Correlation Between Phase Stability and Tensile Properties of the Ni-Based Superalloy MAR-M247
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Correlation Between Phase Stability and Tensile Properties of the Ni‑Based Superalloy MAR‑M247 Linxu Li1,2 · Xiufang Gong1 · Changshuai Wang3 · Yunsheng Wu3 · Hongyao Yu4,5 · Haijun Su2 · Lanzhang Zhou3 Received: 9 June 2020 / Revised: 14 July 2020 / Accepted: 23 July 2020 © The Chinese Society for Metals (CSM) and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Phase stability and its effect on tensile properties of MAR-M247 alloy have been investigated during thermal exposure at 800–900 °C for up to 10,000 h. Detailed investigations reveal that the larger secondary γ′ phase has no obvious growth, but the smaller tertiary γ′ phase obviously coarsens and the coalescence occurs during thermal exposure at 850 °C and below. γ′ coarsening behavior is consistent with the description of Ostwald ripening theory before γ′ coalescence. Hf-rich blocky MC carbide shows excellent thermal stability, but Ta-rich script-type MC carbide gradually degenerates via reac 23C6 carbides. With increasing thermal exposure time, tion, MC + γ → M23C6 + γ′ and finally forms γ ׳film around MC and M the tensile strength decreases. The ductility first increases and then decreases during exposure at 800 °C, but it decreases continuously at 900 °C. In addition, the ductility keeps almost constant when the exposure time is longer than 5000 h. Keywords Ni-based superalloy · Phase stability · Tensile properties · Fractural behavior
1 Introduction Polycrystalline cast Ni-based superalloy MAR-M247 containing high W (10 wt%) and Hf (1.5 wt%) has been widely used as turbine components in industrial gas turbines (IGT) operating at elevated temperature and stress due to its high strength, excellent corrosion and oxidation resistance at high temperature, and good castability [1]. Available online at http://link.springer.com/journal/40195. * Changshuai Wang [email protected] * Haijun Su [email protected] 1
State Key Laboratory of Long‑Life High Temperature Materials, Dong Fang Turbine Co., Ltd, Deyang 618000, China
2
State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China
3
Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
4
Beijing Key Laboratory of Advanced High Temperature Materials, Beijing 100081, China
5
Beijing CISRI-GAONA Materials and Technology CO., LTD, Beijing 100081, China
As a precipitation strengthening alloy, the excellent elevated temperature performance of MAR-M247 alloy is originated mainly from L 12-type ordered γ′ phase within grain and MC carbides within grain and at grain boundary [2]. Considerable investigations on Ni-based superalloys indicate that γ′ phase and carbides are metastable phase [3–6]. Long-term service at elevated temperature can induce phase instability such as γˊ coarsening and coalescence, and MC degeneration [7, 8]. Phase instability will degrade the elevated performance of Ni-based superalloys, thus definitely reducing the service life of IGT components [3–9]. IGT components service
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