The effect of reheat treatments on recovering the creep behavior of a corrosion-resistant nickel-based superalloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2013-01, Vol.560, p.25-33
• Main Authors: Hou, J.S., Zhou, L.Z., Yuan, C., Tang, Z., Guo, J.T., Qin, X.Z., Liaw, P.K.
• Format: Article
• Language: English
• Subjects: Alloys; Applied sciences; Carbides; Corrosion; Corrosion prevention; Creep; Creep (materials); Creep life; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Formations; Fractures; Materials science; Mathematical analysis; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Nickel base alloys; Nickel-based superalloy; Physics; Recovering; Reheat treatment; Solid solution, precipitation, and dispersion hardening; aging; Superalloys; Treatment of materials and its effects on microstructure and properties; γ′ rafting; σ phase
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2012.07.068

The present work is an attempt to possibly obtain the most suitable reheat treatment, which could provide the optimal microstructural characteristics for creep-exposed superalloys. After creep at 850°C/350MPa for 96h and 140h a cast nickel-based superalloy was reheat-treated with different programs, and then the specimens were subjected to creep again at the same condition. Creep tests indicate that during reheat treatment applying aging at lower temperature, 850°C, for proper time (4h) before aging at 1050°C rather than a repeated standard heat treatment is beneficial to restore creep life. Creep-induced changes in the microstructure, such as excessive grain-boundary secondary M23C6 and/or M6C carbides formation, and primary MC carbides decomposition, are noticeably more advanced in the reheat-treated alloys. A quantitative study on the dissolution of σ phases and the formation of cavitations is presented. After the interrupted creep, the γ′ particles at dendrite cores remained cubic-shaped. However, the rafting of cuboidal γ′ precipitates was observed in the same creep condition by the reheat treatment programs. Design of a reheat treatment for recovering the creep properties should emphasize the promotion of ductility rather than strength of the alloy. An equation based on the continuum damage-mechanics theory, was suggested to evaluate the remaining creep life.