Researchers report that varying the spacing between twin boundaries, as opposed to maintaining consistent spacing throughout, produces dramatic improvements in a metal’s strength and rate of work hardening—the extent to which a metal strengthens when deformed.
Huajian Gao, a professor in the School of Engineering at Brown University, said these findings could lead to new manufacturing techniques for high-performance materials.
He explained, “This work deals with what’s known as a gradient material, meaning a material in which there's some gradual variation in its internal makeup. Gradient materials are a hot research area because they often have desirable properties compared to homogeneous materials. In this case, we wanted to see if a gradient in nanotwin spacing produced new properties.”
The research team created copper samples using four distinct components, each with different nanotwin boundary spacing. Spacings ranged from 29 nm between boundaries to 72 nm. The copper samples comprised different combinations of the four components arranged in different orders across the thickness of the sample. The researchers then tested the strength of each composite sample, as well as the strength of each of the four components. Testing showed that all of the composites were stronger than the average strength of the four components from which they were made. One of the composites was actually stronger than the strongest of its constituent components. Other tests showed that the composites also had higher rates of work hardening than the average of their constituent components.
While copper was used for this study, nanotwins can be produced in other metals as well, said Gao, meaning that it is possible that nanotwin gradients could improve the properties of other metals.