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

Hongtao Zhang,Yina Huang,Huanpo Ning,Ceri A Williams,Andrew J London,Karl Dawson,Zuliang Hong,Michael J Gorley,Chris R.M Grovenor,Gordon J Tatlock,Steve G Roberts,Michael J Reece,Haixue Yan,Patrick S Grant

doi:10.1016/j.jnucmat.2015.04.029

Abstract

Ferritic steels strengthened with Ti–Y–O nanoclusters are leading candidates for fission and fusion reactor components. A Fe–14Cr–0.4Ti+0.25Y2O3 (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 50MPa for 5min had a high density (99.6%), a random grain orientation and a bimodal grain size distribution (<500nm and 1–20μm). Synchrotron X-ray diffraction patterns showed bcc ferrite, Y2Ti2O7, FeO, and chromium carbides, while transmission electron microscopy and atom probe tomography showed uniformly dispersed Y2Ti2O7 nanoclusters of <5nm diameter and number density of 1.04×1023m−3. 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.

Highlights

The increasing global demand for energy coupled with a need to reduce carbon dioxide and other emissions associated with fossil fuels has revived interest in new-build nuclear energy generation
We show that the densification of the 14YT alloy using Spark plasma sintering (SPS) is significantly improved by increased sintering temperatures
The distribution peak shifted towards larger diameters with a mean diameter according to laser diffraction of 316 lm

Summary

Introduction

The increasing global demand for energy coupled with a need to reduce carbon dioxide and other emissions associated with fossil fuels has revived interest in new-build nuclear energy generation. The relatively recent confirmation of very fine nanoclusters (NCs) of 2–5 nm diameter in mechanically alloyed and heat treated ferritic alloys containing Ti using transmission electron microscopy (TEM) [3,4] and atom probe tomography (APT) [5,6] has opened a new area of study of ODS steels for nuclear applications, since finer NC dispersoid sizes give an increase in NC number density for an equivalent volume fraction of oxide-forming addition. Ji et al [32] attributed the development of a hetero-nanostructure containing nano (

Powder processing by MA and SPS

Microstructural characterisation

Powder morphology before and after MA

Effect of SPS sintering temperature on densification of 14YT alloys

Microstructure of 14YT alloys

Conclusions