Quantitative Evaluation of Spinodal Decomposition in Fe-Cr by Atom Probe Tomography and Radial Distribution Function Analysis

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.

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“…After constructing the normalized RDFs, the amplitude of phase decomposition could be estimated using the following equation [29].…”

Section: Methodology Experimentsmentioning

confidence: 99%

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

et al. 2016

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“…The decomposition process in Fe-Cr is typically investigated by transmission electron microscopy (TEM), 1 M€ ossbauer spectroscopy, 2,3 atom probe tomography (APT), 4,5 or smallangle neutron scattering (SANS). [6][7][8] While each technique has its specific advantages, only SANS readily offers the possibility to perform time-resolved in-situ measurements at elevated temperatures.…”

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confidence: 99%

Early stages of spinodal decomposition in Fe–Cr resolved by in-situ small-angle neutron scattering

Hörnqvist

Thuvander

Steuwer

et al. 2015

Applied Physics Letters

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In-situ, time-resolved small-angle neutron scattering (SANS) investigations of the early stages of the spinodal decomposition process in Fe-35Cr were performed at 773 and 798 K. The kinetics of the decomposition, both in terms of characteristic distance and peak intensity, followed a power-law behaviour from the start of the heat treatment (a 0 ¼ 0.10-0.11 and a 00 ¼ 0.67-0.86). Furthermore, the method allows tracking of the high-Q slope, which is a sensitive measure of the early stages of decomposition. Ex-situ SANS and atom probe tomography were used to verify the results from the in-situ investigations. Finally, the in-situ measurement of the evolution of the characteristic distance at 773 K was compared with the predictions from the Cahn-Hilliard-Cook model, which showed good agreement with the experimental data (a 0 ¼ 0.12-0.20 depending on the assumed mobility). Spinodal decomposition of the bcc phase in Fe-Cr alloys into an Fe-rich and a Cr-rich phase is a widely studied phenomenon. The reason is two-fold: First, the system is the basis of the industrially important stainless steel family, where the decomposition of the bcc phase in ferritic, duplex and to some extent martensitic and d-ferrite containing austenitic grades, is partially responsible for degradation of the mechanical properties over time during elevated temperature exposure in service. Second, the Fe-Cr system is ideal to study the fundamentals of the spinodal decomposition process, since it offers a combination of a wide miscibility gap, a rather wide temperature range where the kinetics of the decomposition is suitable for practical measurements and minor coherency strains.The decomposition process in Fe-Cr is typically investigated by transmission electron microscopy (TEM), 1 M€ ossbauer spectroscopy, 2,3 atom probe tomography (APT), 4,5 or smallangle neutron scattering (SANS). [6][7][8] While each technique has its specific advantages, only SANS readily offers the possibility to perform time-resolved in-situ measurements at elevated temperatures. However, so far only very few investigations have taken advantage of this possibility of direct continuous tracking of the kinetics without any specimen-to-specimen variations in composition, starting structure, or isothermal temperature. For the Fe-Cr(-Ni) system, there are only two readily available reports of in-situ SANS experiments, 9,10 although other systems have been investigated more recently, e.g., Fe-Co-Mo. 11 In Refs. 9 and 10, acquisition times of several hours were used, which resulted in poor temporal resolution. Furusaka et al. 12 used in-situ SANS to investigate the critical scattering of Fe-Cr alloys in the vicinity of the Curie temperature, but the subsequent investigations of aged alloys were performed ex-situ.The existence and location of the spinodal in the binary Fe-Cr system are today rather well described, both from thermodynamic modelling and experiments (see, e.g., Ref. 13, and references therein). Direct observations from three dimensional APT investigations have also...

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“…In contrast, the phase decomposition was reported recently (Jing et al, 2013) to take place via spinodal decomposition during aging of Fe-Cr alloys with Cr contents between 25 and 36 wt.% Cr.…”

Section: Introductionmentioning

confidence: 69%

Análisis de la descomposición espinodal en aleaciones Fe-32 y 40 %at. Cr utilizando el método de campo de fases basado en las ecuaciones lineal y no lineal de Cahn y Hilliard

et al. 2016

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Spinodal decomposition was studied during aging of Fe-Cr alloys by means of the numerical solution of the linear and nonlinear Cahn-Hilliard differential partial equations using the explicit finite difference method. Results of the numerical simulation permitted to describe appropriately the mechanism, morphology and kinetics of phase decomposition during the isothermal aging of these alloys. The growth kinetics of phase decomposition was observed to occur very slowly during the early stages of aging and it increased considerably as the aging progressed. The nonlinear equation was observed to be more suitable for describing the early stages of spinodal decomposition than the linear one. RESUMEN: Análisis de la descomposición espinodal en aleaciones Fe-32 y 40 %at. Cr utilizando el método de campo de fases basado en las ecuaciones lineal y no lineal de Cahn y Hilliard.La descomposición espinodal se estudió durante el envejecido de aleaciones Fe-Cr mediante la solución numérica de las ecuaciones diferenciales parciales lineal y no linear de Cahn y Hilliard usando el método de diferencias finito explícito. Los resultados de la simulación numérica permitieron describir apropiadamente el mecanismo, morfología y cinética de la descomposición de fases durante el envejecido isotérmico de estas aleaciones. La cinética de crecimiento de la descomposición de fases ocurrió muy lentamente durante las primeras etapas de envejecido, y se incrementó considerablemente con el tiempo de envejecido. La ecuación no lineal parece ser más apropiada para describir las primeras etapas de la descomposición espinodal que la ecuación lineal.

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Quantitative Evaluation of Spinodal Decomposition in Fe-Cr by Atom Probe Tomography and Radial Distribution Function Analysis

Cited by 110 publications

References 46 publications

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

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

Early stages of spinodal decomposition in Fe–Cr resolved by in-situ small-angle neutron scattering

Análisis de la descomposición espinodal en aleaciones Fe-32 y 40 %at. Cr utilizando el método de campo de fases basado en las ecuaciones lineal y no lineal de Cahn y Hilliard

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