系的研究[J]. 航空学报, 2000, 21(1): 7-12.
XU H B, GONG S K, LIU F S.Recent Development in Materials Design of Thermal Barrier Coatings for Gas Turbine[J]. Acta Aeronautica et Astronautica Sinica, 2000, 21(1): 7-12.
[4] 曹学强. 热障涂层新材料和新结构[M]. 北京: 科学出版社, 2016: 20.
CAO X Q.New Materials and Structures of Thermal Barrier Coatings[M]. Beijing: Science Press, 2016: 20.
[5] PADTURE N P.Advanced Structural Ceramics in Aerospace Propulsion[J]. Nature Materials, 2016, 15(8): 804-809.
[6] CAO X Q, VASSEN R, TIETZ F, et al.New Double-Ceramic-Layer Thermal Barrier Coatings Based on Zirconia-Rare Earth Composite Oxides[J]. Journal of the European Ceramic Society, 2006, 26(3): 247-251.
[7] MOVCHAN B A, YAKOVCHUK K Y.Graded Thermal Barrier Coatings, Deposited by EB-PVD[J]. Surface and Coatings Technology, 2004, 188: 85-92.
[8] BRANDL W, GRABKE H J, TOMA D, et al.The Oxidation Behaviour of Sprayed MCrAlY Coatings[J]. Surface and Coatings Technology, 1996, 86: 41-47.
[9] VAßEN R, JARLIGO M O, STEINKE T, et al. Overview on Advanced Thermal Barrier Coatings[J]. Surface and Coatings Technology, 2010, 205(4): 938-942.
[10] EVANS A G, MUMM D R, HUTCHINSON J W, et al.Mechanisms Controlling the Durability of Thermal Barrier Coatings[J]. Progress in Materials Science, 2001, 46(5): 505-553.
[11] CLARKE D R, LEVI C G.Materials Design for the Next Generation Thermal Barrier Coatings[J]. Annual Review of Materials Research, 2003, 33: 383-417.
[12] TOLPYGO V K, CLARKE D R, MURPHY K S.The Effect of Grit Blasting on the Oxidation Behavior of a Platinum-Modified Nickel-Aluminide Coating[J]. Metallurgical and Materials Transactions A, 2001, 32(6): 1467-1478.
[13] 于大千, 卢旭阳, 马军, 等. 梯度NiCrAlY涂层的1 000和1 100 ℃氧化行为研究[J]. 金属学报, 2012, 48(6): 759-768.
YU D Q, LU X Y, MA J, et al.Study of Oxidation Behavior of the Gradient NiCrAlY Coating at 1 000 and 1 100 ℃[J]. Acta Metallurgica Sinica, 2012, 48(6): 759-768.
[14] 郭磊, 辛会, 张馨木, 等. 激光表面改性对熔盐环境下热障涂层相稳定性和微观结构的影响[J]. 表面技术, 2020, 49(1): 41-48.
GUO L, XIN H, ZHANG X M, et al.Effects of Laser Surface Modification on Phase Stability and Microstructures of Thermal Barrier Coatings in V₂O₅ Molten Salt[J]. Surface Technology, 2020, 49(1): 41-48.
[15] 刘嘉航, 吕哲, 周艳文, 等. 热障涂层先进结构设计研究进展[J]. 表面技术, 2023, 52(4): 85-99.
LIU J H, LYU Z, ZHOU Y W, et al.Research Progress of Advanced Structural Design of Thermal Barrier Coatings[J]. Surface Technology, 2023, 52(4): 85-99.
[16] GUO L, ZHANG X M, LIU M G, et al.CMAS + Sea Salt Corrosion to Thermal Barrier Coatings[J]. Corrosion Science, 2023, 218: 111172.
[17] GUO L, ZHANG B, HE Q, et al.Fabrication and Characterization of Thermal Barrier Coatings for Internal Combustion Engines via Suspension Plasma Spray with High Solid Loading[J]. Surface and Coatings Technology, 2024, 479: 130523.
[18] GUO L, ZHANG B, GAO Y, et al.Interaction Laws of RE₂O₃ and CMAS and Rare Earth Selection Criterions for RE-Containing Thermal Barrier Coatings Against CMAS Attack[J]. Corrosion Science, 2024, 226: 111689.
[19] SHEN Z Y, HE L M, XU Z H, et al.Morphological Evolution and Failure of LZC/YSZ DCL TBCS by Electron Beam-Physical Vapor Deposition[J]. Materialia, 2018, 4: 340-347.
[20] WINTER M R, CLARKE D R.Oxide Materials with Low Thermal Conductivity[J]. Journal of the American Ceramic Society, 2007, 90(2): 533-540.
[21] KARAOGLANLI A C, DOLEKER K M, DEMIREL B, et al.Effect of Shot Peening on the Oxidation Behavior of Thermal Barrier Coatings[J]. Applied Surface Science, 2015, 354: 314-322.
[22] 关琦, 宫文彪, 李于朋, 等. 等离子喷涂制备AlCoCrFeNi高熵合金涂层的组织与性能[J]. 表面技术, 2025, 54(11): 243-251.
GUAN Q, GONG W B, LI Y P, et al.Microstructure and Properties of High Entropy Alloy Coatings of AlCoCrFeNi Prepared by Plasma Spraying[J]. Surface Technology, 2025, 54(11): 243-251.
[23] SHEN Z Y, HE L M, MU R D, et al.Effects of Gradient Transitional Layer on Thermal Cycling Life and Failure of LaZrCeO/YSZ Thermal Barrier Coatings[J]. Corrosion Science, 2020, 163: 108224.
[24] SHEN Z Y, LIU G X, HE L M, et al.Thermal Property and Failure Behaviors of Gd Doped LaZrCeO Coatings with Feathery Microstructure[J]. npj Materials Degradation, 2022, 6: 17.
[25] 张玉娟, 孙晓峰, 管恒荣, 等. NiCrAlY涂层的表面状态对高温氧化行为的影响[J]. 中国有色金属学报, 2002, 12(6): 1099-1103.
ZHANG Y J, SUN X F, GUAN H R, et al.Influence of Surface Roughness of NiCrAlY Coatings on Its High-Temperature Oxidation Behavior[J]. The Chinese Journal of Nonferrous Metals, 2002, 12(6): 1099-1103.
[26] ZHANG K, WANG Q M, SUN C, et al.Preparation and Oxidation Behavior of NiCrAlYSi Coating on a Cobalt-Base Superalloy K40S[J]. Corrosion Science, 2008, 50(6): 1707-1715.
[27] 钟锦岩, 牟仁德, 何英, 等. NiCoCrAlYHf涂层与一种Ni基单晶高温合金循环氧化行为研究[J]. 材料工程, 2013, 41(8): 28-35.
ZHONG J Y, (MOU/MU) R D, HE Y, et al. Thermal Cyclic Oxidation Behavior between NiCoCrAlYHf Bond Coat and a Kind of Ni-Based Single Crystal Superalloy[J]. Journal of Materials Engineering, 2013, 41(8): 28-35.
[28] POLLOCK T M, LIPKIN D M, HEMKER K J.Multifunctional Coating Interlayers for Thermal-Barrier Systems[J]. MRS Bulletin, 2012, 37(10): 923-931.
[29] CHEN Y, ZHAO X F, XIAO P.Effect of Microstructure on Early Oxidation of MCrAlY Coatings[J]. Acta Materialia, 2018, 159: 150-162.
[30] WU J, WEI X Z, PADTURE N P, et al.Low-Thermal-Conductivity Rare-Earth Zirconates for Potential Thermal-Barrier-Coating Applications[J]. ChemInform, 2003, 34(10): 200310007.
[31] NICHOLLS J R, LAWSON K J, JOHNSTONE A, et al.Methods to Reduce the Thermal Conductivity of EB-PVD TBCS[J]. Surface and Coatings Technology, 2002, 151: 383-391.
[32] LEHMANN H, PITZER D, PRACHT G, et al.Thermal Conductivity and Thermal Expansion Coefficients of the Lanthanum Rare-Earth-Element Zirconate System[J]. Journal of the American Ceramic Society, 2003, 86(8): 1338-1344.
[33] ZHAO M, PAN W, WAN C L, et al.Defect Engineering in Development of Low Thermal Conductivity Materials: A Review[J]. Journal of the European Ceramic Society, 2017, 37(1): 1-13.
[34] MA K K, SCHOENUNG J M.Isothermal Oxidation Behavior of Cryomilled NiCrAlY Bond Coat: Homogeneity and Growth Rate of TGO[J]. Surface and Coatings Technology, 2011, 205(21/22): 5178-5185.
[35] TOMIMATSU T, ZHU S, KAGAWA Y.Effect of Thermal Exposure on Stress Distribution in TGO Layer of EB-PVD TBC[J]. Acta Materialia, 2003, 51(8): 2397-2405.
[36] NAUMENKO D, SHEMET V, SINGHEISER L, et al.Failure Mechanisms of Thermal Barrier Coatings on MCrAlY-Type Bondcoats Associated with the Formation of the Thermally Grown Oxide[J]. Journal of Materials Science, 2009, 44(7): 1687-1703.
[37] LIU G X, SHEN Z Y, HUANG G H, et al.Effects of Shot Peening on Microstructure, Thermal Performance, and Failure Mechanism of Thermal Barrier Coatings[J]. Journal of the American Ceramic Society, 2022, 105(6): 4521-4531.
[38] MOVCHAN B A, MARINSKI G S.Gradient Protective Coatings of Different Application Produced by EB-PVD[J]. Surface and Coatings Technology, 1998, 100: 309-315.
[39] GUO H B, GONG S K, AIK KHOR K, et al.Effect of Thermal Exposure on the Microstructure and Properties of EB-PVD Gradient Thermal Barrier Coatings[J]. Surface and Coatings Technology, 2003, 168(1): 23-29.
[40] GUO H B, GONG S K, XU H B.Evaluation of Hot-Fatigue Behaviors of EB-PVD Gradient Thermal Barrier Coatings[J]. Materials Science and Engineering: A, 2002, 325(1/2): 261-269.
[41] GUO H B, GONG S K, ZHOU C G, et al.Investigation on Hot-Fatigue Behaviors of Gradient Thermal Barrier Coatings by EB-PVD[J]. Surface and Coatings Technology, 2001, 148(2/3): 110-116.
[42] GUO H B, BI X F, GONG S K, et al.Microstructure Investigation on Gradient Porous Thermal Barrier Coating Prepared by EB-PVD[J]. Scripta Materialia, 2001, 44(4): 683-687.
[43] NARAPARAJU R, PUBBYSETTY R P, MECHNICH P, et al.EB-PVD Alumina (Al₂O₃) as a Top Coat on 7YSZ TBCS Against CMAS/VA Infiltration: Deposition and Reaction Mechanisms[J]. Journal of the European Ceramic Society, 2018, 38(9): 3333-3346.
[44] QIN S Y, CAO H T, GAO Z H, et al.A New Al₂O₃-Protected EB-PVD TBC with Superior CMAS Resistance[J]. Advanced Science, 2024, 11(5): 2305479.
[45] LIU G X, SHEN Z Y, LUO Y Q, et al.Interplay of Thermal Properties, Microstructure Evolution and Spallation Mechanism in LaEuZrO/YSZ Duplex TBCS Fabricated by EB-PVD[J]. Corrosion Science, 2025, 255: 113086.
[46] MARINO K A, CARTER E A.The Effect of Platinum on Al Diffusion Kinetics in β-NiAl: Implications for Thermal Barrier Coating Lifetime[J]. Acta Materialia, 2010, 58(7): 2726-2737.
[47] CHEN Y, ZHAO X, BAI M, et al.A Mechanistic Understanding on Rumpling of a NiCoCrAlY Bond Coat for Thermal Barrier Coating Applications[J]. Acta Materialia, 2017, 128: 31-42.
[48] SHEN Z Y, HE L M, MU R D, et al.A Study of Crack Formation and Propagation in LaZrCeO/YSZ Thermal Barrier Coatings at Different Temperatures[J]. Inorganic Chemistry Frontiers, 2019, 6(12): 3468-3474.
[49] SHEN Z Y, ZHONG B T, HE L M, et al.LaZrCeO/YSZ TBCS by EB-PVD: Microstructural Evolution, Residual Stress and Degradation Behavior[J]. Materials Chemistry Frontiers, 2019, 3(5): 892-900.

Funding

National Science and Technology Major Project (J2019-Ⅶ-0010-0150); National Natural Science Foundation of China (52202073); Ultra- high Temperature Corrosion-resistant Thermal Barrier Coating Technology Project (30204)