Boeing Phantom Works is hoping that "structurally amorphous aluminium" will make future aircraft smaller, lighter and more durable, as its initial results under a US Defense Advanced Research Projects Agency (DARPA) programme have demonstrated aluminium alloys 25% stronger than those used today.
DARPA is funding the Boeing team, which consists of 17 subcontractors including seven universities, as part of its three-year $10 million structurally amorphous metals (SAM) project, which aims to demonstrate the strength, hardness, corrosion- and wear-resistance of SAMs compared with conventional crystalline metals.
Conventional metals are limited by the regularity of their crystal structures, but using nanostructured "metallic glass", scientists can manipulate the structure at the atomic level, dramatically improving performance. Boeing wants to produce aluminium alloys that deliver titanium's strength in a much lighter and cheaper material.
Amorphous metals are based on the discovery that some alloys form a metallic glass when solidified in a controlled way. With high solidification rates and controlled thermal treatments of the glass - a process called devitrification - the nano-scale microstructural features of the alloys can be manipulated.
Boeing says it has already made first-generation aluminium alloys with a tensile strength of 830MPa (120,000lb/in2), about 25% greater than commercial aluminium alloys, although real applications are probably "five to 10 years" away.
DARPA hopes that amorphous steels could achieve a strength of 2.8GPa (400,000lb/in2), a hardness of 15GPa and a fracture toughness of up to 300MPa.m0.5 (270,000lb.in-1.5), compared to baseline values of 1GPa, 5.5GPa and 70MPa.m0.5 for conventional high-strength steel. Its emphasis will be on developing alloy materials based on aluminium, iron, magnesium, titanium and refractory metals.
Source: Flight International