Neutron small-angle scattering study of unmixing in FeCr alloys

Bley, F.

doi:10.1016/0956-7151(92)90094-u

Cited by 88 publications

(69 citation statements)

References 25 publications

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“…The value of K after 10 h ageing at 773 K also agrees well with the reported modulation wavelength measured by APT, 5 see Table I. The obtained exponents (a 0 ¼ 0.10-0.11, a 00 ¼ 0.67-0.86) are in the same range as the available literature data, [6][7][8]10,12,26 although a 0 is slightly smaller than usually observed. This may be related to the early stages of decomposition studied, since the data presented in, e.g., Ref.…”

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confidence: 80%

“…Direct observations from three dimensional APT investigations have also demonstrated the transition of the phase separation mechanism from nucleation-and-growth to spinodal decomposition in the composition range of 25-35% Cr at 773 K. 13 Whereas the spinodal nature of the decomposition process have been questioned for similar systems, e.g., Fe-Cr-Co, 14 based on the development of the SANS invariant during ageing, similar studies of the Fe-Cr binary system show no such indications. 6 During the spinodal decomposition, a characteristic interconnected structure with nano-scale modulations of the composition forms. This results in the appearance of an interference peak in the structure factor at scattering vector Q p (Q ¼ 4p sin h=k, where k is the neutron wavelength and h is half the scattering angle) corresponding to a characteristic length scale K ¼ 2p=Q p , usually interpreted as the modulation wavelength of the decomposed structure.…”

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confidence: 99%

“…[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.…”

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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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confidence: 80%

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confidence: 99%

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confidence: 99%

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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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“…Vintaykin et al 7) showed a good agreement between experimental results and the Cahn-Hilliard theory of spinodal decomposition. In contrast, several works 8,9) reported that the decomposition kinetics can be described satisfactorily by the non linear theories of spinodal decomposition in this type of alloys. Besides, the phase decomposition has been also studied in Fe-Cr alloys by the Monte Carlo simulation.…”

Section: Introductionmentioning

confidence: 95%

Spinodal Decomposition in an Fe-32 at%Cr Alloy during Isothermal Aging

et al. 2009

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Phase decomposition was studied during aging of an Fe-32 at%Cr alloy by means of TEM, hardness and the numerical solution of the linear Cahn-Hilliard differential partial equation 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 this alloy. The growth kinetics of phase decomposition was observed to be very slow during the early stages of aging and it increased considerably as the aging progressed. The morphology of decomposed phases consisted of an interconnected irregular shape with no preferential alignment for short aging times and a further aging caused the change to a plate shape of the decomposed Cr-rich phase aligned in the h110i directions of the Fe-rich matrix. The increase in hardness seems to be associated with the coherency and nanometer size of the spinodally-decomposed phases in the aged alloy.

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“…For such applications, these alloys face severe embrittlement problems because their service temperature lies in the range of 373-823 K. In this temperature range, the response of the material to extreme conditions (high temperature, irradiation as the origin of swelling and corrosion) is partly determined by the extent of the α -α phase separation. Thus, in the last few years, the binary Fe-Cr model alloys have been the focus of significant basic research [3][4][5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%