Subsurface microstructural changes in a cast heat resisting alloy caused by high temperature corrosion

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author -deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 3807 b s t r a c tA cast HP ModNb alloy (Fe-25Cr-35Ni-1Nb, wt.%) was oxidised and carburised in CO-CO 2 corresponding to a C = 0.1 and p O 2 = 3 Â 10 À16 atm at 1080°C. Formation of an external, chromium-rich oxide scale led to depletion of this metal in a deep alloy subsurface zone. Within that zone, secondary chromium-rich carbides dissolved, primary carbides oxidised, solute silicon and aluminium internally oxidised, and extensive porosity developed. Pore volumes correspond to the difference between metal loss by scaling and metal displacement by internal oxidation, assuming the scale-metal interface to be fixed. The pores are concluded to be Kirkendall voids.

Intergranular oxidation of Ni-base alloy 718 with a focus on additive manufacturing

“…Moreover, in certain cases, voids were found near the oxides formed at grain boundaries and within the bulk inside the Cr-depleted zone, for long-duration oxidation of Ni-15.1Cr-1.1Al and Ni-28.8Cr-1.0Al at 1000°C and 1200°C [20]. The formation of these voids was attributed to a Kirkendall effect, as seen in other studies on Ni-Cr alloys [15,21,22].…”

Microstructure and Carburization Detection in HP Alloy Pyrolysis Tubes

“…The Cr-and Si-rich oxide scales and the chromium precipitate free zone that were observed at the inner and outer diameters of the ex-service tube are consistent with observations of HP alloys exposed to oxidizing and carburizing environments at elevated temperatures [28,29]. Inwards from the chromium-rich precipitate free zone at the outer diameter, the M 23 C 6 carbides in the carbide network transformed into a different chromium-rich precipitate, which had a blocky appearance and a darker contrast in BSE images compared to the medium gray M 23 C 6 carbides.…”

A comparison of the high-temperature oxidation behaviour of conventional wrought and laser beam melted Inconel 625

“…It is well known that the transfer of atoms from the alloy to the oxide lattice may involve the generation of a counterflow of vacancies into the substrate (vacancy injection) [32]. The formation of the high density of voids during oxidation was studied by Oquab et al [33] on a chromia-forming alloy (Fe-25Cr-35Ni-1Nb in wt. %).…”