Temperature-dependent free formation energies of Y, Ti and O in bcc Fe: A first principles study


Temperature-dependent free formation energies of Y, Ti and O in bcc Fe: A first principles study

Devaraj, M.; Posselt, M.

The dispersion of thermally stable nanosized oxide particles in the ferritic matrix remarkably increases the high temperature mechanical strength of these alloys. These alloys are referred to as Nanostructured ferritic alloys (NFA) or Oxide Dispersion Strengthened (ODS) steels and are potential candidate for use as structural materials in advanced fast breeder and fusion nuclear reactors. NFA possess excellent creep strength compared to conventional ferritic/martensitic steels. These alloys are also found to be highly resistant against long term neutron and radiation fluxes and act as sinks for transmutation helium, vacancies and self-interstitial. The physical mechanisms leading to the formation of these oxide nanoclusters in ferritic matrix is not yet fully understood. The basic properties of these clusters containing Y, Ti, O and vacancies are investigated by Density Functional Theory (DFT). Further, the formation and binding energies obtained from DFT calculations are being used as input for Monte Carlo simulations. In this multiscale approach, the results of calculations crucially depend on the input parameters obtained from DFT calculations. In previous studies only DFT data determined at T=0 have been used as inputs. The main objective of present work is to calculate the temperature-dependent free formation energies of Y, Ti and O point defects in bcc Fe. For this purpose DFT is used to obtain the corresponding vibrational free energies within the framework of the harmonic approximation. The present work is motivated by the assumption that the knowledge of the temperature dependence of free formation and binding energies is very important to understand the thermodynamics of the formation of the oxide nanoclusters at high consolidation temperatures. The results obtained in this work are compared with recent theoretical calculations and discussed in relation to experimental solubility data.

Keywords: iron; foreign atoms; free formation energy; DFT

  • Lecture (Conference)
    EUROMAT 2013, 08.-13.09.2013, Sevilla, Spain

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Publ.-Id: 19203