Structural change strengthens materials

‘If you looked at metal under a microscope you’d see that it is composed of millions of closely-packed grains,’ said Yuntian Zhu, a professor of materials science and engineering at NC State and senior author of two papers on the new work. ‘The size and disposition of those grains affect the metal’s physical characteristics.’

‘Having small grains on the surface makes the metal harder, but also makes it less ductile – meaning it can’t be stretched very far without breaking,’ said Xiaolei Wu, a professor of materials science at the Chinese Academy of Sciences’ Institute of Mechanics, and lead author of the two papers. ‘But if we gradually increase the size of the grains lower down in the material, we can make the metal more ductile. You see similar variation in the size and distribution of structures in a cross-section of bone or a bamboo stalk. In short, the gradual interface of the large and small grains makes the overall material stronger and more ductile, which is a combination of characteristics that is unattainable in conventional materials.