N22A-T015 TITLE: Additive Manufacturing of High Performance Copper-Based Components and Materials

OUSD (R&E) MODERNIZATION PRIORITY: General Warfighting Requirements (GWR)

TECHNOLOGY AREA(S): Materials / Processes

OBJECTIVE: Develop additive manufacturing (AM) processes to produce high performance copper-based components and materials.

DESCRIPTION: Additive manufacturing (AM) has matured rapidly over the past decade and is currently a viable manufacturing process in many industries. This is especially true in the production of polymer parts. AM not only allows production of specialized components in small quantities, but it also makes possible the creation of devices and materials that cannot be otherwise produced by traditional means. Additive manufacturing of metals has also matured rapidly; however, the utility of metal AM has not been realized as fully as for polymer processes. This is especially true in the defense electronics and defense systems industries.

To a large extent, AM has been seen as a tool for the production of solid models (rapid prototyping), on-demand manufacturing, and in the fabrication of complete parts where traditional fabrication techniques would require the joining of multiple components. However, the full potential of AM lies in the fabrication of parts and materials that cannot be realized by any other means. This is already being exploited in polymer AM processes where the material constituents can be changed "on the fly" during the fabrication process to achieve gradations in material properties that create specific performance characteristics. For example, the current state of the art for polymer-based materials allows the dielectric constant of a part to be varied throughout the part using advanced additive techniques.

In defense electronics, stringent requirements place unparalleled demands on materials selection and performance, which directly increases cost. Mechanical and especially thermo-mechanical properties of metals used in high performance radio frequency (RF) and laser systems are a primary concern during design and material selection. These metals typically serve as mechanical supports and heat transfer paths for high power electronics. In other applications they serve directly as RF circuit components (such as connectors, transmission lines, waveguides, and antenna elements). Modern vacuum electronics use metal and ceramic construction exclusively, with material purity and performance being of paramount concern.

The Navy has a compelling interest in developing components and materials that increase the overall performance of high-power sensor (radar and electronic warfare) and weapon systems. Specifically, for this topic, this means developing AM processes for copper and copper-based materials and structural elements (at very small scales) that provide performance characteristics exceeding what can be obtained through traditional manufacturing processes. "Copper-based materials" include both copper alloys and metal matrix composites (including hybrid composites) where the primary metal constituent is copper. For structural (three-dimensional vice planar) elements, the interior dimensions of WR-10 waveguide (0.100 X 0.050 inches) serve as the benchmark for the feature size and aspect ratio desired. That is, RF circuit components are assumed to require this level of resolution and cooling channels should achieve these dimensions (or smaller) to be useful.

There are two key aspects to this STTR topic: (1) the demonstration of three-dimensional structures with fine (high aspect ratio) features, tight tolerances and smooth surfaces, and (2) the development of innovative materials. Either may be selected and addressed, both may be addressed separately, or both may be addressed in combination. For the demonstration of three-dimensional structures, a 10X improvement in feature aspect ratio, tolerance, and surface roughness over the current state of the art is the goal. The objective is to demonstrate through the production and testing of prototypes the ability of the innovative process (or combination of processes) to deliver parts that cannot be manufactured by traditional (non-AM) means. And while either new structures or new materials may be addressed under this effort, innovative AM processes and techniques that demonstrate multiple benefits and utility for wide application are most desirable.

Of particular interest to the Navy are materials and components for thermal management of high power electronic modules. These may be solid heat spreaders or small cooling structures (base plates) incorporating small channels for liquid cooling. Along these lines, thin oscillating heat pipes (OHPs) are an area that embodies multiple technical challenges of particular interest (for example, feature size, tolerance, finish, and affordability). Typically, these components find their most challenging application in transmit and receive (T/R) modules incorporating high power monolithic microwave integrated circuit (MMIC) amplifiers and in high power laser modules incorporating large numbers of solid-state laser diodes. In these cases, differences in the coefficient of thermal expansion (CTE) between the device being cooled and the module structural elements create significant design challenges. Therefore, materials that show superior heat transfer and CTE matching performance through the gradation of material constituents and properties are of great interest. Likewise, innovative structures or composites that provide built-in strain relief as well as superior thermal performance are also of interest. In either approach, AM solutions that provide comparable performance (to the current state of the art) while reducing overall cost (target of 50%) through the elimination of other components or assembly steps are also desired.

Another particularly challenging application of interest is the fabrication of components for vacuum electron devices (VEDs), especially high frequency (>28 GHz) amplifiers such as traveling wave tubes (TWTs). The metal components used in fabrication of a TWT are, by nature, three dimensional with large aspect ratios, require demanding mechanical tolerances, and exhibit high standards of finish and metallurgical quality. Copper is widely used in all VEDs for its good electrical and thermal conductivity properties and for the vacuum properties copper exhibits when produced in its high purity grade. However, copper is relatively soft, deforms and melts at relatively low temperatures, and can be difficult to machine. Consequently, VED fabrication typically includes the joining of copper to other metals and ceramics through brazing and, to a lesser extent, welding. So, AM processes that produce superior copper parts for VED fabrication are also of great interest. This includes processes that improve mechanical and heat transfer performance, improve the joining of parts, and reduce cost by the elimination of traditional machining steps. Again, this may be done through the development of innovative structures or innovative copper-based materials (or combinations of both).

The Navy seeks to develop an AM capability that benefits the RF and electro-optical electronics industry and not to produce any particular part. The solution is assumed to include the development of new AM hardware, feedstock, tooling, design methodologies, and fabrication steps. It also includes the identification of, development of, refinement of, and application of measurement techniques for use both as in-process checks and for use post-fabrication to assess the efficacy of the new capability. Copper is chosen because of its relevance to the electronics industry and because of the particular challenges it presents to AM. Prototype devices and structures should be selected to demonstrate the innovative AM capability. These prototypes should be "real" components that demonstrate relevance to the electronics industry, not just material samples ("blanks") for testing. Prototype components and devices should demonstrate utility and performance that cannot be achieved through manufacturing by traditional means. Otherwise, the selection of prototypes is not restricted and the examples cited above are not exhaustive. It should also be noted that the overall solution may include traditional treatment techniques such as annealing, chemical polishing, and hot isostatic pressing. However, solutions that require extensive "clean-up" machining are not considered sufficiently additive in nature and will not be considered. Processes that use traditionally fabricated parts or stock as foundations for further fabrication of AM structures and materials are acceptable.

PHASE I: Propose a concept for additive manufacturing of high performance copper and copper-based materials that meets the objectives stated in the Description. The concept shall include specific prototypes by which the proposed AM process technology will be demonstrated. These prototypes will subsequently be produced and used (in Phase II) to verify, by testing and analysis, the efficacy of the proposed AM concept. During Phase I, feasibility of the concept shall be demonstrated by a combination of analysis, modelling, simulation, and evaluation of proposed process steps against established manufacturing methods. The Phase I Option, if exercised, will include the initial process specifications, AM equipment requirements, test specifications, and capabilities description to build a prototype additive manufacturing facility in Phase II.

PHASE II: Develop and demonstrate a prototype facility for AM of high performance copper-based components and materials. In this context, "facility" refers to the combination of equipment, tooling, and process steps required to demonstrate the end-to-end additive manufacturing capability provided by the proposer, not the actual physical facility. Demonstration of the AM process (or multiple processes) shall be accomplished by fabrication and evaluation of the prototype components and materials identified during Phase I. Multiple prototype components and samples are expected during execution of this Phase as the process development is assumed to be necessarily iterative in nature. However, at the conclusion of Phase II, at least one example of each proposed prototype component or material sample shall be delivered to the Government with no fewer than five total prototype samples delivered overall. Test data shall also be delivered with each prototype sample delivered.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Government use. Identify specific products and material formulations appropriate to the new AM processes and, in conjunction with the broader industry, develop specific production flows and process parameters to either market finished copper-based AM products or transition the technology to produce them in quantity.

The technology resulting from this effort is anticipated to have broad commercial application in the electronics industry as well as niche application to the broader industry for applications such as heat exchangers and thermal management components for electrical power conversion.

REFERENCES:

1. Horn, Timothy J. and Gamzina, Diana. "ASM Handbook, Volume 24, Additive Manufacturing Processes." ASM International, Cleveland, Ohio, 2020, pp. 388-418. https://dl.asminternational.org/handbooks/book/119/chapter-abstract/2350563/Additive-Manufacturing-of-Copper-and-Copper-Alloy.
2. Jordan, Nicholas M., et al. "Additively Manufactured High Power Microwave Anodes." IEEE Transactions on Plasma Science, Vol. 44, August 2016, pp. 1258-1264. https://ieeexplore.ieee.org/document/7479563.

KEYWORDS: Copper Alloys; Metal Matrix Composites; Thermal Management; Heat Spreaders; Oscillating Heat Pipes; Vacuum Electron Devices