Multiscale investigations of nanoprecipitate nucleation, growth, and coarsening in annealed low-Cr oxide dispersion strengthened FeCrAl powder

Abstract

A major challenge in the design of oxide dispersion strengthened (ODS) FeCrAl alloys is the optimization of the fine-scale particle size distribution that provides both beneficial mechanical properties and irradiation resistance. To address this obstacle, the nucleation, growth, and coarsening of the fine-scale (Y,Al,O) nanoprecipitates within an ODS FeCrAl was studied using atom probe tomography (APT) and small-angle neutron scattering (SANS). Mechanically alloyed Fe-10Cr-6.1Al-0.3Zr+Y2O3 wt.% (CrAZY) powders were heated in-situ from 20-1000°C to capture the nucleation and growth the nanoprecipitates using SANS. Furthermore, CrAZY powders were annealed at 1000°C, 1050°C, and 1100°C at ageing times from 15 min to 500 h followed by either APT or magnetic SANS to study the structure, composition, and coarsening kinetics of the nanoprecipitates. In-situ SANS results indicate nanoprecipitate nucleation and growth at low temperatures (200-600°C). APT results indicate compositions corresponding to the YAG stoichiometry with a possible transition towards the YAP phase for larger precipitates after sufficient thermal ageing. However, magnetic SANS results suggest a defective structure for the nanoprecipitates indicated by deviations of the calculated A-ratio from stochiometric (Y,Al,O) phases. Particle coarsening kinetics follow n=6 power law kinetics, but the mechanism cannot be explained through the dislocation pipe diffusion mechanism. The potential effect of precipitate coarsening during pre-and post-consolidation heat treatments on the irradiation resistance of ODS FeCrAl alloys is discussed with respect to sink strength maximization.

Nano-oxide precipitation kinetics during the consolidation process of a ferritic oxide dispersion strengthened steel.

“…This is in agreement with previous studies that already detect precipitates after annealing at 600°C [31,32,34] and gives the onset of precipitation with an unprecedented precision. Massey et al demonstrated a similar continuous increase of scattering between 200, 400 and 500°C related to the nucleation and growth of Y-Al-O precipitates, different in terms of chemistry but close in terms of manufacturing process [33]. Simultaneously, the apparent volume fraction increases.…”

“…Precipitates were found in all specimens and were observed to coarsen slightly with increasing temperature. On a Fe-10Cr-11.5Al-Zr-Y ODS alloy, Massey et al observed the nucleation and growth of Y-Al-O precipitates from 200°C to 600°C by in-situ SANS analysis [33]. He et al performed in-situ isothermal holding with temperature ranging up to 1000°C using SANS on a Fe-9Cr ODS steel [34], however the limited flux of the neutron source resulted in sparse data in terms of time resolution.…”

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.…”

Effect of Hot Rolling on the Microstructure and Properties of Nanostructured 15Cr ODS Alloys with Al and Zr Addition

“…Oxide dispersion strengthened (ODS) alloys are considered as the promising structural material candidate for future advanced reactors, due to their excellent performance [ 1 , 2 , 3 ]. The combined addition of Al and Zr elements to the high Cr (≥13 wt.%) ODS alloys can significantly improve corrosion resistance and strength, based on excellent radiation resistance [ 4 , 5 ].…”