Symmetrical tilt grain boundaries in body-centred cubic transition metals: An ab initio local-density-functional study

We perform a first-principles calculation to investigate the effects of He in an Fe Σ5(310)/[001] grain boundary (GB) with the SIESTA code, for which the reliability of the pseudopotential and the basis set are systematically tested. We calculate the formation and segregation energies for different substitutional and interstitial cases in order to determine the site preference and the segregation properties of He in the Fe GB. It is demonstrated that the He segregation either breaks (substitution) or weakens (interstitial) the surrounding interfacial Fe-Fe bonds, leading to the GB tensile strength reduction.

Section: Methodsmentioning

confidence: 99%

First-principles study of He effects in a bcc Fe grain boundary: site preference, segregation and theoretical tensile strength

Zhang

Shu

Jin

et al. 2010

“…The conjugate gradient (CG) algorithm was used for the energy minimization process. To allow for further relaxation, the GB with the lowest excess energy was subsequently subject to a low-temperature annealing process for 100 ps and then slowly quenched to 0 K. Considering the high mobility of low-angle GBs [36], the annealing temperature was chosen to be 100 K. We should also point out that, due to the rigid translation process, the mirror symmetry of the low-angle GB is broken, which has been frequently observed in previous studies [37,38].…”

Section: Simulation Cellmentioning

confidence: 99%

Interplay between intrinsic point defects and low-angle grain boundary in bcc tungsten: effects of local stress field

Niu

Zhang

Shu

et al. 2015

We have used molecular statics in conjunction with an embedded atom method to explore the interplay between native point defects (vacancies and self-interstitials (SIAs)) and a low-angle grain boundary (GB) in bcc tungsten. The low-angle GB has biased absorption of SIAs over vacancies. We emphasize the significance of phenomena such as vacancy delocalization and SIA instant absorption around the GB dislocation cores in stabilizing the defect structures. Interstitial loading into the GB can dramatically enhance the interaction strength between the point defects and the GB due to SIA clustering (SIA cloud formation) or SIA vacancy recombination. We propose that the 'maximum atom displacement' can complement the 'vacancy formation energy' in evaluating unstable vacancy sites. Calculations of point defect migration barriers in the vicinity of GB dislocation cores show that vacancies and SIAs preferentially migrate along the pathways in the planes immediately above and below the core, respectively.

“…In this work, a theoretical ab initio technique for quantitative calculations of both atomistic and electronic structures, which previously has successfully given microscopic descriptions of grain boundaries in transition metals [11] and in α-Al 2 O 3 [12,13], is employed to analyse the 3 (111) twin boundary in SrTiO 3 . In the following, the essential references and computational parameters of the computational method are given in section 2.…”

Section: Introductionmentioning

confidence: 99%

Density functional study of the Σ3 (111) [1bar10] symmetrical tilt grain boundary in SrTiO₃

Hutt

Köstlmeier²,

Elsässer³

2001

Density functional supercell calculations were carried out by a mixed-basis pseudopotential method for the 3 (111) [1 10] symmetrical tilt grain boundary in strontium titanate, SrTiO 3 , as a prototype planar defect in an electroceramic material. A low grain boundary energy of 0.52 J m −2 was obtained. Minor structural relaxations compared to the coincidence site lattice model are obtained close to the grain boundary plane by theory and previous experiment. Within the limits of the rather small supercell model employed in the calculations, the calculated geometric structure agrees well with the experimental one. An analysis of calculated local electron densities of states shows that the perturbation due to the grain boundary is localized in the near vicinity of the boundary plane. From the present results for the small supercell model, there is no evidence for the build-up of a space-charge layer at this highly ordered and undoped twin boundary in SrTiO 3 .