Processing and microstructure characterisation of oxide dispersion strengthened Fe–14Cr–0.4Ti–0.25Y2O3 ferritic steels fabricated by spark plasma sintering

Abstract

h i g h l i g h t sNanostructured ODS steels were successfully produced by SPS. Presence of Y 2 Ti 2 O 7 nanoclusters was confirmed by synchrotron XRD and microscopy. The chemistry of nanoclusters tested by ATP indicated they are Y-Ti-O oxides. a b s t r a c tFerritic steels strengthened with Ti-Y-O nanoclusters are leading candidates for fission and fusion reactor components. A Fe-14Cr-0.4Ti + 0.25Y 2 O 3 (14YT) alloy was fabricated by mechanical alloying and subsequently consolidated by spark plasma sintering (SPS). The densification of the 14YT alloys significantly improved with an increase in the sintering temperature. Scanning electron microscopy and electron backscatter diffraction revealed that 14YT SPS-sintered at 1150°C under 50 MPa for 5 min had a high density (99.6%), a random grain orientation and a bimodal grain size distribution (<500 nm and 1-20 lm). Synchrotron X-ray diffraction patterns showed bcc ferrite, Y 2 Ti 2 O 7 , FeO, and chromium carbides, while transmission electron microscopy and atom probe tomography showed uniformly dispersed Y 2 Ti 2 O 7 nanoclusters of <5 nm diameter and number density of 1.04 Â 10 23 m À3 . Due to the very much shorter consolidation times and lower pressures used in SPS compared with the more usual hot isostatic pressing routes, SPS is shown to be a cost-effective technique for oxide dispersion strengthened (ODS) alloy manufacturing with microstructural features consistent with the best-performing ODS alloys.

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.…”

“…[1][2][3][4][5] The widely practiced processing route for these ODS steels is essentially a two-step powder metallurgy process, consisting of mechanical alloying (MA) of 10-to 90-lm-diameter pre-alloyed Fe-based alloy powder together with a normally nano-sized (20 to 50 nm) Y 2 O 3 powder until fine-scale mixing/alloying is achieved, followed by consolidation of the powder into a bulk form typically by hot isostatic pressing (HIP) or related technique. [5][6][7][8][9][10] This MA approach is now well optimized and convenient for laboratory-based studies, providing good quality material sufficient for detailed microscopy, irradiation, and mechanical property assessment. However, in technological terms, disadvantages of the MA route include prolonged processing time, small batch size, tendency for contamination associated with the high specific area of the powder, and the high inherent cost of the pre-alloyed feedstock powders, which combine to restrict wider commercial implementation of the MA-based route.…”

Processing metal powders via field assisted sintering technology (FAST): A critical review

“…Boulnat et al [41,42] mechanically alloyed titanium hydride (TiH 2 ) and Y 2 O 3 powder with prealloyed Fe-14Cr-1W powder, followed by FAST at 1100°C for 20 min, showing a heterogeneous microstructure of submicron grains surrounded by larger grains, which provided a combination of high tensile strength and good ductility. Zhang et al [43] mechanically alloyed 0.4 wt-% titanium and 0.25 wt-% Y 2 O 3 powders with Fe-14Cr powder and FAST processed at 900-1150°C for 5 min. A density of 99.6% was reported with a heterogeneous microstructure ( < 500 nm grains surrounded by larger 1-20 μm grains) and good dispersoid distribution after FAST at 1150°C.…”

Inhibition Effect of Ti on the Formation of Martensite Lath in 14Cr Oxide Dispersion Strengthened Steel

“…Y 2 O 3 particles act as the pinning points for dislocation motion and grain boundaries migration, which plays a key role in ODS steel. Moreover, Y 2 O 3 is able to combine with Ti, forming the Y-Ti-O nanoparticles [34][35][36][37][38][39]. The main aim of Y 2 O 3 addition is to improve the dispersion strengthening effect and irradiation resistance of the ODS steel.…”