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| 2. |
- Karkina, L. E., et al.
(författare)
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Solute-grain boundary interaction and segregation formation in Al : First principles calculations and molecular dynamics modeling
- 2016
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Ingår i: Computational materials science. - : Elsevier. - 0927-0256 .- 1879-0801. ; 112, s. 18-26
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between solute atoms (Mg, Si, Ti) and grain boundaries (GBs) of different types in Al are investigated using two approaches: first principles total energy calculations and large scale atomistic simulations. We have found that both deformation (size effect) and electronic (charge transfer) mechanisms play an important role in solute-GB interaction. The deformation and electronic contributions to GB segregation energy for the considered solutes have been analyzed in dependence on the impurity and the GB type. Mg and Si atoms are calculated to segregate to GBs, while Ti atoms to repel from, GBs in Al. For the case of a symmetric special-type GB the interaction is found to be short-ranged. For a general-type GB the range of GB-solute interaction is found to be considerably longer. A method to estimate the segregation capacity of a GB has been proposed, which takes into account the solute-solute interactions, and shown to be able to correctly describe the GB enrichment in alloying elements. The features of the segregation formation in fine-grained materials produced by severe plastic deformation are discussed.
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| 3. |
- Karkin, I. N., et al.
(författare)
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Effect of Ni and Al on the Decomposition Kinetics and Stability of Cu-Enriched Precipitates in Fe-Cu-Ni-Al Alloys : Results of MD plus MC Simulation
- 2021
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Ingår i: Physics of metals and metallography. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 0031-918X .- 1555-6190. ; 122:5, s. 498-503
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Tidskriftsartikel (refereegranskat)abstract
- To understand the effects of doping elements on the formation and structure of Cu-enriched precipitates, different stages of Fe-Cu-Ni-Al alloy decomposition are studied using the combined MC + MD approach, which includes the Monte Carlo (MC) and molecular dynamics (MD) simulations. It is shown that the surface of the precipitates enriches in the doping elements at early stages of the decomposition, which is significant for the structure stability against the bcc -> 9R transition of the copper enriched precipitates.
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| 4. |
- Kar'kin, I. N., et al.
(författare)
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Kinetics of Early Decomposition Stages in Diluted bcc Fe-Cu-Ni-Al Alloy : MC plus MD Simulation
- 2019
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Ingår i: Physics of the solid state. - : PLEIADES PUBLISHING INC. - 1063-7834 .- 1090-6460. ; 61:4, s. 601-608
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Tidskriftsartikel (refereegranskat)abstract
- A combined approach including the Monte Carlo and molecular-dynamics simulation, decomposition kinetics and segregation formation in the multicomponent low-alloy Fe-1.5Cu-2Ni-1.5Al (at %) alloy is studied. It is shown that the formation of Cu nanoparticles surface-enriched with Ni and Al (coprecipitation mode) includes several stages: (i) the formation of clusters consisting of several Cu atoms, (ii) their enrichment with Ni and Al atoms, and (iii) redistribution of Ni and Al atoms with the formation of a surface layer providing stabilization of Cu nanoparticles. Observed structural features of segregations and their stability in Fe-Cu-Ni-Al alloys is discussed.
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| 5. |
- Kar'kin, I. N., et al.
(författare)
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Monte Carlo Simulation of the Kinetics of Decomposition and the Formation of Precipitates at Grain Boundaries of the General Type in Dilute BCC Fe-Cu Alloys
- 2017
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Ingår i: Physics of the solid state. - : MAIK NAUKA/INTERPERIODICA/SPRINGER. - 1063-7834 .- 1090-6460. ; 59:1, s. 106-113
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of decomposition of a polycrystalline Fe-Cu alloy and the formation of precipitates at the grain boundaries of the material have been investigated theoretically using the atomistic simulation on different time scales by (i) the Monte Carlo method implementing the diffusion redistribution of Cu atoms and (ii) the molecular dynamics method providing the atomic relaxation of the crystal lattice. It has been shown that, for a small grain size (D similar to 10 nm), the decomposition in the bulk of the grain is suppressed, whereas the copper-enriched precipitates coherently bound to the matrix are predominantly formed at the grain boundaries of the material. The size and composition of the precipitates depend significantly on the type of grain boundaries: small precipitates (1.2-1.4 nm) have the average composition of Fe-40 at % Cu and arise in the vicinity of low-angle grain boundaries, while larger precipitates that have sizes of up to 4 nm and the average composition of Fe-60 at % Cu are formed near grain boundaries of the general type and triple junctions.
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| 6. |
- Karkin, I. N., et al.
(författare)
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Segregation of Mg to generic tilt grain boundaries in Al : Monte Carlo modeling
- 2015
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Ingår i: Materials Physics and Mechanics. - : Institute of Problems of Mechanical Engineering. - 1605-2730 .- 1605-8119. ; 24:3, s. 201-210
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Tidskriftsartikel (refereegranskat)abstract
- The formation of equilibrium segregations at tilt grain boundaries of several different types in Al-Mg alloys has been investigated in the framework of a combined approach, which includes molecular dynamics simulation and thermodynamic Monte Carlo modeling. The concentration profile of Mg distribution in GB vicinity was calculated in dependence on the alloy concentration and temperature. We found that width of segregation on generic GB determined by feature of their structure and is match bigger in comparison with special lowenergy GB. It is shown that segregation formation is control not only energy gain due to moving solute on GB but also interaction between solute atoms; as results, maximal enrichment of GB is not exceed 25 at.%. Possible origins of the formation of extended segregation on GB in materials subjected by severe plastic deformation have been discussed.
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| 7. |
- Karkin, A. E., et al.
(författare)
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Monitoring an insulator-metal transition in icosahedral AlPdRe by neutron irradiation
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:9
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Tidskriftsartikel (refereegranskat)abstract
- The intrinsic disorder effect on the electrical resistivity and magnetoresistance (MR) of icosahedral AlPdRe is studied by use of high-energy neutron irradiation. The icosahedral phase is preserved under irradiation with a decrease of x-ray peak intensity and volume of the coherent icosahedral phase. An insulator-metal transition, as observed in the MR, can be driven by the irradiation and is monitored by the resistance ratio R[=rho(4.2 K)/rho(295 K)]. The relation of MR vs R was found to be similar for samples of a widely different history.
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| 8. |
- Rapp, Östen, et al.
(författare)
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Electronic and atomic disorder in icosahedral AlPdRe
- 2008
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:11, s. 114120-
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Tidskriftsartikel (refereegranskat)abstract
- Relations between electronic and atomic disorder of i-AlPdRe have been investigated by studies of neutron irradiated and annealed samples. The advantage with this technique is that a single sample can be monitored over a significant range of varying electronic properties, without concern for any influence of varying impurities. X-ray diffraction, the electrical resistivity and its temperature dependence, and the magnetoresistance are studied. The results show that annealings of an irradiated sample lead to improvement of the atomic order, as reflected in increased intensities of the x-ray diffraction peaks, while electronic properties change in the direction of increasing electronic disorder towards a metal-insulator transition. The observed relation in quasicrystals that improved atomic structure is associated with stronger anomalies in transport properties is thus also seen in i-AlPdRe. In particular, the variation of the diffusion constant in the region of small values of the resistivity is found to be similar for annealed polygrain samples and for single grain samples with varying Pd concentration, as evaluated from literature data, indicating a similar development of electronic disorder in both sets of samples. However, the problem remains as to why the resistivity is small in single grain samples which are atomically well-ordered. The possibility of a strong sensitivity to concentration differences is pointed out.
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| 9. |
- Rapp, Östen, et al.
(författare)
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Neutron irradiation and annealing recovery in the AlPdRe quasicrystal
- 2006
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Ingår i: Low Temperature Physics, Pts A and B. - MELVILLE, NY : AMER INST PHYSICS. - 9780735403475 ; , s. 1307-1308
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Konferensbidrag (refereegranskat)abstract
- The effect of high energy neutron irradiation and subsequent low temperature annealings of icosahedral AlPdRe has been studied. For an insulating sample, brought into a metallic state by irradiation, the resistivity rho, at 4.2 K was found to increase with increased annealing temperature T-a, while the resistance ratio R=rho(4.2 K)/rho(295 K) increased according to a previously established general relation for as prepared samples. The intensity of X-ray diffraction peaks were found to increase with increasing T-a, thus indicating improved icosahedral order. It is concluded that irradiation and annealing offers a method to reversibly tune a single icosahedral AlPdRe sample over a range of R-values, that R is therefore not sensitive to external impurities, and is a useful parameter to tune the metal-insulator transition.
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