Extraordinary strain hardening by gradient structure

By Xiaolei Wu, P. Jiang, Liu Chen, Fuh-Gwo Yuan, Yuntian Zhu. Proceedings of the National Academy of Sciences of the United States of America, 2014

1,211 citations recorded by the source corpus.

Significance Nature creates the gradient structure (GS) for a purpose: to make biological systems strong and tough to survive severe natural forces. For the grain-size GS, the deformation physics is still unclear. One wonders if the grain-size GS in the nanomicroscale would also benefit materials engineered by mankind. In this paper, a universal strain hardening mechanism is revealed in the GS. We discovered a unique extra strain hardening that is intrinsic to the GS. Its mechanism is the presence of strain gradient together with the stress state change. A superior combination of strength and ductility that is not accessible to conventional homogeneous materials is obtained. As a novel mechanism, extra strain hardening renders high ductility in the GS materials. Gradient 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.

Subfields: Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/f1c34df019ea09f55d52f74c79ead0faff5686b7

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Materials Chemistry

1. Yuntian Zhu
2. Xiaolei Wu
3. R. Valiev
4. I. Ovid’ko
5. Huajian Gao
6. Ke Lu
7. Lei Lu
8. Ting Zhu

Citations in the corpus

• Critical microstructures and defects in heterostructured materials and their effects on mechanical properties (2020, background): “In recent years, it has been frequently reported that some HS materials show mechanical properties superior to that predicted by the rule of mixtures [12,17,18,21].”
• Gradient plasticity in gradient nano-grained metals (2016, methodology): “[5] used surface mechanical attrition treatment to prepare GNG samples of body-centered cubic (BCC) steel with a sandwich sheet structure, i.”
• Ductility by shear band delocalization in the nano-layer of gradient structure (2018, background): “This induces strain gradient in the depth direction and back-stress hardening to prevent the LSZ from propagating into the depth [12,31,34].”
• Heterostructured materials: superior properties from hetero-zone interaction (2020, background): “change of a particular microstructural feature, including grain size [27,29], twin density [31,63–65], chemical composition [66], constituent phase ratio and/or precipitates [67], from the specimen surface.”
• Improved back stress and synergetic strain hardening in coarse-grain/nanostructure laminates (2018, background): “sizes, such as gradient and laminate structures, have attracted extensive interests in recent years [1-15].”