Researchers from the U.S. Army Research Laboratory and Arizona State University (ASU) have designed a super-strong alloy of copper and tantalum that can withstand extreme impact and temperature. It's likely the closest material on earth to vibranium, a rare, fictitious metallic substance found in Marvel's Wakanda and used in Captain America's shield.
Its structure and deformation response make it a candidate for ballistic impact or protective applications for military vehicles or personal protection for soldiers, said Dr. Kristopher Darling, a materials scientist with ARL's Lightweight and Specialty Metals Branch. Darling said that even beyond the Army, "anywhere there's high strength and good electrical conductivity required, these alloys can be thought of as a model system whose structure can be passed on to other alternative material systems. Materials based on iron or aluminum, for instance, could be used for protection and lethality applications."
The ARL team, which includes Darling and Drs. Cyril Williams and B. Chad Hornbuckle, joined with ASU Professors Kiran Solanki, Professor Pedro Peralta and six doctoral students in materials science and mechanical engineering on the project. Solanki, an associate professor in the Ira A. Fulton School of Engineering, is working on the copper and tantalum alloy, which has the potential to be used also on spacecraft for deep-space exploration. The same methodology can also be applied to other materials, such as nickel or iron, to develop more resilient transportation and sustainable infrastructures.
Most structural metals experience sudden deformation when subjected to extreme impact and temperature, such as the force from an automobile accident or the impact that occurs during a ballistic event. When a typical metal deforms at a fast rate, it loses its ability to deform in a ductile way and becomes brittle, absorbing relatively little energy prior to fracture or failure. This instability has motivated the multidisciplinary research team to improve the toughness of coarse-grained metals and alloys to prevent metal deformation and failure. They created a nanocrystalline alloy of copper and tantalum with engineering-enhanced properties to make it maintain a relatively consistent level of mechanical strength and microstructure stability.
"The technical challenge was to make a material with an average grain size of about 50 nanometers (billionths of a meter) and remain stable when formed into usable parts or shapes," said Solanki.
The unusual combination of properties in the copper-tantalum alloy results from a processing route that creates distinct nanoclusters of tantalum. As temperature increases, these nanoclusters don't significantly change in size or spacing, which leads to the material's notable stability and strength.
"Within these very small grains, we built in a microstructure that's even smaller than the grain size due to tantalum's nanoclusters," Darling said. "This doubles the material's strength and stability, making it immune to the deformation response."
The alloy can withstand high rates of impact and temperatures in excess of 80 percent of their melting point, which is higher than 1,073 Kelvin or greater than 1,472 degrees Fahrenheit, with very little change in its microstructure.
The copper-tantalum alloy was originally developed to replace copper-beryllium, a high-performance alloy known for its strength, conductivity, hardness and corrosion resistance. Copper-beryllium is critical for a range of applications, but the handling, manufacturing and machining of beryllium can cause a serious lung condition called chronic beryllium disease. Thus, the International Agency for Research on Cancer and the National Toxicology Program have designated the alloy as a carcinogen.
The team continues to work toward replacing copper-beryllium with an equally superior metal alloy with similarities in its mechanical properties of strength, conductivity, hardness and corrosion resistance. The copper-tantalum alloy is a step in that direction.