Revisiting Temporal Evolution of Cu-Rich Precipitates in Fe–Cu Alloy: Correlative Small Angle Neutron Scattering and Atom-Probe Tomography Studies

Abstract

Binary Fe–Cu alloys are effective prototypes for investigating radiation-induced formation and growth of nanometric Cu-rich precipitates (CRPs) in nuclear reactor pressure vessels. In this report, the temporal evolution of CRPs during thermal aging of Fe–Cu binary alloys has been investigated by using complementary techniques such as atom probe tomography (APT) and small-angle neutron scattering (SANS). We report a detailed quantitative evolution of a rarely observed morphological transformation of Cu precipitates from spherical to ellipsoid with a significant change (approximately two times) in aspect ratio, an effect known to be associated with the 9R-3R structural transition of the precipitates. It is demonstrated through APT that the precipitates remain spherical up to 8 h, however, they subsequently convert to oblate ellipsoid upon further aging. SANS analysis also detected signs of this morphological transition in reciprocal space. Furthermore, SANS quantifies evolution of the precipitates and corroborates well with the APT results. Interestingly, the power-law exponent of the temporal evolution for mean size and number density agree reasonably well with the Lifshitz–Slyozov–Wagner model, in spite of the complex morphological evolution of the precipitates.

Monte Carlo study of Cu precipitation in bcc-Fe: temperature-dependent cluster expansion versus local chemical environment potentials

“…The simulations support the view that larger Cu-precipitates are typically almost free from Fe atoms at later stages of the precipitation process whereas they incorporate substantial amounts of Fe if they are in the nucleation stage [17]. This view is also supported by combined 3D-APT and SANS experiments [18], which reveal that the Cu-content of the precipitates increases with aging time and size. Similar results are also found by combining statistical sampling techniques and Monte Carlo (MC) simulations [19].…”

Metrology of small particles and solute clusters by atom probe tomography

“…6 the apparent size of the particles as a function of their real size as reported by experimental studies using both SAXS or SANS and APT. The crosses correspond to data from recent literature [41][42][43][44][45][46][47][48][49][50][51] covering a range of alloy systems, including maraging steels, Fe-Cu alloys, ODS-steels, Al-based alloys. We simply plot the values reported in tables or graphs.…”

“…In addition to the data points from Fig. 3, we have extracted data from recent literature as crosses [41][42][43][44][45][46][47][48][49][50][51]. The symbols outside the axis correspond to clusters in Al-Mg-Si alloys where SAS sizes are unavailable but they are expected to be very small.…”

A Combinatorial Approach to Reliable Quantitative Analysis of Small Nano-Sized Precipitates: A Case Study with α′ Precipitates in Fe–20 at% Cr Alloy

“…It is now quite a well-established practice to complement APT results by SANS (Briggs et al, 2017; Simm et al, 2017; Ahlawat et al, 2019; Tissot et al, 2019). Current work adds another complementary technique, TEM, to improve the quantification.…”

“…The determination of number density and volume fraction from SANS analysis, independently, is not attempted as it requires Δ ρ value in equation (2) as an input, which depends on the chemical composition of the precipitate and the matrix. Estimation of size of the precipitate is possible as the shape of the scattering curve depends on the form factor (function of radius only) [with arbitrary Δ ρ value in equation (2)] and the experimental curve can be simulated to determine the spherical equivalent precipitate size (Ahlawat et al, 2019; Sarkar et al, 2019).…”