Laboratoire National des Champs Magnétiques Pulsés CNRS – INSA

Development of a new co-axial CuNbCuNb nanocomposite wires
A new nanocomposite structure has been designed with a superposition of Nb and Cu nanotubes. We have added
nanometric phases reminding the extraordinary strengthening of the co-cylindrical structure. A conductor
containing 85 3 Nb nanowhiskers, Cu nanotubes and Nb nanotubes, embedded in a copper matrix has been
obtained. The Cu/Nb/Cu/Nb system is therefore more efficient than the Cu/Nb filamentary and the Cu/Nb/Cu cocylindrical
system for high-strength applications in magnets: it exhibits a controlled microstructure and an
efficient strengthening in the nanocomposite zones.
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Prototypes LNCMP - LMP- CEA 85 3
CuNbCu UTS(RT)
CuNbCuNb UTS(RT)
CuNbCu UTS(77K)
CuNbCuNb UTS(77K)
0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2
diamètre conducteur (mm)
Bulk precursors N=85 3 ,after drawing UTS of co-axial CuNbCuNb and co-cylindrical
CuNbCu nanocomposite wires versus diameter
Effects of size and geometry on the plasticity of copper/tantalum wires
The material optimization procedure led to the use
of tantalum to strengthen the copper matrix, instead
of Nb because of the highest value of its shear
modulus which is assumed to increase the whiskers
effect. The microstructure of the Cu/Ta
nanofilamentary conductors (N=85 3 ), cold-drawn to
a diameter of 1.5mm, has been investigated and
correlated to the mechanical properties. After heavy
drawing, the Cu matrix is nanostructured and the Ta
nanofilaments develop a strong ribbon-like shape
resulting in an early microstructural refinement.
The macroscopic strength is in excess from rule of
mixtures predictions as confirmed by nanohardness
values. The strengthening is however
lower as expected (UTSRT=711MPa), because of
the distorted ribbon morphology of the Ta fibers
preventing them from behaving as nanowhiskers,
like Nb fibers in Cu/Nb wires. This result shows
that size and geometry play key roles in the
plasticity of nanomaterials (Acta Mat 54 (4) (2006)
1063-1075).
(a), (b), (c) SEM image of the multi-scale structure of Cu/Ta
nanofilamentary wires (N = 85 3 , h=3.35mm).
(d) High-magnification of the curled Ta fibers
Bright-field TEM images of transverse section of Cu/Ta (N=85 3 ,
d=1.293 mm) after heavy drawing: ribbon-like shape of Ta fibers
Prevention of fracture during Accumulative Drawing and Bundling (ADB) process
The third way to improve the properties of Cu/X wires is to optimize the processing parameters. The colddrawing
of the Cu/Nb/Cu co-cylindrical conductors, reinforced by niobium nanotubes filled with copper
nanowhiskers, has been improved with respect to the elimination of the central bursting defects following the
conditions of the criterion of Avitzur and led to the obtention of more then 20 meters of conductors without
fracture. Several attempts have been performed to insulate these conductors without loosing their strength with
different kind of materials and different ways of application (heat-retractable PTFE sheath, PTFE in spray,
Kevlar fiber…).
More details on the three ways of optimization of the Cu/X nanofilamentary can be found in the Ph.D thesis of
Vanessa Vidal (“Optimisation des propriétés mécaniques des conducteurs nanofilamentaires Cu/X (X= Nb ou
Ta) par l’étude des mécanismes élémentaires de déformation“, Ph.D Thesis, INSA Toulouse, n°855, 2006)