Improved metals applied to marine vehicle.

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, Peterson said.

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 steps further.

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 track."

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 Research.

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, Kabacoff noted.