Revistas
Revista:
JOURNAL OF NUCLEAR MATERIALS
ISSN:
0022-3115
Año:
2021
Vol.:
548
Págs.:
152841
Precipitation hardened CuCrZr alloy is the baseline option as heat sink material for the water cooled W divertor concept of DEMO owing to its combination of high thermal conductivity and strength. However, traditional processing of CuCrZr by casting and forging or hot rolling involves several challenges: coarsening of Cr precipitates, microstructures highly heterogeneous, or difficulties in obtaining complex geometries. Additive Manufacturing (AM) enables creating innovative solutions with complex structures for heat exchangers and heat sinks. Compared to Laser Powder Bed Fusion (L-PBF), the EB-PBF (Electron Beam Powder Bed Fusion) AM technology offers advantages when processing copper alloys: it avoids difficulties associated to the high thermal conductivity and reflectivity of copper-based materials and prevents their oxidation by working under high vacuum. In this work the study of AM of a CuCrZr alloy with nominal composition 0.6?0.9 Cr, 0.07?0.15 Zr (wt.%) has been performed by EB-PBF. A detailed process parameters study has been performed to identify the process window and obtain dense materials free of defects. The process parameters, including post-built heat treatments like age hardening, were correlated with the microstructural evolution, the thermal conductivity and the hardness. ? 2021 The Authors. Published by Elsevier B.V. All rights reserved. Precipitation hardened CuCrZr alloy is the baseline option as heat sink material for the water cooled W divertor concept of DEMO owing to its combination of high thermal conductivity and strength. However, traditional processing of CuCrZr by casting and forging or hot rolling involves several challenges: coarsening of Cr precipitates, microstructures highly heterogeneous, or difficulties in obtaining complex geometries. Additive Manufacturing (AM) enables creating innovative solutions with complex structures for heat exchangers and heat sinks. Compared to Laser Powder Bed Fusion (L-PBF), the EB-PBF (Electron Beam Powder Bed Fusion) AM technology offers advantages when processing copper alloys: it avoids difficulties associated to the high thermal conductivity and reflectivity of copper-based materials and prevents their oxidation by working under high vacuum. In this work the study of AM of a CuCrZr alloy with nominal composition 0.6?0.9 Cr, 0.07?0.15 Zr (wt.%) has been performed by EB-PBF. A detailed process parameters study has been performed to identify the process window and obtain dense materials free of defects. The process parameters, including post-built heat treatments like age hardening, were correlated with the microstructural evolution, the thermal conductivity and the hardness.
Autores:
Maier, H.; Schwarz-Selinger, T.; Neu, R.; et al.
Revista:
NUCLEAR MATERIALS AND ENERGY
ISSN:
2352-1791
Año:
2019
Vol.:
18
Págs.:
245 - 249
The tungsten "heavy alloy" HPM 1850, a liquid-phase sintered composite material with two weight percent Ni and one weight percent Fe, as well as the self-passivating tungsten alloy W-10Cr-0.5Y, a high temperature oxidation resistant alloy with 10 weight percent of Cr and 0.5 weight percent of Y, were investigated with respect to their deuterium retention. The samples were deuterium loaded in an electron cyclotron resonance plasma up to a fluence of 10(25) m(-2). The deuterium retention was then investigated by Nuclear Reaction Analysis and by Thermal Desorption. In HPM 1850 the observed deuterium amount was similar to pure tungsten, however the outgassing behaviour during thermal desorption was considerably faster. In W-10Cr-0.5Y the released deuterium amount during thermal desorption was about one order of magnitude higher; by comparison of nuclear reaction analysis and thermal desorption this was attributed to deeper diffusion of deuterium into the bulk of the material.
Autores:
Pazos, D.; Suarez, M. ; Fernandez, A. ; et al.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2019
Vol.:
146
Págs.:
2328 - 2333
Once the feasibility of the STARS route (Surface Treatment of gas Atomized powder followed by Reactive Synthesis) has been demonstrated to produce ODS ferritic steels by internal oxidation avoiding mechanical alloying, two strategies are proposed in this work to enhance precipitation of oxide nanopArtículos. Firstly, consolidation by Spark Plasma Sintering (SPS) is used to produce finer microstructures compared to HIP consolidation. SPS parameters like temperature, heating rate, pressure and time of exposure under pressure were explored, and dense samples (up to 99,5%RD) were obtained. Secondly, precipitation of nanopArtículos is achieved through a combination of HIP consolidation at low temperature (700-900 degrees C) followed by hot deformation under the presence of metastable oxides, to increase the density of dislocations, preferential nucleation sites for the precipitation of nanometric Y-Ti-O oxides. Deformation dilatometry and plane strain compression tests were performed to simulate hot deformation under different hot rolling schedules. Total deformation, number of passes, time between passes or initial and final rolling temperatures are some of the parameters explored. Microstructural characterization by Scanning Electron Microscopy (SEM) of consolidated materials is presented.
Autores:
Mihalache, V. (Autor de correspondencia); Walter, M.; Mercioniu, I.; et al.
Revista:
METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE
ISSN:
1073-5623
Año:
2019
Vol.:
50A
N°:
7
Págs.:
3282 - 3294
Oxide dispersion-strengthened ferritic steels (ODSFSs) are promising structural materials for applications in fusion and fission power reactors, but further improvement in their (high-temperature) mechanical properties and ferrite phase stability is required. This work demonstrates that an approach to produce Fe14Cr ODSFSs with a stable ferrite phase and improved strength could involve grain size strengthening by long-term milling with a tiny amount of nitrogen. Fe-14Cr-3W-0.4Ti-0.25Y(2)O(3) powders were ball-milled up to 170 hours under an argon atmosphere. In addition to X-ray diffraction, the change in product quality during milling and upon heating was thoroughly investigated by more sensitive magnetic and thermal analysis by measuring the saturation magnetization sigma(s), coercivity H-c, Curie temperature T-c, and temperature of ferrite-austenite (alpha ->gamma) transition T-alpha ->gamma. A pronounced modification of magnetic and microstructure parameters was observed when milling over 70 hours and upon heating above 800 degrees C and was found to be generated by long-term milling with a tiny amount of nitrogen. Upon heating, the nitrogen, incorporated during milling, developed a transition region, with the decomposition of nitrides precipitated at the earlier stage of heating followed by austenite decomposition, nitrogen degassing, and microstructure refinement to a grain size of a few tenths of a nm (e.g., 28 nm by heating at 910 degrees C of 100-hour milled powder). The resulting ferrite phase with refined grains is highly stable to (further) heating. The powders milled for 70 and 100 hours containing 0.175 and 0.500 wt pct nitrogen, respectively, were consolidated at 1100 degrees C with subsequent annealing at 1050 degrees C and subjected to Vickers hardness and 3-point bending tests. The steel produced from the powder milled for 70 hours shows lower hardness, higher density (close to the theoretical value of 7.8 g/cm(3)), and fracture strain. The ductility of this ODS alloy (0.075 fracture strain) is comparable with Eurofer97 (0.075 fracture strain), whereas its strength (2070 MPa ultimate stress) is significantly higher than that of Eurofer97 (1222 MPa ultimate stress). This improvement was attributed to grain size strengthening-the refined grains (promoted by milling with nitrogen) could be effectively pinned by Y-Ti-O dispersoids.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0958-0611
Año:
2018
Vol.:
70
Págs.:
45 - 55
Six suppliers from several countries were asked to furnish parallelepiped 10 × 30 × 80 mm3 samples of commercial purity tungsten machined from rolled plates in view of selecting a provider of tungsten bricks for the target of the European neutron spallation source, ESS, under construction in Lund (Sweden). Sample surfaces were to be ground and free from visible defects or oxidation. The material should be rolled after sintering. A minimum room temperature tensile strength of 600 MPa was specified. The samples were submitted to different blind mechanical tests, measurement of physical properties and structural observations in order to assess their suitability for the application. We present here a summary of their main measured properties. The dispersion of results is noteworthy; the exercise allowed to sort-out technically eligible candidates for the application.
Autores:
Pazos, D.; Cintins, A.; de Castro, V. ; et al.
Revista:
NUCLEAR MATERIALS AND ENERGY
ISSN:
2352-1791
Año:
2018
Vol.:
17
Págs.:
1 - 8
Oxide Dispersion Strengthened Ferritic Stainless Steels (ODS FS) are candidate materials for structural components in fusion reactors. Their ultrafine microstructure and the presence of a very stable dispersion of Y-Ti-O nanoclusters provide reasonable fracture toughness, high mechanical and creep strength, and resistance to radiation damage at the operation temperature, up to about 750 degrees C. An innovative route to produce ODS FS with composition Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3) (wt.%), named STARS (Surface Treatment of gas Atomized powder followed by Reactive Synthesis), is presented. This route avoids the mechanical alloying (MA) of the elemental or prealloyed powders with yttria to dissolve the yttrium in the ferritic matrix. In this study, starting powders containing Ti and Y are obtained by gas atomization at laboratory and industrial scale. Then, a metastable Cr-and Fe-rich oxide layer is formed on the surface of the powder particles. During consolidation by HIP the metastable oxide layer at Prior Particle Boundaries (PPBs) dissociates, the oxygen diffuses towards saturated solutions or metallic Ti-and Y-rich particles, and Y-Ti-O nano-oxides (mainly Y2TiO5) precipitate in the ferritic matrix. Detailed Microstructural characterization by X-ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of powders and consolidated materials is presented and correlated with mechanical behaviour.
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2018
Vol.:
73
Págs.:
29 - 37
Self-passivating tungsten based alloys for the first wall armor of future fusion reactors are expected to provide a major safety advantage compared to pure tungsten in case of a loss-of-coolant accident with simultaneous air ingress, due to the formation of a stable protective scale at high temperatures in presence of oxygen which prevents the formation of volatile and radioactive WO3. This work analyses the oxidation and thermal shock resistance of W-Cr-Y alloys obtained by mechanical alloying followed by HIPing. Alloys with different Cr and Y contents are produced in fully dense form with nanocrystalline or ultrafine-grained microstructure and a dispersion of Y-rich oxide nanoparticles located mainly at the grain boundaries. Isothermal oxidation experiments confirm an excellent oxidation resistance due to the formation of protective oxide scales at the very surface. These layers mainly consist of Cr2O3 and mixed Y-W and Cr-W oxides. The superior oxidation resistance of these alloys is confirmed by tests simulating accident-like conditions. The thermal conductivity of these alloys at 600-1000 degrees C is 2-3 times higher than standard Ni-base superalloys like Inconel-718. The material also exhibits outstanding thermal shock resistance: 1000 pulses of 0.19 GW/m(2) power density and 1 ms duration at 400 degrees C base temperature resulted in no damage, while an increased power density of 0.38 GW/m(2) resulted in the formation of a crack-network and slight surface roughening. An additional thermal treatment at 1550 degrees C improves slightly the oxidation resistance and significantly the thermal shock resistance of the alloy.
Revista:
JOURNAL OF NUCLEAR MATERIALS
ISSN:
0022-3115
Año:
2018
Vol.:
504
Págs.:
8 - 22
Oxide Dispersion Strengthened Ferritic Steels (ODS FS) are candidate materials for structural components in future fusion reactors. Their high strength and creep resistance at elevated temperatures and their good resistance to neutron radiation damage is obtained through extremely fine microstructures containing a high density of nanometric precipitates, generally yttrium and titanium oxides. This work shows transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) characterization of Fe-14Cr-2W-0.3Ti-0.24Y ODS FS obtained by the STARS route (Surface Treatment of gas Atomized powder followed by Reactive Synthesis), an alternative method to obtain ODS alloys that avoids the mechanical alloying to introduce Y2O3 powder particles. In this route, FS powders already containing Ti and Y, precursors of the nanometric oxides, are obtained by gas atomization. Then, a metastable Cr- and Fe-rich oxide layer is formed on the surface of the powder particles. During consolidation by HIP at elevated temperatures, and post-HIP heat treatments above the HIP temperature, this oxide layer at Prior Particle Boundaries (PPBs) dissociates, the oxygen diffuses, and Y-Ti-O nano-oxides precipitate in the ferritic matrix. TEM characterization combined with XAFS and XANES analyses have proven to be suitable tools to follow the evolution of the nature of the different oxides present in the material during the whole processing route and select appropriate HIP and post-HIP parameters to promote profuse and fine Y-Ti-O nanometric precipitates. (C) 2018 Elsevier B.V. All rights reserved.
Revista:
APPLIED SURFACE SCIENCE
ISSN:
0169-4332
Año:
2018
Vol.:
427
N°:
Part: A
Págs.:
182 - 191
An innovative powder metallurgy route to produce ODS FS, named STARS, has succeeded in atomizing steel powders containing the oxide formers (Y and Ti) and, hence, avoids the mechanical alloying (MA) step to dissolve Y in the matrix. A metastable oxide layer forms at the surface of atomized powders and dissociates during HIP consolidation at high temperatures, leading to precipitation of more stable Y-Ti-O nanoparticles.
Autores:
Litnovsky, A.; Wegener, T.; Klein, F.; et al.
Revista:
NUCLEAR FUSION
ISSN:
0029-5515
Año:
2017
Vol.:
57
N°:
066020
Tungsten is currently deemed as a promising plasma-facing material (PFM) for the future power plant DEMO. In the case of an accident, air can get into contact with PFMs during the air ingress. The temperature of PFMs can rise up to 1200 °C due to nuclear decay heat in the case of damaged coolant supply. Heated neutron-activated tungsten forms a volatile radioactive oxide which can be mobilized into the atmosphere.
New self-passivating 'smart' alloys can adjust their properties to the environment. During plasma operation the preferential sputtering of lighter alloying elements will leave an almost pure tungsten surface facing the plasma. During an accident the alloying elements in the bulk are forming oxides thus protecting tungsten from mobilization.
Good plasma performance and the suppression of oxidation are required for smart alloys. Bulk tungsten (W)¿chroimum (Cr)¿titanium (Ti) alloys were exposed together with pure tungsten (W) samples to the steady-state deuterium plasma under identical conditions in the linear plasma device PSI 2. The temperature of the samples was ~576 °C¿715 °C, the energy of impinging ions was 210¿eV matching well the conditions expected at the first wall of DEMO. Weight loss measurements demonstrated similar mass decrease of smart alloys and pure tungsten samples. The oxidation of exposed samples has proven no effect of plasma exposure on the oxidation resistance. The W¿Cr¿Ti alloy demonstrated advantageous 3-fold lower mass gain due to oxidation t
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2017
Vol.:
124
Págs.:
999 - 1003
The blanket of ITER protects the vacuum vessel from neutrons and other energetic particles produced in the fusion plasma. Each of the 215 Normal Heat Flux (NHF) panels of the blanket consists of a shield block and a First Wall (FW) panel. The NHF FW panels are a complex bimetallic structure of AISI 316L(N) stainless steel (SS) backing plate and a copper alloy (CuCrZr) heat sink, covered with beryllium armor tiles. joining of these materials is done by solid state diffusion bonding. Under the framework of a R&D roadmap parallel to the manufacturing of a full-scale prototype of a FW panel of ITER, this work describes studies on the microstructure and strength of CuCrZr/SS and CuCrZr/CuCrZr joints of a simplified 10 fingers prototype of a FW panel manufactured by Hot Isostatic Pressing (HIP). Results on mechanical tests performed following ITER recommendations are compared to F4E specifications. Microstructural characterization of the interface was performed. Thermal history of the component is correlated with the mechanical behavior of the interfaces. Results show that appropriate parameters of the solution annealing after HIP and of the CuCrZr ageing during final HIP diffusion bonding are essential to achieve the specified strength of the joints.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2017
Vol.:
124
Págs.:
1118 - 1121
The use of self-passivating tungsten alloys for the first wall armor of future fusion reactors is advantageous concerning safety issues in comparison with pure tungsten. Bulk W-10Cr-0.5Y alloy manufactured by mechanical alloying followed by HIP resulted in a fully dense material with grain size around 100 nm and a dispersion of Y-rich oxide nanoparticles located at the grain boundaries. An improvement in flexural strength and fracture toughness was observed with respect to previous works. Oxidation tests under isothermal and accident-like conditions revealed a very promising oxidation behavior for the W-10Cr-0.5Y alloy. Thermo-shock tests at JUDITH-1 to simulate ELM-like loads resulted in a crack network at the surface with roughness values lower than those of a pure W reference material. An additional thermal treatment at 1550 degrees C improves slightly the oxidation and significantly thermo-shock resistance of the alloy. (C) 2017 The Authors. Published by Elsevier B.V.
Autores:
Litnowski, A.; Wegener, T.; Klein, F.; et al.
Revista:
NUCLEAR MATERIALS AND ENERGY
ISSN:
2352-1791
Año:
2017
Vol.:
12
Págs.:
1363 - 1367
Revista:
PHILOSOPHICAL MAGAZINE
ISSN:
1478-6435
Año:
2016
Vol.:
96
N°:
32 -34
Págs.:
3570 -3585
The brittle fracture strength of a self-passivating W-Cr10-Ti2 alloy (in wt.%) was measured through un-notched cantilever bending at the microscopic scale. The material behaved purely elastic and fractured catastrophically in an unstable fashion. An average nominal strength of 5.9 GPa was measured. The scatter in strength was shown to be significantly higher than the sum of all random errors indicating an inherent variability of the material¿s strength. The measurements from 28 tests followed a Weibull distribution with a modulus of m = 12. Results from a size effect study at the microscopic scale were successfully predicted through Weibull scaling. Extrapolation into the macroscopic range overestimated the measured three-point bend strength, which is likely due to the presence of large-scale heterogeneities. The test technique sampled a material thickness of only several micrometres and is hence suitable for future ion irradiation studies.
Revista:
NUCLEAR MATERIALS AND ENERGY
ISSN:
2352-1791
Año:
2016
Vol.:
9
Págs.:
422 - 429
Self-passivating tungsten based alloys for the first wall armour of future fusion reactors are expected to provide a major safety advantage compared to pure tungsten in case of a loss of coolant accident with simultaneous air ingress, due to the formation of a stable protective scale at high temperatures in presence of oxygen which prevents the formation of volatile and radioactive WO3. Bulk W-15Cr, W-10Cr-2Ti and W-12Cr-0.5Y alloys were manufactured by mechanical alloying followed by can encapsulation and HIP. This route resulted in fully dense materials with nano-structured grains. The ability of Ti and especially of Y to inhibit grain growth was observed in the W-10Cr-2Ti and W-12Cr-0.5Y alloys. Besides, Y formed Y-rich oxide nano-precipitates at the grain boundaries, and is thus expected to improve the mechanical behaviour of the Y-containing alloy. Isothermal oxidation tests at 800 degrees C (1073 K) and oxidation tests under accident-like conditions revealed that the W-12Cr-0.5Y alloy exhibits the best oxidation behaviour of all alloys, especially in the accident-like scenario. Preliminary HHF tests performed at GLADIS indicated that the W-10Cr-2Ti alloy is able to withstand power densities of 2 MW/m(2) without significant damage of the bulk structure. Thermo-shock tests at JUDITH-1 to simulate mitigated disruptions resulted in chipping of part of the surface of the as-HIPed W-10Cr-2Ti alloy. An additional thermal treatment at 1600 degrees C (1873 K) improves the thermo-shock resistance of the W-10Cr-2Ti alloy since only crack formation is observed. (C) 2016 The Authors. Published by Elsevier Ltd.
Revista:
PHYSICA SCRIPTA
ISSN:
0031-8949
Año:
2016
Vol.:
T167
N°:
014041
Self-passivating tungsten based alloys will provide a major safety advantage compared to pure tungsten when used as first wall armor of future fusion reactors, due to the formation of a protective oxide layer which prevents the formation of volatile and radioactive WO3 in case of a loss of coolant accident with simultaneous air ingress. Bulk WCr10Ti2 alloys were manufactured by two different powder metallurgical routes: (1) mechanical alloying (MA) followed by hot isostatic pressing (HIP) of metallic capsules, and (2) MA, compaction, pressureless sintering in H-2 and subsequent HIPing without encapsulation. Both routes resulted in fully dense materials with homogeneous microstructure and grain sizes of 300 nm and 1 mu m, respectively. The content of impurities remained unchanged after HIP, but it increased after sintering due to binder residue. It was not possible to produce large samples by route (2) due to difficulties in the uniaxial compaction stage. Flexural strength and fracture toughness measured on samples produced by route (1) revealed a ductile-to-brittle-transition temperature (DBTT) of about 950 degrees C. The strength increased from room temperature to 800 degrees C, decreasing significantly in the plastic region. An increase of fracture toughness is observed around the DBTT.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2016
Vol.:
59
N°:
5
Págs.:
359 - 369
The conventional PM ODS Ferritic Steel (FS) processing route includes gas atomisation of steel powder and its mechanical alloying (MA) with Y2O3 powder particles to dissolve yttrium and form, during consolidation, a dispersion of oxide nanoparticles (Y-Ti-O) in a nanostructured matrix. This work presents an alternative route to produce ODS steels avoiding MA: STARS (Surface Treatment of gas Atomized powder followed by Reactive Synthesis). STARS FS powders with composition Fe-14Cr-2W-0.3Ti-0.23Y, already containing the nanoparticles precursors, were gas-atomized. Oxygen, Y and Ti contents were tailored to the required values to form Y-Ti-O nanoparticles during processing. Powders were HIPped at 900, 1220 and 1300 degrees C. Specimens HIPped at 900 and 1220 degrees C were heat treated (HT) at temperatures ranging from 1200 to 1320 degrees C. The microstructural evolution with HIP and HT temperatures, including characterisation of nanoparticles and feasibility of achieving complete dissolution of prior particle boundaries (PPBs) were assessed.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2015
Vol.:
96-97
Págs.:
142 - 148
Several mock-ups, each of them consisting of six rectangular channels with dimensions according to the EU Test Blanket Modules (TBMs) specifications, were manufactured by selective laser melting (SLM) technology using P91, a ferritic-martensitic 9%Cr-1%Mo-V steel with a metallurgical behavior similar to EUROFER, the reference structural material for DEMO blanket concepts. SLM parameters led to an as-built density of 99.35% Theoretical Density (TD) that increased up to 99.74% after hot isostatic pressing (HIP). Dimensional control showed that the differences between the original design and the component are below 100 pm. By the appropriate selection of normalization and tempering parameters it was possible to obtain a material fulfilling P91 specification. The microstructure was investigated after SLM, HIP and normalizing and tempering treatments. In all cases, it consisted of thin martensitic laths. Subsize tensile samples were extracted from the mock-ups to measure the mechanical tensile properties after each step of the manufacturing process. The effect of thermal treatments on hardness was also evaluated.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2015
Vol.:
98 - 99
Págs.:
1973 -1977
Nanostructured Oxide Dispersion Strengthened Reduced Activation Ferritic Stainless Steels (ODS RAF) are promising structural materials for fusion reactors, due to their ultrafine microstructure and the presence of a dispersion of Y-Ti-O nanoclusters that provide excellent creep strength at high temperatures (up to 750 °C). The traditional powder metallurgical route to produce these steels is based on Gas Atomization (GA) + Mechanical Alloying (MA) + HIP + ThermoMechanical Treatments (TMTs). Recently, alternative methods have arisen to avoid the MA step. In line with this new approach, ferritic stainless steel powders were produced by gas atomization and HIPped, after adjusting their oxygen, Y and Ti contents to form Y¿Ti¿O nanoclusters during subsequent heat treatments. The microstructure of as-HIPped steels mainly consists of ferrite grains, Y-Ti precipitates, carbides and oxides on Prior Particle Boundaries (PPBs). Post-HIP heat treatments performed at high temperatures (1270 and 1300 °C) evaluated the feasibility of achieving a complete dissolution of the oxides on PPBs and a precipitation of ultrafine Ti- and Y-rich oxides in the Fe14Cr2W matrix. FEG-SEM with extensive EDS analysis was used to characterize the microstructure of the atomized powders and the ODS-RAF specimens after HIP consolidation and post-HIP heat treatments. A deeper characterization of atomized powder was carried out by TEM.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2014
Vol.:
89
N°:
7-8
Págs.:
1611 - 1616
Self-passivating tungsten based alloys are expected to provide a major safety advantage compared to pure tungsten when used as first wall armour of future fusion reactors, due to the formation of a protective oxide scale, preventing the formation of volatile and radioactive WO3 in case of a loss of coolant accident with simultaneous air ingress. In this work results of isothermal oxidations tests at 800 and 1000 degrees C on bulk alloy WCr12Ti2.5 performed by thermogravimetric analysis (TGA) and by exposure to flowing air in a furnace are presented. In both cases a thin, dense Cr2O3 layer is found at the outer surface, below which a Cr2WO6 scale and Ti2CrO5 layers alternating with WO3 are formed. The Cr2O3, Cr2WO6 and Ti2CrO5 scales act as protective barriers against fast inward O2- diffusion. The oxidation kinetics seems to be linear for the furnace exposure tests while for the TGA tests at 800 degrees C the kinetics is first parabolic, transforming into linear after an initial phase. The linear oxidation rates are 2-3 orders of magnitude lower than for pure W.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2014
Vol.:
89
N°:
7-8
Págs.:
1274 - 1279
Thermally and electrically insulating porous SiC ceramics are attractive candidates for Flow Channel Inserts (FCI) in dual-coolant blanket concepts thanks to its relatively inexpensive manufacturing route. To prevent tritium permeation and corrosion by Pb-15.7 a dense coating has to be applied on the porous SiC. Despite not having structural function, FCI must exhibit sufficient mechanical strength to withstand strong thermal gradients and thermo-electrical stresses during operation. This work summarizes the results on the development of coated porous SiC for FCI. Porous SiC was obtained following the sacrificial template technique, using Al2O3 and Y2O3 as sintering additives and a carbonaceous phase as pore former. Sintering was performed in inert gas at 1850-1950 degrees C during 15 min to 3 h, followed by oxidation at 650 degrees C to eliminate the carbonaceous phase. The most promising bulk materials were coated with a similar to 30 mu m thick dense SiC by CVD. Results on porosity, bending tests, thermal and electrical conductivity are presented. The microstructure of the coating, its adhesion to the porous SiC and its corrosion behavior under Pb-17.5Li are also shown.
Autores:
Rieth, M.; Dudarev, S.L.; Gonzalez de Vicente, S.M.; et al.
Revista:
JOURNAL OF NUCLEAR MATERIALS
ISSN:
0022-3115
Año:
2013
Vol.:
442
N°:
1-3 Supl.1
Págs.:
S173 - S180
The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on "Materials Science and Modeling." This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modeling, and validation experiments.
Revista:
JOURNAL OF NUCLEAR MATERIALS
ISSN:
0022-3115
Año:
2013
Vol.:
442
N°:
1-3 Supl.1
Págs.:
S219 - S224
Self-passivating tungsten based alloys are expected to provide a major safety advantage compared to pure tungsten, presently the main candidate material for first wall armour of future fusion reactors. In case of a loss of coolant accident with simultaneous air ingress, a protective oxide scale will be formed on the surface of W avoiding the formation of volatile and radioactive WO3. Bulk WCr12Ti2.5 alloys were manufactured by mechanical alloying (MA) and hot isostatic pressing (HIP), and their properties compared to bulk WCr10Si10 alloys from previous work. The MA parameters were adjusted to obtain the best balance between lowest possible amount of contaminants and effective alloying of the elemental powders. After HIP, a density >99% is achieved for the WCr12Ti2.5 alloy and a very fine and homogeneous microstructure with grains in the submicron range is obtained. Unlike the WCr10Si10 material, no intergranular ODS phase inhibiting grain growth was detected. The thermal and mechanical properties of the WCr10Si10 material are dominated by the silicide (W,Cr)(5)Si-3; it shows a sharp ductile-to brittle transition in the range 1273-1323 K. The thermal conductivity of the WCr12Ti2.5 alloy is close to 50 W/mK in the temperature range of operation; it exhibits significantly higher strength and lower DBTT - around 1170 K - than the WCr10Si10 material.
Revista:
JOURNAL OF NUCLEAR MATERIALS
ISSN:
0022-3115
Año:
2011
Vol.:
417
N°:
1-3
Págs.:
612 - 615
The erosion yield by deuterium impact was determined for various doped carbon-based materials. Ion beam bombardment with 30 and 200 eV at elevated temperatures (600-850 K) and low temperature plasma exposure with 30 eV ion energy (similar to 7 x 10(20) ions/m(2)s) and about 170 times higher thermal atomic deuterium flux at 300 K and 630 K were performed. The total yield of fine-grain graphites doped with 4 at.% Ti and Zr is reduced by a factor of 4 for 30 and 200 eV D impact at elevated temperatures at D fluences above 10(24) m(-2) compared to undoped graphite. Extensive carbide particle loss can be excluded up to fluences of similar to 10(25) m(-2).
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2011
Vol.:
86
N°:
9-11
Págs.:
2526 - 2529
SiC is the primary candidate for the flow channel inserts in dual-coolant blanket concepts. Porous SiC ceramics are attractive candidates for this non-structural application, since they can satisfy the required properties through a low cost manufacturing route, compared to SiC(f)/SiC. This work shows first results of the manufacturing of porous SiC ceramics prepared with different amounts of Y(2)O(3) and Al(2)O(3) as sintering additives. C powders were used as pore-formers by their burnout during oxidation after sintering. Comparison of microstructure, porosity, flexural strength, thermal and electrical conductivity and corrosion under Pb-15.7Li of porous SiC without and with sintering additives is presented. The addition of 2.5 wt.% of Y(2)O(3) and Al(2)O(3) improves the mechanical properties, and reduces the thermal and electrical conductivity down to reasonable values. Preliminary corrosion tests under Pb-15.7 Li at 500 degrees C show that the absence of a dense coating on porous SiC leads to poor corrosion behavior. (C) 2011 Elsevier B.V. All rights reserved.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2011
Vol.:
86
N°:
9-11
Págs.:
1719 - 1723
Self-passivating tungsten-based alloys may provide a major safety advantage in comparison with pure tungsten, which is presently the main candidate material for the plasma-facing protection of future fusion power reactors. WCrSi alloys were manufactured by mechanical alloying (MA) and HIP at 1300 degrees C and 200 MPa for 1 h. Different MA conditions were investigated to obtain powders with lowest possible amount of contaminants and small and homogeneous particle and crystallite size. Milling in WC vials under Ar without process control agent provided best results. After HIP densities close to 100% were obtained. First oxidation tests on preliminary alloys showed self-passivating behavior with rates comparable to WCrSi thin films at 800 degrees C but worse performance at 1000 degrees C. In all cases a Cr(2)WO(6) protective layer is formed at the surface.
Revista:
PHYSICA SCRIPTA
ISSN:
0031-8949
Año:
2011
Vol.:
T145
N°:
014018
Self-passivating tungsten-based alloys are expected to provide a major safety advantage compared to pure tungsten, which is at present the main candidate material for the first wall armour of future fusion reactors. WC10Si10 alloys were manufactured by mechanical alloying (MA) in a Planetary mill and subsequent hot isostatic pressing (HIP), achieving densities above 95%. Different MA conditions were studied. After MA under optimized conditions, a core with heterogeneous microstructure was found in larger powder particles, resulting in the presence of some large W grains after HIP. Nevertheless, the obtained microstructure is significantly refined compared to previous work. First MA trials were also performed on the Si-free system WCr12Ti2.5. In this case a very homogeneous structure inside the powder particles was obtained, and a majority ternary metastable bcc phase was found, indicating that almost complete alloying occurred. Therefore, a very fine and homogeneous microstructure can be expected after HIP in future work.
Revista:
MICROPOROUS AND MESOPOROUS MATERIALS
ISSN:
1387-1811
Año:
2010
Vol.:
134
N°:
1-3
Págs.:
141 - 149
The porosity of undoped and Zr- and Ti-doped graphites has been determined using ultra small and small angle neutron scattering, nitrogen adsorption and helium pycnometry To differentiate between open and closed in the neutron measurements the contrast matching technique was employed It is shown that the combination of the three techniques is necessary for an accurate determination of the porosity and for the assessment of the structural modifications arising from the doping which results in the transformation of open porosity to closed