Publications (17)9.92 Total impact
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Article: Methodological challenges in combining quantum-mechanical and continuum approaches for materials science applications
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ABSTRACT: Multi-methodological approaches combining quantum-mechanical and/or atomistic simulations with continuum methods have become increasingly important when addressing multi-scale phenomena in computational materials science. A crucial aspect when applying these strategies is to carefully check, and if possible to control, a variety of intrinsic errors and their propagation through a particular multi-methodological scheme. The first part of our paper critically reviews a few selected sources of errors frequently occurring in quantum-mechanical approaches to materials science and their multi-scale prop-agation when describing properties of multi-component and multi-phase polycrystalline metallic alloys. Our analysis is illustrated in particular on the determination of i) thermodynamic materials properties at finite temperatures and ii) integral elastic responses. The second part addresses methodological challenges emerging at interfaces between electronic structure and/or atomistic modeling on the one side and selected continuum methods, such as crystal elasticity and crystal plasticity finite element method (CEFEM and CPFEM), new fast Fourier transforms (FFT) approach, and phase-field modeling, on the other side.Eur. Phys. J. Plus. 01/2011; 126(126). -
Article: Theory of size mismatched alloy systems: many-body Kanzaki forces
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ABSTRACT: A perturbative approach to determining the strain-induced effective interactions in binary alloys with large atomic size mismatch is presented. Using the chemical energy as the reference state, the strain-induced energy of the alloy is cast into a many-body (Kanzaki) force expansion that depends on both the configurational and displacive degrees of freedom. It is shown that the k-space energy expansion is valid for all wavelengths. The theory is then applied to the Cu3Au alloy where, due to the large difference between atomic sizes, considerable relaxations are observed from first-principles calculations. We found that the inhomogeneous contribution () dominates the strain energy in Cu3Au, whereas the homogeneous part (k = 0), notwithstanding its configurational dependence, contributes only a few per cent.Journal of Physics Condensed Matter 01/2008; 20(4):045207. · 2.55 Impact Factor -
Article: Temperature and concentration dependence of the effective pair interaction parameters in Ni-Pd from high-energy x-ray diffuse scattering
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ABSTRACT: The atomic interaction potential between different alloy components is encoded in the diffuse scattering caused by configurational short-range order and lattice distortions in the disordered phase. We performed in situ measurements of the x-ray diffuse scattering on macroscopic Ni55Pd45 and Ni25Pd75 single crystals in the temperature range from 20 °C up to 920 °C. We describe in detail the experiments and the data analysis where we use a formalism based on the spherical model and the Kanzaki-force concept in combination with a simulated annealing algorithm. We demonstrate that one single measurement is sufficient to retrieve the effective pair interaction potentials as well as thermal and elastic properties of the system. With only seven independent and physically motivated parameters we are able to describe short-range-order correlations, lattice distortions, and thermal parameters in a large temperature and concentration range.Phys. Rev. B. 05/2006; 73(18). -
Article: Competition between order and phase separation in Au-Ni.
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ABSTRACT: We have measured and theoretically analyzed the diffuse scattering in the binary alloy system Au-Ni, which has been proposed as a testing ground for theories of alloy phase stability. We found strong evidence that in the alloys Au3Ni and Au3Ni2, fluctuations of both ordering- and clustering-type are competing with each other. Our results resolve a long-standing controversy on the balance of relaxation and mixing energies in this alloy system and explain recent findings of ordering in thin Au-Ni films.Physical Review Letters 01/2006; 95(23):235703. · 7.37 Impact Factor -
Article: Interplay between long-range elastic and short-range chemical interactions in Fe-C martensite formation
Physical Review B, v.79, 224112-1-224112-5 (2009). -
Article: Omega-like diffuse X-ray scattering in Ti–V caused by static lattice distortions
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ABSTRACT: The diffuse scattering of body-centered cubic β-Ti–V was measured using high-energy synchrotron X-rays and two-dimensional detectors. The study included in situ experiments of the equilibrium β-phase and room temperature measurements of the quenched metastable state. The kinematical X-ray scattering revealed details in reciprocal space that could not be detected by the electron diffraction employed in previous studies. The signal was analyzed using a statistical thermodynamic approach based on physically motivated parameters. The characteristic features attributed to an ω-like structure or a “diffuse ω-phase” in the past are explained by static lattice distortions due to atomic size mismatch.Acta Materialia. -
Article: Ab initio based multi−scale approaches to the elasticity of polycrystals
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Article: Order/disorder transition of defects in ferrite: Ab initio based multi-scale approach
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Article: Martensite formation in dilute Fe-based solid solutions: Ab initio based multi-scale approach
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Article: Interplay between long-range elastic and short-range chemical interactions in Fe-C martensite formation
Physical Review B, v.79 (2009). -
Article: Determining the elasticity of materials employing quantum mechanical approaches: From the electronic ground state to the limits of materials stability
Steel Research International, v.82, 86-100 (2011). -
Article: Correlation correction algorithm for binary systems
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ABSTRACT: We develop a simple iterative algorithm for successive corrections of the correlation function and the free energy of a binary system. The main characteristics of the formalism are the use of an exact statistical-thermodynamic relations and the absence of the small parameters. The only approximation involved is the form of the configurational free energy which serves as a starting point for the iterative procedure. Two iterations within this algorithm for a dispersion-free and a microscopic model of fluctuations are presented starting with a one-site mean-field approximation. We obtain closed analytical expressions for the correlation function and thermodynamic potentials in each iteration. The algorithm can be widely applied, as in the calculation of phase diagrams, and segregation profiles at surfaces and thin films, and in k-space kinetic theories of atomic ordering and decomposition in alloys.Phys. Rev. B. 74(2). -
Article: Topological k-space refinement of the configurational energy of alloys
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ABSTRACT: We present an iterative refinement procedure for the construction of k-space interactions in binary alloys. The procedure consists of successive steps, which refine the topological features of the k-space interactions and naturally incorporate long-ranging interactions. We apply this scheme to the fcc lattice and create a limited set of ordered structures, which allows us to calculate interactions at selected k-space points. We demonstrate that the energies of a few ab initio calculated input structures are sufficient for the construction of the relevant k-space interaction parameters in Cu3Au.Phys. Rev. B. 72(14). -
Article: Analytical correlation correction of the chemical potential of solid solutions
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ABSTRACT: This version is available at the following Publisher URL: http://prb.aps.org -
Article: q-space configurational energy and short-range order in alloys with atomic size mismatch
Physical Review B, v.65 (2002). -
Article: Kinetic correlation effects in binary alloys
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ABSTRACT: We derive analytical expressions for the relaxation time of disordered binary alloys, which quantify the influence of correlations on the relaxation behavior of the concentration wave amplitudes within a linear kinetic theory. The main characteristic of our model is that it does not limit the effective radius of atomic interaction and correlations in the system. Lattice displacements caused by atomic size mismatch are naturally contained in the formalism. The results are applied to an ordering model system. Using two iterations of the recently developed correlation correction algorithm, we show that only a highly accurate correlation function allows one to predict the most stable modes of the fluctuation spectrum.Phys. Rev. B. 77(5). -
Article: Orientational ordering of interstitial atoms and martensite formation in dilute Fe-based solid solutions
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ABSTRACT: We study the thermodynamic stability of dilute C, N, O, B, and C+N interstitial distributions in bcc iron, combining parameter-free density functional theory (DFT) in the generalized gradient approximation and microscopic elasticity theory. This scheme allows us to fully capture the long-range elastic impurity-impurity interactions using moderately sized DFT calculations. Employing this approach we compute temperature-concentration phase diagrams including the effects of external pressure, and provide direct insight into the formation mechanisms of martensite. For all investigated impurities, except for B, tetragonal states are predicted to be preferred even at low impurity concentrations. The preference is shown to originate from a thermodynamically driven orientational ordering of the interstitials.Phys. Rev. B. 83(18).
