New understanding of nano-scale interstitial dislocation loops in BCC iron

Abstract

Complex states of nanoscale interstitial dislocation loop can be described by its habit plane and Burgers vector. Using atomistic simulations, we provide direct evidences on the change of the habit plane of a 1/2〈1 1 1〉 loop from {1 1 1} to {1 1 0} and {2 1 1}, in agreement with TEM observations. A new {1 0 0} habit plane of this loop is also predicted by simulations. The non-conservation of the Burgers vector is approved theoretically for: (1) dislocation reactions between loops with different Burgers vectors and (2) the transition between 〈1 0 0〉 loops and 1/2〈1 1 1〉 loops. The rotation from a 1/2〈1 1 1〉 to a 〈1 0 0〉 loop has also been explored, which occurs at 570 K for time on the order of 10 s. The dislocation-precipitate phase duality and change of habit plane are then proposed as new features for nano-scale dislocation loops.

Mechanisms for <100> interstitial dislocation loops to diffuse in BCC iron

“…Since local, minimum energy states are explored by SAAMD, the above results indicate that the energy difference between these states is expected to be limited. The change of habit planes has also been observed for 1D diffusion of a single 1/2 <111> loop in BCC Fe between {111}, {110}, and {211} planes 11 . For the 1/2 <111> loop, the intersection of these three planes is a line which has a direction along the <110> direction, while the habit planes of a <100> loop described above intersect at a point.…”

“…Until now, the structures and properties of dislocation lines or loops have been a well-researched area. Among the dislocation loops, the prismatic interstitial dislocation loops (PIDLs) formed by quenching, deformation, and irradiation interactions in body-centered cubic (BCC) iron (Fe) and Fe-based alloys have been studied for decades, because of their critical importance to both the mechanical behavior under normal conditions, and the radiation damage of materials used in fission and fusion reactors [1][2][3][4][5][6][7][8][9][10][11] . From a mechanical viewpoint, the PIDLs can be regarded as hard obstacles, thus the preexisting dislocations would bow around them by the Orowan mechanism.…”

“…In BCC Fe, there are mainly two types of PIDLs observed along the following Burgers vectors (B): 1/2 <111> and <100> [2][3][4][5][6][7]10,11 . Based on previous investigations, the following phenomena have been observed for these two types of loops: the first occurs during low temperature irradiations, and diffuses fast with a low-energy barrier and the second is almost immobile after its formation during irradiation.…”

Atomistic Simulation of Interstitial Dislocation Loop Evolution under Applied Stresses in BCC Iron

“…The properties of such a loop identified by the DXA method is shown in Figure (c), that is, the Burgers vector is still 1/2 but with a {100} habit plane. Detailed analysis of this new loop configuration has been provided elsewhere . Thus, in this state, the Burgers vector is not perpendicular to the habit plane.…”

“…Detailed analysis of this new loop configuration has been provided elsewhere. [16] Thus, in this state, the Burgers vector is not perpendicular to the habit plane. When the shear stress is increased further, the loop totally changes its property from a prismatic loop to a shear loop, as shown in Figure 3(d)-(f), that is, the Burgers vector lies in the loop plane.…”