A surprising discovery by researchers has upended previous notions about metal deformation, which could also help in creating a stronger, more durable material.
"This creates new opportunities for materials design. It adds another parameter we can control to enable strength and ductility," said Izabela Szlufarska, a professor of materials science and engineering at UW-Madison.
Ductility is the ability of a metal to bend. Most approaches to increase a metal's strength do so at the expense of flexibility and as metals become more resistant to bending, they're more likely to crack under pressure.
However, the researchers' new mechanism for bending might allow engineers to strengthen a material without running the risk of fractures, reported the study published in the journal of Nature Communications.
"Professor Szlufarska has opened up an entirely new area for exploration for structural materials processing and design. By making such a high-impact discovery, Professor Szlufarska has potentially laid the technical foundation for the development of a new generation of advanced structural materials that could eventually be employed in future Army equipment and vehicles," said Michael Bakas, synthesis and processing programme manager at Army Research Office in the U.S. Army Combat Capabilities Development Command Army Research Laboratory.
Engineers typically manipulate the strength of metal through techniques such as cold working or annealing, which exert their effects through small, yet important, structural irregularities called dislocations.
Normal metals bend because dislocations are able to move, allowing material to deform without ripping apart every single bond inside its crystal lattice at once.
Strengthening techniques typically restrict the motion of dislocations. So it was quite a shock when Szlufarska and colleagues discovered that the material samarium cobalt is known as an intermetallic bent easily, even though its dislocations were locked in place.
"It was believed that metallic materials would be intrinsically brittle if dislocation slip is rare. However, our recent study shows that an intermetallic can be deformed plastically by a significant amount even when the dislocation slip is absent," said Hubin Luo, a former staff scientist in Szlufarska's lab.
Instead, 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.
Those amorphous bands allowed the metal to bend.
"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," said Szlufarska.
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