A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic

Abstract

At elevated temperatures, heavy liquid metals and their alloys are known to create a highly corrosive environment that causes irreversible degradation of most iron-based materials. It has been found that an appropriate concentration of oxygen in the liquid alloy can significantly reduce this issue by creating a passivating oxide scale that controls diffusion, especially if Al is present in Fe-based materials (by Al-oxide formation). However, the increase of the temperature and of oxygen content in liquid phase leads to the increase of oxygen diffusion into bulk, and to promotion of the internal Al oxidation. This can cause a strain in bulk near the oxide layer, due either to mismatch between the thermal expansion coefficients of the oxides and bulk material, or to misfit of the crystal lattices (bulk vs. oxides). This work investigates the strain induced into proximal bulk of a Fe-Cr-Al alloy by oxide layers formation in liquid lead-bismuth eutectic utilizing synchrotron X-ray Laue microdiffraction. It is found that internal oxidation is the most likely cause for the strain in the metal rather than thermal expansion mismatch as a two-layer problem.Dear Sir, I re-submit our paper entitled: "A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic" on behalf of all co-authors to Acta Materialia, after addressing all the revisions stated by the reviewer. In the study, we analyze a strain in the near-interface bulk of ferritic FeCrAl alloy after its exposure to heavy liquid metals. Two possible origins of strain were considered: internal oxidation of aluminum in bulk, and thermal expansion mismatch between the oxide and the bulk. A positive correlation of dislocation density with peak width distribution indicates that strain comes from plastic deformation, while the evidence of grain refinement and sub-grain formation indicates a noticeable internal oxidation. Based on the comparison with theoretical predictions, we conclude that internal oxidation is more dominant mechanism of strain induction.Sincerely, Miroslav P. Popovic, UC Berkeley Cover LetterWe thank the reviewer for his/her time and effort.Below we address all reviewer's comments (labeled "C") in detail, marked in green (labeled "A").C 0: -Dear authors, congratulations for this interesting work.A 0: We thank the reviewer for his/her assessment of our paper. C1-1: You are studying the deformation and strain induced in the bulk of a Fe-Cr-Al alloy (Alkrothal 720) by oxide scales that form in liquid LBE. Alkrothal is a bcc alloy, a fact that you should clearly mention when you describe the material in the Experimental section (not just mention that it is a ferritic alloy), giving some basic information on the lattice parameters. A1-2: We thank the reviewer for this suggestion. We made changes in the manuscript and modified our statement (in the first paragraph of section 2. Experimental), so it reads now as following: C1-2. What you neglect to mention, however, is th...

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