Microstructure and Properties of HVOF-Sprayed NiCrAlY Coatings Modified by Rare Earth
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S.F. Chen, S.Y. Liu, Y. Wang, X.G. Sun, Z.W. Zou, X.W. Li, and C.H. Wang (Submitted June 11, 2013; in revised form February 11, 2014) Rare earth (RE)-modified NiCrAlY powders were prepared by ultrasonic gas atomization and deposited on stainless steel substrate by high-velocity oxygen fuel spraying. The effects of the RE on the microstructure, properties, and thermal shock resistance of the NiCrAlY coatings were investigated. The results showed that the NiCrAlY powders were refined and distributed uniformly after adding RE, while the number of unmelted particles in the coatings was reduced. Moreover, the RE-modified coatings showed improved microhardness and distribution uniformity. The microhardness of the coating reached a maximum after adding 0.9 wt.% RE, being 34.4 % higher than that of coatings without RE. The adhesive strength increased and reached a maximum after adding 0.6 wt.% RE, being 18.8 % higher than that of coatings without RE. Excessive RE decreased the adhesive strength. The thermal cycle life of NiCrAlY coatings increased drastically with RE addition. The coating with 0.9 wt.% RE showed optimum thermal shock resistance, being 21.2 % higher than that of coatings without RE.
Keywords
HVOF, NiCrAlY, RE alloying, ultrasonic gas atomization
1. Introduction MCrAlY coatings (M = Ni, Co, Ni + Co) are commonly used for oxidation protection of components for applications such as industrial gas turbines and jet engines with elevated service temperatures because they can form a protective surface scale during high-temperature operation (Ref 1, 2). The operating temperature of high-temperature alloy protective coatings is gradually rising with the continuous increase in engine operating temperature. Preparation of MCrAlY coatings with excellent high-temperature oxidation resistance has therefore received increasing attention (Ref 3, 4). To date, research on improvement of the hightemperature oxidation resistance of MCrAlY coatings has mainly concentrated on the following areas: rational choice of the coating preparation process (Ref 5), and postprocessing of the prepared coatings, e.g., by vacuum heat treatment (Ref 6), particle bombardment processing (Ref 7), or addition of rare-earth and other active eleS.F. Chen, Department of Materials Science, Harbin Institute of Technology, Harbin 150001, China; and Department of Technology and Quality, CFHI TianJing Heavy Industries Co., Ltd., Tianjin 300310, China; and S.Y. Liu, Y. Wang, X.G. Sun, Z.W. Zou, X.W. Li, and C.H. Wang, Department of Materials Science, Harbin Institute of Technology, Harbin 150001, China. Contact e-mails: [email protected] and [email protected].
Journal of Thermal Spray Technology
ments (Ref 8). In previous work by the authors (Ref 9), it was confirmed that rare earth addition can increase the high-temperature sulfidation resistance of MCrAlY coatings by more than twofold. The mechanical properties and thermal shock resistance of nanoceria-modified NiCrAlY coating were also improved compared with conventional NiCrAlY coatings (
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