| 1. |
- Li, Wei, et al.
(författare)
-
Generalized stacking fault energy of gamma-Fe
- 2016
-
Ingår i: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 96:6, s. 524-541
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the generalized stacking fault energy ( [GRAPHICS] -surface) of paramagnetic [GRAPHICS] -Fe as a function of temperature. At static condition, the face-centred cubic (fcc) lattice is thermodynamically unstable with respect to the hexagonal close-packed lattice, resulting in a negative intrinsic stacking fault energy (ISF). However, the unstable stacking fault energy (USF), representing the energy barrier along the [GRAPHICS] -surface connecting the ideal fcc and the intrinsic stacking fault positions, is large and positive. The ISF is calculated to have a strong positive temperature coefficient, while the USF decreases monotonously with temperature. According to the recent plasticity theory, the overall effect of temperature is to move paramagnetic fcc Fe from the stacking fault formation regime ( [GRAPHICS] K) towards maximum twinning ( [GRAPHICS] K) and finally to a dominating full-slip regime ( [GRAPHICS] K). Our predictions are discussed in connection with the available experimental observations.
|
|
| 2. |
- Li, Wei, et al.
(författare)
-
Generalized stacking fault energies of alloys
- 2014
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:26, s. 265005-
-
Tidskriftsartikel (refereegranskat)abstract
- The generalized stacking fault energy (gamma surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the. surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the. surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys. Based on our. surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.
|
|
| 3. |
- Li, Wei, et al.
(författare)
-
The effect of Al on the 475 degrees C embrittlement of Fe-Cr alloys
- 2013
-
Ingår i: Computational materials science. - : Elsevier BV. - 0927-0256 .- 1879-0801. ; 74, s. 101-106
-
Tidskriftsartikel (refereegranskat)abstract
- Aluminum addition to ferritic stainless steels was found to effectively suppress the deleterious 475 degrees C embrittlement resulting from the phase decomposition in concentrated Fe-Cr alloys. With the aim of revealing the mechanism behind this prosperous phenomenon, here we investigate the effect of Al on the interfacial energy and formation energy of Fe-Cr solid solutions. The interface between the decomposed Fe-rich alpha and Cr-rich alpha' phases carries a positive excess energy, which is of significant importance on determining the process of phase separation. Using ab initio alloy theory, we show that for the alpha-Fe70Cr20Al10/alpha'-Fe100-x-yCryAlx (0 <= x <= 10, 55 <= y <= 80) interface, the Al content (x) barely changes the interfacial energy. However, for the alpha-Fe100-x-yCryAlx/alpha'-Fe10Cr90 (0 <= x <= 10, 0 <= y <= 25) interface, the interfacial energy increases with Al content due to the variation of the formation energies of the Fe-Cr alloys upon Al alloying. Our ab initio results are supported by CALPHAD calculations, and suggest that the beneficial effect of Al on ferritic steels is mainly due to its thermodynamical effect on the alpha' phase.
|
|
| 4. |
- Li, Xiaoqing, et al.
(författare)
-
Elastic properties of vanadium-based alloys from first-principles theory
- 2012
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:1, s. 014105-
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of Cr and Ti on the fundamental mechanical properties of V-Cr-Ti alloys has been investigated using the all-electron exact muffin-tin orbitals method in combination with the coherent-potential approximation. The static lattice constant and elastic parameters have been calculated for the body-centered-cubic V1-x-yCrxTiy (0 <= x,y <= 0.1) random solid solution as a function of composition. Our theoretical predictions are in good agreement with the available experimental data. Alloys along the equicomposition region are found to exhibit the largest shear and Young's modulus as a result of the opposite alloying effects obtained for the two cubic shear elastic constants. The classical solid-solution hardening (SSH) model predicts larger strengthening effect in V1-yTiy than in V1-xCrx. By considering a phenomenological expression for the ductile-brittle transition temperature (DBTT) in terms of Peierls stress and SSH, it is shown that the present theoretical results can account for the variations of DBTT with composition.
|
|
| 5. |
- Lu, Song, et al.
(författare)
-
Composition and orientation dependence of the interfacial energy in Fe-Cr stainless steel alloys
- 2011
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 248:9, s. 2087-2090
-
Tidskriftsartikel (refereegranskat)abstract
- Using a first-principles quantum mechanical method, we calculated the (001) and (110) interfacial energies between the low temperature alpha and alpha' phases of Fe-Cr alloys as functions of chemical composition. Weshow that the interfacial energies and the interfacial energy anisotropy are highly composition dependent. In particular, the increasing interfacial energy anisotropy with decreasing compositional gap may induce different morphology of the decomposed phases for different compositions of the host alloys.
|
|
| 6. |
- Lu, Song, et al.
(författare)
-
Determining the minimum grain size in severe plastic deformation process via first-principles calculations
- 2012
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 60:11, s. 4506-4513
-
Tidskriftsartikel (refereegranskat)abstract
- Although the stacking fault energy (SFE) is a fundamental variable determining the minimum grain size (d(min)) obtainable in severe plastic deformation (SPD) processes, its accurate measurement is difficult. Here we establish the SFEs of binary Pd-Ag, Pd-Cu, Pt-Cu and Ni-Cu solid solutions using the axial interaction model and the supercell model in combination with first-principles theory. The two models yield consistent formation energies. For Pd-Ag, Pd-Cu and Ni-Cu, the theoretical SFEs agree well with those from the experimental measurements. For Pt-Cu no experimental results are available, and thus our calculated SFEs represent the first reasonable predictions. We discuss the correlation of the SFE and d(min), in SPD experiments and show that the d(min) values can be evaluated from first-principles calculations.
|
|
| 7. |
- Lu, Song, et al.
(författare)
-
First-principles study of fcc-Ag/bcc-Fe interfaces
- 2013
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:22, s. 224104-
-
Tidskriftsartikel (refereegranskat)abstract
- Ab initio calculations are employed to determine the lower and upper bounds of the interfacial energy and work of separation of a fcc-Ag/bcc-Fe interface. The strain-free interfacial energy of the coherent interface is taken as the lower bound and the interfacial energy of the commensurate incoherent interface as the upper bound of the interfacial energy of a realistic semicoherent interface. The latter is estimated by applying an averaging scheme based on the interfacial energies obtained for the coherent interfaces. Similar calculations are performed for determining the bounds of the work of separation. We justify the use of the averaging scheme by carrying out large supercell calculations for a semicoherent interface. For a Fe(110)/Ag(111) semicoherent interface, we show that taking either Fe or Ag as the underlying lattice, our averaging scheme can yield a reasonable estimation of the work of separation of the semicoherent interface. However, when taking Ag as the underlying lattice, the averaged interfacial energy of the semicoherent interface is significantly underestimated due to the magnetism. The structure and magnetism at the coherent and semicoherent interfaces are discussed.
|
|
| 8. |
- Lu, Song, et al.
(författare)
-
Magnetic effect on the interfacial energy of the Ni(111)/Cr(110) interface
- 2014
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 26:35, s. 355001-
-
Tidskriftsartikel (refereegranskat)abstract
- The work of separation and interfacial energy of the Ni(1 1 1)/Cr(1 1 0) interface are calculated via first-principles methods. Both coherent and semicoherent interfaces are considered. We find that magnetism has a significant effect on the interfacial energy, i.e. removing magnetism decreases the interfacial energy of the semicoherent interface by around 50% . Electronic, magnetic and atomic structures at the interface are discussed. An averaging scheme is used to estimate the work of separation and interfacial energy of semicoherent interfaces based on the results of coherent interfaces. The limitations of the scheme are discussed.
|
|
| 9. |
- Lu, Song, et al.
(författare)
-
Stacking fault energies of Mn, Co and Nb alloyed austenitic stainless steels
- 2011
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 59:14, s. 5728-5734
-
Tidskriftsartikel (refereegranskat)abstract
- The alloying effects of Mn, Co and Nb on the stacking fault energy (SFE) of austenitic stainless steels, Fe-Cr-Ni with various Ni contents, are investigated via quantum-mechanical first-principles calculations. In the composition range (c(Cr) = 20%, 8 <= c(Ni) <= 20%, 0 <= c(Mn), c(Co), c(Nb) <= 8%, balance Fe) studied here, it is found that Mn always decreases the SFE at 0 K but increases it at room temperature in high-Ni (c(Ni) greater than or similar to 16%) alloys. The SFE always decreases with increasing Co content. Niobium increases the SFE significantly in low-Ni alloys; however, this effect is strongly diminished in high-Ni alloys. The SFE-enhancing effect of Ni usually observed in Fe-Cr-Ni alloys is inverted to an SFE-decreasing effect by Nb for c(Nb) greater than or similar to 3%. The revealed nonlinear composition dependencies are explained in terms of the peculiar magnetic contributions to the total SFE.
|
|
| 10. |
- Punkkinen, Marko Patrick John, et al.
(författare)
-
Adhesion of the iron-chromium oxide interface from first-principles theory
- 2013
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:49, s. 495501-
-
Tidskriftsartikel (refereegranskat)abstract
- We determine the interface energy and the work of separation of the Fe/Cr2O3 interface using first-principles density functional theory. Starting from different structures, we put forward a realistic interface model that is suitable to study the complex metal-oxide interaction. This model has the lowest formation energy and corresponds to an interface between Fe and oxygen terminated Cr2O3. The work of separation is calculated to be smaller than the intrinsic adhesion energy of pure Fe or Cr2O3, suggesting that stainless steel surfaces should preferentially break along the metal-oxide interface. The relative stabilities and magnetic interactions of the different interfaces are discussed. Next we introduce Cr atoms into the Fe matrix at different positions relative to the interface. We find that metallic Cr segregates very strongly to the (FeCr)/Cr2O3 interface, and increases the separation energy of the interface, making the adhesion of the oxide scale mechanically more stable. The Cr segregation is explained by the enthalpy of formation.
|
|
