Browsing by Author "Voskoboinikov, RE"
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- ItemEffective gamma-surfaces in {111} plane in FCC Ni and L1(2) Ni3Al intermetallic compound(Springer, 2013-07-14) Voskoboinikov, REThe well-known concept of γ surfaces originally suggested by Prof. Vitek is extended to the case of a shift of one part of a crystal with respect to the other part in two adjacent {111} planes of a stacking fault. The proposed approach is used to construct the effective γ surfaces in the {111} plane in fcc Ni and L12 Ni3Al of intermetallic compound. It is shown that Ni3Al can have five metastable stacking faults in this plane, namely, an intrinsic superlattice stacking fault, an extrinsic superlattice stacking fault, a complex stacking fault, an antiphase boundary, and a complex extrinsic stacking fault. The existence of the latter in the {111} plane in the L12 Ni3Al intermetallic compound has not been reported previously. The shift of the crystal in two close-packed planes in fcc Ni makes it possible to avoid the formation of a high-energy stacking fault which arises when constructing an ordinary γ-surface, as well as to self-consistently include the extrinsic stacking fault into consideration. © 2013, Pleiades Publishing, Ltd.
- ItemHydrogen accommodation in α-iron and nickel(Elsevier, 2014-02-25) Fullarton, ML; Voskoboinikov, RE; Middleburgh, SCAb initio calculations have been used to study the effects of hydrogen on vacancy concentrations in αα-Fe and Ni. The presence of H interstitials aided vacancy formation in both metals but via two different mechanisms. In αα-Fe, trapping of H by a vacancy is favourable. However binding of further hydrogen atoms was not predicted to proceed. The thermal equilibrium concentration of H interstitials in comparison to vacancies in αα-Fe is many orders of magnitude higher over a wide temperature range. Excessive H interstitials in solid solution facilitate vacancy formation, lowering the required energy by 0.79 eV (down to 1.41 eV). In Ni, a single H interstitial is not expected to have an impact on the vacancy population, increasing the vacancy formation energy by 0.32 eV. Two bound H interstitials however are predicted to decrease the vacancy formation energy by 0.52 eV with expected arrangement along a 〈〈1 1 1〉〉 direction around the vacancy. The calculations show reasonable agreement with experimental data when comparing crystal lattice contractions of the pure metals and predicted melting temperature of the Me–H alloys. © 2013, Elsevier B.V.
- ItemHydrogen induced vacancy formation in tungsten(Elsevier, 2014-05) Middleburgh, SC; Voskoboinikov, RE; Guenette, MC; Riley, DPAtomic scale modelling methods have been used to study the change in vacancy population when H is introduced into the W bulk matrix. Vacancy defects are predicted to dominate in pure W, and the vacancy concentration is expected to be very small. A mechanism whereby H solutes facilitate vacancy formation has been outlined and a single H interstitial is predicted to reduce the vacancy formation energy from 2.95 eV to 2.23 eV. Clustering of H interstitials in W is predicted to be unfavourable without a W vacancy. H has also been shown to affect the vacancy binding characteristics in W, changing the behaviour from a repelling interaction in pure W, retarding the formation of small vacancy clusters, to an attractive interaction when vacancy-H clusters are considered. The changes in defect behaviour predicted, will have observable implications to operational properties and the application of W in fusion reactor components. © 2014, Elsevier B.V.
- ItemInteraction of collision cascades with an isolated edge dislocation in aluminium(Elsevier, 2013-05-15) Voskoboinikov, REThe velocity-Verlet molecular dynamics has been applied to study the radiation damage created in collision cascades in an aluminium crystal harbouring an isolated edge dislocation with 1/2〈110〉 Burgers vector. The total of more than 150 displacement cascades formed by the recoil of primary knock-on atoms with energy EPKA=5keV in crystals at temperatures 100K⩽T⩽600K were simulated. Three different mechanisms of the interaction of collision cascades with edge dislocations in aluminium have been observed. At low and room temperatures the dislocations climb by absorption of displaced atoms from the collision cascade region. Capture of vacancies and displaced atoms by dislocation core at high temperatures leads to dislocation climb up and down. At room and especially at high temperatures dislocation climb by absorbing displaced atoms is accompanied by the formation of stacking fault tetrahedra in the vicinity of the dislocation line. In order to quantify the redistribution of radiation defects, the number of residual vacancies and self-interstitials created in collision cascades near edge dislocations was evaluated and compared with the number of Frenkel pairs formed in collision cascades in the pristine material under the same irradiation conditions. © 2012, Elsevier B.V.
- ItemMD simulations of collision cascades in the vicinity of a screw dislocation in aluminium(Elsevier, 2015-05-15) Voskoboinikov, REMolecular dynamics has been applied to study the interaction of collision cascades with 1=2h110i screw dislocations in aluminium. Primary knock-on atoms (PKA) with energy EPKA ¼ 5 keV were initiated in Al crystals at temperatures ranging from 100 K to 600 K at different distances from the dislocation line. Capture of the displaced atoms from the collision cascade region by the dislocation core has been observed at all simulation temperatures and led to the formation of a helical dislocation segment. Apart from that, in the material subjected to external loading a displacement cascade in the vicinity of a screw dislocation can trigger dislocation cross-slip. Under applied stress the dislocation unpins from the helical segment with the formation of a mobile dislocation loop with 1=2h110i Burgers vector. The number of residual vacancies and self-interstitial atoms produced in collision cascades near 1=2h110i screw dislocations is evaluated and compared with the number of Frenkel pairs formed in collision cascades in the pristine material under the same irradiation conditions. © 2013 Elsevier B.V.
- ItemMD study of primary damage in L1(0) TiAl structural intermetallics(Elsevier, 2013-05-15) Voskoboinikov, REComputer modelling by molecular dynamics has been applied to study the radiation damage created in collision cascades in L10 TiAl intermetallic compound. Either Al or Ti primary knock-on atoms (PKA) with energy 5 keV ⩽ EPKA ⩽ 20 keV were introduced in the intermetallic crystals at temperatures ranging from 100 K to 900 K. At least 24 different cascade for each (EPKA, T, PKA type) set were modelled in order to simulate a random spatial and temporal distribution of PKAs and provide statistical reliability of the results. The total yield of more than 760 simulated cascades is the largest yet reported for this binary intermetallic material. A comprehensive treatment of the modelling results has been carried out. The number of Frenkel pairs, fraction of Al and Ti vacancies, self-interstitial atoms and anti-sites as a function of (EPKA, T, PKA type) has been established. Preferred formation of Al self-interstitial atoms has been detected in L10 TiAl structural intermetallics exposed to irradiation. © 2012, Elsevier B.V.
- ItemMolecular dynamics simulations of radiation damage in D0(19) Ti3Al intermetallic compound(Elsevier, 2013-07-15) Voskoboinikov, REMolecular dynamics (MD) has been applied to simulate the radiation damage created in displacement cascades in D019 Ti3Al structural intermetallics. Collision cascades formed by the recoil of either Al or Ti primary knock-on atoms (PKA) with energy EPKA = 5, 10, 15 or 20 keV were considered in Ti3Al single crystals at T = 100, 300, 600 and 900 K. At least 24 different cascades for each (EPKA, T, PKA type) set were simulated. A comprehensive treatment of the modelling results has been carried out. We have evaluated the number of Frenkel pairs, fraction of Al and Ti vacancies, self-interstitial atoms and anti-sites as a function of (EPKA; T, PKA type). Preferred formation of both Al vacancies and self-interstitial atoms in D019 Ti3Al exposed to irradiation has been detected.© 2013, Elsevier B.V.
- ItemPreferential formation of al self-interstitial defects in gamma-TiAl under irradiation(Elsevier, 2013-01-01) Voskoboinikov, RE; Lumpkin, GR; Middleburgh, SCEmpirical dynamic calculations were used to observe a distinct increase in aluminium interstitial defects compared to titanium interstitial species remaining after a displacement cascade (even though Frenkel formation energies for both species were found to be similar). Thermodynamic data from static ab-initio models support this interesting result. Calculations were then used to determine whether these interstitials are free to move and therefore have the possibility of migrating to a surface where a passive Al2O3 layer can be formed. © 2012, Elsevier Ltd.