Researchers at Pacific Northwest National Laboratory (PNNL) have used shear assisted processing and extrusion (ShAPE) (earlier post) to synthesize macro-scale copper-graphene composites with a simultaneously lower temperature coefficient of resistance (TCR) and improved electrical conductivity over copper-only samples.

PNNL has been developing ShAPE to enable more cost- and energy-efficient production of high-strength structures from metals and metal alloys for a number of years, with application to a range of different metals.

In an open-access paper published in the journal Materials & Design, the PNNL researchers reported that the addition of 18 ppm of graphene decreased the temperature coefficient of resistance (TCR) of C11000 alloy by nearly 11% and increased conductivity by ∼1.4 %.

Gwalani et al.

This is relevant for the manufacturing of electric vehicle motors, where an 11% increase in electrical conductivity of copper wire winding translates into 1% gain in motor efficiency.

This discovery runs counter to what’s generally known about the behavior of metals as conductors. Typically, introducing additives into a metal increases its temperature coefficient of resistance, meaning they heat up faster at the same current levels compared to pure metals. We are describing a new and exciting property of this metal composite where we observe enhanced conductivity in a manufactured copper wire.

—Keerti Kappagantula, corresponding author

Previously, the research team performed detailed structural and physics-based computational studies to explain the phenomenon of enhancing the electrical conductivity of metals using graphene.

In this study, they showed that the solid-phase processing used to extrude the composite wire leads to a uniform, near pore-free microstructure punctuated with tiny flakes and clusters of graphene that may be responsible for decreasing coefficient of resistance of the composite.

The research team continues its work to customize the copper-graphene material and measure other essential properties, such as strength, fatigue, corrosion, and wear resistance—all of which are crucial to qualify such materials for industrial applications. For these experiments, the research team is manufacturing wires that are about the thickness of a US penny (1.5 millimeters).

Resources

• Bharat Gwalani, Xiao Li, Aditya Nittala, Woongjo Choi, Md. Reza-E-Rabby, Julian Escobar Atehortua, Arun Bhattacharjee, Mayur Pole, Joshua Silverstein, Miao Song, Keerti Kappagantula (2024) “Unprecedented electrical performance of friction-extruded copper-graphene composites,” Materials & Design, Volume 237, 112555 doi: 10.1016/j.matdes.2023.112555