Atomistic simulations on ductile-brittle transition in ⟨111⟩ BCC Fe nanowires

Abstract

Molecular dynamics simulations have been performed to understand the influence of temperature on the tensile deformation and fracture behavior of <111> BCC Fe nanowires. The simulations have been carried out at different temperatures in the range 10-1000 K employing a constant strain rate of 1× 10 8 s −1 . The results indicate that at low temperatures (10-375 K), the nanowires yield through the nucleation of a sharp crack and fails in brittle manner. On the other hand, nucleation of multiple 1/2<111> dislocations at yielding followed by significant plastic deformation leading to ductile failure has been observed at high temperatures in the range 450-1000 K. At the intermediate temperature of 400 K, the nanowire yields through nucleation of crack associated with many mobile 1/2<111> and immobile <100> dislocations at the crack tip and fails in ductile manner. The ductile-brittle transition observed in <111> BCC Fe nanowires is appropriately reflected in the stress-strain behavior and plastic strain at failure. The ductile-brittle transition increases with increasing nanowire size. The change in fracture behavior has been discussed in terms of the relative variations in yield and fracture stresses and change in slip behavior with respect to temperature. Further, the dislocation multiplication mechanism assisted by the kink nucleation from the nanowire surface observed at high temperatures has been presented.

Oxyhydroxide of metallic nanowires in a molecular H2O and H2O2 environment and their effects on mechanical properties

“…16 Sainath et al studied the influence of temperature, ranging from 10 to 1000 K, on the tensile deformation and fracture behavior of h111i BCC Fe NWs using MD simulation under a constant strain rate of 1 Â 10 8 s À1 . 14 Similarly, they also observed that the subsequent deformation of all the NWs exhibits non-linear deformation behaviour after the initial linear elastic regime until the onset of the plastic deformation regime at relatively high strains 4B0.04, which is in close agreement with our linear yield strain values. Notably, non-linear deformation highly depends on the temperature of the system.…”

“…Once plastic deformation is begun for all NWs, the nucleation and growth of twinning occurs at a relatively smaller stress value, but it fluctuates almost at a constant value of the flow stress, as seen from the stress-strain curves. 14,17,55 The work of hardening rate of all the Fe NWs is obtained by integration of the area under the tensile stress-strain curves. 33 The oxide shell layer including local structure has an effect on the work of hardening rate as is observed from the tensile stress-strain curves.…”

“…[1][2][3]6,10 The environmental conditions dictate the strength, lifetime, and failure of reactive metallic materials. 3,14,15 In particular, the resulting oxide shell layer drastically alters the physical and chemical properties of the exposed surface layer, and as a result, eventually, the strength of Fe NWs may be weakened substantially compared to the corresponding un-oxidized counterparts. 2,3,10,16,17 However, the presence of undesirable oxide shell layer (or desirable oxide-coating) on the free Fe NW surfaces is associated with surface/interface finite-size effects which help distinctly to achieve potentially additional interesting and unique chemical, 3 physical, 8 optical, 18 mechanical, 17 and magnetic properties 5,8,11 as compared to the un-oxidized counterparts.…”

“…Furthermore, numerous MD studies have been performed to investigate the strengthening of pure Fe NWs using fixed charge interatomic potentials under tensile and compressive loading. 14,15,[28][29][30][31][32] In these studies, Fe NWs were considered simply in vacuum, and thereby, the effects of the surface oxide layer on the mechanical behaviors were ignored. Many of these studies have focused on exploring the influence of geometry, size, loading, grain size, surface geometry, and temperature on the mechanical deformation mechanisms and related properties of metallic Fe NWs.…”

Adhesive contact of a diamond sphere with an iron substrate caused by interatomic interaction

“…21 Therefore, the constitutive parameters in this paper are obtained from stress-strain behavior based on nanowire stretching. 21,22 Then the mechanical behaviors of the substrate are investigated in detail, which include the indentation load-displacement curves, pressures, adhesive regions as well as the stress distributions. Because molecular dynamics (MD) can be used to predict particles trajectory by interatomic potentials or MD force fields [23][24][25][26] in the adhesive contact, in the end, the proposed method is compared with MD simulation.…”