Designing a very strong metal is one thing. Allowing it to deform without breaking is another. Researchers from Purdue University have succeeded in bringing these two qualities closer together in a material based on cobalt and aluminum, up to ten times stronger than certain construction steels.
The studied compound, called CoAl, belongs to the family of intermetallics. Its atoms are arranged in a highly ordered structure, which gives it great strength and good high-temperature performance. However, this organization also makes it brittle: under high stress, it can break before deforming.
Foundry - Image Wikimedia
This weakness limits its use in parts subjected to extreme conditions, such as aircraft turbines. These components must withstand heat, vibrations, and considerable forces over long periods. A material capable of remaining solid while absorbing some of the shock would therefore be of major interest.
To achieve this, the team did not try to eliminate all the material's defects. Instead, they deliberately introduced dislocations, tiny irregularities in the stacking of atoms. In a metal, these allow atomic layers to slide over each other rather than causing a sudden break.
The researchers also created very thin amorphous interfaces, that is, areas where the atoms no longer follow the usual crystalline order. Under compression, these boundaries become active and promote the formation of new dislocations. The material thus finds more ways to deform.
The tests revealed a yield strength greater than 6 GPa, compared to about 0.6 to 1 GPa for very strong structural steels. In parallel, the nanolaminate withstood more than 15% plastic deformation in compression at room temperature, without immediate fracture.
The current material is a nanoscale layered structure obtained by vapor deposition, not a bulk part ready for industrialization. Moving to larger-scale production is now one of the main objectives.
However, the interest of the study goes beyond just cobalt-aluminum. If this method works with other intermetallics, it could open a path to designing materials better suited to aeronautics, energy, or space exploration, where conventional metals reach their limits.
