Cascade Overlap in hcp Zirconium: Defect Accumulation and Microstructure Evolution with Radiation using Molecular Dynamics Simulations

ABSTRACTMolecular dynamics simulations are performed to investigate the defect accumulation and microstructure evolution in hcp zirconium (Zr) – a material which is widely used as clad for nuclear fuel. Cascades are generated with a 3 keV primary knock-on atom (PKA) using an embedded atom method (EAM) potential with interactions modified for distances shorter than 0.1 Å. With sequential cascade simulations we show the emergence of stacking faults both in the basal and prism planes, and a Shockley partial dislocation on the basal plane.

Transformation–dislocation dipoles in Laves phases: A high-resolution transmission electron microscopy analysis

Images of synchro-Shockley partial dislocation arrangements in the Laves phases NbCr2 and HfCr2 have been obtained by high-resolution transmission electron microscopy. The analysis of the stacking sequences around these arrangements revealed the role of the constituting partial dislocations in enabling the polytypic C14 → C36/6H phase transformation in both alloys. The synchro-Shockley partial dislocations occur in and move through the crystals mainly as dipoles of partials of opposite signs, leading to—as compared to isolated partials—strain fields of lesser extent. In NbCr2 a single, probably quenched synchro-Shockley partial dislocation dipole, consisting of two partials with Burgers vectors of opposite sign, was identified. The ordered passage of a series of this type of line defects brings about the C14 → C36 transformation. In HfCr2 a complex synchro-Shockley partial dislocation configuration was revealed. It can be regarded as an “antiphase boundary” between two C36 domains. It is likely that this defect structure had formed by impingement of two domains of C36 growing perpendicular to the stacking direction by glide of synchro-Shockley partial dislocation dipoles.

Deformation Mechanisms of Nanocrystalline Hexagonal Close-Packed Metals

ABSTRACTUsing molecular dynamics simulation of nanocrystalline (nc) samples with grain size of 10 nm, a reverse martensitic transformation from hexagonal close-packed (hcp) to face-centered cubic (fcc) structure is observed in nc-cobalt and nc-zirconium undergoing plastic deformation. In nc-cobalt hcp-to-fcc transformation is prevalent and deformation twinning is rarely observed. The transformation mechanism involves the motion of Shockley partial dislocation 1/3<1100> in every other (0001)hcp /(111)fcc plane. In nc-zirconium the hcp-to-fcc transformation competes with the deformation twinning. From the simulation results, it is suggested that the interaction among partials should be considered to understand the deformation mechanisms of hcp nc metals.

Creation and Motion of Edge Dislocations in Copper Single Crystals

ABSTRACTDislocations were created near the center of the surface (110) of copper small crystals whose surfaces are (111), (111), (110), (110), (112), and (112) by use of n-body atom potentials and molecular dynamics. At first, a Heidenreich-Shockley partial dislocation was created. As the partial dislocation proceeds, the partial dislocation and the surface was connected with a stacking fault until the next Heidenreich-Shockley partial dislocation was created at the surface.Just before the creation of a partial dislocation the stress was the highest. For larger crystals, forming a step on (110) plane was not enough and a shear was necessary to move dislocations.

Computer Simulation of Creation of Dislocations in Copper Small Crystals

Dislocations were created near the center of the surface (101) of copper small crystals whose surfaces are (111), (111), (101), (101), (121), and (121) by use of n-body atom potentials and molecular dynamics. At first, a Heidenreich-Shockley partial dislocation was created., As the partial dislocation proceeds, the partial dislocation and the surface was connected with a stacking fault until the next Heidenreich-Shockley partial dislocation was created at the surface.Just before the creation of a partial dislocation the stress was the highest.