Microstructure evolution of alloy 625 foil and sheet during creep at 750 °C

Foil and sheet forms of the nickel-based superalloy 625 have been examined in an ‘as-processed’ condition and following creep-rupture testing in air at 750 °C and 100 MPa. Both scanning and transmission electron microscopies were employed to correlate microstructures with creep behavior, and indicat...

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Bibliographic Details
Published in:Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2008-12, Vol.498 (1), p.412-420
Main Authors: Evans, Neal D., Maziasz, Philip J., Shingledecker, John P., Yamamoto, Yukinori
Format: Article
Language:English
Subjects:
Analytical electron microscopy
Applied sciences
Austenitic steels
Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
Creep
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
Materials science
Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology
Metals. Metallurgy
Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
Phase field modeling
Phase transformations
Physics
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Summary:Foil and sheet forms of the nickel-based superalloy 625 have been examined in an ‘as-processed’ condition and following creep-rupture testing in air at 750 °C and 100 MPa. Both scanning and transmission electron microscopies were employed to correlate microstructures with creep behavior, and indicate the additional processing required to achieve foil form reduces creep life compared to thicker-section wrought product forms. Prior to creep testing, the microstructure consists of γ phase with M 6C precipitates. This microstructure changes during creep into one consisting of orthorhombic δ phase extending across the γ grains, and grain boundaries dominated by the presence of rhombohedral μ phase, δ phase, and a Si-rich variant of diamond-cubic M 6C (η phase). Thermodynamic modeling was also used to calculate the stable temperature ranges and compositions of equilibrium phases. The phases predicted by modeling and their compositions generally agree with those observed within alloy 625 after creep testing.
ISSN:0921-5093
1873-4936
DOI:10.1016/j.msea.2008.08.017