Zirconium alloys are used in the core of nuclear reactors. Some of them contain 1 to 3 wt% Nb and ~0.1 to 0.2 wt% Fe. I observed in them the tiny precipitates of cubic beta-Nb phase with ~10 wt% Zr and ~3 wt% Fe in solid solution, but some of my colleagues insist that Fe cannot be present in niobium with ~10 wt% Zr.
Dear Dr Perriere,
Thank you for your interest and kind answer to my question.
The Zr-alloys I'm studying are actual Zr-2.5Nb-0.1Fe pressure tubes as used in CANDU reactors. In the article I most recently uploaded in the RG, I investigated the partitioning of Fe in these alloys as a function of annealing temperature below 580oC and time. The samples have not been irradiated, but came from offcuts of actual cold worked pressure tubes taken prior to their installation.
My technique used, Mossbauer spectroscopy is capable to observe Fe and its various forms in such alloys. My results suggest that after prolonged annealing near 580oC, Fe remains in beta-90%Zr-10%Zr. This is in agreement with some earlier electron microscopy examinations, but some colleagues claim that Fe cannot be present in this phase. I understand that the electron microscopy is not sensitive enough to analyze Fe properly in such very small (~10 nm) precipitates located largely at the alpha-alpha and alpha-beta grain boundaries. For instance, microscopists observed Fe in some such particles but not in the other ones, but their particle number counts in their studies were very small. So the controversy continues.
This topic is also very much related to the microstructure of Zr-alloys used in the French power reactors such as M5. I'm looking for contacts and advice from you and your colleagues in France in this regard.
Dear Prof. J. A. Sawicki
Unfortunately I cannot make the metalic alloy in our laboratory.
I try to ask somebody.
Best regards
kiyoshi Nomura
Dear Dr Sawicki,
At high temperature Nb and Zr form a total solid solution (beta phase), as shown on the phase diagram enclosed.
About the iron content that is possible to insert into this solid solution, it is difficult to answer, and I would say that it depends on the process. If your alloy is prepared with a sufficiently high cooling rate, it is possible that you precipitate out of equilibrium phases, such as the one you describe.
Moreover, were your observations performed onto irradiated materials? it might be of importance as well, since this phase could be the result of irradiation...
Hope my message can be of some help.
Best regards,
L.Perriere
Dear Dr Perriere,
Thank you for your interest and kind answer to my question.
The Zr-alloys I'm studying are actual Zr-2.5Nb-0.1Fe pressure tubes as used in CANDU reactors. In the article I most recently uploaded in the RG, I investigated the partitioning of Fe in these alloys as a function of annealing temperature below 580oC and time. The samples have not been irradiated, but came from offcuts of actual cold worked pressure tubes taken prior to their installation.
My technique used, Mossbauer spectroscopy is capable to observe Fe and its various forms in such alloys. My results suggest that after prolonged annealing near 580oC, Fe remains in beta-90%Zr-10%Zr. This is in agreement with some earlier electron microscopy examinations, but some colleagues claim that Fe cannot be present in this phase. I understand that the electron microscopy is not sensitive enough to analyze Fe properly in such very small (~10 nm) precipitates located largely at the alpha-alpha and alpha-beta grain boundaries. For instance, microscopists observed Fe in some such particles but not in the other ones, but their particle number counts in their studies were very small. So the controversy continues.
This topic is also very much related to the microstructure of Zr-alloys used in the French power reactors such as M5. I'm looking for contacts and advice from you and your colleagues in France in this regard.
Dear Dr. Sawicki,
Please find a isothermal cut of the ternary diagram ZrNbFe which might help you understanding the hermodynamics of your system. I only could find a cut at 500°C, not at room temperature. Yellow areas are triphased, white biphased and blue monophased domains.
After reflexion, I think the presence of your precipitates is linked to the limits of solubility of your different elements.
For instance, max Fe solubility in Zr is only 0.03 at.% into alpha-Zr, and around 6 at.% into beta-Zr. Moreover, Fe solubility into Nb is around 7-8 at.%
If I understood your previous messages right, your alloy should be mainly an alpha Zr-based phase, according to its chemical composition. Then, I would say that since all the Fe you have into your alloy cannot get into solid solution into the main phase, some of it precipitates under the beta NbZrFe phase that you observe.
Dear Jerzy A. Sawicki, regarding the short comment by Kiyoshi Nomura, I would like to draw your interest on spray forming processes which allow to make alloys that are not possible by mold casting processes. I cannot tell right away if your alloy can be made on our spray forming facilities, but I can check it out if you are interested in test material.
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