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Chinese Journal of Materials Research  2025, Vol. 39 Issue (3): 198-206    DOI: 10.11901/1005.3093.2024.198
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Effect of Heat Treatment on Microstructure and Tensile Properties of a Typical γʹ-strengthened Co-based Superalloy
ZHANG Huifang1,2, WU Hao1, XIAO Chuanmin3, LI Qi1, XIE Jun1(), LI Jinguo1, WANG Zhenjiang1, YU Jinjiang1
1.Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2.School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
3.Third Military Representative Room in Shenyang Area Air Force Equipment, Shenyang 110016, China
Cite this article: 

ZHANG Huifang, WU Hao, XIAO Chuanmin, LI Qi, XIE Jun, LI Jinguo, WANG Zhenjiang, YU Jinjiang. Effect of Heat Treatment on Microstructure and Tensile Properties of a Typical γʹ-strengthened Co-based Superalloy. Chinese Journal of Materials Research, 2025, 39(3): 198-206.

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Abstract  

A typical γʹ-strengthened Co-based superalloy was focused on in this research, and various characterization methods were employed to investigate the microstructure of the as-cast alloy. Subsequently, a heat treatment regime was developed based on the characteristics of the as-cast microstructure, and the effect of heat treatment on the microstructure and room temperature/high-temperature tensile properties of the alloy was assessed. The results showed that: the microstructure of the as-cast alloy consisted of γ matrix, γʹ phases, MC carbides, γ/γʹ eutectic and M3B2 borides. After solution and aging heat treatments, the γ/γʹ eutectic disappeared, and the M3B2 borides were mostly dissolved, with uniformly sized γ′ phases precipitating in the matrix. In comparison to the as-cast alloy, the room temperature tensile strength of the heat-treated alloy decreased, but plasticity slightly improved. Tensile tensile at 950 °C showed that the strength and plasticity of the heat-treated alloy were improved to some extent. Both the as-cast and heat-treated alloys exhibited a characteristic of cleavage fracture during room temperature tensile testing, while the fracture mechanism under high-temperature tensile conditions was a ductile fracture of the micropore aggregation type.

Key words:  metallic materials      Co-based superalloy      microstructure characteristics      heat treatment      tensile properties     
Received:  08 May 2024     
ZTFLH:  TG132.32  
Fund: National Key Research and Development Program of China(2023YFB3712003);National Science and Technology Major Project(J2019-VI-0018-0133);AECC Independent Innovation Special Fund Project(ZZCX-2022-040);Youth Innovation Promotion Association Project, Chinese Academy of Sciences(2020198)
Corresponding Authors:  XIE Jun, Tel: (024)23978341, E-mail: junxie@imr.ac.cn

URL: 

https://www.cjmr.org/EN/10.11901/1005.3093.2024.198     OR     https://www.cjmr.org/EN/Y2025/V39/I3/198

Fig.1  Schematic diagram of tensile specimen (unit: mm)
Fig.2  OM micrographs of as-cast alloy (a) low magnification, (b) high magnification
PhaseCoNiCrTiCBTaW
MCMass fraction%1.690.210.1210.839.38-75.8820.24
Atom fraction%1.820.230.1514.3949.72-26.697.01
M3B2Mass fraction%4.543.081.542.45-4.7344.4537.22
Atom fraction%4.884.742.674.62-39.5422.6918.78
Table 1  EPMA analysis of the precipitated phase in as-cast alloy
Fig.3  Phase identification of as-cast microstructure with EBSD (a) SEM image, (b) M3B2 phase identification, (c-d) M3B2 EDS mapping
Fig.4  SEM images of γʹ precipitates in as-cast alloy (a) dendritic core area, (b) interdendritic area
Fig.5  DSC heating curves of as-cast alloy
Fig.6  SEM images of incipient melting at different temperatures (a) 1235 oC, (b) 1205 oC, (c) 1175 oC, (d) 1155 oC, (e) 1145 oC, (f) 1135 oC
Fig.7  SEM micrographs of as-cast alloy (a), the heat-treated microstructure after solutioned at 1120 oC for 3 h (b) and the heat-treated microstructure after solutioned at 1120 oC for 6 h (c)
Fig.8  Heat treatment process of alloy
Fig.9  Microstructure of heat-treatment alloy (a) low magnification SEM image, (b) high magnification SEM image, (c) γʹ precipitates
AlloyTemperature / oCRp0.2 / MPaRm / MPaA / %Z / %
As-castRT6909998.516
Heat-treatmentRT5768849.017
As-cast9503624718.016
Heat-treatment95036749710.035
Table 2  Tensile properties of as-cast and heat-treatment alloys at different temperatures
Fig.10  Tensile fracture surface morphologies of as-cast alloy at different temperatures (a) low magnification micromorphology at RT, (b) high magnification micromorphology at RT, (c) low magnification micromorphology at 950 oC, (d) high magnification micromorphology at 950 oC
Fig.11  Tensile fracture surface morphologies of heat-treatment alloy at different temperatures (a) low magnification micromorphology at RT, (b) high magnification micromorphology at RT, (c) low magnification micromorphology at 950 oC, (d) high magnification micromorphology at 950 oC
Fig.12  Microstructure of the longitudinal section near the fracture after tensile rupture to fracture of as-cast alloy at different temperatures (a~c) RT, (d~f) 950 oC
Fig.13  Microstructure of the longitudinal section near the fracture after tensile rupture to fracture of heat-treatment alloy at different temperatures (a~c) RT, (d~f) 950 oC
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