Plastic deformation mechanism transition of Ti/Ni nanolaminate with pre-existing crack: Molecular dynamics study*

Abstract

Tensile behaviors of Ti/Ni nanolaminate with model-I crack are investigated by molecular dynamics simulations. The Ti/Ni nanolaminates with center crack either in Ti layer or in Ni layer under different loading directions are utilized to systematically study the mechanical performance of the cracked material. The results indicate that pre-existing crack dramatically changes the plastic deformation mechanism of the Ti/Ni nanolaminate. Unlike the initial plastic deformation originating from the interface or weak Ti layer of the crack-free samples, the plastic behavior of cracked Ti/Ni nanolaminate first occurs at the crack tip due to the local stress concentration. Subsequent plastic deformation is dominated by the interaction between the crack and interface. The Ti/Ni interface not only impedes the movement of the initial plastic deformation carriers (dislocation, slip band, and deformation twinning) from the crack tip, but also promotes the movement of interfacial dislocations in the tension process. Microstructure evolution analysis further confirms that the plastic deformation mechanism transition is ascribed to the orientation-dependent tensile behavior at the crack tip, which is intrinsically attributed to the anisotropy of the certain crystal structure and loading direction of the cracked Ti/Ni nanolaminate. In addition, by analyzing the effects of different plastic deformation carriers on crack propagation in specific crystal, it can be discovered that the interfacial dislocations moving towards the crack tip can further promote the crack growth.

Effect of void size and Mg contents on plastic deformation behaviors of Al–Mg alloy with pre-existing void: Molecular dynamics study

“…In recent years, extensive research using MD simulations has been conducted to probe mechanical behaviors of nanoporous materials and the effect of voids. [17][18][19] Shang et al investigated the size-dependent effect of pre-void in the Ni/Ni 3 Al interface on tensile strength, and found that the small void disperses the local energy caused by lattice misfit at the interface, generating higher yield stress than the defect-free structure. [20] Guan et al simulated the dynamic response of Al containing spherical void under different loading patterns.…”

Molecular dynamics study of coupled layer thickness and strain rate effect on tensile behaviors of Ti/Ni multilayered nanowires*

“…For the case of isopachous Ti/Ni nanowires with larger layer thickness, the plastic behaviors are greatly different from those of previous two samples. The microstructure evolutions of the longest Ti/Ni MNW (λ = 7.17 nm) are presented in ior, which has also been discovered in simulation [21,22,[37][38][39] and experiment [40,41] of HCP materials. Hereafter, the newly formed Ti/Ni nanowire undergoes another elastic stage until the tensile strain reaches the 0.073.…”

“…After that, the FCC phase grows and occupies the entire Ti layer as a result of dense basal dislocations' propagation and accumulation of FCC stack faults. [37,38,42] And the specific orientational relationship of grain reorientation and the phase transformation have been described specifically in our previous work. [26] 096201-5 At the second strain rate, the plastic deformations are similar to those at ε = 1.0 × 10 8 s −1 , which contains the grain reorientation, allotropic phase transition and dislocations' movement in Ti layer, while Ni layer provides spring support in the tensile process.…”

Strengthening and softening in gradient nanotwinned FCC metallic multilayers

“…[27] The common neighbor analysis (CNA) and dislocation extraction algorithm (DXA) are adopted to identify the atom feature and defect, where the grey means other atoms, the red represents HCP atoms, the blue expresses BCC atoms, the green suggests FCC atoms, and the lines in green regions indicate partial dislocations. [28,29] 3. Results and discussion…”