Spinodal Decomposition in Multilayered Fe-Cr System: Kinetic Stasis and Wave Instability

Abstract

Used as fuel cladding in the Gen IV fission reactors, ODS steels would be held at temperatures in the range of 350°C to 600°C for several months. Under these conditions, spinodal decomposition is likely to occur in the matrix, resulting in an increase of material brittleness. In this study, thin films consisting of a modulated composition in Fe and in Cr in a given direction have been elaborated. The time evolution of the composition profiles during aging at 500°C has been characterized by atom probe tomography, indicating an apparent kinetic stasis of the initial microstructure. A computer model has been developed on the basis of the Cahn-Hilliard theory of spinodal decomposition, associated with the mobility form proposed by Martin (1990). We make the assumption that the initial profile is very close to the amplitudedependent critical wavelength. Our calculations show that the thin film is unstable relative to wavelength modulations, resulting in the observed kinetic stasis.

Structural Characterization of Phase Separation in Fe-Cr: A Current Comparison of Experimental Methods

“…[3] Due to the high technical relevance and its suitability as a model material for phase separation studies, binary Fe-Cr alloys have been extensively investigated. Theoretical tools such as phase-field modeling [4][5][6] and kinetic Monte Carlo [7][8][9][10] are frequently adopted to simulate the nanostructure evolution, and experimental tools such as Mo¨ssbauer spectroscopy (MS), [11][12][13][14] transmission electron microscopy (TEM), [4,5,[15][16][17] small-angle neutron scattering (SANS), [18][19][20][21][22][23][24][25] atom probe field ion microscopy (APFIM), [7][8][9]26,27] and later atom probe tomography (APT) [10,[28][29][30][31][32][33][34] have been applied. Most of the studies in the literature focus on the rather late stages of phase decomposition, when the embrittlement is already severe, and today it is still considered a major challenge to quantitatively characterize the nanostructure in technically relevant cases, when the length-scale is in the order of a few atomic distances and the concentration variations between a and a¢ are only a few atomic percent.…”