Some success has been achieved in a development program directed toward improving the mechanical properties of electroformed copper-alloy structural components. Typical of such components are bundles of tubes and other heat-exchange devices that have complex shapes. Electroforming of copper alloys is an attractive means for manufacturing such a component because of the high thermal conductivity of copper and because electroforming both produces the alloy and forms the component in nearly net shape in a single process.
Prior to the efforts reported here, electroformed unalloyed copper and copper alloys were found to be too weak for some applications and to lose mechanical strength at moderate operating temperatures. Electroformed nickel — the traditional electroformed structural material — has mechanical properties that are more than adequate for many applications, but its thermal conductivity is less than that of copper. Thus, there is a need to be able to electroform unalloyed or low-alloy copper to obtain high thermal conductivity while producing components strong enough to compete with nickel components at temperatures up to and beyond 200 °C (392 °F). Electroformed copper components could then be used more widely in applications that involve higher temperatures.
The specific objectives and achievements of the program were the following:
- An effort to develop copper or copper alloy electrodeposits having mechanical properties competitive with those of electrodeposited nickel was successful. Although a tensile strength of 689 MPa (100 kpsi) was exceeded in limited samples, it was not possible to maintain this level of strength during the long electroforming process times encountered in production facilities. Tensile strengths of 517 to 551 MPa (75 to 80 kpsi) accompanied by acceptably large yield strength and ductility were found to be practical in production deposits from an acid copper sulfate bath containing a single proprietary high-molecular-weight organic polymeric additive called "PEG-B." These deposits responded well to heat treatments at temperatures from 149 to 371 °C (300 to 700 °F) and were found to retain yield strengths far higher than that of wrought annealed oxygen-free high-conductivity (OFHC) copper. Unlike typical acid copper electrodeposits, these materials exhibited acceptably large ductility at elevated temperature.
- An effort to make low-additive, non-alloyed electrolytic copper deposits with yield strengths of at least 49.7 MPa (7.2 kpsi) and 10-percent elongation at 371 °C (700 °F) was partially successful: The goals were not achieved at 371 °C (700 °F), but were achieved at 260 °C (500 °F) with deposits from acid copper sulfate baths containing single additives. In each case, the single additive was either chloride ions, xylose, triisopropanolamine, or PEG-B.
- Partial success was achieved in an effort to demonstrate low-alloy-copper deposits with resistance to recrystallization at temperatures up to 500 °C (932 °F) and strengths greater than those of traditional copper deposits. All of these deposits were found to recrystallize to some degree at 371 °C (700 °F). However, after heat treatment at 371 °C (700 °F), deposits from acid bath that contained certain additives exhibited mechanical strengths greater than those of traditional copper deposits; in each case, the additive was either a combination of triisopropanolamine and D+ xylose, a dispersion of submicron-sized a and g alumina particles, or PEG-B. It was also demonstrated that electrodeposited copper alloyed with a small amount of platinum is a heat-treatable material that exhibits an excellent microstructure after one hour at 371 °C (700 °F), outstanding ductility, and yield strength far greater than that of traditionally electrodeposited copper or wrought annealed copper.
- It was shown that fullerenes could be codeposited with copper to form a dispersion alloy of superior strength with no loss of thermal conductivity. It was also shown that dispersion strengthening could be achieved by codeposition of copper alloys (including copper-platinum alloys) with submicron alumina particles.
- The figure depicts the interior of a tube-bundle thrust chamber (part of a rocket engine) designed and fabricated by electroforming of copper, taking advantage of the developments described above. This is the first tube-bundle thrust chamber made entirely without welding, brazing, or other thermal joining processes; the avoidance of such processes makes it possible to preserve the desired mechanical properties of the copper.
This work was done by G. A. Malone, W. Hudson, B. Babcock, and R. Edwards of Electroformed Nickel, Inc., for Glenn Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Materials category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center,
Commercial Technology Office,
Attn: Steve Fedor,
Mail Stop 4—8,
21000 Brookpark Road,
Cleveland, Ohio 44135.
Refer to LEW-16887.