Design of novel silver – copper nanocomposite wires to break the usual strength-resistivity trade-off

The generation of record pulsed magnetic fields above 100 T requires the use of coils wound with low- resistivity wires in order to limit the heating, and with a very high mechanical strength in order to be able to resist the Lorentz forces. The LNCMI and the CIRIMAT are exploring the design of novel silver – copper nanocomposite wires with the aim to break the usual strength-resistivity trade-off.
Composite wires containing only 1 vol.% silver nanowires dispersed in a bimodal (1 µm / 20 µm) copper matrix are prepared by a combination of powder metallurgy, Spark Plasma Sintering and room-temperature wire- drawing.

We bring to light that:
  It is possible to improve the low resistivity – high ultimate tensile strength (UTS) compromise of the composite wires by simply adding large grains of Cu during the composite powder preparation step.
The larger copper grains act as channels for fast electron conduction thus allowing to maintain a low electrical resistivity (0.45 μΩ.cm, at 77 K).
Compared to wires with only fine-grained copper, this represents a 12 % lower electrical resistivity for the same UTS (1082 MPa at 77 K), which is provided by the finer copper grains and the silver nanowires.
The strength – resistivity trade-off can be fine-tuned simply by adjusting the large grain / fine grain proportion.

Schematic representation of the method and the expected microstructure of the powder, cylinder and wire samples.

UTS vs electrical resistivity at 77 K for wires with diameter from 1 mm to 0.2 mm for W_50/50 (), W_75/50 () and W₁₀₀ (). The dotted lines are used to indicate wires with a diameter of 1 mm and the 0.2 mm wire in the case of W_50/50.

Publication : S. Tardieu, D. Mesguich, A. Lonjon, F. Lecouturier-Dupouy, N. Ferreira, G. Chevallier, A. Proietti, C. Estournès, C. Laurent, Influence of bimodal copper grain size distribution on electrical resistivity and tensile strength of silver – copper composite wires, Materials Today Communications 107403 (2023)

Contact: simon.tardieu@lncmi.cnrs.fr, florence.lecouturier@lncmi.cnrs.fr