Effect of Long-term Thermal Exposure on Microstructure and Stress Rupture Properties of GH3535 Superalloy

doi:10.1016/j.jmst.2014.07.021

Abstract

Abstract: The evolution of microstructure and the stress rupture properties of long term thermally exposed GH3535 alloy have been investigated. It was found that M₆C carbides presented in the solid solution heat treated samples. During long term thermal exposure at 700 °C, fine M₁₂C carbides precipitated preferentially at grain boundaries. These carbides coexisted with the pre-exiting M₆C. The stress rupture life of 700 °C/1000 h exposed sample under creep testing at 650 °C/324 MPa is 93 h. It is much longer than that of the solid solution samples. No noticeable changes could be detected in both the microstructure and stress rupture lives when the samples were exposed for time longer than 1000 h M₁₂C carbides were found to be beneficial to the creep properties. The cracks initiated at the interface of M₆C carbides and matrix, which led to a lower creep rupture life.

Key words: GH3535 superalloy, Long term thermal exposure, Microstructure, Carbide, M6C, M12C

T. Liu, J.S. Dong, L. Wang, Z.J. Li, X.T. Zhou, L.H. Lou, J. Zhang. Effect of Long-term Thermal Exposure on Microstructure and Stress Rupture Properties of GH3535 Superalloy[J]. J. Mater. Sci. Technol., 2015, 31(3): 269-279.

Figures/Tables 18

Microstructure of the solid solution heat treated specimen (1177 °

C for 1 h): (a) the optical microscopy metallurgical structure of the alloy, (b) white blocky and rod-like phase, (c) and (d) the M6C carbide and its SAED pattern.

X-ray diffraction pattern of the solid solution heat treated specimen.

Microstructure of the solid solution heat treated specimen: (a) BEI image and the area distribution analysis of (b) C, (c) Si, (d) Mo, (e) Cr and (f) Fe by EPMA.

Deep etched specimens with different long term thermal exposure time: (a) 0 h, (b) 10 h, (c) 50 h, (d) 100 h, (e) 300 h, (f) 500 h.

Microstructure of the specimen aged at 700 °

C for 1000 h: (a) the optical microscopy metallurgical structure of the alloy, (b) the primary M6C carbide and secondary fine M12C carbide precipitated at the grain boundaries.

Microstructure of the specimen aged at 700 °

C for 5000 h: (a) the optical microscopy metallurgical structure of the alloy, (b) the primary M6C carbide and secondary fine M12C carbide precipitated at the grain boundaries.

Microstructure of the specimen aged at 700 °

C for 10,000 h: (a) the optical microscopy metallurgical structure of the alloy, (b) the primary M6C carbide and secondary fine M12C carbide precipitated at the grain boundaries.

TEM image for microstructure of the specimen aged at 700 °

C for 1000 h: (a) and (b) the morphology of the M12C carbide and its SAED pattern, respectively.

X-ray diffraction pattern of the specimen aged at 700 °

C: (a) for 1000 h, (b) 5000 h, and (c) 10,000 h.

Microstructure of the specimen aged at 700 °

C for 1000 h: (a) BEI image and the area distribution of (b) C, (c) Si, (d) Mo, (e) Cr and (f) Fe by EPMA.

Microstructure of the specimen aged at 700 °

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