Defect engineering, a path to make ultra-high strength low-dimensional nanostructures

H Attariani and SE Rezaei and K Momeni, COMPUTATIONAL MATERIALS SCIENCE, 151, 307-316 (2018).

DOI: 10.1016/j.commatsci.2018.05.005

A current understanding is that materials with perfect structures have better mechanical properties. Thus, lowering the defect concentration, particularly by reducing the size of synthesized materials such as nanowires (NWs), is one of the key goals in the fabrication of new materials. In contrast, here we demonstrate the possibility of enhancing the mechanical properties of the low-dimensional nanostructures by engineering defects using the classical molecular dynamics technique. Our results show that NWs with high-density of I-1 stacking faults (I-1-SFs) have higher Young's Module (up to 14% in compression) and critical stress (about 37% under compression) in comparison to the perfect structure over a wide range of temperatures. This enhancement is in agreement with the in-situ experimental measurements of highly defective NWs and is explained by the interplay between surface stresses and the stress field of immobile SFs. The overlap of SF-induced stresses in regions confined by SFs partially relaxes with increasing temperature, while it remains the main reason for this nontrivial strengthening. Furthermore, a unique stress relaxation mechanism, twin boundary formation, is revealed for highly defective NWs. The twin boundary formation postpones the phase transition and increases the resilience of the nanostructure over a wide range of temperatures, which results in a stress plateau in a highly defective NW and an increase in ductility. Defect engineering is demonstrated as a new route for synthesizing advanced materials with superior mechanical properties, and increasing their stiffness, strength, and ductility for applications under extreme environments.

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