Effect of solution treatment on spinodal decomposition during aging of an Fe-46.5 at.% Cr alloy

Abstract

Spinodal decomposition is a key phase transition in advanced materials and a significant effort is paid to the quantitative modeling of the phenomenon. The initial materials condition is often assumed to be random during modeling, but this may be an oversimplification. In this work, the effect of solution treatment above the miscibility gap, on spinodal decomposition during subsequent aging, has been investigated for an Fe-46.5 at.% Cr alloy. By atom probe tomography (APT), it is found that different extents of quenched-in Cr clustering exist after solution treatments at different temperatures. The clustering is pronounced at 800°C but decreases significantly with increasing temperature to 900°C. Thermodynamic Monte Carlo simulations show that there is a difference in atomic short range order between the different solution treatment temperatures. By APT, it is, furthermore, found that the kinetics of spinodal decomposition at 500°C, i.e., within the miscibility gap, is enhanced in the initial alloy condition, where Cr was less randomly distributed. These observations are supported by kinetic Monte Carlo simulations, predicting a similar but less pronounced qualitative effect on spinodal decomposition kinetics. Other possible reasons for the enhanced kinetics could be related to clustering of interstitial elements and/ or sigma phase, but neither was found in the experiments. Nonetheless, the observations in this work suggest that it is necessary to implement a modeling strategy, where the initial structure is properly accounted for when simulating spinodal decomposition.

Effect of cooling rate after solution treatment on subsequent phase separation during aging of Fe-Cr alloys: A small-angle neutron scattering study

“…Theoretical calculations predicted a similar tendency for the short-range order (SRO) parameter with a change of sign with increasing Cr content [17][18][19][20][21]. The tendency of Cr clustering in Fe-Cr alloys with higher Cr contents has also been shown by Zhou et al [10,11,22].…”

“…5f. However, it has been found that, at present, this effect seems to be difficult to handle even with atomistic simulations [11]. Further work on the modeling of the effect of the initial structure on the PS kinetics is therefore necessary to find a viable modeling route.…”

“…Instead, compositional fluctuations of Cr may occur already during the solution treatment and depends on the solution treatment temperature as well as the cooling rate after solution treatment [3][4][5][6][7][8][9][10][11]. Huston et al [3] simulated spinodal decomposition (SD) during continuous cooling, using the linearized Cahn-Hilliard model.…”

Morphology and Kinetics Evolution of Nanoscale Phase in Fe–Cr Alloys under External Strain

“…As one of the potential candidates for cladding and structural materials in future fusion reactors, Fe–Cr alloys, the basic alloy of high-chromium duplex stainless steels, exhibit a combination of beneficial properties [1,2,3,4]. The separation of the two-phase mixture of Fe-rich α phase and nanoscale Cr-rich α′ phases in ferrite [1,3] can induce embrittlement by enhancing the hardness of the alloys.…”

“…Therefore, the phase separation in Fe–Cr alloys has attracted a great deal of attention [5,6,7,8,9,10,11]. The clustering of Cr atoms inside the miscibility gap of Fe–Cr alloys was studied by Zhou et al [1] by kinetic Monte Carlo simulations and atom probe tomography (APT) experiment. Dahlström et al [8] studied the initial stage phase separation in Fe–Cr alloys by 3D-APT, and their results showed that phase separation is related to the nanostructure evolution and that Cr-rich regions form at the initial stages of decomposition.…”