The 475°C embrittlement in Fe–20Cr and Fe–20Cr–X (X=Ni, Cu, Mn) alloys studied by mechanical testing and atom probe tomography

Hedström, Peter; Huyan, Fei; Zhou, Jing; Wessman, Sten; Thuvander, Mattias; Odqvist, Joakim

doi:10.1016/j.msea.2013.03.016

Cited by 59 publications

(26 citation statements)

References 16 publications

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“…[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.…”

Section: Introductionmentioning

confidence: 99%

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

Odqvist

Colliander

et al. 2016

Metall Mater Trans A

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Self-assembly due to phase separation within a miscibility gap is important in numerous material systems and applications. A system of particular interest is the binary alloy system Fe-Cr, since it is both a suitable model material and the base system for the stainless steel alloy category, suffering from low-temperature embrittlement due to phase separation. Structural characterization of the minute nano-scale concentration fluctuations during early phase separation has for a long time been considered a major challenge within material characterization. However, recent developments present new opportunities in this field. Here, we present an overview of the current capabilities and limitations of different techniques. A set of Fe-Cr alloys were investigated using small-angle neutron scattering (SANS), atom probe tomography, and analytical transmission electron microscopy. The complementarity of the characterization techniques is clear, and combinatorial studies can provide complete quantitative structure information during phase separation in Fe-Cr alloys. Furthermore, we argue that SANS provides a unique in-situ access to the nanostructure, and that direct comparisons between SANS and phase-field modeling, solving the non-linear Cahn Hilliard equation with proper physical input, should be pursued.

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Section: Introductionmentioning

confidence: 99%

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

Odqvist

Colliander

et al. 2016

Metall Mater Trans A

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“…The coherency strains generated between the Fe-rich (a) and Cr-rich (a') domains cause hardening [3], which presumably leads to the embrittlement. Furthermore, it has been reported that, e.g., solute clustering [4], C segregation [5], and G-phase formation [6,7] could also contribute to the embrittlement in Fe-Cr-based multicomponent alloys.…”

Section: Introductionmentioning

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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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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“…The aim is to investigate the short-time kinetics of spinodal decomposition in the relevant stages where embrittlement often occurs. 18 Furthermore, the in-situ a) magnus.hornqvist@chalmers.se …”

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“…The aim is to investigate the short-time kinetics of spinodal decomposition in the relevant stages where embrittlement often occurs. 18 Furthermore, the in-situ data are used to make comparisons with theoretical predictions from the Cahn-Hilliard-Cook (CHC) model. 7,19 The binary Fe-Cr alloy was produced by vacuum arc melting (see Ref.…”

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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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The 475°C embrittlement in Fe–20Cr and Fe–20Cr–X (X=Ni, Cu, Mn) alloys studied by mechanical testing and atom probe tomography

Cited by 59 publications

References 16 publications

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

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

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

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