[SY-B1] Thermal stability of carbon-vacancy complexes in iron alloys and steels
Many industrially important alloys and steels are intentionally processed and explored, as metastable microstructures comprising a supersaturation of crystal defects in various forms of aggregation. Even though it is well understood that this microstructural complexity governs the material performance, the defects composition, thermal stability, how they are distributed and in which concentrations are not yet resolved experimentally. Hardened ferritic steels are important example where the lattice defects play deterministic role in their deformation behavior..
While it is long-known that carbon atoms dispersed in the matrix of iron and steels have an influence on the type of defects produced, it is only recently that atomistic simulations have clearly and quantitatively revealed that carbon atoms bind very strongly to vacancies, giving rise to the formation of a whole fauna of carbon-vacancy (mCnV) complexes. These complexes may act as traps for other defects, which suggests that hardening in iron and its alloys will be the consequence of the interaction of dislocations with complex defects formed by not only point defects but also carbon atoms. In this context, the formation of mCnV clusters is the triggering mechanisms for the growth of other complex defects.
In this study, the focus is given on the examination of relaxation processes which occur in the internal friction spectra of a variety of iron alloys and steels with different carbon concentrations, and out-of-equilibrium vacancy concentrations, achieved either by fast cooling (quenching) or plastic deformation. The relaxation peaks are analyzed on the basis of the Debye relaxation model and their activation energies and integrated intensities are determined. By comparing the results with theoretical calculation, positron annihilation spectroscopy results, and magnetic after effect measurements, the observed relaxation processes are assigned to the dissolution of carbon-vacancy (mCnV) clusters [1]. Dissolution energies and relaxation strengths (concentrations) of various mCnV clusters are found to be in the correct energy range according to density functional calculations.
[1] M. J. Konstantinović and L. Malerba, Phys. Rev. Mat. 1, 053602 (2017).
While it is long-known that carbon atoms dispersed in the matrix of iron and steels have an influence on the type of defects produced, it is only recently that atomistic simulations have clearly and quantitatively revealed that carbon atoms bind very strongly to vacancies, giving rise to the formation of a whole fauna of carbon-vacancy (mCnV) complexes. These complexes may act as traps for other defects, which suggests that hardening in iron and its alloys will be the consequence of the interaction of dislocations with complex defects formed by not only point defects but also carbon atoms. In this context, the formation of mCnV clusters is the triggering mechanisms for the growth of other complex defects.
In this study, the focus is given on the examination of relaxation processes which occur in the internal friction spectra of a variety of iron alloys and steels with different carbon concentrations, and out-of-equilibrium vacancy concentrations, achieved either by fast cooling (quenching) or plastic deformation. The relaxation peaks are analyzed on the basis of the Debye relaxation model and their activation energies and integrated intensities are determined. By comparing the results with theoretical calculation, positron annihilation spectroscopy results, and magnetic after effect measurements, the observed relaxation processes are assigned to the dissolution of carbon-vacancy (mCnV) clusters [1]. Dissolution energies and relaxation strengths (concentrations) of various mCnV clusters are found to be in the correct energy range according to density functional calculations.
[1] M. J. Konstantinović and L. Malerba, Phys. Rev. Mat. 1, 053602 (2017).