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

Abstract

Oxide Dispersion Strengthened (ODS) steels are candidates for nuclear applications. ODS are produced by mechanical alloying of Fe-14Cr, Y2O3 and TiH2 powders and consolidation at 1100°C, resulting in finely dispersed nano-oxides. Their precipitation kinetics has been quantitatively determined by in-situ Small Angle X-ray Scattering during continuous heating up to 1100°C. Clusters, found in the as-milled state start growing at 450°C until 1100°C, while almost no coarsening was recorded during subsequent isothermal annealing. The nano-oxides resulting from these in-situ experiments were found to be representative of those in materials processed by hot isostatic pressing and hot extrusion.

Chemical and structural evolution of nano-oxides from mechanical alloying to consolidated ferritic oxide dispersion strengthened steel

“…The SAXS integrated intensity (from which apparent volume fraction can be calculated) of this study displayed an initial increase followed by a decrease before a stabilization after reaching the 900 °C plateau. The same behavior was more clearly identified in our previous paper, which allowed to monitor the precipitation kinetics of Fe-14Cr ODS nano-oxides up to 1100 °C in-situ with an excellent time resolution, but was not fully understood at the time [60]. The apparent volume fraction measured by SAXS or SANS is the product between the actual volume fraction and the contrast in scattering length density [61].…”

“…Our previous article focused on the description of the precipitation kinetics (evolution of mean radius comparing two heating rates) using in-situ SAXS is available in reference [60], the present section will therefore only focus on the chemical evolution of the nano-oxides, especially using the anomalous scattering analysis (previously not reported). The SAXS intensity curves for the in-situ heat treatment and for interrupted thermal treatments can be founded in ref.…”

Innovative method of ODS steels manufacturing by direct introduction of pyrochlore phase through milling

“…The precipitates number density of both samples are in the range of 10 23 precipitates/m 3 . This value is a slighlty smaller than the typical values for ODS steel found in the literature [29], [32], [33] .. 0.5P-I3 and 0.5CV-I3 samples both display a close density of nanoprecipitates.…”

Precipitation kinetics in metallic alloys: Experiments and modeling

“…SAS is a diffraction technique, where the intensity scattered in reciprocal space by the precipitates depends on the contrast in scattering length density (electronic density for X-rays) between the precipitates and matrix, and on the size, morphology and size distribution of the precipitates. Recording the X-ray signal in-situ during a heat treatment allows, in principle, to follow any kind of kinetics: precipitation kinetics has been monitored from room temperature up to 1100°C for some oxide-dispersion steels [30], or in combination with plastic deformation [31] and even during welding [32]. SAS is particularly adapted to characterize very small objects, since there is no lower limit to the size it can detect.…”

“…The second situation where non-isothermal effects are important happens when ageing is carried out using non-isothermal routes. In most industrial situations, the heating of parts to the ageing temperature can take several hours, which renders ageing non-isothermal by necessity [30,248]. In some cases, the ageing treatments are purposely non-isothermal or multi-stage, usually with increasing temperature (like the two-stage classical ageing of 7xxx series Aluminum alloys [246]) or more complex (like the retrogression and re-ageing treatment of the same alloys [130] or two stage ageing to promote bi-modal precipitate distributions [249]).…”