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

Abstract

Under high pressures, phase transition, as well as deformation twins, are constantly reported in many BCC metals, whose interactions are of fundamental importance to understand strengthen mechanism of these metals under extreme conditions. However, the interactions between twins and phase transition in BCC metals are remain largely unexplored. In this work, interactions between coherent twin boundaries and α↔ε phase transition of iron are investigated using both non-equilibrium molecular dynamics simulations and nudge elastic band method. Mechanisms of both twin-assisted phase transition and reverse phase transition are studied and orientation relationships between BCC and HCP phase are found to be 〈111 ̅ 〉 ||〈1 ̅ 21 ̅ 0〉 and 〈11 ̅ 0〉 ||〈0001〉 for both cases. The twin boundary corresponds to *101 ̅ 0+ after the phase transition. It is amazing that the reverse transition seems to be able to "memory" and recover the initial BCC twins. The memory would partly loss when plastic slips take place in the HCP phase before the reverse transition. In the recovered initial BCC twins, three major twin spacing are observed, which are well explained in terms of energy barriers of the transition from HCP phase to BCC twin. Besides, variant selection rule of the twin assisted phase transition is also discussed. The results of present work could be expected to give some clues for producing ultra-fine grain structure in materials exhibiting martensitic phase transition.

Phase Transition in Iron Thin Films Containing Coherent Twin Boundaries: A Molecular Dynamics Approach

“…This orientation relationship has been also found in strain induced bcc→hcp transitions [ 13 , 23 ]. Note that in the Burgers [ 57 ] path, the close packed plane and direction in the bcc structure are parallel to the close packed plane and direction in hcp structure.…”

“…Among these crystal defects, TB provides one example that dramatically influents the mechanical properties, for instance, the twinning induced plasticity (TWIP) steel [ 21 , 22 ], and the transition behavior [ 4 , 14 ]. However, most of the studies focused on the effect of deformation twin on the transition behavior [ 4 , 23 ]. Another type of TB, the annealing twin or growth twin, is also present in Fe [ 24 , 25 , 26 ], which may also have effect on the phase transition, especially in the nanoscaled system such as the Fe thin film.…”

Discovering minimum energy pathways via distortion symmetry groups

“…Minimum energy paths (MEPs) 1 are of utmost importance in physical sciences where they are used to study any arbitrary distortion in a material, such as changes in molecular confirmations and chemical reactions [2][3][4] , structural or electronic phase transitions [5][6][7] , diffusion 4,8,9 , ferroelectric and magnetic switching [10][11][12][13][14] , surface reconstructions and the motion of interfaces such as dislocations 15,16 and domain walls 17,18 . All of these processes require knowledge of the underlying atomic motion provided by the MEPs.…”

Structural studies of metastable and equilibrium vortex lattice domains in MgB2

“…There are similarities between the supercooled VL discussed above and structural martensitic phase transitions. Examples of the latter include the tetragonal-to-orthorhombic transition in cuprate superconductors [25,26] or the α-to-ò transition in iron [9,27]. In both cases, the system has two equal energy pathways from the initial to the final structure, and a final configuration consisting of a periodic twin-boundary lattice rather a single global domain which has the lowest energy.…”

“…Domain nucleation and growth governs the behavior of a wide range of physical systems, and it is natural to expect similarities between the VL and for example martensitic phase transitions [9], domain switching in ferroelectrics [10] or the skyrmion lattice where field/temperature history dependent metastability has also been reported in connection with structural transitions [11][12][13]. Recently, we have studied the MgB 2 VL kinetics as it is driven from the MS to the equilibrium state (ES) by an AC magnetic field [14,15].…”