deformation twinning is an important mode of plastic dissipation process of nanoscale body-Centered Cubic (BCC) metals, but its origin and space-time characteristics have been unclear. It has been theoretically predicted that the interaction mechanism between dislocations and twins is affected by the material scale. Recently, researchers at Wuhan University reported the adjustment of size effect on twinning behavior and twin boundary-dislocation interaction mechanism in body-centered cubic metal iron nanowires using transmission electron microscopy in situ tensile experiments. They found that iron nanowires have a critical diameter (d)-about 2.5 nm. At a scale smaller than this, the main carrier of plastic deformation is dislocation slip. Above this critical diameter, plasticity is mainly determined by deformation twins rather than dislocation slip. For example, when the iron nanowires with a diameter of about 9 nm are stretched, the nanowires will undergo elastic deformation at the initial stage, and then the twin nucleation will gradually expand to the whole nanowire. In addition, in situ studies of iron nanowires with diameters less than 17 nm and diameters greater than 17 nm, they also found two different twin-related deformation mechanisms, including twin modification reorientation (twin variant re-orientation) and twin boundary fracture (TB cracking). The former is the result of the interaction of twins and dislocations, and the latter is the result of the interaction of twins and twins. Further molecular dynamics and statics simulations revealed the basic mechanism of size-dependent plastic deformation, which was largely ignored in previous experimental studies. The results of this study emphasize the importance of grain size in regulating the deformation behavior of nano-scale iron, and provide possible guidance for exploring single-crystal and polycrystalline iron-based materials (such as steel) with optimal mechanical properties. The relevant research results of

are published in Journal of Materials Science & Technology under the title of "Strong size effect on deformation twin-mediated plasticity in body-centered-cube iron. Zhao Ligong and Chen Guoxujia of Wuhan University are the co-first authors of the paper, and Professor Wang Jianbo and Professor Zheng He are the corresponding authors of the paper.

Original Link: https://www.sciencedirect.com/science/article/abs/pii/S100503022200857X?via=ihub

Fig. 1 Study on Plastic Deformation Mechanism of Full Dislocation Modulation of Ultra-small Scale Iron Nanowires (d < 2.5 nm)

Full dislocation-mediated plastic deformation in ultrasmall-sized Fe NW

Fig. 21 1/12<111> twinning (Twinning) and detwinning (Detwinning) process observation of partial dislocation modulation

Twinning and detwinning processes of Fe NW

Fig. 3 lattice reorientation of twin modulation

Twinning-mediated lattice re-orientation in Fe NW (d ~ 9 nm)

Fig. 4 Fracture Research at Twin Boundary of Slightly Larger Size Iron Nanowires (d ~ 18 nm)

TB cracking in Fe NW (d ~ 18 nm)

In this research result: the researchers used small-scale iron nanowires as the research object, and systematically studied the effects of different sizes on the tensile plastic deformation mechanism of iron nanowires under tensile action. They found that there is a critical size (d ~ 2.5 nm). At a particularly small size (d < 2.5 nm), dislocation slip dominates, and above this critical size (2.5 nm-35 nm), deformation twinning The mechanism dominates the plastic deformation of iron nanowires. In addition, when the size increases from d < 17 nm to d > 17 nm, the twin nanowires will undergo a change in twin reorientation (re- orientation)-twin boundary fracture (TB cracking) under tension. Further simulation and theoretical analysis reveal the origin of the size effect on the deformation mechanism. This work provides atomic-scale evidence for the study of the deformation mechanism of nano-scale body-centered cubic (BCC) metals, and provides a reference for the optimization of the strength and ductility of iron-based materials.

Figure The PicoFemto of Zeyau Technology (ZEPTOOLS) was used in this study.®The series of in-situ TEM-STM sample rods set up an in-situ test environment.

Figure Experimental Method