High-temperature-oxidation-induced ordered structure in Inconel 939 superalloy exposed to oxy-combustion environments

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 566; no. C; pp. 134 - 142
• Main Authors: Zhu, Jingxi, Wise, Adam, Nuhfer, Thomas, Holcomb, Gordon R., Jablonski, Paul D., Sridhar, Seetharaman, Laughlin, David E.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 20.03.2013; Elsevier
• Subjects: Condensed matter: structure, mechanical and thermal properties; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Convergent-beam electron diffraction, selected-area electron diffraction, nanodiffraction; Cross-disciplinary physics: materials science; rheology; Electron diffraction and scattering; Exact sciences and technology; High temperature oxidation; High-resolution transmission electron microscopy; Inconel 939 superalloy; MATERIALS SCIENCE; Ordered structure; Oxy-fuel combustion; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Inconel 939 superalloy; Ordered structure; High-resolution transmission electron microscopy; Oxy-fuel combustion; High temperature oxidation; Strengthening; Cubic lattices; Electron diffraction; High temperature; Superalloys; Internal oxidation; Hardening; Dual phase structure; Temperature effects; Gamma phase; Subsurface; Crystal structure; Nickel base alloys; Phase transformations; Lattice parameters; Precipitates; Orientation relation; Transmission electron microscopy; Solid solutions; Steam; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2012.12.074

In the integrated oxy-fuel combustion and the turbine power generation system, turbine alloys are exposed to high temperature and an atmosphere comprised of steam, CO2 and O2. While surface and internal oxidation of the alloy takes place, the microstructure in the subsurface region also changes due to oxidation that results in the loss of the strengthening precipitates. In an earlier study of the oxidation of Inconel 939 Ni-based superalloy exposed to oxy-fuel combustion environment for up to 1000h, a high-temperature-oxidation-induced phase transformation in the sub-surface region was noticed and a two-phase region formed at the expense of strengthening γ' phase. While one of the two phases was identified as the Ni-matrix γ solid solution, face-center-cubic) phase, the other product phase remained unidentified. In this study, the crystal structure of the unknown phase and its orientation relationship with the parent Ni-matrix phase was investigated through electron diffraction and high-resolution transmission electron microscopy. It was determined that the crystal structure of the unknown phase could be modeled as a ternary derivative of the ordered η-Ni3Ti phase (D024) structure with lattice parameters of a=.5092nm and c=.8336nm, α=90°, β=90° and γ=120°.