Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Personnel involved:
Materials Science
Permanent: F. Lecouturier, N. Ferreira, L. Bendichou, J.P. Laurent, J.M. Lagarrigue, J. Billette
Ph.D Student: V.Vidal, J.B. Dubois
Non permanent: M. Mainson (CDD)
Collaboration: L. Thilly & P.O Renault (PHYMAT, Poitiers), V. Vidal (MTM-Leuven, ENSTIMAC-Albi),
H. van Swygenhoven & S. van Petegem (POLDI-Paul Scherrer Institut, Switzerland),
B. Schmitt (SLS-PSI, Switzerland), P. Olier (CEA-LTMEX, Saclay), A. Devred & C. Berriaud
(CEA-SACM, Saclay), H. Jones (Clarendon Laboratory, University of Oxford), S. Svyagin
(HLD, Dresden), C. Verwaerde (MSA-Alstom), M. Sandim (University of São Paulo, Brazil)
Ultra-high strength nanocomposite Cu/X (X=Nb, Ta) conductors
The development of reinforced conductors, with high electrical conductivity and high strength, is essential to
provide non-destructive high pulsed magnetic fields over 80 Tesla: a compromise is obtained with Cu-based
continuous nanofilamentary wires (2 GPa ultimate tensile strength and 0.6 µohm.cm electrical resistivity at 77K).
The fabrication process of these nanocomposite wires is based on severe plastic deformation applied by
accumulative drawing and bundling (ADB), leading to a multi-scale copper matrix containing up to N=85 5 (4.4
10 9 ) continuous and parallel niobium fibers. Three ways of optimization have been investigated and are
summarized below: they deal with the geometry of the reinforcement, the material and the process.
Cu nanowhiskers embedded in Nb nanotubes inside a multiscale Cu matrix: the way to reach
extreme mechanical properties in high strength conductors
Finally, the validity of the Cu/Nb/Cu
nanocomposite wires (N=853 , �1mm), insulated
with Kevlar fiber), without any loss in strength, has
been demonstrated in the thumb-coils configuration
(Ph.D work of S. Batut). First neutrons diffractions
experiments on Cu/Nb/Cu aged coils have been
performed at the continuous spallation neutron
source SINQ (POLDI, PSI, Switzerland).
For the development of non destructive resistive
pulsed magnets over 80T, Cu/Nb/Cu wires with
geometrical optimization, composed of a multiscale
Cu matrix embedding Nb nanotubes were
produced by ADB. TEM reveals good codeformation
compatibility between the reinforcing
Nb nanotubes and the multi-scale Cu. While a sharp
single-component fibre texture is developed
in Nb nanotubes, a double texture with and
orientations is observed in the copper matrix.
The mechanical properties are improved compared
to nanofilamentary Cu/Nb wires. The extraordinary
strengthening of the co-cylindrical structure is
related to: (i) an increase of Cu-Nb interfaces
surface acting as dislocations barriers; (ii) a rapid
and controlled access to nanometre scale where size
effect operates on the plasticity mechanisms; (iii)
the contribution of an additional reinforcing phase:
the Cu-f nanofilaments embedded in the Nb
nanotubes behave as whiskers with strong size
dependence. The Cu/Nb/Cu system is therefore
more efficient than the Cu/Nb system for the highstrength
applications in magnets: it exhibits a
controlled microstructure and an efficient
strengthening in the nanocomposite zones, where
size and also geometry play major roles (Scripta
Mat 57 (3) (2007) 245-248).
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(a), (b), (c) SEM image of the multi-scale structure of Cu/Nb/Cu
co-cylindrical wires (N = 85 3 , d=1.511mm). (d) High-magnification
cross-section SEM image of the nanocomposite area showing
the Nb nanotubes, the Cu fibers and the interfilamentary Cu.