Uniting tensile ductility with ultrahigh strength via composition undulation

Heng Li, Hongxiang Zong, Suzhi Li, Shenbao Jin, Yan Chen, Matthew J. Cabral, Bing Chen, Qianwei Huang, Yan Chen, Yang Ren, Kaiyuan Yu, Shuang Han (), Xiangdong Ding (), Gang Sha (), Jianshe Lian, Xiaozhou Liao (), En Ma () and Jun Sun
Additional contact information
Heng Li: Jilin University
Hongxiang Zong: Xi’an Jiaotong University
Suzhi Li: Xi’an Jiaotong University
Shenbao Jin: Nanjing University of Science and Technology
Yan Chen: Jilin University
Matthew J. Cabral: The University of Sydney
Bing Chen: Xi’an Jiaotong University
Qianwei Huang: The University of Sydney
Yan Chen: Xi’an Jiaotong University
Yang Ren: City University of Hong Kong
Kaiyuan Yu: China University of Petroleum-Beijing
Shuang Han: Jilin University
Xiangdong Ding: Xi’an Jiaotong University
Gang Sha: Nanjing University of Science and Technology
Jianshe Lian: Jilin University
Xiaozhou Liao: The University of Sydney
En Ma: Xi’an Jiaotong University
Jun Sun: Xi’an Jiaotong University

Nature, 2022, vol. 604, issue 7905, 273-279

Abstract: Abstract Metals with nanocrystalline grains have ultrahigh strengths approaching two gigapascals. However, such extreme grain-boundary strengthening results in the loss of almost all tensile ductility, even when the metal has a face-centred-cubic structure—the most ductile of all crystal structures1–3. Here we demonstrate that nanocrystalline nickel–cobalt solid solutions, although still a face-centred-cubic single phase, show tensile strengths of about 2.3 gigapascals with a respectable ductility of about 16 per cent elongation to failure. This unusual combination of tensile strength and ductility is achieved by compositional undulation in a highly concentrated solid solution. The undulation renders the stacking fault energy and the lattice strains spatially varying over length scales in the range of one to ten nanometres, such that the motion of dislocations is thus significantly affected. The motion of dislocations becomes sluggish, promoting their interaction, interlocking and accumulation, despite the severely limited space inside the nanocrystalline grains. As a result, the flow stress is increased, and the dislocation storage is promoted at the same time, which increases the strain hardening and hence the ductility. Meanwhile, the segment detrapping along the dislocation line entails a small activation volume and hence an increased strain-rate sensitivity, which also stabilizes the tensile flow. As such, an undulating landscape resisting dislocation propagation provides a strengthening mechanism that preserves tensile ductility at high flow stresses.

Date: 2022
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DOI: 10.1038/s41586-022-04459-w

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