Effect of Small Variations in Zr Content on the Microstructure and Properties of Ferritic ODS Steels Consolidated by SPS

Andrea García-Junceda,Mónica Campos,Dariusz Garbiec,José M Torralba,Marta Serrano,Eric Macía

doi:10.3390/met10030348

Abstract

Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3 oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently processed by spark plasma sintering (SPS) at two different heating rates: 100 and 400 °C·min−1. Non-textured bimodal microstructures composed of micrometric and ultrafine grains were obtained. The increase in Zr content led to a higher percentage of Zr nano-oxides and larger regions of ultrafine grains. These ultrafine grains also seem to be promoted by higher heating rates. The effective pinning of the dislocations by the Zr dispersoids, and the refining of the microstructure, have significantly increased the strength exhibited by the ODS steels during the small punch tests, even at high temperatures (500 °C).

Highlights

The harsh environments that will stand the Generation IV nuclear fission reactors have motivated the need of using materials capable to resist these extreme conditions
The oxide dispersion-strengthened (ODS) steels developed in this investigation were obtained by mechanical alloying (MA) of a prealloyed Fe-14Cr-5Al-3W powder supplied by Sandvik Osprey (Neath Port Talbot, UK), a high pure elemental Ti powder provided by GfE mbH (Nuremberg, Germany), an Y2 O3 nanopowder from TJ
The results indicate that the addition of Zr promotes the precipitation of new highly stabilised nano-oxides serving as effective pinning points for the dislocation movement, and favouring the increase of the strength of the material at all the temperatures tested, in comparison to the ODS

Summary

Introduction

The harsh environments that will stand the Generation IV nuclear fission reactors have motivated the need of using materials capable to resist these extreme conditions Within this framework, FeCrAl oxide dispersion-strengthened (ODS) steels have been considered in the past decades to withstand both the high operation temperatures and the neutron fluxes [1,2]. W was incorporated in order to increase the properties at high temperature by solid solution strengthening and to decrease the creep strain rate [7] In those cases where special requirements of corrosion resistance were needed, such as materials dealing with liquid metals and supercritical water, Al and Cr were suitable elemental candidates in order to improve the Metals 2020, 10, 348; doi:10.3390/met10030348 www.mdpi.com/journal/metals

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Conclusion