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  • Publication
    Microstructural stability of secondary phases in an ODS ferritic steel after thermal aging at 873 K
    (Elsevier Inc., 2024-01-01) Oñoro Salaices, Moisés; Castro Bernal, María Vanessa de; Leguey Galán, Teresa; Pöppelová, J.; Huizenga, R M; Auger Martinez, Maria Angustias
    An oxide dispersion strengthened (ODS) steel with nominal composition Fe-14Cr-2W-0.4Ti-0.3Y2O3 (wt. %) has been manufactured by mechanical alloying of pre-alloyed powders with nanosized Y2O3, compacted by hot isostatic pressing and hot cross rolled. In order to evaluate the long-term thermal resistance of the alloy, it has been subjected to 2000 hours of thermal aging at 873 K, which is a relevant temperature for nuclear reactor applications. A thermodynamic equilibrium simulation indicates the precipitation of Laves phase under the aging parameters used. This prediction is confirmed from the detailed multi-technique characterization performed. Before aging, Ti-rich oxides, Cr-W-rich precipitates (M23C6 type) and a homogeneous Y-rich nanoprecipitate dispersion are observed. After aging, some W-rich precipitates are identified as Laves phase, while M23C6 carbides, Ti-rich oxides and Y-rich nanoprecipitates remain stable. Mechanical characterization performed in a previous research showed higher hardness, a loss of total elongation and a slight shift of the ductile-to-brittle transition temperature (DBTT) towards a higher value after aging, with similar strength values before and after the long-term thermal treatment. These changes can be due to the redistribution of precipitates together with the Laves phase formation. The mechanical properties not being dramatically affected seem to be due to the observed stability of Y-rich nanoprecipitates distribution.
  • Publication
    Microstructural stability of ODS Fe-14Cr (-2W-0.3Ti) steels after simultaneous triple irradiation
    (Elsevier, 2016-12-01) Scepanovic, Masa; Castro Bernal, María Vanessa de; Leguey Galán, Teresa; Auger, María A.; Lozano Pérez, Sergio; Pareja Pareja, Ramiro; Comunidad de Madrid; European Commission; Ministerio de Economía y Competitividad (España)
    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.
  • Publication
    In-vitro evaluation of Polylactic acid (PLA) manufactured by fused deposition modeling
    (Springer Nature, 2017-09-12) Wurm, Matthias C.; Möst, Tobias; Bergauer, Bastian; Rietzel, Dominik; Neukman, Friedrich Wihelm; Cifuentes Cuéllar, Sandra Carolina; Wilmowsky, Cornelius Von
    Background: With additive manufacturing (AM) individual and biocompatible implants can be generated by using suitable materials. The aim of this study was to investigate the biological effects of polylactic acid (PLA) manufactured by Fused Deposition Modeling (FDM) on osteoblasts in vitro according to European Norm / International Organization for Standardization 10,993-5. Method: Human osteoblasts (hFOB 1.19) were seeded onto PLA samples produced by FDM and investigated for cell viability by fluorescence staining after 24 h. Cell proliferation was measured after 1, 3, 7 and 10 days by cell-counting and cell morphology was evaluated by scanning electron microscopy. For control, we used titanium samples and polystyrene (PS). Results: Cell viability showed higher viability on PLA (95,3% +/- 2.1%) than in control (91,7% +/- 2,7%). Cell proliferation was highest in the control group (polystyrene) and higher on PLA samples compared to the titanium samples. Scanning electron microscopy revealed homogenous covering of sample surface with regularly spread cells on PLA as well as on titanium. Conclusion: The manufacturing of PLA discs from polylactic acid using FDM was successful. The in vitro investigation with human fetal osteoblasts showed no cytotoxic effects. Furthermore, FDM does not seem to alter biocompatibility of PLA. Nonetheless osteoblasts showed reduced growth on PLA compared to the polystyrene control within the cell experiments. This could be attributed to surface roughness and possible release of residual monomers. Those influences could be investigated in further studies and thus lead to improvement in the additive manufacturing process. In addition, further research focused on the effect of PLA on bone growth should follow. In summary, PLA processed in Fused Deposition Modelling seems to be an attractive material and method for reconstructive surgery because of their biocompatibility and the possibility to produce individually shaped scaffolds.
  • Publication
    Dielectric response of II-VI semiconductor core-shell ensembles: study of the lossless optical condition
    (Elsevier, 2014-09-01) Cruz Fernández, Rosa María de la; Kanyinda-Malu Kabiena, Clément
    We theoretically investigate optical properties of II-VI core-shell distribution mixtures made of two type-I sized-nanoshells as a plausible negative dielectric function material. The nonlocal optical response of the semiconductor QD is described by using a resonant excitonic dielectric function, while the shell response is modeled with Demangeot formula. Achieving the zero loss at an optical frequency omega, i.e., epsilon(eff) = epsilon'(eff) + i epsilon ''(eff) with epsilon'(eff) < 0 and epsilon ''(eff) = 0, is of fundamental importance in nanophotonics. Resonant states in semiconductors provide a source for negative dielectric function provided that the dipole strength and the oscillator density are adequate to offset the background. Furthermore, the semiconductor offers the prospect of pumping, either optically or electrically, to achieve a gain mechanism that can offset the loss. We analyse optimal conditions that must be satisfied to achieve semiconductor-based negative index materials. By comparing with II-VI semiconductor quantum dots (QDs) previously reported in the literature, the inclusion of phonon and shell contributions in the epsilon(eff) along with the finite barrier Effective Mass Approximation (EMA) approach, we found similar qualitative behaviours for the epsilon(eff). The lossless optical condition along with epsilon'(eff) < 0 is discussed in terms of sizes, volume fractions and embedding medium of the mixtures' distributions. Furthermore, we estimated optical power to maintain nanocrystals density in excited states and this value is less than that previously obtained in II-VI semiconductor QDs.
  • Publication
    Large linear magnetoelectric effect and field-induced ferromagnetism and ferroelectricity in DyCrO4
    (Springer, 2019-09-27) Shen, Xudong; Zhou, Long; Chai, Yisheng; Wu, Yan; Liu, Zhehong; Yin, Yun Yu; Cao, Huibo; De La Cruz, Clarina; Sun, Young; Jin, Changqing; Muñoz Castellanos, Ángel; Alonso, Jose Antonio; Long, Youwen; Ministerio de Economía y Competitividad (España)
    All the magnetoelectric properties of scheelite-type DyCrO4 are characterized by temperature- and fielddependent magnetization, specific heat, permittivity, electric polarization, and neutron diffraction measurements. Upon application of a magnetic field within ±3 T, the nonpolar collinear antiferromagnetic structure leads to a large linear magnetoelectric effect with a considerable coupling coefficient. An applied electric field can induce the converse linear magnetoelectric effect, realizing magnetic field control of ferroelectricity and electric field control of magnetism. Furthermore, a higher magnetic field (>3 T) can cause a metamagnetic transition from the initially collinear antiferromagnetic structure to a canted structure, generating a large ferromagnetic magnetization up to 7.0 μB f.u.−1. Moreover, the new spin structure can break the space inversion symmetry, yielding ferroelectric polarization, which leads to coupling of ferromagnetism and ferroelectricity with a large ferromagnetic component.
  • Publication
    Positron annihilation study of the vacancy clusters in ODS Fe-14Cr alloys
    (Taylor & Francis, 2017-01-19) Domínguez Reyes, Ricardo; Auger, María A.; Monge Alcázar, Miguel Ángel; Pareja Pareja, Ramiro
    Oxide dispersion strengthened Fe14Cr and Fe14CrWTi alloys produced by mechanical alloying and hot isostatic pressing were subjected to isochronal annealing up to 1400 °C, and the evolution and thermal stability of the vacancy-type defects were investigated by positron annihilation spectroscopy (PAS). The results were compared to those from a non-oxide dispersion strengthened Fe14Cr alloy produced by following the same powder metallurgy route. The long lifetime component of the PAS revealed the existence of tridimensional vacancy clusters, or nanovoids, in all these alloys. Two recovery stages are found in the oxide dispersion strengthened alloys irrespective of the starting conditions of the samples. The first one starting at T > 750 °C is attributed to thermal shrinkage of large vacancy clusters, or voids. A strong increase in the intensity of the long lifetime after annealing at temperatures in the 800–1050 °C range indicates the development of new vacancy clusters. These defects appear to be unstable above 1050 °C, but some of them remain at temperatures as high as 1400 °C, at least for 90 min.
  • Publication
    Effects of thermal aging at 873 K on the impact properties of an ODS ferritic steel
    (Elsevier, 2023-09-01) Oñoro Salaices, Moisés; Leguey Galán, Teresa; Castro Bernal, María Vanessa de; Auger, María A.; Comunidad de Madrid; Agencia Estatal de Investigación (España)
    This investigation presents the effects of long-term thermal aging on the impact properties of an ODS reduced activation ferritic steel. The ODS ferritic steel, with composition Fe-14Cr-2W-0.4Ti-0.3Y2O3 (wt. %), was manufactured by mechanical alloying, compacted by hot isostatic pressing and hot cross rolled. A 1273 K annealing treatment was applied, followed by thermal aging at 873 K for 2000 h in Ar, to evaluate the thermal stability of the alloy. Charpy impact testing was performed from 77 to 473 K to investigate the mechanical response of the material under dynamic loads. The ductile-to-brittle transition temperature (DBTT) showed a slight increase with values of 255 ± 12 K before aging, and 270 ± 20 K after aging. The aging treatment softened the steep character of the Charpy impact curves inducing a wider transition regime with mixed brittle and ductile fracture mechanisms. This behavior was confirmed by the analysis of Force vs. Displacement Charpy curves and fractographic observations. Hot cross rolling induced a crack divider geometry and secondary cracks formation by delamination. Ductile fracture was less evident after aging due to the redistribution and transformation of Cr-W-rich precipitates along grain boundaries. Electron Backscattered Diffraction highlighted the features of transgranular brittle cracks at temperatures below the DBTT and showed misoriented and deformed regions near the fracture surface at temperatures above the DBTT.
  • Publication
    Enhancing the Néel temperature in 3d/5d R2NiIrO6 (R=La, Pr and Nd) double perovskites by reducing the R3+ ionic radii
    (Elsevier, 2021-04-01) Kayser, P.; Muñoz Castellanos, Ángel; Martinez, J. L.; Fauth, F.; Fernandez Diaz, M. T.; Alonso, J. A.; Ministerio de Economía y Competitividad (España)
    Double perovskites containing Ir4+ were synthesised by a citrate technique, followed by an annealing treatment in air at 1100 °C. The crystal structure of the three compounds, with formula R2NiIrO6 (R= La, Pr and Nd), were determined using a combined refinement against neutron powder diffraction (NPD) and synchrotron x-ray powder diffraction (SXRPD) data sets. At room temperature, all the samples were indexed in the space group P21/n and the monoclinic symmetry remains in the 300 to 1273 K temperature range. Magnetization measurements suggest competitive antiferromagnetic and ferromagnetic interactions, with an unexpected increment of the ordering temperature (TN) along the series. The magnetic structures of all the samples were defined with the propagation vector k = 0; the Ni2+ and Ir4+ moment arrangement, different for each compound, shows a strong dependence on the nature of the rare-earth ion.
  • Publication
    Texture and microstructural changes after thermal cycling of 6061Al-20vol%SiCw metal matrix composite: The role of microscopic internal stresses
    (Elsevier, 2022-12-01) Eddahbi, Mohamed Ou Lahcen; Fernández, Ricardo; Llorente, I.; González Doncel, Gaspar; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
    The dramatic texture and microstructural changes observed in 6061Al-20vol%SiCw metal matrix composite undergoing severe thermal cycles, under the absence and the simultaneous action of an external tensile stress, are studied. Under only thermal cycles (100–450 °C) homogenization and disorientation of the SiC whisker reinforcement and crystallographic texture randomization occurs. However, when a simultaneous tensile stress is applied, the whiskers rotate so that their long direction aligns with the tensile axes. Furthermore, a strong texture and large deformations (superplasticity), higher than 1000%, are achieved. These results are explained on the basis of the microscopic stress fields generated at the different microstructural scales (stresses of type II and type III) and well-known observation of dislocation generation at the SiC-metal interface during the cooling period of the cycles. We propose that moving dislocations (responsible of type III stresses) operate differently under the absence or the presence of the external stress. Under no stress, dislocation motion (occurring mainly during the heating period) is driven only by the type II internal stress. However, dislocation motion is improved when an external stress is applied, leading to texture changes and large elongations. Despite that a low external stress is applied, it overcomes the effect of the internal stresses for dislocation motion.
  • Publication
    Quantum control of tunable-coupling transmons using dynamical invariants of motion
    (IOP Science, 2023-04) Espinós, H.; Panadero, I.; García-Ripoll, J.J.; Torrontegui Muñoz, Erik; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España)
    We analyze the implementation of a fast nonadiabatic CZ gate between two transmon qubits with tunable coupling. The gate control method is based on a theory of dynamical invariants which leads to reduced leakage and robustness against decoherence. The gate is based on a description of the resonance between the 11 and 20 using an effective Hamiltonian with the six lowest energy states. A modification of the protocol allows us to take into account the higher-order perturbative corrections of this effective model. This enables a gate fidelity several orders of magnitude higher than other quasiadiabatic protocols, with gate times that approach the theoretical limit.
  • 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
    Plasma nitriding of an air-hardening medium manganese forging steel
    (De Gruyter, 2022-08-25) Gramlich, A.; Auger Martínez, Maria Angustias; Richter, S.
    The impact of plasma nitriding on the microstructure and the hardness of a recently developed 4 wt.-% medium manganese steel are presented. In contrast to standard quench and tempering steels, the investigated material achieves its martensitic microstructure by air-cooling from the forging heat, which enables the reduction of the carbon footprint of the forged components. The influence of nitriding on this grade of steel has not been investigated so far, but fundamental differences in comparison to standard nitriding steels are expected due to the increased manganese concentration. To address this issue, nitriding treatments with different temperatures (350 °C, 580 °C and 650 °C) have been performed, followed by examinations of the microstructure, the phase composition, the obtained hardness profiles and the tensile properties of the bulk material after nitriding, accompanied by thermodynamic equilibrium calculations. It is demonstrated that after nitriding at 580 °C similar hardness profiles like standard nitriding steels are achieved, with a shorter process as austenitization and hardening were omitted, reaching a hardness of approximately 950 HV0.1. Furthermore, it was demonstrated that austenite can be stabilized by manganese and nitrogen partitioning to room temperature during nitriding in the intercritical phase region.
  • Publication
    Characterization and evaluation of CuCrFeV(Ti, Ta, W) system for High Heat Flux applications
    (Elsevier, 2022-06) Rodríguez López, Álvaro; Savoini Cardiel, Begoña; Monge Alcázar, Miguel Ángel; Muñoz Castellanos, Ángel; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España); Universidad Carlos III de Madrid
    Cu5Cr35Fe35V20-X5, with X = Ti, Ta or W, alloys were produced by arc melting to assess their feasibility to be used as structural materials and as interlayer in cooling systems. The microstructure and mechanical properties of the materials were analyzed in as-cast and aged states. In the as-cast state the structure of the three alloys is BCC, but formation of the intermetallic Fe7Ta3 is observed in Cu5Cr35Fe35V20Ta5. Thermal aging treatment at 700 °C caused significant changes in the microstructure of Cu5Cr35Fe35V20W5 and the formation of the sigma phase. Thermal treated Cu5Cr35Fe35V20Ta5 and Cu5Cr35Fe35V20W5 exhibit high mechanical strength and excellent compressive ductility but show work softening due to the appearance of dynamic recovery mechanisms. Type-A serration behavior is observed for Cu5Cr35Fe35V20W5. Both, the complexity of their microstructures and their differences are responsible for the different mechanical behavior of the three alloys.
  • Publication
    Fabrication and characterization of Y₂O₃ dispersion strengthened copper alloys
    (Elsevier, 2014-12) Carro Sevillano, Gabriel; Muñoz Castellanos, Ángel; Monge Alcázar, Miguel Ángel; Savoini Cardiel, Begoña; Pareja Pareja, Ramiro; Ballesteros Pérez, Carmen Inés; Adeva, P.; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
    Three copper base materials were fabricated following different routes: cast Cu–1 wt.%Y (C-Cu1Y) produced by vacuum induction melting, and Cu–1 wt.%Y (PM-Cu1Y) and Cu–1 wt.%Y2O3 (PM-Cu1Y2O3) both processed by a powder metallurgy route and sintering by hot isostatic pressing. PM-Cu1Y alloy was prepared by cryomilling and PM-Cu1Y2O3 by conventional milling at room temperature. The materials were characterized by X-ray diffraction, optical and electron microscopy and microhardness measurements. C-Cu1Y presents a characteristic eutectic microstructure while PM-Cu1Y2O3 exhibits a composite like microstructure. Electron microscopy analyses of as-HIP PM-Cu1Y revealed irregular decoration of yttrium-rich oxides at the grain boundaries and an inhomogeneous dispersion of polygonal shaped yttrium-rich oxides dispersed in the Cu matrix. Tensile tests performed on PM-Cu–1Y on the temperature range of 293–773 K have showed a decrease of the yield strength at temperatures higher than 473 K, and monotonically decrease of the ultimate tensile strength and maximum plastic strain on increasing temperature.
  • Publication
    Influence of 2 (wt%) titanium addition on the oxidation resistance of tungsten
    (Elsevier, 2022-06) Perez Zubiaur, Pablo; Monge Alcázar, Miguel Ángel; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España); Universidad Carlos III de Madrid
    The oxidation behaviour of W-2Ti (wt%) alloy has been evaluated in dry air at 600, 700 and 800 °C for 100 h and the kinetics compared with those for pure tungsten. Titanium addition exerts a beneficial effect on the oxidation resistance of pure tungsten. The mass gain is almost five times smaller than in the case of commercial tungsten and three times smaller than that of tungsten prepared by powder metallurgy at 600 °C. This effect is even higher at 700 and 800 °C, where the titanium addition suppresses catastrophic oxidation of pure tungsten. Major influence of titanium regards the suppression of massive microcracking in the scale, avoiding the development of the typical non-protective multilayered scale pattern formed on pure tungsten.
  • Publication
    Production and characterization of the Cr35Fe35V16.5Mo6Ti7.5 high entropy alloy
    (Elsevier, 2022-03) Ortega, Yanicet; Monge Alcázar, Miguel Ángel; Savoini Cardiel, Begoña; Muñoz Castellanos, Ángel; Perez Zubiaur, Pablo; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España); Universidad Carlos III de Madrid
    The microstructure, thermal stability, and mechanical properties of a novel Cr35Fe35V16.5Mo6Ti7.5 high-entropy alloy were studied. The mechanical properties were mapped by nanoindentation, and the results correlated with the microstructure and the Vickers microhardness measurements. The alloy was produced by arc melting in a low pressure He atmosphere. Thermal treatments were performed to study the thermal stability of the alloy. The as-cast microstructure of the alloy exhibited a body-centered cubic phase with morphology of dendrites, outlined by a very thin interdendritic phase with a crystallographic structure compatible with Fe2Ti. The presence of the intermetallic particles was predicted by a free-energy based model, in contrast with the single solid solution alloy predicted by a parameter-based model. The volume fraction of the dendrites in the alloy is ∼ 94 % after arc melting. A small fraction of sparse Ti-rich particles, ∼0.4 vol%, was observed. The thermal treatments produced an increase of the population of Ti-rich particles, the formation of a σ-phase and nucleation of precipitates enriched with Fe and Ti into the previous dendrites. The material in as-cast condition exhibited a microhardness value of 6.2 ± 0.3 GPa, while the alloy aged at 960 °C resulted in 7.1 ± 0.4 GPa. Nanoindentations maps showed an excellent correlation with the microstructure, and their statistical analyses yielded a nanohardness mean value of 8.2 ± 0.4 GPa in the dendritic BCC regions of the as-cast and thermal treated samples and 14.1 ± 0.6 GPa for the σ-phase. The onset of the plastic behavior has been studied by analyzing the pop-in phenomenon observed in the nanoindentation loading curves. For the as-cast alloy, this analysis showed that the elastic-to-plastic transition seems to be triggered by dislocation nucleation. The alloy has a low thermal diffusivity in the measured temperature range that increases on increasing temperature.
  • Publication
    High-heat flux Cu-0.8Y alloys investigated by positron annihilation spectroscopy
    (Elsevier, 2022-04-15) Domínguez Reyes, Ricardo; Monge Alcázar, Miguel Ángel; Galiana Blanco, Beatriz; Ortega, Yanicet; Muñoz Castellanos, Ángel; Carro Sevillano, Gabriel; Comunidad de Madrid; Ministerio de Economía y Competitividad (España); Ministerio de Ciencia e Innovación (España); Universidad Carlos III de Madrid
    This work studies the thermal stability of the microstructure and the evolution of the defects of two high-heat flux Cu-0.8 wt%Y alloys fabricated following two alternative powder metallurgy routes. One batch was produced by direct hot isostatic pressing (HIP) consolidation of Cu-0.8 wt%Y pre-alloyed atomized powders while an additional ball milling processing step was introduced before HIP sintering for the second alloy. The stability and recovery characteristics of the vacancy type defects in these alloys in the as-produced state and after processing by severe equal channel angular pressing to achieve a refine microstructure have been investigated by positron lifetime and coincidence Doppler broadening measurements in samples subjected to isochronal annealing from room temperature to 900 °C. Microhardness measurements and electron transmission microscopy analysis have also been performed to support the results obtained from the positron annihilation spectroscopy analysis techniques. The recovery curves of the positron lifetime and S-W plots show a recovery stage in agreement with the recovery stage V for Cu. However, a full recovery is not accomplished, and a stage that reverts the previous recovery takes place after annealing above ~600 °C, that leads to the formation of very stable defects at temperatures up to 900 °C, identified as vacancy aggregates and nanocavities. The characteristic shape of the coincidence Doppler broadening indicates that the dispersed Y-O particles in the Cu matrix appear to be responsible for stabilizing the vacancy aggregates and nanocavities for temperatures above 600-700 °C.
  • Publication
    Microstructural and mechanical characteristics of W-2Ti and W-1TiC processed by hot isostatic pressing
    (Elsevier, 2014-12-01) Muñoz Castellanos, Ángel; Savoini Cardiel, Begoña; Tejado, E.; Monge Alcázar, Miguel Ángel; Pastor, J.Y.; Pareja Pareja, Ramiro; Ministerio de Economía y Competitividad (España); Comunidad de Madrid
    W-2Ti and W-1TiC alloys were produced by mechanical alloying and consolidation by hot isostatic pressing. The composition and microstructural characteristics of these alloys were studied by X-ray diffraction, energy dispersion spectroscopy and scanning electron microscopy. The mechanical behavior of the consolidated alloys was characterized by microhardness measurements and three point bending tests. The mechanical characteristics of the W-2Ti alloy appear to be related to solution hardening. In W-1TiC, the residual porosity should be responsible for the poor behavior observed in comparison with W-2Ti.