Creep behavior of Ni–38Cr-3.8Al alloy with lamellar structure formed by discontinuous precipitation

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 766; p. 138333
• Main Authors: Koyanagi, Yoshihiko, Takabayashi, Hiroyuki, Ueta, Shigeki, Cho, Ken, Yasuda, Hiroyuki Y.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 24.10.2019; Elsevier BV
• Subjects: Alloys; Binary alloys; Collapse; Cracks; Creep property; Creep strength; Creep tests; Deformation; Discontinuous precipitation; Gamma phase; Gamma-prime phase (crystals); Grain boundaries; Interface stability; Lamellar structure; Ni alloy; Precipitates; Precipitation hardening; Structural stability; Thermal stability; Discontinuous precipitation; Ni alloy; Lamellar structure; Creep property
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2019.138333

The creep behavior of Ni–38Cr-3.8Al (mass%) alloy with the lamellar structure composed of the γ and α-Cr phases were examined focusing on the thermal stability of microstructure. The lamellar structure is formed by a discontinuous precipitation from the γ grain boundary, and the initial γ gains are subdivided into small lamellar cells. The γ' phase is also precipitated in the γ phase in the lamellar structure. Thermal stability of the lamellar cells plays an important role in the creep behavior. The lamellar structure consisting of the γ and α-Cr phases with the Kurdjumov-Sachs orientation relationship is thermally stable up to 873 K. On the other hand, during annealing at high temperatures, especially at and above 973 K, the lamellar structure starts to collapse at initial γ grain boundary and the interface between the lamellar cells, and consequently, coarse γ, γ' and α-Cr phases are formed. Based on the activation energy and the stress exponent of the deformation, the creep behavior of Ni–38Cr-3.8Al alloy is similar to that of pure-Ni and Ni–Cr binary alloys rather than γ' precipitation strengthening Ni alloy even though this alloy precipitates the γ' phase. As the result of evaluation after creep test, the creep properties was lower even in the most of lamellar structure existed excepting for initial γ grain boundary and the interface between the lamellar cells. This is because the creep deformation occurs preferentially at the coarse γ phase formed due to the collapse of the lamellar structure. This result indicates that the creep properties of Ni–38Cr-3.8Al is strongly influenced by the thermal stability of lamellar structure at initial γ grain boundary and the interface between the lamellar cells, which lead to the formation of cracks/voids and creep rupture.