Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers
Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers
The paper presents a new approach, based on controlled oxidation of nanoscale metallic multilayers, to produce strong and hard oxide/metal nanocomposite coatings with high strength and good thermal stability. The approach is demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale metallic multilayers and investigating the evolution of their microstructure and mechanical properties by combining analytical transmission electron microscopy, nano-mechanical tests and finite element models. As-deposited multilayers were annealed at 350 °C in air for times ranging between 1 and 336 h. The elastic modulus increased by ?20% and the hardness by ?42% after 15 h of annealing.
Longer annealing times did not lead to changes in hardness, although the elastic modulus increased up to 35% after 336 h. The hcp Zr layers were rapidly transformed into monoclinic ZrO2 (in the first 15 h), while the Nb layers were progressively oxidized, from top surface down towards the substrate, to form an amorphous oxide phase at a much lower rate.
The sequential oxidation of Zr and Nb layers was key for the oxidation to take place without rupture of the multi-layered structure and without coating spallation, as the plastic deformation of the metallic Nb layers allowed for the partial relieve of the residual stresses developed as a result of the volumetric expansion of the Zr layers upon oxidation. Moreover, the development of residual stresses induced further changes in mechanical properties in relation to the annealing time, as revealed by finite element simulations.
1-10
Monclus, M.A.
eab76faa-a2c2-444f-91a2-40248b78d35f
Callisti, M.
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Polcar, T.
c669b663-3ba9-4e7b-9f97-8ef5655ac6d2
Yang, L.W.
c5a2bc84-075b-4a8a-b457-282c4e2c0416
Llorca, J.
c0c99edb-84b0-45b1-8909-ba8e5842e48d
Molina-Aldareguia, J.M.
f4d7ff0d-2b62-4d10-a5dc-9f7acca97064
1 January 2017
Monclus, M.A.
eab76faa-a2c2-444f-91a2-40248b78d35f
Callisti, M.
093b5320-2398-4d72-8b09-278d22a08937
Polcar, T.
c669b663-3ba9-4e7b-9f97-8ef5655ac6d2
Yang, L.W.
c5a2bc84-075b-4a8a-b457-282c4e2c0416
Llorca, J.
c0c99edb-84b0-45b1-8909-ba8e5842e48d
Molina-Aldareguia, J.M.
f4d7ff0d-2b62-4d10-a5dc-9f7acca97064
Monclus, M.A., Callisti, M., Polcar, T., Yang, L.W., Llorca, J. and Molina-Aldareguia, J.M.
(2017)
Selective oxidation-induced strengthening of Zr/Nb nanoscale multilayers.
Acta Materialia, .
(doi:10.1016/j.actamat.2016.09.021).
Abstract
The paper presents a new approach, based on controlled oxidation of nanoscale metallic multilayers, to produce strong and hard oxide/metal nanocomposite coatings with high strength and good thermal stability. The approach is demonstrated by performing long term annealing on sputtered Zr/Nb nanoscale metallic multilayers and investigating the evolution of their microstructure and mechanical properties by combining analytical transmission electron microscopy, nano-mechanical tests and finite element models. As-deposited multilayers were annealed at 350 °C in air for times ranging between 1 and 336 h. The elastic modulus increased by ?20% and the hardness by ?42% after 15 h of annealing.
Longer annealing times did not lead to changes in hardness, although the elastic modulus increased up to 35% after 336 h. The hcp Zr layers were rapidly transformed into monoclinic ZrO2 (in the first 15 h), while the Nb layers were progressively oxidized, from top surface down towards the substrate, to form an amorphous oxide phase at a much lower rate.
The sequential oxidation of Zr and Nb layers was key for the oxidation to take place without rupture of the multi-layered structure and without coating spallation, as the plastic deformation of the metallic Nb layers allowed for the partial relieve of the residual stresses developed as a result of the volumetric expansion of the Zr layers upon oxidation. Moreover, the development of residual stresses induced further changes in mechanical properties in relation to the annealing time, as revealed by finite element simulations.
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Accepted/In Press date: 14 September 2016
e-pub ahead of print date: 28 September 2016
Published date: 1 January 2017
Additional Information:
Funded by:
EU: Multiscale Modelling and Materials by Design of interface-controlled Radiation Damage in Crystalline Materials (RADINTERFACES) (263273)
EPSRC: South of England Analytical Electron Microscope (EP/K040375/1)
EU: Virtual Design, Virtual Processing and Virtual Testing of Metallic Materials (VIRMETAL) (669141)
Organisations:
nCATS Group
Identifiers
Local EPrints ID: 400691
URI: http://eprints.soton.ac.uk/id/eprint/400691
ISSN: 1359-6454
PURE UUID: 39622cd3-62e5-4268-aff9-148954b6efda
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Date deposited: 23 Sep 2016 12:20
Last modified: 15 Mar 2024 05:54
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Contributors
Author:
M.A. Monclus
Author:
M. Callisti
Author:
L.W. Yang
Author:
J. Llorca
Author:
J.M. Molina-Aldareguia
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