Bimodal Grain Size Distribution of Nanostructured Ferritic ODS Fe–Cr Alloys

Abstract

Oxide dispersion strengthened Fe–Cr alloys produced by mechanical alloying and spark plasma sintering were found to form different heterogeneous hardness distribution and microstructures depending on the milling parameters. Microstructure investigations by means of electron‐diffraction techniques and atom probe tomography revealed the presence of large particle‐free zones in one material, which is, together with the inhomogeneous deformation at short milling times, considered the main reason for the formation of a heterogeneous microstructure. The inhomogeneous temperature distribution in the sample volume during the sintering process is also expected to contribute to the formation of a heterogeneous grain size distribution in the final material.

SiC-ODS Alloy Gradient Nanocomposites as Novel Cladding Materials

“…The grain size is on average 15 μm but the microstructure has a mixture of very large grains (~45 μm) and plenty of small grains (4-5 μm). Such a bimodal grain size distribution has been previously observed in various SPS sintered ODS alloys[63][64][65]. The behavior is attributed to variations in dislocation density and inhomogeneous distribution of Y-Ti-O nanoclusters, which create inhomogeneous grain boundary pinning effects and also local variations in heat distribution due to the joule heating effect during the SPS process.…”

Effect of the heating rate on the microstructure of a ferritic ODS steel with four oxide formers (Y-Ti-Al-Zr) consolidated by spark plasma sintering (SPS)

“…This is the moment in which ultrafine grain size appears whose regions are not affected by the abnormal grain growing [134]. This abnormal growing appears in the micrometric regions whose behaviour is controlled by the heterogeneous energy and the pinning pressure exerted by particles [135,136,139,154,155]. Time is also a parameter which is determining the grain growth.…”

Development of a Novel Melt Spinning-Based Processing Route for Oxide Dispersion-Strengthened Steels

“…Unlike ODS steels produced by conventional MA-based processing, abnormal grain growth was not observed. [8,9,[37][38][39] It was not possible to confirm the exact reason for the comparative homogeneity of grain size but a likely factor may be the higher (up to four times) Y and Ti concentrations in the ribbons compared with typical ODS steels, [8,9,[37][38][39] producing a higher fraction of Y-and/or Ti-enriched oxides that pin grain growth during consolidation. This hypothesis is consistent with investigations of increasing the Y 2 O 3 fraction from 0.2 to 0.8 wt pct in an ODS steel produced by conventional MA-based processing, [40] which increased the pinning oxide fraction and approximately halved the proportion of lm-sized coarse grains.…”

“…This hypothesis is consistent with investigations of increasing the Y 2 O 3 fraction from 0.2 to 0.8 wt pct in an ODS steel produced by conventional MA-based processing, [40] which increased the pinning oxide fraction and approximately halved the proportion of lm-sized coarse grains. Since the recovery and recrystallization of ODS steels is determined by the balance between the driving force dominated by stored energy of cold work and the retarding force exerted by the Y-and/or Ti-enriched oxides, [39,41,42] another possible factor for the relatively homogeneous grain size distribution in the annealed alloy may be the lower amount of work hardening for the pulverized melt-spun ribbons compared with conventional MA powder, which reduced the driving force for recrystallization and grain growth at elevated temperature during consolidation.…”