Interaction of a dislocation pileup with {332} tilt grain boundary in bcc metals studied by MD simulations

Abstract

The sustainability and capacity of macroscopic deformation by polycrystalline metals and metallic alloys is controlled by the propagation of dislocation-mediated slip through grains. In this paper, the interaction of a pileup of 1 /2 111 dislocations with the {332} tilt grain boundary (GB) is studied as a function of temperature in three bcc metals: iron (Fe), chromium (Cr), and tungsten (W). The interaction results in the transformation of the crystal dislocation into GB dislocations. The {332} tilt GB absorbs the crystal dislocations of the pileup, neither the transmission nor reflection of dislocations was observed. The reaction product at the GB is determined by the crystallography of the GB and the features of the crystal dislocations involved, specifically, the orientation of the Burgers vector and the glide plane of the dislocation. In general, the decomposition results in the formation of a sessile GB dislocation with a riser that facets the GB and several elementary disconnections that glide away. In some cases, the riser increases its length with the number of dislocations absorbed and a new asymmetrical grain boundary of {112}/{110} type is created. For a given external shear stress, the number of dislocations absorbed depends on the orientation of the Burgers vector, glide plane of the pileup, and material.

Atomic-level study on the interaction of plastic slip with Σ3{112} tilt grain boundary and {112} twins in bcc metals

“…GB-DPU interactions were modeled by using a hybrid model combining atomistic and continuous approaches, initially described in [51] and applied in [32,52]. In the continuum region, the positions of the dislocations are calculated as a function of the external stress σ , number of dislocations in the pileup n, and the position of the heading dislocation that is held fixed, according to the expression n = Lσ /A [53], where L is the total distance between the first and last dislocations and A is a parameter depending on the Burgers vector, the character of the dislocation, and the material.…”

“…The GBDs and TBDs that step the interface are named disconnections (interfacial line defects with both dislocation and step character [21,22]); among them, we distinguish the gliding elementary disconnections (EDisc) [23], with the Burgers vector parallel to the interface, which are responsible for the shear-coupled boundary migration [17,18,[23][24][25][26][27][28][29] and for the twin growth [30]. The GBDs could favor either the shear-coupled GB migration or the nucleation of other defects such as twins [31][32][33] and dislocations [34]; this behavior occurs in GBs of the most common crystallographic structures in metals, i.e., bcc, fcc, and hcp [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37].…”

“…(ii) The influence of the local shear stress is evidenced by comparing the interaction of a single dislocation with the interaction of a pileup of dislocations since for the latter the local shear stress at the interaction region is dominated by the incoming dislocations. An illustrative example of the abovedescribed behavior is the interaction of dislocations with a symmetric {332} 110 tilt GB studied by molecular dynamics simulation [31,32]. In fact, the {332} GB absorbs 1/2 111 crystal dislocations, transforming them into disconnections which modify the GB shape, but there is no transmission of the dislocations to the adjacent grain.…”

“…Then, in the presence of {332} GBs, plastic deformation is accommodated by the combination of the motion of the {332} GB and the growth of {112} twins inside the grain. If a pileup of dislocations interacts with the GB [32], a disconnection with a much larger stepped core is formed by absorption of the dislocations of the pileup, which forms a new asymmetric GB {112}/{110}. In this case no twins are formed.…”

Disconnection-mediated motion of 〈110〉 tilt grain boundaries in α -Fe

“…These defects are characterized by the Burgers vector (BV) and the height of the step (b, h) and, being glissile, they are responsible for the displacement of the GB. Recent computer atomistic studies in α-Fe [12][13][14][15] are examples of the importance of disconnections on the GB migration but also on the interaction between GBs and crystal dislocations. Another relevant finding is that in the event of glissile disconnection absence the plasticity mechanisms are not able to include SCGBM [16].…”