Decomposition kinetics in iron-chromium alloys

doi:10.1016/0378-4363(83)90413-8

Physica B+C

Volume 120, Issues 1–3, May 1983, Pages 392-396

https://doi.org/10.1016/0378-4363(83)90413-8 Get rights and content

Abstract

The decomposition kinetics of FeCr alloys aged at several temperatures have been investigated over a wide composition range by means of neutron small-angle scattering. The concentration and aging temperature dependence of time evolution of the scattered intensity are compared with predictions of recent theories and computer simulations. The experimental results show that the decomposition kinetics have much more complicated aspects than the results of the theories and the computer simulations although several essential features of the kinetics are explained by these predictions.

References (9)

J.W. Cahn
Acta Metall.
(1961)
J.S. Langer
Physica
(1974)
J.S. Langer et al.
Phys. Rev.
(1975)
K. Binder et al.
Phys. Rev. Lett.
(1974)

There are more references available in the full text version of this article.

Cited by (23)

Reconciliation between simulated and measured microstructures of metastable FeCr alloys: A phase field approach
2023, Acta Materialia
This work presents a novel phase field method for modeling the microstructure induced by the thermal decomposition of immiscible metastable binary alloys. This approach bypasses the problem associated with the modeling of the nucleation process introducing a random distribution of critical precipitates as an initial condition for the Cahn–Hilliard equation, extensively used to model the microstructure in the spinodal regime. The comparison between simulated and measured microstructures obtained from atom probe tomography measurements performed on ultra pure Fe $_{0.81}$ Cr $_{0.19}$ samples justifies the validity of our method. In particular, we succeeded modeling the evolution of the chemical composition of $α^{'}$ clusters produced during annealing. Such an evolution has been many times reported from atom probe tomography measurements but never explained. Moreover, these simulations allowed proposing a physical mechanism to explain the increase of the yield strength, observed in many annealed FeCr samples.
Quantitative evaluation of spinodal decomposition in thermally aged binary Fe-35 at.% Cr alloys by correlative atom probe tomography and small angle neutron scattering analyses
2021, Materialia
In this work, spinodal decomposition (SD) in Fe-35 at.% Cr alloy is quantified by correlatively combining two complimentary techniques namely, Atom Probe Tomography (APT) and Small Angle Neutron Scattering (SANS). In order to overcome the uncertainty often encountered in quantification of the characteristic SD parameters (wavelength λ_SD, amplitude A and volume fraction of Cr-rich α^/-phase $Φ$ ), we adopt the following: (i) utilize the unique specific attribute of a technique suitable for evaluating any particular SD parameter; (ii) incorporate such reliably extracted parameter as input for evaluating other parameters wherever applicable. This novel correlative approach builds on each other's strength and provides improved accuracy. λ_SD is determined independently from APT and SANS analyses. For evaluation of A and $Φ$ , APT analysis utilizes the value of λ_SD determined from SANS, whereas the phase compositions evaluated by APT are utilized in SANS analysis. With progressive phase separation, α/α^/ compositional difference increases continually (from 19.8% after 10 h to 48.2% after 500 h) along with concomitant contraction of the interface (from 1.92 nm to 1.55 nm), underscoring the distinctive characteristics of SD process. Signature of rarely observed early stage of phase separation in the form of a dense population (9.78 × 10²⁴/m³) of extremely small (0.67 nm radius) Cr-rich nanoclusters is registered after aging only for 1 h. In addition, temporal evolution of λ_SD clearly distinguishes early stage of SD (time exponent of 0.15) from the coarsening stage (time exponent of 0.29, 120 h onwards).
Small-angle neutron scattering quantification of phase separation and the corresponding embrittlement of a super duplex stainless steel after long-term aging at 300°C
2020, Materialia
Citation Excerpt :
Phase separation in Fe-Cr alloys has been investigated extensively because Fe-Cr is the base system for the important stainless steel alloy category [1–7].
Small-angle neutron scattering (SANS) was applied to quantify the nanostructural evolution during spinodal decomposition in a 25Cr-7Ni (wt.%) super duplex stainless steel isothermally aged at 300 °C, for up-to 48,000 h. Prior to the application on the 25Cr-7Ni alloy, the SANS methodology was validated by comparing results from SANS measurements on binary Fe-Cr alloys with atom probe tomography results. SANS results on the 25Cr-7Ni alloy indicated that decomposition wavelength decreased from 5.1 nm to 4.5 nm, whereas the amplitude increased from 15.0 to 33.4 at.%. This quantitative nanostructural evolution correlated to a hardening of the ferrite phase by 190 HV and a reduction of the sub-size Charpy-V impact toughness from 60 J to 25 J.
Effect of cooling rate after solution treatment on subsequent phase separation during aging of Fe-Cr alloys: A small-angle neutron scattering study
2017, Acta Materialia
The effect of cooling rate after solution treatment on the initial structure of concentrated binary Fe-Cr alloys and the effect of the initial structure on phase separation during subsequent aging has been investigated. The nano-scale compositional fluctuations in the bulk of the alloys are studied using small-angle neutron scattering and the results are compared with simulations using the Cahn-Hilliard-Cook (CHC) model. The alloys investigated represent different mechanisms of phase separation and at higher Cr content, when spinodal decomposition (SD) is favored, the initial Cr compositional fluctuations due to slow cooling after solution treatment reduce the kinetics of phase decomposition, whereas, at lower Cr composition when nucleation and growth is favored, the kinetics of phase decomposition is more rapid. Regardless of the nominal Cr composition of the alloy, the phase decomposition after extended aging up to 300 h at 748 K is always larger for the more non-random initial structure. The CHC modeling of the cooling process and subsequent initial aging (below 10 h) is in reasonable qualitative agreement with the experimental results for the Fe-40 wt.% Cr alloy decomposing via SD. However, the modeling approach must be refined for accurate quantitative modeling of the full SD process, including coarsening.
Kinetic analysis of spinodal decomposition process in Fe-Cr alloys by small angle neutron scattering
2000, Acta Materialia
The rate of spinodal decomposition depends on the spatial composition distribution. In order to estimate the time dependence of its rate experimentally, the structure change was investigated in Fe–30 at.% Cr and Fe–50 at.% Cr alloys aged at 748, 773, 798, and 823 K via small angle neutron scattering and a kinetic analysis of experimental data was carried out by using the Langer–Bar-on–Miller (LBM) theory. Their theory contains a rate term of a physical meaning similar to the diffusion coefficient. As a result, it becomes clear that the rate term corresponding to the diffusion coefficient decreases as decomposition advances and this fact can be explained by the modified LBM theory considering the composition-dependent mobility.
Excess free energy due to the composition gradient for ferromagnetic alloys
1999, Acta Materialia
The magnetic free energy for alloy systems contains the magnetic alloying excess free energy that is thermodynamically described by using the magnetic interaction parameter. We reveal the statistical meaning of this parameter by using the Ising model and Weiss's molecular field approximation. Ginzburg–Landau-type free energy, which includes the excess free energy of the composition gradient, is often used in order to simulate the phase separation process. Using the magnetic interaction parameter, we estimated the gradient energy due to spatial distribution of ferromagnetic atoms in the alloy. This study made possible the accurate simulation of phase separation in ferromagnetic alloys.

View all citing articles on Scopus

View full text

Non-equilibrium systemsDecomposition kinetics in iron-chromium alloys

Abstract

Acta Metall.

Physica

Phys. Rev.

Phys. Rev. Lett.

Non-equilibrium systems
Decomposition kinetics in iron-chromium alloys