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

Abstract

In the integrated oxy-fuel combustion and 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 1000 hours, 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 = 0.5092 nm and c = 0.8336 nm, α = 90º, β = 90º and γ = 120º. Highlights Oxidation products of the turbine material, Inconel 939 Ni-based superalloy, were studied in simulated oxy-fuel combustion conditions, focusing on the products of the decomposition the strengthening γ' precipitates.  An oxidation-induced phase transformation occurred in the subsurface region.  One of the two product phases was not included in the Ni database of ThermoCalc.  Through systematic electron microscopy investigation, this unknown phase was determined (modeled) as a ternary derivative of the ordered η-Ni 3 Ti phase (D0 24 ) in Ni-Ti-Ta system. AbstractIn the integrated oxy-fuel combustion and turbine power generation system, turbine alloys are exposed to high temperature and an atmosphere comprised of steam, CO 2 and O 2 . 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 Manuscript Click here to view linked References 2 strengthening precipitates. In an earlier study of the oxidation of Inconel 939 Ni-based superalloy exposed to oxy-fuel combustion environment for up to 1000 hours, a hightemperature-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 model...

A systematic review of Inconel 939 alloy parts development via additive manufacturing process

“…TEM analysis pointed out the coherent distribution of γ′-precipitates in the case of both LPBF and as-cast samples with slightly larger size in the former with the composition determined to be of (Ni …) 3 (Al, Ti, …) type. Additionally, brittle phases were observed in aged LPBF samples, which were found to be η-type precipitates that vary in morphology and composition compared to γ′ degrees [ 33 , 34 ].…”

"Investigation of microstructure evolution of Inconel 939 joint diffusion brazed using an amorphous liquated Ni-Cr-Fe-Si-B interlayer "

“…Nickel-based superalloys are broadly utilized in various sectors, especially in the aerospace and energy industries, because of their outstanding resistance to oxidation and significant creep behavior at high temperatures [1][2][3]. Among them, cast nickel-based high--chromium superalloys such as Inconel 939 (IN-939) have received much attention in different industries, such as aircraft components, chemical plant equipment, and petrochemical equipment, because of their extraordinary resistance to hot corrosion and oxidation.…”

Oxidation Behavior and Mechanism of Inconel 740H Alloy for Advanced Ultra-supercritical Power Plants Between 1050 and 1170 °C

“…In an investigation of Inconel 600 alloy, NiO and Cr 2 O 3 were the main oxides formed during oxidation at high temperature (970-1170 K), while only NiO came into formation at low temperature (870 K) [7]. Zhu et al [8] studied the oxidation of Inconel 939 alloy and a variety of oxides were found in the surface and subsurface of the oxide film. The external layer was Cr 2 O 3 and the thread-like internal oxides were typically Al 2 O 3 , sometimes TiO x and/or NiAl 2 O 4 .…”