Twin boundary activated α → ω phase transformation in titanium under shock compression

Abstract

The role of grain boundary structures on the shock response of hexagonal-closepacked (hcp) metals is little understood. We use molecular dynamics simulations to investigate deformation mechanisms in shock compressed Ti bicrystals with three types of grain boundary (GB) microstructure. Our results show the shock response of phase Ti polycrystals are influenced by the GB characteristics, i.e., elastic shock wave induced inelastic deformation occurs on both sides of the {1012} coherent twin boundaries (CTBs) but only on one-side of the symmetric incoherent twin boundaries (ITB) or {1210} tilt grain boundaries regions. In particular, we find that the elastic shock wave can readily trigger the α→ω transformation at {1012} CTBs but not the other two GBs, and the α→ω transformation at CTBs leads to considerable wave attenuation (i.e., the elastic precursor decay). Combined with first principle calculations, we find that CTBs can facilitate the overcoming of the energy barrier for the α→ω transformation. Our findings have the potential to influence interface engineering and materials design under extreme conditions.

A metastable phase of shocked bulk single crystal copper: an atomistic simulation study

“…It should be mentioned that RDF plots have been used to demonstrate structural phase transition in materials 38 , 39 . Thus, RDF plots are also considered to analyze in this work.…”

Interactions between coherent twin boundaries and phase transition of iron under dynamic loading and unloading

“…However, the roles of CTBs played in the phase transition of iron are still not clear. Most recently, researches on CTB and phase transition in Ti has brought out some new insights into deformation mechanisms, as well as its interactions with phase transition, under shock or uniaxial compressions [31][32][33][34][35]. Zong et.…”

“…al. [31] also studied the roles of three types of GBs played in the phase transition of Ti under shock compressions, and found that CTB can facilitate nucleation of the phase transition because the CTB is more similar to metastable state in transition path from α to ω phase, and thus helps overcome energy barrier of the phase transition. Despite of these progresses, interactions between CTB and the direction or reverse phase transition at lattice level are still a mystery in BCC metals.…”

Role of twinning on the omega-phase transformation and stability in zirconium

“…[5,8,10,15,17]. Three distinctive characteristics of shock loading and HPT conditions are worth noting: (i) both impose significant shear to the material and as such, naturally activate large amounts of twinning in addition to dislocation glide [18,19]; (ii) postmortem microscopy analysis of shock-loaded Zr shows that the retained αgrains are lath-shaped, which resembles closely the conventional morphology of deformation twins [7,20]; (iii) atomistic calculations show that under shock loading, coherent twin boundaries in Ti act as favorable nucleation sites for the α-to-ω phase transformation compared to incoherent twin boundaries and random grain boundaries [21]. Taken together, we speculate that under shock loading and HPT conditions, αgrains first twin and then the ω-phase nucleates at or in the vicinity of twin boundaries.…”