作者: Victor V. Tcherdyntsev, S.D. Kaloshkin, I.A. Tomilin, E.V. Shelekhov, V.N. Serdyukov

361

作者: Alice Redermeier, Ernst Kozeschnik

摘要: In the present study, we investigate the performance of efficient pair potentials in comparison to accurate *ab initio* potentials as energy descriptions for Monte Carlo simulations of solid-state precipitation. As test scenario, we take the phase decomposition kinetics in binary Fe_{1-x}Cu_{x}. In a first effort, we predict thermodynamic equilibrium properties of bcc-rich Cu precipitates in an Fe-rich solution with a temperature and composition dependent Cluster Expansion. For this Cluster Expansion, combined *ab inito* and phonon calculations for various configurations serve as input. Alternatively, we apply the Local Chemical Environment approach, where the energy is described by computationally efficient pair potentials, which are calibrated on the first principles cluster expansion results. We observe that these fundamentally different approaches provide similar information in terms of the precipitate radius, chemical composition and interface constitution, however, the computational effort for the Local Chemical environment approach is significantly lower.

1564

作者: Rajashekhara Shabadi, Roland Taillard, Bertrand Radiguet, Jérémie De Baerdemaeker, Elke Leunis

摘要: Effect of the third alloying element Mn on Cu-precipitation was studied in a binary Fe-1.3% Cu alloy. Precipitation in both the alloys was investigated after homogenization treatment and subsequent artificial aging. Advanced characterization techniques such as Positron Annihilation Spectroscopy (PAS) and Tomographic Atom Probe (TAP) were used to establish the chemical composition, morphology, size and number density of the Cu-rich phases. Combined results of PAS and TAP were particularly useful in order to follow the Cu precipitation in the binary alloy. At short aging times, addition of Mn significantly increased the kinetics of hardening while its effect on the magnitude of precipitation strengthening is only marginal. It further increases the over-aging kinetics.

297

作者: Shigeto R. Nishitani, Atsuto Seko, Koretaka Yuge, Isao Tanaka

摘要: Our recently proposed calculating method reliably predicts the nucleation free energy
barrier of the homogeneous and coherent precipitations. Helmholtz free energy change is clearly
defined and calculated by the purely enthalpic and entropic contributions between the initial state of
the isolated solute atoms scattering around the matrix and the final state of the cluster of size n
traveling around the matrix. The enthalpic term is calculated by the reliable first principles
method and the entropic term is estimated by the ideal solution model. The vibrational free
energy is also included by the quasi-harmonic approximation. The model calculation was
performed on bcc Cu precipitations in the Fe-Cu system. The predicted values of the critical
number of 12 atoms and the critical free energy barrier of 0.6eV show good agreement with the
experimentally estimated ones for the annealing temperature of 773K and the initial concentration
of 1.4at%Cu.

2395

作者: Boris Minov, Luc Dupré, Milan J. Konstantinović

摘要: The effect of Cu-precipitation on the dislocation dynamics is studied by internal friction and magnetic after-effect measurements of thermally aged Fe1%CuC. We found that the copper precipitation in these alloys is accompanied by carbon redistribution. The results of both experiments showed that the hardening regime is governed by an increase of the dislocation density due to the growth of copper precipitates, while in the softening regime carbon redistribution plays a major role.

215

作者: Michel Perez, Fabien Perrard, Véronique Massardier-Jourdan, Xavier Kleber, Vincent Schmitt, Alexis Deschamps

摘要: The solubility limit of copper in iron at temperature lower than 700°C is not precisely
known because copper diffusion is too slow to reach an equilibrium with classical experimental techniques involving long range diffusion. However, fine precipitation of copper can lead to an equilibrium in a reasonable ageing time. Hence, coupling ThermoElectric Power and Small Angle X-ray Scattering techniques leads to a precise estimation of this solubility limit in the temperature range 500°C-700°C. Values obtained are confirmed by Tomographic Atom Probe and give results much higher than what is usually extrapolated from high temperature experiments.

631

作者: G. Martin, Pascal Bellon, Frédéric Soisson

97