The growth mechanism of grain boundary carbide in Alloy 690

Journal Article · Mon Jul 15 00:00:00 EDT 2013 · Materials Characterization

DOI:https://doi.org/10.1016/J.MATCHAR.2013.04.005· OSTI ID:22285053

Li, Hui ^[1]; Xia, Shuang; Zhou, Bangxin ^[2]; Peng, Jianchao ^[1]

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1. Key Laboratory for Microstructures, Shanghai University, Shanghai 200444 (China)
2. Institute of Materials, Shanghai University, Shanghai 200072 (China)

The growth mechanism of grain boundary M{sub 23}C{sub 6} carbides in nickel base Alloy 690 after aging at 715 °C was investigated by high resolution transmission electron microscopy. The grain boundary carbides have coherent orientation relationship with only one side of the matrix. The incoherent phase interface between M{sub 23}C{sub 6} and matrix was curved, and did not lie on any specific crystal plane. The M{sub 23}C{sub 6} carbide transforms from the matrix phase directly at the incoherent interface. The flat coherent phase interface generally lies on low index crystal planes, such as (011) and (111) planes. The M{sub 23}C{sub 6} carbide transforms from a transition phase found at curved coherent phase interface. The transition phase has a complex hexagonal crystal structure, and has coherent orientation relationship with matrix and M{sub 23}C{sub 6}: (111){sub matrix}//(0001){sub transition}//(111){sub carbide}, <112{sup ¯}>{sub matrix}//<21{sup ¯}10>{sub transition}//<112{sup ¯}>{sub carbide}. The crystal lattice constants of transition phase are c{sub transition}=√(3)×a{sub matrix} and a{sub transition}=√(6)/2×a{sub matrix}. Based on the experimental results, the growth mechanism of M{sub 23}C{sub 6} and the formation mechanism of transition phase are discussed. - Highlights: • A transition phase was observed at the coherent interfaces of M{sub 23}C{sub 6} and matrix. • The transition phase has hexagonal structure, and is coherent with matrix and M{sub 23}C{sub 6}. • The M{sub 23}C{sub 6} transforms from the matrix directly at the incoherent phase interface.

• OSTI ID: 22285053
• Journal Information: Materials Characterization, Vol. 81; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CARBIDES
CRYSTAL LATTICES
CRYSTALS
GRAIN BOUNDARIES
NICKEL
NICKEL BASE ALLOYS
PHASE TRANSFORMATIONS
TRANSMISSION ELECTRON MICROSCOPY