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  • Publication
    Microstructure and mechanical properties of an ITER-grade Cu-Cr-Zr alloy processed by equal channel angular pressing
    (Elsevier, 2014-09-29) Hernández Pérez, Aaron; Eddahbi, Mohamed Ou Lahcen; Monge Alcázar, Miguel Ángel; Muñoz Castellanos, Ángel; Savoini Cardiel, Begoña; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
    An ITER-grade Cu–Cr–Zr alloy was subjected to equal channel angular pressing (ECAP) at 400 °C via routes BC and C, i.e. rotated 90° or 180° around the extrusion axis before subsequent passes. The microstructure of ECAP deformed samples showed shear bands confining small recrystallized grains of about ∼0.2–1 μm in size. The best mechanical properties were observed for sample ECAP processed via route BC for which the density of shear bands is high and the interaction among them is notable.
  • Publication
    Influence of 1 and 5 wt% TiC additions on the oxidation behaviour of pure tungsten
    (Elsevier, 2020-08) Pérez, Pablo; Monge Alcázar, Miguel Ángel; Muñoz Castellanos, Ángel; Adeva, Paloma; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
    The influence of 1 and 5 wt% of TiC nanoparticles on the oxidation behaviour of reinforced tungsten has been evaluated up to 700 °C in dry air. Isothermal thermogravimetric tests prove that the addition of 5 wt% of TiC particles is detrimental, increasing the mass gain of pure tungsten by a factor of ten. TiC particles act as stress concentrators, facilitating microcracking events within the scale and promoting decohesion between TiC-free boundaries and TiC-containing regions of the material. Compared to pure tungsten, lowering TiC addition to 1 wt% significantly improves the oxidation resistance at 700 °C by reducing about seven times the mass gain, while at 600 °C both materials exhibit similar resistance. At 700 °C, the presence of 1 wt% of TiC particles inhibits massive microcracking events occurring in the scale formed on pure tungsten, rendering the oxide scale denser and more protective.
  • Publication
    Microstructural and mechanical characterization of Cu-0.8wt%Y
    (Elsevier, 2015-10) Carro Sevillano, Gabriel; Muñoz Castellanos, Ángel; Monge Alcázar, Miguel Ángel; Savoini Cardiel, Begoña; Pareja Pareja, Ramiro; Ministerio de Economía y Competitividad (España); Comunidad de Madrid
    Dispersion strengthened Cu-0.8 wt.%Y has been produced by a powder metallurgy route and subsequent consolidation by hot isostatic pressing at 1123 K and 172 MPa. A fully dense alloy has been obtained that exhibits a microstructure characterized by equiaxed grains with sizes ranging from 0.5 to 50 μm. Yttrium-rich particles with an average size of 0.92 μm have been observed inside the grains and decorating the grain boundaries. As expected, the tensile tests carried out from room temperature to 773 K have revealed that both the YS and the UTS decrease with increasing temperature. This alloy exhibits better tensile properties and microhardness than OFHC Cu. This improvement is attributed to the presence of the Y-rich particles.
  • Publication
    Microstructure and mechanical properties of hot rolled ODS copper
    (Elsevier BV., 2020-08-01) Muñoz Castellanos, Ángel; Savoini Cardiel, Begoña; Monge Alcázar, Miguel Ángel; Eddahbi, Mohamed Ou Lahcen; Dura, O. J.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
    Dispersion strengthened copper alloys have been produced by following a powder metallurgy route that have consisted of milling copper and yttrium acetate powders in a planetary ball milling and subsequently sintering by hot isostatic pressing (HIP). In order to increase the degree of densification of the materials, they were subjected to a thermal treatment in vacuum and to a hot rolling process at 1173 K. The decomposition of the yttrium acetate during the thermal treatments resulted in the formation of voids, with a loss of densification that could not be satisfactorily improved with the hot rolling processing. The microstructure and the mechanical and thermal properties of the alloys were analyzed by scanning electron microscopy, electron backscattering diffraction, micro and nanohardness measurements, and compression tests and thermal conductivity measurements, both in the range 300–780 K. The best mechanical properties were obtained for the as-HIP material, with a mean grain size of 0.3 ± 0.3 μm and a yield strength value at room temperature of 520 MPa. In contrast, the material with the highest thermal conductivity for the entire range of temperature was found to be the alloy thermal treated in vacuum at 1273 K and later subjected to the hot rolling processing. The different microstructural characteristics of the alloys such as grain size, defects present in the grains and size of voids seems to be responsible of the differences on their thermal conductivity values.
  • Publication
    Shortcuts to quantum adiabaticity processes
    (IOP Publishing Ltd., 2011-07-08) Muga, J. G.; Chen, Xi; Torrontegui Muñoz, Erik; Ibáñez, S.; Lizuain, Ion; Ruschhaupt, A.; Ministerio de Ciencia e Innovación (España)
    We review different ways to accelerate adiabatic processes in cold atom physics and atomic state preparation. Trap expansions or contractions and atomic transport may be accelerated by an invariant-based inverse engineering approach. Berry's inverse engineering method is also applied to produce fast versions of adiabatic passage methods.
  • Publication
    Microstructure and mechanical properties of ultrafine-grained Fe─14Cr and ODS Fe─14Cr model alloys
    (Elsevier, 2009-09) Auger, María A.; Leguey Galán, Teresa; Muñoz Castellanos, Ángel; Monge Alcazar, Miguel Ángel; Castro Bernal, María Vanessa de; Fernández, P.; Garcés, G.; Pareja Pareja, Ramiro
    Reduced activation ferritic Fe─14 wt%Cr and Fe─14 wt%Cr─0.3 wt%Y₂O₃ alloys were produced by mechanical alloying and hot isostatic pressing followed by forging and heat treating. The alloy containing Y₂O₃ developed a submicron-grained structure with homogeneous dispersion of oxide nanoparticles that enhanced the tensile properties in comparison to the Y₂O₃ free alloy. Strengthening induced by the Y₂O₃ dispersion appears to be effective up to 873 K, at least. A uniform distribution of Cr-rich precipitates, stable upon a heat treatment at 1123 K for 2 h, was also found in both alloys.
  • Publication
    Review on the EFDA work programme on nano-structured ODS RAF steels
    (Elsevier, 2011-10) Baluc, N.; Boutard, J.L.; Dudarev, S.L.; Rieth, M.; Brito Correia, J.; Fournier, B.; Henry, J.; Legendre, F.; Leguey Galán, Teresa; Lewandowska, M.; Lindau, R.; Marquis, E.; Muñoz Castellanos, Ángel; Radiguet, B.; Oksiuta, Z.
    The 2008─2009 work programme of the European research project on nano-structured oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels is being organized along the four following programmatic lines: (1) improve the present generation of nano-structured ODS RAF steels; (2) start the industrial fabrication of the present generation of nano-structured ODS RAF steels; (3) develop an optimised generation of nano-structured and nano-grained ODS RAF steels; (4) investigate the stability of present and optimised generation of nano-structured ODS RAF steels under creep and irradiation. This paper presents the main objectives of current R&D activities being performed within the European research project on nano-structured ODS RAF steels, the main obtained results and the main future activities in the case of the four programmatic lines mentioned just above.
  • Publication
    Analytical characterization of secondary phases and void distributions in an ultrafine-grained ODS Fe─14Cr model alloy
    (Elsevier, 2011-10) Castro Bernal, María Vanessa de; Leguey Galán, Teresa; Auger, María A.; Lozano-Pérez, S.; Jenkins, M.L.
    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.
  • Publication
    Mechanical properties of tungsten alloys with Y₂O₃ and titanium additions
    (Elsevier, 2011-10) Aguirre, M. V.; Martín, A.; Pastor, J.Y.; Monge Alcazar, Miguel Ángel; Pareja Pareja, Ramiro; Llorca, Javier
    n this research the mechanical behaviour of pure tungsten (W) and its alloys (2 wt.% Ti─0.47 wt.% Y₂O₃ and 4 wt.% Ti─0.5 wt.% Y₂O₃ ) is compared. These tungsten alloys, have been obtained by powder metallurgy. The yield strength, fracture toughness and elastic modulus have been studied in the temperature interval of 25 °C to 1000 °C. The results have shown that the addition of Ti substantially improves the bending strength and toughness of W, but it also dramatically increases the DBTT. On the other hand, the addition of 0.5% Y₂O₃, is enough to improve noticeably the oxidation behaviour at the higher temperatures. The grain size, fractography and microstructure are studied in these materials. Titanium is a good grain growth inhibitor and effective precursor of liquid phase in HIP. The simultaneous presence of Y₂O₃ and Ti permits to obtain materials with low pores presence.
  • Publication
    Influence of processing route and yttria additions on the oxidation behavior of tungsten
    (Elsevier, 2011-10) Muñoz Castellanos, Ángel; Monge Alcázar, Miguel Ángel; Cifuentes Cuéllar, Sandra Carolina; Pérez, P.
    The oxidation resistance in dry air of pure tungsten and tungsten reinforced with a dispersion of 0.6 wt.% Y₂O₃ nanoparticles has been evaluated between 873 and 1073 K, temperature range that divertor in fusion power plants should endure during long-term times in the case of loss of coolant accident and/or air ingress in the vessel. Both materials were prepared by a powder metallurgy route involving hot isostatic pressing of ball milled tungsten powders and tungsten with dispersed Y₂O₃ nanoparticles. The results have been compared with those of pure tungsten processed by conventional techniques. Thermogravimetric tests at 873 K revealed that the processing route as well as yttria addition considerably affected the oxidation resistance of pure tungsten. Mass gain of W-0.6Y₂O₃ at 873 K was five and two times lower than that of pure tungsten prepared by conventional processing techniques and by powder metallurgy, respectively. This different behavior was related to changes in the structure and composition of the oxide scale. Above 873 K, the kinetics were significantly accelerated for all materials due to the development of a non-protective oxide scale from the earliest oxidation stages, although the kinetics of Y₂O₃-containing material were still the slowest, specially at 973 K. It was analyzed how yttria additions modify the oxidation mechanism of tungsten.
  • Publication
    Tensile and fracture characteristics of oxide dispersion strengthened Fe─12Cr produced by hot isostatic pressing
    (Elsevier, 2011-10) Castro Bernal, María Vanessa de; Garces Usan, José María; Leguey Galán, Teresa; Pareja Pareja, Ramiro
    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.
  • Publication
    Mechanical behavior of tungsten-vanadium-lanthana alloys as function of temperature
    (Elsevier, 2011-10) Palacios, T.; Pastor, J.Y.; Aguirre, M. V.; Martín, A.; Monge Alcázar, Miguel Ángel; Muñoz Castellanos, Ángel; Pareja Pareja, Ramiro
    The mechanical behavior of three tungsten (W) alloys with vanadium (V) and lanthana (La₂O₃) additions (W–4%V, W–1%La2O3, W–4%V–1%La₂O₃) processed by hot isostatic pressing (HIP) have been compared with pure-W to analyze the influence of the dopants. Mechanical characterization was performed by three point bending (TPB) tests in an oxidizing air atmosphere and temperature range between 77 (immersion tests in liquid nitrogen) and 1273 K, through which the fracture toughness, flexural strength, and yield strength as function of temperature were obtained. Results show that the V and La₂O₃ additions improve the mechanical properties and oxidation behavior, respectively. Furthermore, a synergistic effect of both dopants results in an extraordinary increase of the flexure strength, fracture toughness and resistance to oxidation compared to pure-W, especially at higher temperatures. In addition, a new experimental method was developed to obtain a very small notch tip radius (around 5–7 μm) and much more similar to a crack through the use of a new machined notch. The fracture toughness results were lower than those obtained with traditional machining of the notch, which can be explained with electron microscopy, observations of deformation in the rear part of the notch tip. Finally, scanning electron microscopy (SEM) examination of the microstructure and fracture surfaces was used to determine and analyze the relationship between the macroscopic mechanical properties and the micromechanisms of failure involved, depending on the temperature and the dispersion of the alloy.
  • Publication
    Microstructure and temperature dependence of the microhardness of W-4V-1La₂O₃ and W-4Ti-1La₂O₃
    (Elsevier, 2013-11) Savoini Cardiel, Begoña; Martinez, J.; Muñoz Castellanos, Ángel; Monge Alcázar, Miguel Ángel; Pareja Pareja, Ramiro
    W–4V–1La₂O₃ and W–4Ti–1La₂O₃ (wt.%) alloys have been produced by mechanical alloying and subsequent hot isostatic pressing. Electron microscopy observations revealed that these alloys exhibit a submicron grain structure with a dispersion of La oxide nanoparticles. Large V or Ti pools with martensitic characteristics are found segregated in the interstices between the W particles of the respective alloys. Microhardness tests were carried out over the temperature range 300–1073 K in vacuum. The microhardness–temperature curve for W–4V–1La₂O₃ exhibited the expected decreasing trend with increasing temperature although the microhardness stayed constant between ~473 and 773 K. The W–4Ti–1La₂O₃ presented quite different temperature dependence with an anomalous microhardness increase for temperatures above ~473 K.
  • Publication
    Effects of heat treatment conditions on the microstructure and impact properties of EUROFER 97 ODS steel
    (The Royal Swedish Academy of Sciences, 2011-05) Di Martino, S.F; Faulkner, R.G.; Riddle, N.B.; Monge Alcázar, Miguel Ángel; Muñoz Castellanos, Ángel
    Probably the most important range of materials to consider for the blanket material in the tokamak design for fusion reactors such as ITER and DEMO is the high alloy Fe9Cr oxide dispersion strengthened (ODS) ferritic steels. These steels possess exceptional thermal conductivity and low thermal expansion while being strongly resistant to void swelling. Their main drawback is the high ductile-to-brittle transition temperature (DBTT), particularly in the ODS versions of the material. This paper describes attempts that are being made to reduce this DBTT in as yet unirradiated materials by a novel heat treatment procedure. The principle behind this approach is that low DBTT in the unirradiated materials will lead to relatively low DBTT even in He-containing material that has been irradiated with fusion blanket-type irradiations. New batches of high alloy Fe9Cr ODS (EUROFER) ferritic steel have been produced by a powder metallurgical route, and relatively homogeneous material has been produced by a hot isostatic pressing procedure. Mini-Charpy test specimens were made from materials that had been subjected to a matrix of heat treatments designed to show up variations in solution treatment (ST) temperature, cooling rate from the ST temperature and tempering treatment. The initial DBTT was in the range 150&-200 C. Extremely interesting results have been obtained. DBTT downward shifts of up to 200 C have been observed by using a high 1300 C ST temperature and a low cooling rate. The paper goes on to describe the microstructure of this material, and discusses the possible microstructural factors needed to produce these very high DBTT downward shifts. Low dissolved carbon and higher proportions of low-angle grain boundaries seem to provide the key to the understanding of the alloy behaviou .
  • Publication
    La₂O₃-reinforced W and W-V alloys produced by hot isostatic pressing
    (Elsevier, 2011-10) Muñoz Castellanos, Ángel; Monge Alcázar, Miguel Ángel; Savoini Cardiel, Begoña; Rabanal Jiménez, María Eugenia; Garcés Plaza, Gerardo; Pareja Pareja, Ramiro
    W and W–V alloys reinforced with La₂O₃ particles have been produced by MA and subsequent HIP at 1573 K and 195 MPa. The microstructure of the consolidated alloys has been characterized by scanning electron microscopy, energy dispersive spectroscopy analyses and X-ray diffraction. The mechanical properties were studied by nanoindentation measurements. The results show that practically full dense billets of W–V, W–V–La₂O₃ and W–La₂O₃ alloys can be produced. The microstructure analysis has shown that islands of V are present in W–V and W–V–1La₂O₃ alloys. In W–1La₂O₃ islands of La₂O₃ are also present. The nanohardness of the W matrix increases with the addition of V, while decreases with the addition of La₂O₃.
  • Publication
    Microstructural and mechanical characteristics of EUROFER'97 processed by equal channel angular pressing
    (Elsevier, 2011-10) Fernández, P.; Eddahbi, Mohamed Ou Lahcen; Auger, María A.; Leguey Galán, Teresa; Monge Alcazar, Miguel Ángel; Pareja Pareja, Ramiro
    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.
  • Publication
    Microstructural characterization of Y₂O₃ ODS-Fe-Cr model alloys
    (Elsevier, 2007-12) Castro Bernal, María Vanessa de; Leguey Galán, Teresa; Muñoz Castellanos, Ángel; Monge Alcazar, Miguel Ángel; Pareja Pareja, Ramiro; Marquis, E.A.; Lozano-Pérez, S.; Jenkins, M. L.
    Two Fe-12 wt% Cr alloys, one containing 0.4 wt% Y₂O₃ and the other Y₂O₃ free, have been produced by mechanical alloying followed by hot isostatic pressing. These oxide dispersion strengthened and reference alloys were characterized both in the as-HIPed state and after tempering by transmission electron microscopy and atom-probe tomography. The as-HIPed alloys exhibited the characteristic microstructure of lath martensite and contained a high density of dislocations. Small voids with sizes <10 nm were also observed. Both alloys also contained M₃C and M₂₃C₆ carbides (M = Cr, Fe) probably as a result of C ingress during milling. After tempering at 1023 K for 4 h the microstructures had partially recovered. In the recovered regions, martensite laths were replaced by equiaxed grains in which M₂₃C₆ carbides decorated the grain boundaries. In the ODS alloy nanoparticles containing Y were commonly observed within grains, although they were also present at grain boundaries and adjacent to large carbides.
  • Publication
    Microstructure and tensile properties of oxide dispersion strengthened Fe–14Cr– 0.3Y₂O₃ and Fe–14Cr–2W–0.3Ti–0.3Y₂O₃
    (Elsevier, 2011-10) Auger, María A.; Castro Bernal, María Vanessa de; Leguey Galán, Teresa; Monge Alcazar, Miguel Ángel; Muñoz Castellanos, Ángel; Pareja Pareja, Ramiro
    Two 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.
  • Publication
    Thermal stability of the grain structure in the W-2V and W-2V-0.5Y₂O₃ alloys produced by hot isostatic pressing.
    (2012-09) Muñoz Castellanos, Ángel; Savoini Cardiel, Begoña; Monge Alcázar, Miguel Ángel; Martínez Gómez, Javier; Armstrong, D.E.J.; Pareja Pareja, Ramiro
    W-2V and ODS W-2V-0.5Y₂O₃ alloys have been produced following a powder metallurgy route consisting of mechanical alloying and a subsequent high isostatic pressing HIP at 1573 K. The grain microstructure and microhardness recovery of the alloys have been studied in samples subjected to isothermal treatments in vacuum in temperature range 1073–1973 K. Both alloys exhibit a duplex grain size distribution consisting of a submicron-sized grain and a coarse-grained population. It has been found that the Y₂O₃ addition inhibits growth of the coarse grains at T < 1973 K. Submicron grain growth, with activa-tion enthalpy of 1.9 and 2.49 eV for W-2V and W-2V-0.5Y₂O₃, respectively, was observed at T ≥ 1573 K. It resulted that the rate constant for grain growth is 30 times higher in W-2V-0.5Y₂O₃ than in W-2V. The considerable enhancement of the microhardness in the W-2V-0.5Y₂O₃ appears to be associated to dispersion strengthening.
  • Publication
    Characterization of novel W alloys produced by HIP
    (Elsevier, 2007-12) Monge Alcazar, Miguel Ángel; Auger, María A.; Leguey Galán, Teresa; Bolzoni, Leandro; Gordo Odériz, Elena; Pareja Pareja, Ramiro
    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.