Edge Dislocation In Iron Research Articles

Relaxed energy and structure of edge dislocation in iron

With modified analytical embedded-atom method and molecular dynamics simulation, this paper simulates the strain energy and the equilibrium core structure of a〈100〉 edge dislocation in BCC metal iron on atomistic scale. In addition, the trapping effect of dislocation on vacancy is investigated as well. The results show that the equilibrium dislocation core is quite narrow and has a C2v symmetry structure. Calculated strain energy Es of the dislocation is a linear function of ln(R/2b) while R ≥ 5.16 Å (1 Å = 0.1 nm), in excellent agreement with the elasticity theory prediction. Determined core radius and energy are 5.16 Å and 0.62 eV/Å, respectively. The closer the vacancy to the dislocation line is, the lower the vacancy formation energy is, this fact implies that the dislocation has a trend to trap the vacancy, especially for a separation distance of the vacancy from dislocation line being less than two lattice constants.

Influence of the stress field due to pressurized nanometric He bubbles on the mobility of an edge dislocation in iron

Voids and He bubbles are strong obstacles to dislocation, which induce hardening and loss of ductility. In Fe, molecular dynamics simulation is used to investigate the basic mechanisms of the interaction between a moving edge dislocation and a void or He bubble, as a function of its He content, temperature, interatomic potentials and interaction geometry. Different interatomic potentials for Fe–Fe and Fe–He interactions are used. It appears that temperature eases the dislocation release, due to the increased mobility of the screw segments appearing on the dislocation line upon bowing from the void or He bubble. The mobility includes the cross-slipping of these segments, which leads to the formation of a jog. It appears that the He bubble induces an inhomogeneous stress field in its surroundings, which strongly influences the dislocation passage depending on the geometry of the interaction.

Effect of helium on irradiation-induced hardening of iron: A simulation point of view

Irradiation-induced hardening and loss of ductility of ferritic/martensitic materials envisaged for future fusion reactor is still difficult to understand. In particular, helium (He), produced by transmutation by the fusion neutrons of 14MeV, is known to impact mechanical properties, but its effect at the microstructural level is still unclear. Molecular dynamics simulations of the mobility of an edge dislocation in iron (Fe) are performed to study the effect of He, either as a gas in solid solution or in cavities. Obstacle to the dislocation, the cavity, in the form of a void or a He bubble, is compared to a a0 [100] dislocation loop, all being 2nm in size. Results show that He in solid solution up to 1.0at.% has a little effect on the dislocation mobility. Conversely, the cavities and the a0 [100] dislocation loop are strong obstacles to the passage of the edge dislocation. Interestingly He bubbles present a lower obstacle strength than voids for low He contents, while for high He content the bubble promotes loop punching, which induces a strong resistance to the passage of the dislocation.

Dynamics of drag of self-interstitial clusters by an edge dislocation in iron

Self-interstitial atom (SIA) clusters are created in metals under fast neutron irradiation and are believed to interact with dislocations and increase the flow stress. In this paper, atomic-scale computer simulations are used to investigate the dynamic interaction between an edge dislocation and small SIA loops that do not intersect the dislocation glide plane and whose Burgers vector is parallel to it. Such loops can be dragged by a moving dislocation and this effect is simulated as a function of temperature and loop size, spacing, stand-off distance and Burgers vector orientation. The results can be understood in terms of the one-dimensional mobility of SIA loops.

高純度鉄単結晶の機械的性質に及ぼす水素の影響

It has not yet been clear whether or not hydrogen hardens iron. In the present work, high purity iron single crystal specimens were used in order to clarify the effect of hydrogen on the mechanical properties of iron.When hydrogen was electrolytically introduced into the specimens during plastic deformation at 195 K, the flow stress was considerably decreased. On the other hand, it was increased when hydrogen was introduced in an unloaded state. The amount of the decrease in flow stress decreased with increasing deformation temperature. The flow stress at 300 K was increased by the hydrogen charging during the plastic deformation.The mobility of screw dislocations as well as that of edge dislocations in iron was found to be decreased by the presence of hydrogen atoms. It is likely that the remarkable decrease in the flow stress at 195 K is due mainly to the easy motin of edge dislocations generated at the specimen surface with the aid of hydrogen charged during the plastic deformation.

Microdiffraction Calculations For Dislocations

The new generation of STEM instruments offer the possibility of recording the diffuse elastic scattering from the core region of an isolated dislocation. In order to use this information for core-structure analysis it is important to be able to compute this scattering including all dynamical and instrumental effects. Preliminary results of such a calculation using the multi-slice method of periodic continuation (1) are shown in figures 1-4 for the case of an end-on [100] undissociated edge dislocation in iron. Theoretical core atom coordinates (2) have been used to form a periodic array of dislocations as shown in figures 1 and 2. These atomic coordinates are calculated for a single isolated dislocation, however the scattering from the periodic array of dislocations shown closely approximates that from an isolated dislocation if the illuminating spot is small compared to the superlattice unit cell. No relaxation has been allowed in the beam direction.

Structure of the 〈100〉 Edge Dislocation in Iron

The positions of atoms around the core of a 〈100〉 edge dislocation in iron have been calculated using atomic potentials developed by Johnson, boundary conditions based on anisotropic or isotropic elasticity and the GRAPE computer program. The dislocation is quite narrow and the atoms below the extra half-plane relax into a microcrack. It is shown that particular care must be taken in introducing the dislocation and choosing the potential. The configuration of this particular dislocation is only slightly sensitive to the choice of boundary conditions and the size of the model.