UW-Madison engineers have made a surprising discovery that could help create stronger, more durable materials.
The discovery upends a century-old notion of how metals bend, helping open up new opportunities for materials design, asserts team lead and UW-Madison professor, Izabela Szlufarska.
Ductility is the ability of a metal to bend. Most approaches to increase a metal’s strength do so at the expense of flexibility – which also makes them more susceptible to cracks when under pressure.
UW-Madison’s approach is revolutionary as it allows engineers to strengthen a material without running the risk of fractures.
The process is being keenly followed by the US Army which is on the look-out for strong and durable materials that keep troops safe in combat zones.
The go-to-process for strengthening metals is cold working or annealing, which exerts its effects through small, yet important, structural irregularities called dislocations.
Dislocations are tiny irregularities in the otherwise well-ordered crystal lattice of a metal. They arise on account of slight mismatches.
Normal metals bend because dislocations are able to move, allowing a material to deform without ripping apart every single bond inside its crystal lattice at once.
Strengthening techniques are known to restrict the motion of dislocations.
That is why Szlufarska and her colleagues were surprised to find the material samarium cobalt – an intermetallic – bent easily, even though its dislocations were locked in place.
The bending samarium cobalt caused narrow bands to form inside the crystal lattice, where molecules assumed a free-form ‘amorphous’ configuration instead of the regular, grid-like structure in the rest of the metal.
It was those amorphous bands that allowed the metal to bend, intones Szlufarska.
“It’s almost like lubrication. We predicted this in simulations, and we also saw the amorphous shear bands in our deformation studies and transmission electron microscopy experiments.”
The researchers are now planning to search for other materials that might also bend in this peculiar manner.
They hope the phenomenon will ultimately help them tune a material’s properties for strength and flexibility.
Image and content: Sam Million-Weaver/UW-Madison