Fusion Engineering and Design 86 (2011) 2417–2420 Contents lists available at ScienceDirect Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes Influence of Y 2 O 3 and Fe 2 Y additions on the formation of nano-scale oxide particles and the mechanical properties of an ODS RAF steel Z. Oksiuta a,∗ , M. Lewandowska b , P. Unifantowicz c , N. Baluc c , K.J. Kurzydlowski b a Bialystok Technical University, Bialystok, Poland b Warsaw University of Technology, Warsaw, Poland c Ecole Polytechnique Fédérale de Lausanne (EPFL), Centre de Recherches en Physique des Plasmas, 5232 Villigen PSI, Switzerland article info Article history: Available online 16 February 2011 Keywords: ODS ferritic steel Mechanical alloying Hot isostatic pressing Nanoparticles Charpy impact properties Vickers microhardness abstract The main goal of this work was to manufacture an oxide dispersion strengthened (ODS) reduced activation ferritic steel from a pre-alloyed, gas atomised Fe–14Cr–2W–0.2Ti (in wt.%) powder mechanically alloyed with either 0.3%Y 2 O 3 or 0.5%Fe 2 Y particles and consolidated by hot isostatic pressing, and to investigate its microstructure, microhardness and Charpy impact properties. A lower oxygen content was measured in the ODS Fe 2 Y steel than in the ODS Y 2 O 3 steel. However, the mean size of nanoclusters in the ODS Fe 2 Y steel was found larger, whereas density was smaller, than in the ODS Y 2 O 3 steel. In addition, the nanoclusters in the ODS Fe 2 Y steel appear less stable upon thermal annealing at 1350 ◦ C for 1 h. Vickers microhardness measurements revealed that after HIPping the ODS Y 2 O 3 is about 40% harder (366 HV 0.1 ) than the ODS Fe 2 Y (260 HV 0.1 ). After heat treatment at 1350 ◦ C the microhardness of both alloys was found smaller by about 30%. The ODS Fe 2 Y steel was found to exhibit a much better Charpy impact behaviour, with an upper shelf energy of 8.8 J and a ductile- to-brittle transition temperature of -24 ◦ C. The differences in mechanical properties were discussed in terms of the oxygen content as well as in the mean size, number density and crystallographic structure of the nanoclusters. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels are promising candidate materials for first wall and breeding blanket applications in the future fusion reactors. These materials are attractive due to their excellent high temperature mechanical properties and good resistance to neutron irradiation [1–3]. Powder metallurgy (PM) technique yields the formation of small grains and a high density of nanoclusters enriched with Y, Ti and O. However, there are still some problems with the manufactur- ing route of these materials. It is commonly known that the main issue during fabrication by PM, especially during mechanical alloy- ing (MA), is to control and maintain the level of oxygen and carbon contents as low as possible [4,5]. Several studies have been per- formed on ODS reduced activation ferritic/martensitic (RAF/M) and ODS RAF steels in order to improve understanding of the influence of nanocluster composition on the microstructure and mechanical properties as well as on the nanocluster stability at high tem- ∗ Corresponding author at: Bialystok Technical University, Mechanical Depart- ment, Wiejska 45 C, 15-351 Bialystok, Poland. Tel.: +48 85 746 9254. E-mail address: oksiuta@pb.edu.pl (Z. Oksiuta). peratures [6]. From the literature, it is known that the Y–Ti–O nanoclusters are thermally very stable up to about 1300 ◦ C for short annealing times of about 1 h. However, there is little information available about the impact of the Fe 2 Y intermetallic compound on the mechanical properties and thermal stability of ODS RAF steels. Fe 2 Y is used instead of yttria during the mechanical alloy- ing process to reduce the oxygen content. In this paper the effects of two different types of reinforcing powders, namely yttria (Y 2 O 3 ) nano-particles (size 20–40 nm) and iron-yttrium (Fe 2 Y) intermetal- lic compound particles (size <45 m), have been investigated in terms of thermal stability up to 1350 ◦ C and Charpy impact prop- erties. 2. Experimental procedure A pre-alloyed ODS powder with the chemical composition of Fe–14Cr–2W–0.2Ti, produced by gas atomization in argon, was MA with 0.3Y 2 O 3 or 0.5Fe 2 Y (in wt.%) in a planetary ball mill for 20 h, in a hydrogen atmosphere, followed by hot isostatic press- ing (HIPping) at 1150 ◦ C under a pressure of 200 MPa for 3 h. After consolidation the ODS RAF steel samples were annealed for 1 h, in an argon atmosphere, at a temperature ranging between 850 and 1350 ◦ C. 0920-3796/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2011.01.023