Zhuocheng Xie

Project description

Metallic nanostructures currently receive much attention due to their often superior mechanical properties compared to bulk materials [1]. Similarly, nanocrystalline, and in particular, nanotwinned metals have lately attracted a lot of interest because of their high yield strength [2]. This project combines both aspects by studying the mechanical behavior of twinned nanowires. Like the other projects in project area B6, we closely collaborate with the experimental projects of the GRK (in particular with A1, B3-5). The aim of our work is to complement the experimental investigations and provide qualitative insights in the fundamental deformation mechanisms not readily observable in the experiments, and to derive information for meso- and continuum-scale models of small scale plasticity.

Within this project, we perform atomistic simulations on fcc and bcc metallic nanowires of various crystallographic orientations and under different loading and boundary conditions. In particular, the deformation mechanisms of metallic nanowires under bending were studied in detail together with J.J. Moeller [3]. In agreement with theory and experiments on face-centered cubic nanowires under uniaxial load [4,5], the parts of the wires  under tensile strain deformed by twinning, while plastic deformation in the compressed part was either suppressed or took place by slip of perfect dislocations. The formation of wedge-shaped twins and pseudoelastic unbending were observed before and after instantaneous load removal, respectively, see Fig. 1(a). Currently, tensile tests are being performed on twinned nanowires. The presence of twin boundaries leads to a defined slip transmission process which causes more localized deformation behavior in twinned nanowires as compared to single crystal nanowires, see Fig. 1(b). The simulation results could explain the experimental observations of full dislocation activity in twinned nanowires [6].

References

[1] J.R. Greer, et al., Prog. Mater. Sci. 56 (2011) 654.
[2] L. Lu, et al., Science 323 (2009) 607.
[3] W. Nöhring, et al., EML 8 (2016) 140.
[4] A. Sedlmayr, et al., Acta Mater. 60 (2012) 3985.
[5] S. Lee, et al., ‎Nat. Commun. 5 (2014).
[6] B. Roos, et al., Appl. Phys. Lett. 105 (2014) 201908.