Atomistic study on the cross-slip process of a screw dislocation in magnesium

Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Tsuru, Tomohito

Modelling and Simulation in Materials Science and Engineering, 23(6), p.065002_1 - 065002_19, 2015/09

https://doi.org/10.1088/0965-0393/23/6/065002

The cross-slip process of a screw dislocation from the basal to the prismatic plane in magnesium was studied using the density functional theory and the molecular dynamics calculations. An atomistic method for calculating the total Peierls energy map has been devised to track the transition path of a dissociated and/or constricted screw dislocation in the cross-slip process. The barrier of a screw dislocation from the basal to the prismatic plane is estimated by the density functional theory for the first time. The activation enthalpy for the cross slip is calculated using a line tension model based on the density functional theory to be 1.4 to 1.7 eV, which is in reasonable agreement with experiments. On the basis of the results, the effect of temperature on the cross-slip process of the dissociated screw dislocation on the basal plane is studied in detail using the molecular dynamics method.

Solution softening in magnesium alloys; The Effect of solid solutions on the dislocation core structure and nonbasal slip

Tsuru, Tomohito; Udagawa, Yutaka; Yamaguchi, Masatake; Itakura, Mitsuhiro; Kaburaki, Hideo; Kaji, Yoshiyuki

Journal of Physics; Condensed Matter, 25(2), p.022202_1 - 022202_5, 2013/01

https://doi.org/10.1088/0953-8984/25/2/022202

There is a pressing need to improve the ductility of magnesium alloy toward the advanced application for light-weight structural materials. In this letter we focused attention on the particular potential function for yttrium to activate the non-basal slip. The generalized stacking fault (GSF) energies of both basal and prismatic planes for pure magnesium are calculated by density functional theory (DFT) and EAM potential, and its effect on the dislocation core structures are examined by semidiscrete variation Peierls Nabarro (SVPN) model. Solution softening of added yttrium was similarly estimated by combination of DFT and SVPN model. Yttrium was found to have a particular influence on solution softening by the reduction of the gradient of the GSF energy.

Kinetic Monte Carlo annealing simulation of cascade damage in -Fe

Suzudo, Tomoaki; Golubov, S.*; Stoller, R.*; Yamaguchi, Masatake; Tsuru, Tomohito; Kaburaki, Hideo

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 6 Pages, 2010/10

Molecular dynamics is a useful tool to analyze cascade damage in structural materials of nuclear devices, but the time scale accessible to molecular dynamics is 100 ps. Kinetic Monte Carlo annealing simulation of cascade damage is useful for analyzing the longer time development of cascade damage. We conducted a series of such annealing simulations in -Fe. The surviving displacement ratio to the NRT displacements before annealing is 0.3 in the case of primary knock-on atom's energy more than 10 keV, but it decreased by 30 % through the annealing at 300 K because of recombination of vacancies and self-interstitial atoms, and the recombination ratio increased as the annealing temperature increased. These results are meaningful when applied to the simulation of accumulation of cascades using rate theory. This work is useful for R&D of nuclear materials.

Timoshenko coefficient's effect in wave propagation analysis of a beam

Miyazaki, Akemi; Tsuru, Hideo*

Dai-56-Kai Riron Oyo Rikigaku Koenkai Koen Rombunshu, p.299 - 300, 2007/03

The author has researched stress wave propagation in frame structures in order to clarify the dynamic behavior of complicated assembled structures. A spectrum element method (SEM) has been adopted as one of the effective methods, and numerical simulations of a real-sized piping structure has been performed. The Timoshenko theory is usually used in wave propagation analysis of frame structures because it can relatively well approximate in high frequency domain. The theory uses a so-called Timoshenko coefficient to couple the bending and shear deformation. This coefficient is calculated using the shear deformation distribution within the cross section. In this paper, we re-examined the Cowper's theory which introduced the least assumptions in computing the Timoshenko coefficient. The connection between cross section and dispersion relation was investigated and a numerical simulation was attempted. An importance of an estimation of Timoshenko coefficient was discussed.

Dislocation motion on the prismatic plane in magnesium; Molecular dynamics simulations

Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake; Tsuru, Tomohito

no journal, , 

no abstracts in English

First-principles and molecular dynamics study on the cross-slips of a screw dislocation in Mg

Itakura, Mitsuhiro; Yamaguchi, Masatake; Kaburaki, Hideo; Tsuru, Tomohito

no journal, , 

The Peierls stress of the prismatic slip in Mg single crystal is order of magnitude higher than that of the basal slip, resulting in highly anisotropic plasticity and low workability. To design Mg-based alloy with an improved workability, it is crucial to identify and model the correct prismatic slip behavior based on the first-principles method. In the present work, the migration pathway between split screw dislocations which are spread on two adjacent basal planes is identified using first-principles method and drag method. The line tension energy of a kink configuration is also calculated based on the lattice Green function method in first-principles calculations.

First-principles calculations of c+a screw dislocations in Mg

Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Tsuru, Tomohito

no journal, , 

Fuel cladding in nuclear reactors are made of Zirconium alloy, which has hexagonal crystal structure. Because of the low symmetry of the structure, hexagonal metals are known to have poor ductility and formability, and identification of alloying effect and irradiation effect on the ductility of these metals are currently very important subject. The present study concentrate on the pyramidal dislocations in Mg, which is a typical hexagonal metal suitable for the model studies. The pyramidal dislocations plays a key rolein the ductile deformation and understanding its nature is essential to improve the ductility of the material. The present study revealed for the first time the structure and migration process of the pyramidal dislocations, opening a way to design an alloy of better ductility based on the computational predictions.

Novel cross-slip behavior of the pyramidal screw dislocations in Mg

Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Tsuru, Tomohito

no journal, , 

Dislocations in fcc and hcp metals usually dissociate into a planar shape, and their slip is confined inthe corresponding slip planes. Cross-slip usually requires transformation of the planar dislocation core into a linear, perfect dislocations, which requires some activation energy. Using an extensive DFT calculations, we have found anotable exception to this conventional view. The pyramidal c+a screw dislocation in Mg consists of two partialdislocations connected by a stacking fault, and the stacking fault can migrate perpendicular to the plane by atomshuffling, enabling the dislocation to cross-slip without transforming into a perfect dislocation.

Molecular dynamics study on cross-slip mechanisms of a screw dislocation in magnesium

Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake; Tsuru, Tomohito

no journal, , 

no abstracts in English

A Molecular dynamics study on the structure and formation mechanisms of a c+a dislocation in magnesium

Kaburaki, Hideo; Itakura, Mitsuhiro; Yamaguchi, Masatake; Tsuru, Tomohito

no journal, ,