A process using advanced nano-science in metal processing may provide the material
for a tough, lightweight Marine expeditionary vehicle, Navy researchers predict.
The process known as cryomilling is adding properties to aluminum that may
be used to forge a craft with the toughness and low weight required by the Marine
Corps, according to Rodney Peterson, project manager with the Naval Surface
Warfare Center in Carderock, Md.
The blue-sky hope, Peterson told the audience at a recent conference, is to
design “a 30-ton tank to replace a 70-ton tank” for the Marines.
The Carderock Division is contributing to the development of a future U.S.
Marine Corps family of vehicles, referred to as the Marine Air-Ground Task Force
Expeditionary Family of Fighting Vehicles (MEFFV). Navy technical experts are
managing an advanced materials development program that is generating lightweight
structures and technologies to meet the Corps’ needs.
The MEFFV will replace the M1A1 Abrams tank and the light armored vehicle by
2020. This effort started in 2002 and is halfway through the development process,
Metals are not monolithic slabs of material, but are composed of individual
grains of similar composition with differing crystalline orientations. In general,
smaller grain size means greater strength. Cryomilling takes the concept several
Navy scientists are changing standard aluminum (AL 5083) by introducing grains
of aluminum so small that the material’s properties change. Doing this
requires grinding, or milling, the aluminum powder in extremely cool temperatures
that is obtained by exposure to liquid nitrogen. The process encourages the
formation of nano-scale aluminum oxide and nitride particles, which makes materials
stronger, as well as stabilizing their microscopic orientation and structure.
Initial tests at Carderock indicate yield and tensile strength improvements
of 150 percent over untreated aluminum, Peterson said. “These are initial
findings,” he noted. “But it looks like we’re on the right
He warned, however, that the technologies are new and their performance qualities
are untested when applied to real-world systems. Carderock has submitted a small
business innovative research solicitation to look at ways of making cryomilling
cheaper, he added.
Mixing cryomilled aluminum with standard-sized particles brings the best of
both worlds: increasing strength but keeping the material malleable, said Larry
Kabacoff, program manager for nano-structured materials for the Office of Naval
Materials made from purely cryomilled aluminum are three times as strong but
often too brittle for the real world, while a composite of conventional and
nano-enhanced aluminum is only twice as strong, but with the same ductility.
“It’s not magic,” Kabacoff said. “You still have to
be smart. You still have to do the engineering.”
Standard aluminum is used for armor-hull structures in many other vehicles,
making cryomilling a versatile method for the defense industry. The Bradley
M2/M3 Fighting Vehicle, M109 Paladin Self-Propelled howitzer and M113 Humvee
currently use AL 5083.
The Space Shuttle also will use cryomilled aluminum to replace titanium parts,
which become brittle after repeated exposures to liquid hydrogen fuel burns,