Role of stabilization heat treatment inducing γ′-γ″ co-precipitates and grain boundary η phase on tensile and creep behaviors of Inconel 706

• Published in: Journal of alloys and compounds Vol. 900; p. 163479
• Main Authors: Kim, Chiwon, Park, Jiun, Hong, Hyun-Uk, Gu, Jiho, Song, Youngseok
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.04.2022; Elsevier BV
• Subjects: Antiphase boundaries; Chemical precipitation; Creep; Creep (materials); Dislocation mobility; Ferrous alloys; Grain boundaries; Heat treating; Heat treatment; Microstructure; Nickel base alloys; Precipitates; Shearing; Stabilization; Stacking faults; Superalloys; Synergistic effect; Tensile deformation; Yield strength; γ′-γ″ co-precipitates; η phase; γ′-γ″ co-precipitates; Creep; Superalloys; Stabilization; η phase
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.163479

•The role of stabilization was studied focusing on intergranular η phase and γ′-γ″ co-precipitates.•Stabilization at 840 °C induced the compact γ′-γ″ co-precipitates pre-cursor before double aging.•High fraction of η phase increased creep ductility by accommodating grain boundary deformation.•Compact γ′-γ″ co-precipitates contributed to strengthening by provoking additional APB shearing. [Display omitted] The effects of the stabilization conditions on the microstructure evolution in Ni-Fe-based superalloy Inconel 706 were investigated. In addition, the relationship between the microstructure and tensile and creep properties of the alloy was investigated. Stabilization at 800–840 °C resulted in the precipitation of the η phase at the grain boundaries. With an increase in the stabilization temperature, the η phase fraction increased. Non-compact γ′-γ″ co-precipitates were also formed at 800–840 °C, and their size was the largest when the stabilization was carried out at 840 °C. After double aging, the sample stabilized at 840 °C showed a cuboidal γ′ phase covered entirely with γ″ films, i.e. compact γ′-γ″ co-precipitates were observed along with a coarsened lamellae η phase. The double-aged sample stabilized at 800 °C (S80) exhibited the highest yield strength because of the presence of fine γ′ and γ″ precipitates. The double-aged samples stabilized at 810 and 840 °C (S81 and S84, respectively), exhibited similar yield strengths. Isolated stacking faults were generated in the γ′ particles of the S81 and S84 samples during the tensile deformation, indicating the high mobility of perfect dislocations in the γ-matrix. After creep at 650 °C/650 MPa, S81 and S84 exhibited higher creep strain at a given time than S80. This higher creep strain can be attributed to the synergistic effect of the increased dislocation mobility and η phase fraction, which resulted in strain accumulation at the grain boundaries. The anti-phase boundary shearing observed only in the S84 sample contributed to the strengthening of its γ-matrix and increased its creep rupture life.