Effect of Ta on the Microstructure and Creep Properties of a Hot-Corrosion Resistant Ni-Based Single-Crystal Superalloy After Long-Term Exposure
LIU Jing1,2,3, ZHANG Siqian1(), WANG Dong2, WANG Li2, CHEN Lijia1
1 School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, China 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
Cite this article:
LIU Jing, ZHANG Siqian, WANG Dong, WANG Li, CHEN Lijia. Effect of Ta on the Microstructure and Creep Properties of a Hot-Corrosion Resistant Ni-Based Single-Crystal Superalloy After Long-Term Exposure. Acta Metall Sin, 2024, 60(2): 179-188.
Innovative, massive gas turbines have emerged as critical equipment for achieving the goals of energy conservation and the development of new clean energy sources. As the inlet temperature of industrial gas turbines continues to rise, the high-temperature capabilities of hot corrosion-resistant single-crystal turbine blades should be enhanced. This work investigates the effects of Ta on the microstructural stability and creep properties of hot corrosion-resistant Ni-based single-crystal superalloys with varying Ta contents (2Ta, 5Ta, and 8Ta) during long-term thermal exposure at 900oC. The findings revealed that after various thermal exposure times, the addition of Ta had no observable influence on the size of γ' precipitates, but it considerably increased the cubic degree of γ' precipitates and continuously decreased the number of tertiary γ' precipitates in γ matrix. With the increase of Ta content from 2% to 5%, the volume fraction of γ' precipitates of 5Ta alloy is higher than that of 2Ta alloy except that which is close to each other when thermal exposure at 4000 h. In addition, the volume fraction of γ' precipitates increased was higher than that of 2Ta and 5Ta alloys, as the Ta content increased from 5% to 8% after various thermal exposure times. The creep lives of the three alloys at 900oC and 275 MPa exhibited different trends as thermal exposure time increased; there was no obvious fluctuation in the 2Ta alloy after thermal exposure from 0 to 4000 h, but it significantly decreased after thermal exposure at 8000 h; the creep lives of the 5Ta and 8Ta alloys increased initially and then decreased, and the peak creep lives were 500 and 2000 h, respectively. With the addition of Ta, the steady-state creep rate continuously decreased, the creep life significantly increased, and the peak creep life shifted backward. Simultaneously, the degree and structural integrity of the rafted γ' precipitates after creep rupture increased steadily. Hence, the improvement of the creep life of the alloys was attributed to a combination of factors, such as the increase in the volume fraction of the γ' precipitates in the initial state of the creep, the increase in rafted structural integrity, and thickness of the rafted γ' precipitates during the creep process.
Fund: National Natural Science Foundation of China(51631008);National Natural Science Foundation of China(52071219);National Science and Technology Major Project(J2019-IV-0006-0074);National Science and Technology Major Project(2017-VI-0019-0091);National Science and Technology Major Project(J2019-VI-0010-0124);Science Center for Gas Turbine Project(P2021-A-IV-001-002)
Corresponding Authors:
ZHANG Siqian, professor, Tel: (024)25496339, E-mail: sqzhang@alum.imr.ac.cn
Fig.1 Cross sectional SEM images of 2Ta (a), 5Ta (b), and 8Ta (c) alloys after heat treatment
Fig.2 SEM images of dendritic core at cross section of 2Ta (a), 5Ta (b), and 8Ta (c) alloys after heat treatment
Fig.3 Partitioning ratios of alloying elements in γ and γ' precipitates of three alloys in dendritic core (a) and interdendrite (b)
Fig.4 SEM images at dendritic core of 2Ta (a1-a5), 5Ta (b1-b5), and 8Ta (c1-c5) alloys during thermal exposure at 900oC for 500 h (a1-c1), 1000 h (a2-c2), 2000 h (a3-c3), 4000 h (a4-c4), and 8000 h (a5-c5)
Fig.5 Sizes of γ' precipitates at dendritic core regions (a) and average volume fractions of γ' precipitates (b) for three alloys during long-term thermal exposure at 900oC
Fig.6 Strain-time curves of three alloys at 900oC and 275 MPa after thermal exposure at 900oC for 0 h (a), 500 h (b), 1000 h (c), 2000 h (d), 4000 h (e), and 8000 h (f) (—average of steady-state creep rate)
Fig.7 Variation of creep life of three alloys at 900oC and 275 MPa after thermal exposure at 900oC with various thermal exposure time
Fig.8 SEM images of dendritic core at longitudinal section in 2Ta (a1-a4), 5Ta (b1-b4), and 8Ta (c1-c4) alloys crept rupture at 900oC and 275 MPa after thermal exposure at 900oC for 0 h (a1-c1), 500 h (a2-c2), 2000 h (a3-c3), and 8000 h (a4-c4)
Fig.9 Thicknesses of rafted γ' (a) and widths of γ channel (b) of dendritic core at longitudinal section of 5Ta and 8Ta alloys crept rupture at 900oC and 275 MPa after thermal exposure at 900oC with various thermal exposure time
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