Effect of hot deformation on γ″ and δ phase precipitation of Inconel 718 alloy during deformation&isothermal treatment

• Published in: Journal of alloys and compounds 2017-09, Vol.716, p.65-72
• Main Authors: Zhang, Hongjun, Li, Chong, Liu, Yongchang, Guo, Qianying, Huang, Yuan, Li, Huijun, Yu, Jianxin
• Format: Article
• Language: English
• Subjects: Deformation; Deformation effects; Deformation&isothermal; Hot deformation; Inconel 718 alloy; Isothermal treatment; Nickel base alloys; Phase shift; Precipitates; Precipitation hardening; Recrystallization; Superalloys; γ″ phase; δ phase
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.05.042

A deformation&isothermal treatment is applied to investigate the effect of hot deformation on precipitation of γ″ and δ phase in Inconel 718 alloy. The results show the precipitation behaviors are tailored by the deformation temperatures that γ″ phase precipitation is accelerated at 800 °C in place of δ phase as for 900 °C. Deformation at 800 °C and 900 °C makes the precipitation peaks for γ″ phase shift towards lower temperatures to be 742 °C and 735 °C, while the precipitation peaks for δ phase moving towards higher temperatures to be 941 °C and 943 °C, respectively. When subjected to the deformation&isothermal treatment at 800 °C, the thus formed structure is composed of ellipsoidal, disc and irregular-shaped γ″ precipitates with sizes varying from 80 nm to 440 nm in the interior of broadened GBs, as well as dispersively ultrafine intragranular γ″ particles. As for the specimen deformed at 900 °C, the δ-phase precipitation is promoted under the effect of static recrystallization occurring at the initial aging stage, that granular, disc and needle-shaped δ precipitates with 7.5 vol % are generated in the limited duration of 1 h. •The effects of hot deformation on the precipitation kinetics of γ″ and δ phase are quantitatively measured.•The exceptional precipitation phenomenon of GB-γ″ phase is observed in a novel deformation & isothermal treatment.•The model for GB-γ″ phase transition is established based on the encounter mechanism.•The enhancement of static recrystallization on δ-phase precipitation is discussed.