N14A-T017 TITLE: Processing of High-strength Ultra-Conductive Wire

TECHNOLOGY AREAS: Materials/Processes, Electronics

ACQUISITION PROGRAM: none

OBJECTIVE: The objective of this topic is to develop processing capabilities of high-strength ultra-conductive wire to improve power-to-weight ratios and energy efficiency across military systems.

DESCRIPTION: Electrical wire is a vital component of any military system. The wiring harnesses carry electrical power and data to all parts of the vehicle/vessel. To date, copper is the choice of material for the wire conductor because of its balance of high electrical conductivity, good processability, good corrosion resistance, and moderate cost. As power and data requirements increase, the mass of the wiring harnesses have increased to become a considerable fraction of the vehicle weight. The conductivity and mechanical properties of copper limit the minimum conductor size in a wire one may use reliably in an application. Low cost composite wires, with high strength and ultra-high conductivity, become attractive alternatives to pure copper.

Several groups have succeeded in imbedding nanoscale graphitic carbon (for example carbon nanotubes, graphene nanoscrolls, etc.) into copper and aluminum matrices. They report very high electrical conductivities (as high as 1000% IACS) and strengths as high as 350% that of Oxygen Free High Conductivity (OFHC) copper. This could allow the reduction of the weight of the wiring harness of a Boeing 747 by 1300kg; or of a large communications satellite by as much as 3000kg.

The processes are laboratory-scale batch operations, however, and the yields are low and the repeatability is very poor. Some groups have attempted scale-up feasibility studies; but with such poor repeatability, they are unable to examine the real process control needs and have little confidence in the predictions. Proper assessment of the scale-up of the processes requires a detailed physical understanding of the phenomena that occur during the process, converted to a quantitative description suitable for engineering analysis. It also requires a thorough understanding of structure-property relationships in the material to provide target structures for the processes. This also provides the fundamental tools needed for optimization of unit processes to improve yields, uniformity, and reliability.

The first objective of this project is to develop quantitative structure-property models for the electrical and thermal conductivity of nano-scale carbon modified copper (and aluminum). The second objective is to develop quantitative models for the individual operations for the processes extant in the synthesis/processing of nano-scale carbon modified copper (and aluminum) that are suitable for the design of multi-step processing operations. The third objective is to demonstrate these tools in the design of an overall processing sequence to produce high conductivity nano-scale carbon modified copper (and aluminum). This project supports the goals of the Materials Genome Initiative (MGI) in the area of Integrated Computational Materials Engineering (ICME).

PHASE I: The successful Phase I project will perform characterizations of the microstructures of high-conductivity (successful) and low-conductivity (unsuccessful) materials, and the determination of a set of structure-property relationships (e.g. grain size, volume fraction, orientation distribution, porosity, etc.) that predict suitably for the conductivity of the system. The final activities of the successful Phase I effort will scope out the unit processes associated with the synthesis and processing of wire and plan time and the resources needed to model those operations.

PHASE II: The successful Phase II effort will begin with a determination of target microstructures for acceptable physical properties of a wire product. It will model the major processing unit-step operations associated with the laboratory-scale operations, and introduce structure evolution and process failure envelopes for the unit-step operations. By the end of the successful Phase II effort, the investigators should have models for the major processing steps that communicate sufficiently to allow them to perform preliminary designs for the wire production process.

PHASE III: In a Phase III effort, the investigators will (with partners) begin the design of the processing operations needed to produce reliable high conductivity composite metal wire, and begin to predict the costs of scale-up for a commercial operation. Future activities will refine the models and lead to process optimization and the support of production operations.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Wiring on automobiles, aircraft, consumer electronics, and other applications where high reliability and light weight are desirable.

REFERENCES:

1. Tianhua Yu, Changdong Kim, Bin Yu, "Highly Conductive 3D Nano-Carbon: Stacked Multilayer Graphene System with Interlayer Decoupling", arXiv:1103.4567v3.

2. Hongqi Li, Amit Misra, Zenji Horita, Carl C. Koch, Nathan A. Mara, Patricia O. Dickerson, and Yuntian Zhu, "Strong and ductile nanostructured Cu-carbon nanotube composite", Phys. Rev. Lett. 95, 071907 (2009).

3. Evan Khaleghi, Milton Torikachvili, Marc A. Meyers, and Eugene A. Olevsky, "Magnetic enhancement of thermal conductivity in copper�carbon nanotube composites produced by electroless plating, freeze drying, and spark plasma sintering", Materials Letters 79 (2012) 256�258.

4. Kyung Tae Kim, Jurgen Eckert, Gang Liu, Jin Man Park, Byung Kyu Lim and Soon Hyung Hong, "Influence of embedded-carbon nanotubes on the thermal properties of copper matrix nanocomposites processed by molecular-level mixing", Scripta Materialia 64 (2011) 181�184.