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Title: On the existence of declared 9R phase in Fe–Ni invar alloy

Abstract

An analysis of recently reported electron diffraction patterns suggests that metastable austenitic Fe–32Ni alloy subjected to α → γ transformation upon slow heating does not exhibit any signs of formation of the 9R phase; the conventional nanocrystalline γ phase with an fcc lattice is formed instead. Extended lamellae with a layered structure, erroneously identified as a new phase of the (3R + 9R) type in Fe–32Ni alloy, are conventional twinning (midrib) regions of each initial α crystal, in which γ-phase twin nanolamellae are formed upon heating.

Authors:
; ;  [1]
  1. Russian Academy of Sciences, Institute of Metal Physics, Ural Branch (Russian Federation)
Publication Date:
OSTI Identifier:
22645442
Resource Type:
Journal Article
Resource Relation:
Journal Name: Crystallography Reports; Journal Volume: 61; Journal Issue: 4; Other Information: Copyright (c) 2016 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AUSTENITIC STEELS; CRYSTAL STRUCTURE; CRYSTALS; ELECTRON DIFFRACTION; FCC LATTICES; INVAR; LAMELLAE; NANOSTRUCTURES; TWINNING

Citation Formats

Kabanova, I. G., Sagaradze, V. V., E-mail: vsagaradze@imp.uran.ru, and Kataeva, N. V. On the existence of declared 9R phase in Fe–Ni invar alloy. United States: N. p., 2016. Web. doi:10.1134/S1063774516040088.
Kabanova, I. G., Sagaradze, V. V., E-mail: vsagaradze@imp.uran.ru, & Kataeva, N. V. On the existence of declared 9R phase in Fe–Ni invar alloy. United States. doi:10.1134/S1063774516040088.
Kabanova, I. G., Sagaradze, V. V., E-mail: vsagaradze@imp.uran.ru, and Kataeva, N. V. Fri . "On the existence of declared 9R phase in Fe–Ni invar alloy". United States. doi:10.1134/S1063774516040088.
@article{osti_22645442,
title = {On the existence of declared 9R phase in Fe–Ni invar alloy},
author = {Kabanova, I. G. and Sagaradze, V. V., E-mail: vsagaradze@imp.uran.ru and Kataeva, N. V.},
abstractNote = {An analysis of recently reported electron diffraction patterns suggests that metastable austenitic Fe–32Ni alloy subjected to α → γ transformation upon slow heating does not exhibit any signs of formation of the 9R phase; the conventional nanocrystalline γ phase with an fcc lattice is formed instead. Extended lamellae with a layered structure, erroneously identified as a new phase of the (3R + 9R) type in Fe–32Ni alloy, are conventional twinning (midrib) regions of each initial α crystal, in which γ-phase twin nanolamellae are formed upon heating.},
doi = {10.1134/S1063774516040088},
journal = {Crystallography Reports},
number = 4,
volume = 61,
place = {United States},
year = {Fri Jul 15 00:00:00 EDT 2016},
month = {Fri Jul 15 00:00:00 EDT 2016}
}
  • Polarized neutron scattering experiments have been performed on an Fe/sub 65/Ni/sub 35/ Invar alloy in the paramagnetic phase at T = 1.25T/sub c/. Constant-q spectra were fitted to simple Lorentzian functions and the q-dependence of the half-width GAMMA was found to agree with that of the spin-diffusion model in the measured q range (0.1 A/sup -1/
  • It is well established that Fe-Ni invar alloys have low strength. As it was shown in the previous paper additions of small amounts (about 1 wt.%) Be lead to age-strengthening of these alloys without a significant increase in their linear thermal expansion coefficient (LTEC). The optimal combination of nickel and beryllium in the ternary Fe-Ni-Be alloys has been determined (40 wt.% Ni and 0.8 wt.%Be) to permit an increase in hardness upon aging (at 550 C) while maintaining LTEC at the low level. The aim of the present work is to study the temperature dependence of the LTEC and mechanicalmore » properties of Fe-Ni-Be alloy with the optimal composition.« less
  • We have succeeded in increasing up to 150 K the Curie temperature in the Fe{sub 64}N{sub 36}6 invar alloy by means of a severe mechanical treatment followed by a heating up to 1073 K. The invar behavior is still present as revealed by the combination of magnetic measurements with neutron and x-ray techniques under extreme conditions, such as high temperature and high pressure. The proposed explanation is based in a selective induced microstrain around the Fe atoms, which causes a slight increase in the Fe-Fe interatomic distances, thus reinforcing ferromagnetic interactions due to the strong magnetoelastic coupling in these invarmore » compounds.« less
  • Anti-Invar effect in the f.c.c.-Fe-25.3%Ni-C alloy was revealed, i.e., enhanced thermal expansion coefficient (TEC)({approx}20x10{sup -6} K{sup -1}) which was accompanied by almost temperature-insensitive behavior in a temperature range of 122-525 K that was considerably expanded to the low temperature range due to alloying with carbon. The Moessbauer and small-angle neutron scattering (SANS) experiments with the varying temperature and in an external magnetic field of 1.5-5 T have revealed an existence of inhomogeneous magnetic order in anti-Invar alloy below and above the magnetic transition point. The anti-Invar behavior correlates with the thermally induced change in the magnetic order and interspin interaction.
  • The authors summarize and review critically the existing experimental and theoretical evidence concerning both thermal and irradiation-induced high-temperature miscibility gaps in Fe-Ni based Invar-type alloys. Independent data regarding phase separation are obtained from studies on magnetic, low-expansion Invar-type alloys and model austenitic Fe-Ni based alloys studied for potential nuclear applications. The response of these alloys to long-term thermal aging is found to be inconsistent with that of single-phase alloys predicted by most accepted or proposed phase diagrams. These alloys show anomalies in numerous properties which suggest compositional or magnetic heterogeneities or both. The authors herein model the kinetics and thermodynamicsmore » of spinodal decomposition and nucleation in these alloys under thermal conditions. They can combine their calculations with those of others and also with experimental studies of decomposition to reach a conclusion that suggests a high-temperature miscibility gap for Fe-Ni alloys in the Invar regime. Alloys in the Invar composition range have been subjected to a variety of high fluence irradiation treatments in the 725 to 1,000 K temperature range. The result in most cases was large-scale decomposition into approximately 25 and 50% Ni phases. The apparent miscibility gap under irradiation is much wider than that observed thermally. They discuss these observations in the light of existing theories of irradiation-induced or irradiation-altered alloy decomposition. They conclude that although irradiation-enhanced diffusion speeds up phase separation, other processes must be operating to produce the greatly widened miscibility gap. 68 refs., 16 figs.« less