Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 111, Issue 20, Pages 7197-7201Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1324069111
Keywords
gradient structured metal; nanocrystalline metal
Categories
Funding
- National Natural Science Foundation of China [11072243, 11222224, 50571110, 11021262]
- 973 Program of China [2012CB92203, 2012CB937500 6138504]
- US Army Research Office [W911NF-09-1-0427, W911QX-08-C-0083]
- Nanjing University of Science and Technology
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tGradient structures have evolved over millions of years through natural selection and optimization in many biological systems such as bones and plant stems, where the structures change gradually from the surface to interior. The advantage of gradient structures is their maximization of physical and mechanical performance while minimizing material cost. Here we report that the gradient structure in engineering materials such as metals renders a unique extra strain hardening, which leads to high ductility. The grain-size gradient under uniaxial tension induces a macroscopic strain gradient and converts the applied uniaxial stress to multiaxial stresses due to the evolution of incompatible deformation along the gradient depth. Thereby the accumulation and interaction of dislocations are promoted, resulting in an extra strain hardening and an obvious strain hardening rate up-turn. Such extraordinary strain hardening, which is inherent to gradient structures and does not exist in homogeneous materials, provides a hitherto unknown strategy to develop strong and ductile materials by architecting heterogeneous nanostructures.
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