Anisotropic plasticity of nanocrystalline Ti: A molecular dynamics simulation*

Abstract

Using molecular dynamics simulations, the plastic deformation behavior of nanocrytalline Ti has been investigated under tension and compression normal to the {0001}, { 1 ¯ 010 } , and { 1 ¯ 2 1 ¯ 0 } planes. The results indicate that the plastic deformation strongly depends on crystal orientation and loading directions. Under tension normal to basal plane, the deformation mechanism is mainly the grain reorientation and the subsequent deformation twinning. Under compression, the transformation of hexagonal-close packed (HCP)-Ti to face-centered cubic (FCC)-Ti dominates the deformation. When loading is normal to the prismatic planes (both { 1 ¯ 010 } and { 1 ¯ 2 1 ¯ 0 } ), the deformation mechanism is primarily the phase transformation among HCP, body-centered cubic (BCC), and FCC structures, regardless of loading mode. The orientation relations (OR) of {0001}HCP║{111}FCC and 〈 1 ¯ 210 〉 HCP | | 〈 110 〉 FCC , and { 10 1 ¯ 0 } HCP | | { 1 1 ¯ 0 } FCC and 〈 0001 〉 HCP | | 〈 010 〉 FCC between the HCP and FCC phases have been observed in the present work. For the transformation of HCP → BCC → HCP, the OR is 0001 α 1 | | { 110 } β | | { 10 1 ¯ 0 } α 2 (HCP phase before the critical strain is defined as α 1-Ti, BCC phase is defined as β-Ti, and the HCP phase after the critical strain is defined as α 2-Ti). Energy evolution during the various loading processes further shows the plastic anisotropy of nanocrystalline Ti is determined by the stacking order of the atoms. The results in the present work will promote the in-depth study of the plastic deformation mechanism of HCP materials.

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

“…The HCP material can achieve plastic deformation through phase transformation under a certain crystal structure and loading mode. [37][38][39][40] Atomic shuffle of the basal atoms contributes to the transient phase transformation of HCP-to-BCC structure. [39,40] In this work, due to stress concentration at the Ti/Ni interface, atoms around the interface are more easily to active the atomic shuffle, thus the BCC atoms first emerge near the interface.…”

“…[37][38][39][40] Atomic shuffle of the basal atoms contributes to the transient phase transformation of HCP-to-BCC structure. [39,40] In this work, due to stress concentration at the Ti/Ni interface, atoms around the interface are more easily to active the atomic shuffle, thus the BCC atoms first emerge near the interface. While the phase transformation of BCC-to-FCC structures is mainly caused by dense dislocation propagation and accumulation of FCC stacking faults.…”

“…While the phase transformation of BCC-to-FCC structures is mainly caused by dense dislocation propagation and accumulation of FCC stacking faults. [39,40] For the tensile behavior of crack-free Ti/Ni nanolaminate with loading applied parallel to the interface, the allotropic phase transformation of HCP-BCC-FCC dominates the plastic deformation in Ti layer, and continuous dislocation propagation dominates the plastic behavior in Ni layer. Interface in crack-free Ti/Ni nanolaminate can not only act as dislocations source and sink, but also promote the phase transformation in Ti layer.…”

“…The phase transforma-tion of HCP-to-FCC structure in Ti layer is also related to the dislocation propagation and accumulation of dense stacking faults. [37][38][39][40] Go on loading, the FCC grains gradually grow in Ti layer, and some partial dislocations with 𝑏 2 = 1/6⟨112⟩ nucleate and arise from the crack tip in FCC regions. A mass of partial dislocations with 𝑏 3 = 1/6⟨112⟩ initiated from the interface and are absorbed by the opposite interface in Ni layer as shown by black circles in Fig.…”

The Plastic Deformation Mechanisms of hcp Single Crystals with Different Orientations: Molecular Dynamics Simulations

“…In general, the hcp metals display strong anisotropic mechanical behavior because of their asymmetric crystallographic structure. The orientation effect has a great effect on deformation behavior of such asymmetric structure [ 29 , 30 , 31 , 32 ]. Different deformation mechanisms can be activated under different loading conditions.…”