Additive Manufacturing

A side-by-side comparison of the aluminum alloy powder with carbon nanotubes (CNTs) grown on the particle surfaces, left, and a virgin aluminum alloy powder, right. (U.S. Navy photo)

Nanotubes Strengthen Composite Metals

Researchers Bring Innovative Solutions to Additive Manufacturing at NAWCAD Lakehurst

A team of four engineers from Naval Air Warfare Center Aircraft Division (NAWCAD) Lakehurst have enhanced additive manufacturing (AM) capabilities at the base through their research into using a new type of metal-based powder to 3-D print composite aircraft parts.

“Team INCANTATION” conducted research and testing as part of the six-month Naval Air Systems Command (NAVAIR) Innovation Challenge to determine if composite metal powders could be used in AM, more commonly known as 3-D printing.

“With additive manufacturing we can explore new ways to produce and repair aviation parts in order to deliver those products more efficiently to our Sailors and Marines who need them to complete their missions,” said Kathleen P. Donnelly, director of NAVAIR’s Support Equipment (SE) and Aircraft Launch and Recovery Equipment (ALRE) Department. “I commend the team for their innovative thinking and dedication to finding new ways to bring speed to the fleet.”

A close-up of gas flow verification using water as part of the process to grow the CNTs. (U.S. Navy photo)

Traditionally, 3-D printed aircraft parts have been made using titanium metal powders, which are mechanically strong but dense and heavy compared to a lighter metals like aluminum, said Ron Poveda, NAWCAD Lakehurst Science and Technology (S&T) research engineer.

Poveda proposed a research project to look at introducing carbon nanotubes (CNTs), a nanomaterial, into an aluminum powder to potentially increase its mechanical strength, electrical conductivity and thermal stability.

“When you add carbon-based reinforcing materials to anything, it usually makes for a more thermally-stable structure,” Poveda said. “That’s beneficial due to the fact that the Navy uses their structures and systems in a variety of environments. If we can actually control the properties of a given printed part just by introducing these nanotubes, it would be of great advantage to the Navy.”

An aluminum alloy-based composite would also be lighter and cheaper than the standard Aircraft Grade Titanium, said Patrick Thompson, NAWCAD Lakehurst mechanical engineer.

“If you could get the properties of the titanium out of aluminum, but keep it lighter and cheaper, then that’s an advantage,” he said.

The team used funding from the Innovation Challenge to establish a Cooperative Research and Development Agreement (CRADA) with a New Jersey Institute of Technology professor to grow the CNTs on an aluminum alloy powder.

 

Scanning electron microscope of AlSi10Mg powder with CNTs grown on surface. (U.S. Navy photo)

 

Mixing of CNTs with metal powders has been done in the past through the use of chemical additives and mechanical mixing, said Mike Rossini, NAWCAD Lakehurst mechanical engineer. However, the team was able to grow the CNTs organically on the surface of aluminum alloy powder without using additives through a process called chemical vapor deposition.

“That in and of itself is very helpful in terms of obtaining more optimized properties because the distribution of CNTs is even throughout the entire material,” Poveda said. “You don’t have any small-scale stress points within the material itself that could cause early failure.”

The team then set out to create test builds from the composite aluminum metal powder using a 3-D printer in the NAWCAD Lakehurst AM facility. However, since this was the first time a metal-matrix composite with CNTs grown directly on a metallic powder surface would be 3-D printed, the team had to first be sure the process adhered to government safety and environmental policy, said Igor Bezsonov, NAWCAD Lakehurst systems engineer.

“One of the things that we really had to overcome to even use the machine, is we had to basically explain to safety what these carbon nanotubes are, how they will affect the machine to the best of our knowledge, and what health hazards they posed,” Bezsonov said.

The team had to verify that printing the composite aluminum powder wouldn’t harm the printer, which had previously only printed in pure metallic alloys, such as titanium and steel.

“We worked very closely with them to make sure it wasn’t going to harm the machine and what properties we should use to make sure it was all going to work out okay,” Rossini said.

They worked with various government and academia partners to achieve the required safety, occupational health and environmental standards and made them part of a standard operating procedure.

What resulted not only allowed the team to conduct their research, but opened the door for the base to start experimenting with 3-D printing of aluminum alloys and metal-matrix composites.

Other research into using aluminum powder for AM has already started as a result of this added-base capability, Rossini said.

“This work is leading toward a fundamental grasp of these kinds of materials and getting more comfortable with them and being able to use them on a widespread level,” Thompson said.

The team and AM group agree that as material properties and databases for AM parts continue to evolve, such research can expand on the fundamentals of metal composites and will inform their use-case on future parts, structures and systems.

The team’s time and efforts resulted in the successful printing of a cohesive test build using the composite aluminum metal powder, supporting their theory that 3-D printing composite metals is possible.

Now that the team has proven the feasibility of printing metal matrix composites through AM, they are planning to refine the process and conduct further studies through a three-year Section 219 project.

“One of the advantages that’s easy to imagine is that by adding these carbon nanotubes—which are very strong and very light—to metal, they can make the metal stronger without adding much more weight. One can also reduce the amount of metal needed to create parts, and with the addition of carbon nanotubes, one can make the combination the same strength as the metal would be by itself,” Bezsonov said.

The team is also expanding their network, working with labs across the DOD and academia to combine their knowledge in AM.

“Design requirements are becoming much more demanding these days. People, including the Navy, want lightweight with increased strength and allowing ourselves to have this mix of materials will help get us to that point,” Poveda said.

Allison Barrow is the Naval Air Warfare Center Aircraft Division Lakehurst Public Affairs Officer.