Mechanism of adding rhenium to improve hot corrosion resistance of nickel-based single-crystal superalloys
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Mechanism of adding rhenium to improve hot corrosion resistance of nickel-based single-crystal superalloys Fang-Min Yang, Li-Xian Lian*
, Ying Liu, Xiu-Fang Gong
Received: 4 December 2019 / Revised: 31 January 2020 / Accepted: 30 August 2020 Ó GRINM Bohan (Beijing) Publishing Co., Ltd 2020
Abstract Hot corrosion behavior in sulfate salt at 950 °C of Rene N5 single-crystal superalloys with 3 wt% rhenium (NSR) was investigated compared with that of nickel-based single-crystal superalloys without rhenium (NS). After 30-h corrosion, the surface of the NS superalloy is seriously corroded. Many holes and exfoliation appear on the surface. The NSR superalloys exhibit better hot corrosion resistance than the NS superalloys. After 30-h corrosion, a continuous and compact Al2O3 film is observed on its surface. The Al2O3 film with dense structure formed on the surface provides protection for the matrix. The characterization results show that Al is aggregated in the c0 phase, while Re is aggregated in the c phase during the formation of oxide scale. Considering that Re can inhibit the diffusion of Al in the nickel matrix, it is inferred that Re can inhibit the outward diffusion of Al and prevent the decrease of Al concentration in the c0 phase. High concentration of Al hinders the decomposition of Al2O3 due to the reaction of acid and basic dissolution. Al2O3 keeps its structure intact and provides protection for the matrix. Keywords Single-crystal superalloy; Hot corrosion; Rhenium; Al2O3 film; Element diffusion
F.-M. Yang, L.-X. Lian*, Y. Liu School of Materials Science and Engineering, Sichuan University, Chengdu 610065, China e-mail: [email protected] X.-F. Gong Dongfang Electric Corporation Dongfang Turbine Co., LTD, Deyang 618000, China X.-F. Gong State Key Laboratory of Long-Life High Temperature Materials, Deyang 618000, China
1 Introduction Nickel-based single-crystal superalloys have been widely used in aerospace, naval ships, power generation and other fields because of their excellent high-temperature mechanical properties and creep resistance [1–4]. However, during the application of superalloys, sulfate deposits formed due to the injection of salts into the engine and sulfur from the combustion fuel cause hot corrosion on the surface of alloy blades [5]. Therefore, it is necessary to study the hot corrosion behavior of superalloy materials and improve their hot corrosion resistance [6]. In order to obtain better temperature capability, grain boundaries in single-crystal superalloy turbine blades are removed by directionally solidification, because grain boundaries become weak in high-temperature environment. In addition, the high-temperature properties of single-crystal superalloys are strengthened by adding abundant high melting point alloying elements such as Re, W, Ta and Mo [7–10]. Among all the alloying elements, rhenium plays an important role in improving the high-temperature properties, especially creep properties of nickel-based singlecrystal superalloys, so that the
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