Analytical characterization of secondary phases and void distributions in an ultrafine-grained ODS Fe─14Cr model alloy

Proceedings of the: The 14th International Conference on Fusion Reactor Materials (ICFRM-14) was held at the Sapporo Convention Center in Sapporo, Japan from 7 to 12 September 2009.Two model Fe─14Cr alloys, one containing 0.3 wt.% of Y₂O₃ particles, were fabricated by mechanical alloying of Fe and Cr elemental powders under a He atmosphere. They were subsequently consolidated and thermomechanically treated to produce ultra-fine grained materials. Cr-carbides and oxides were found in both alloys. The oxide dispersion-strengthened (ODS) alloy also contained a fine dispersion of nanoparticles, some of them having a Y─O rich core and a Cr-rich shell. Nanometric sized voids were found in both materials, often attached to secondary phases, dislocations and grain boundaries. Their sizes were significantly smaller in the ODS alloy.This research has been supported by the Fusion Energy Materials Science (FEMaS) FP7 coordination action and the IP3 FP6 ESTEEM project under Contract No. 026019. The financial support from European Fusion Development Agreement (Contract No. 09-240), the Ministerio de Innovacion y Ciencia (Project No. ENE 2008-06403-C06-04 and Juan de la Cierva programme) and the Comunidad de Madrid, through the program ESTRUMAT-CM, Grant S-0505/MAT/0077Publicad

Tensile and fracture characteristics of oxide dispersion strengthened Fe─12Cr produced by hot isostatic pressing

This study is presented of: The Fifteenth International Conference on Fusion Reactor Materials (ICFRM-15) was held October 16–22, 2011, at the Charleston Marriott Hotel in Charleston, South Carolina (American United States).The mechanical characteristics of a model oxide dispersion strengthened (ODS) alloy with nominal composition Fe─12 wt%Cr─0.4 wt%Y₂O₃ were investigated by means of microhardness measurements, tensile tests up to fracture in the temperature range of 298─973 K, and fracture surface analyses. A non-ODS Fe─12 wt%Cr alloy was also studied to assess the real capacity of the oxide dispersion for strengthening the alloy. The materials were produced by mechanical alloying followed by hot isostatic pressing consolidation and heat treatment at 1023 K. The strengthening effect of the oxide nanodispersion was effective at all temperatures studied, although the tensile strength converges towards the one obtained for the reference alloy at higher temperatures. Moreover, the ODS alloys failed prematurely at T < 673 K due to the presence of Y-rich inclusions, as seen in the fracture surface of these alloys.Spanish Ministry of Science and Innovation (project ENE 2010-17462), the Comunidad de Madrid through the program ESTRUMAT-CM (Grant S0505/MAT/0077).Publicad

Powder Particle Size Effects on Microstructure and Mechanical Properties of Mechanically Alloyed ODS Ferritic Steels

Reduced activation ferritic (RAF) steels are expected to be widely used in challenging nuclear industrial applications under severe thermo-mechanical regimes and intense neutron loads. Therefore, actual research panorama is facing the strengthening strategies necessary to maximize both performance and endurance under these conditions. Oxide dispersion strengthened (ODS) RAF steels are leader candidates as structural materials in fusion energy reactors thanks to the reinforcement obtained with a fine dispersion of nanosized oxides in their matrix. In this study, the influence of the initial powder particle size and the selected processing route on the final material has been investigated. Two RAF ODS steels coming from atomized pre-alloyed powders with nominal particle powder sizes of 70 and 30 µm and composition Fe-14Cr-2W-0.4Ti-0.3Y$_{2}$O$_{3}$ (wt. %) were manufactured by mechanical alloying. Alloyed powders were compacted by hot isostatic pressing, hot crossed rolled, and annealed at 1273 K. Initial powder particle size differences minimize after milling. Both steels present an almost completely recrystallized material and similar grain sizes. The same type and distributions of secondary phases, Cr-W-rich, Ti-rich, and Y-Ti oxide nanoparticles, have been also characterized by transmission electron microscopy (TEM) in both alloy samples. The strengthening effect has been confirmed by tensile and Charpy impact tests. The two alloys present similar strength values with slightly better ductile brittle transition temperature (DBTT) and ductility for the steel produced with the smaller powder size

Efecto de la extrusión angular en las propiedades mecánicas del Ti reforzado con partículas de Itria

Comunicaciones presentadas en: XXVI Encuentro del grupo Español de Fractura,Santander, 25 marzo 2009.Se ha investigado la mejora de las propiedades mecánicas del Ti reforzado con una dispersión de partículas de Y₂O₃. Se han preparado muestras de Ti y Ti-0,6wt%Y₂O₃ mediante sinterizado seguido de HIP. Los materiales se han sometido a extrusión angular con sección constante (ECAP) con el fin de refinar su microestructura y mejorar sus propiedades mecánicas. Se han estudiado la microestructura mediante microscopía óptica y electrónica y el comportamiento mecánico a partir de ensayos de tracción entre 295 y 773 K. La extrusión angular induce una mejora cualitativa de las propiedades mecánicas del Ti-0,6Y₂O₃. Este material, que es completamente frágil a T ≤ 473 K, adquiere una buena ductilidad a esta temperatura después de la 1ª pasada de ECAP. Cuando el material se somete a 4 pasadas, puede adquirir a 373 K resistencias mecánicas de 986 MPa y alcanzar deformaciones de fractura del orden del 23 %.Ti and Ti-0.6wt%Y₂O₃ were produced by sintering and subsequent hot isostatic pressing (HIP). Samples of these materials were processed by equal channel angular pressing (ECAP) to induce their microstructural refinement and improvement of their mechanical properties. The microstructural characteristics and the mechanical behavior of these materials have been investigated using techniques of microscopy, and tensile tests in the temperature range 295 – 773 K. The ECAP treatment induces a qualitative improvement of the mechanical properties of P/M Ti-0.6wt%Y₂O₃. This material in as-HIP condition is completely brittle at T≤ 473 K but becomes ductile at this temperature after a single ECAP pass. After being processed by 4 passes via route BA the material can attain a tensile strength as high as 986 MPa with a fracture strain of 23 %.Este proyecto ha sido financiado por la Dirección General de Dirección General de Investigación del MEC a través del proyecto MAT2004-1819, y por la Dirección General de Universidades e Investigación de la Comunidad de Madrid mediante el programa ESTRUMAT-CM (MAT/77)Publicad

Microstructure and mechanical behavior of ODS and non-ODS Fe-14Cr model alloys produced by spark plasma sintering

In this work the spark plasma sintering (SPS) technique has been explored as an alternative consolidation route for producing ultra-fine grained Fe–14Cr model alloys containing a dispersion of oxide nanoparti-cles. Elemental powders of Fe and Cr, and nanosized Y₂O₃ powder have been mechanically alloyed in a planetary ball mill and rapidly sintered in a spark plasma furnace. Two alloys, with nominal compositions Fe–14%Cr and Fe–14% Cr–0.3%Y₂O₃ (wt.%), have been fabricated and their microstructure and mechanical properties investigated. The results have been compared with those obtained for other powder metal-lurgy processed alloys of the same composition but consolidated by hot isostatic pressing. The SPS tech-nique under the present conditions has produced Fe–14Cr materials that apparently exhibit different microstructures yielding inferior mechanical properties than the counterpart material consolidated by hot isostatic pressing. Although the presence of a dispersion of Y-rich particles is evident, the oxide dis-persion strengthened (ODS) Fe–14Cr alloy consolidated by SPS exhibits poor tensile properties. The extensive decoration of the powder particle surfaces with Cr-rich precipitates and the residual porosity appear to be responsible for the impaired properties of this ODS alloy consolidated by SPS.This investigation was supported by the Ministry of Science and Innovation of Spain (Project No. ENE 2008-06403-C06-04), the Comunidad de Madrid through the program ESTRUMAT-CM(Grant No. S0505/MAT/0077), and the European Commission through the European Fusion Development Agreement (Contract No. 09-240), the IP3 FP6 ESTEEM project (Contract No. 026019) and the Fusion Energy Materials Science (FEMaS) FP7 coordination action.Publicad

Characterization of novel W alloys produced by HIP

Proceedings of: The Thirteenth International Conference on Fusion Reactor, Nice (France), 10–14 December 2007.W and W alloys containing 0.5 wt% Y₂O₃, x wt% Ti and (x wt% Ti + 0.5 wt% Y₂O₃) have been prepared, x 2 or 4. Elemental powders were blended or ball milled, canned, degassed and finally consolidated by a two stage HIP process under a pressure of 195 MPa. It is found that Ti addition favours the densification attaining a fully dense material. XRD, SEM and EDX analyses of the material with Ti addition reveal the formation of a microstructure consisting of tungsten particles embedded in a W Ti matrix. The microhardness of these materials increased noticeably with the titanium content.Dirección General de Investigación (Ministry of Education of Spain, Contract MAT2004 1819), the Dirección General de Universidades (Comunidad de Madrid) through the program of ESTRUMAT CM (Grant S 0505/MAT/0077) and EURATOM/CIEMAT Association through Contract 07/006.Publicad

Microstructural and mechanical characteristics of EUROFER'97 processed by equal channel angular pressing

Proceedings of : 14th International Conference on Fusion Reactor Materials (ICFRM-14), 6-11 september, 2009. Sapporo Convention Center Sapporo, Japan.EUROFER'97 was processed by equal channel angular pressing (ECAP) at 823 K for a total of 4 or 8 passes, using a die angle of 105°, and its microstructure and tensile behavior in temperature range 568 873 K investigated. A single ECAP pass developed a deformation texture {1 1 0} 〈0 1 1〉 that was practically stable during subsequent ECAP passes. The materials processed by 1 or 2 passes exhibited a fine microstructure of recovered subgrains and tensile behavior very similar to that for the tempered material in the as-received condition. The materials processed using 4 or 8 passes exhibited nearly equiaxial submicron grained structures with a high density of high-angle grain boundaries. These materials became softer than the as-received material at a testing temperature of ~8764;823 K. EUROFER ECAP processed under the present conditions exhibited hardening ratio somewhat higher than that of the as-received material.This investigation was supported by the EURATOM/CIEMAT association through Contract 09 240, by the Comunidad de Madrid (program ESTRUMAT CM S0505/MAT/0077) and by Spanish Ministry of Science and Innovation Contract ENE 2008 06403 C06 04.Publicad

Microstructural stability of ODS Fe-14Cr (-2W-0.3Ti) steels after simultaneous triple irradiation

Simultaneous triple-ion beam irradiation experiments with Fe5+, He+ and H+ ions were performed to simulate fusion damage on two nanostructured ferritic alloys with nominal composition Fe-14Cr-0.3Y(2)O(3) and Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3). Samples were irradiated at 600 degrees C to an estimated dose of similar to 30 dpa, 60 0 appm He, 150 0 appm H, and the effects on the microstructure of these alloys investigated by analytical transmission electron microscopy. The results reveal the development of nanovoids, or small bubbles, undetected in the unirradiated samples, and a virtual compositional stability of the dispersion. Nevertheless, upon irradiation the measured size distribution indicates a slight growth of those dispersoids having the smaller sizes.This investigation was supported by the Ministerio de Economía y Competitividad (project ENE2012-39787-C6-05), the Comunidad de Madrid through TECHNOFUSION-II (S2013/MAE-2745), the Royal Society, the European Commission through the European Fusion Development Agreement (EFDA), and the EU FP7 through the Integrated Infrastructure Initiative-I3 (Grant Agreement 312483 - ESTEEM2). The authors acknowledge the JANNUS-Saclay team for their scientific and technological advice, support from the EPSRC programme grant “Materials for Fusion and Fission Power” (EP/H018921/1) and EPSRC (grant EP/K040375/1) for the ‘South of England Analytical Electron Microscope’

Analytical characterisation of oxide dispersion strengthened steels for fusion reactors

Special issue articleReduced activation ferritic/martensitic and ferritic steels strengthened by a dispersion of oxide nanoparticles have been considered viable structural materials for fusion applications above 550°C. However, the microstructural stability and mechanical behaviour of these steels subjected to the aggressive operating conditions of these reactors are not well known. An accelerated development of these materials is crucial if they are going to be used in future power reactors. Then, it is indispensable to understand their atomic scale evolution under high temperature and irradiation conditions. The present paper reviews how the combination of transmission electron microscopy and atom probe tomography has been successfully applied for the characterisation of these steels at the near atomic scale, to reveal the nanoparticle structure, grain boundary chemistry and void distribution.The present research has been supported by the FP6 Euratom Research and Training Programme on Nuclear Energy, the Fusion Energy Materials Science (FEMaS) FP7 coordination action, the IP3 FP6 ESTEEM project under contract no. 026019 and the Consejería de Educación de la Comunidad de Madrid, through the program ESTRUMAT-CM S2009MAT-1585. EAM thanks the Royal Society for the financial support (RS Dorothy Hodgkin fellowship)

Microstructure and tensile properties of oxide dispersion strengthened Fe–14Cr– 0.3Y₂O₃ and Fe–14Cr–2W–0.3Ti–0.3Y₂O₃

Proocedings of: 15th International Conference on Fusion Reactor Materials (ICFRM15). Charleston, South Carolina (United States of America), 16-22 october, 2011Two ODS ferritic steels with nominal compositions (wt.%): Fe–14Cr–0.3Y2O3 and Fe–14Cr–2W–0.3Ti–0.3Y2O3 have been produced by mechanical alloying and consolidation by hot isostatic pressing. The microstructure and tensile properties of these materials after being forged and heat treated at 1123 K have been investigated to clarify the interrelation between composition, microstructure and mechanical properties. The second phase precipitates in these alloys have been analyzed by high angle annular dark field imaging in scanning TEM mode and electron diffraction. Fe–14Cr–2W–0.3Ti–0.3Y2O3 exhibits a duplex microstructure consisting of large recrystallized grains, as large as 1.5 μm, and unrecovered regions containing submicron equiaxed grains. In addition, three types of secondary phase particles have been found: large M₂₃C₆ particles containing W and Cr, (Cr + Ti) rich spherical particles with diameters between 50 and 500 nm, and fine (Y + Ti) oxide particles with sizes below 30 nm. In contrast, Fe14CrY shows a uniform structure of equiaxed grains, with sizes in the range 0.5 3 μm, containing a fine disper sion of Y oxide particles (<30 nm) homogeneously distributed inside the grains, as well as large carbide and oxide particles. Tensile tests performed over the temperature range 273 973 K have revealed that the alloy containing W and Ti has lower yield and tensile strengths than Fe–14Cr–0.3Y2O3 at tempera tures up to 773 K, but the opposite appears to occur beyond this temperature.This investigation was supported by the Spanish Ministry of Science and Innovation (Project No. ENE 2008 06403 C06 04 and Juan de la Cierva program), the Comunidad de Madrid through the program ESTRUMAT CM (Grant S0505/MAT/0077), and the European Commission through the European Fusion Development Agreement (Contract No. 09 240), the IP3 FP6 ESTEEM project (Contract No. 026019) and the Fusion Energy Materials Science (FEMaS) FP7 coordination action.Publicad