Revistas
Revista:
INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HARD MATERIALS
ISSN:
0263-4368
Año:
2024
Vol.:
119
Págs.:
106540 - *
Infiltration is an extensively used technique in the production of Diamond Impregnated Bits (DIBs) commonly used for drilling in both mineral exploration and the Oil&Gas industry. This paper describes research into liquid phase sintering (LPS) as an alternative to commonly used infiltration processes. The great wear resistance and high cutting ability necessary for these tools in turn requires a high diamond concentration and a large volume fraction of wear-resistant components, such as tungsten carbide and/or eutectic tungsten carbide particles. With relatively large particles that do not contribute to densification, the LPS system researched was designed with a relatively large amount of permanent liquid phase sintering, with, rearrangement being selected as the primary densification mechanism owing to the stability of the hard phases. After testing various binder phases and evaluating the influence of the liquid phase volume fraction and presence of some sintering aids, results are promising. Bonds with better sintering behaviour were characterized, while hardness, microstructure, abrasive wear resistance, and interaction with diamonds were studied. The proposed 35NiP25Cu40WC bond processed by LPS attained hardness of 66 HRA and wear coefficient of 20 mm3/MPa, levels similar to those obtained by hot pressed components currently used in the diamond drilling tool industry (19 mm3/MPa).
Revista:
HELIYON
ISSN:
2405-8440
Año:
2023
Vol.:
9
N°:
3
Págs.:
e13931 - *
The sinterability of a commercial Fe-Cu pre-alloyed powder, designed to be used as a metallic bond in diamond impregnated tools, has been greatly analyzed by combining dilatometry, computational thermodynamic calculations, and microstructural analysis. The effect of sintering temperature and alloying elements such as graphite and iron phosphide have been taken into consideration in order to demonstrate the capability of tailoring final properties through different strategies, and dilatometry and microstructural analysis have been used to understand the densification process of the alloys. Solid phase sintering was the mechanism taking place during thermal cycle. In fact, a liquid phase appears but because of the high densification level at that time mechanisms associated with LPS do not contribute to densification. Discussion about me-chanical properties has been related to key microstructural phenomena, i.e., grain growth, phase transformation, precipitation, and solid solution. Obtained hardness ranged from 83 HRB to 106 HRB with yield stresses between 450 MPa and 700 MPa and elongations above 3%, while final tensile properties similar to those obtained by cobalt-based powders processed by hot pressing were also obtained.
Autores:
Guzmán, D. (Autor de correspondencia); González, F.; Muranda, D.; et al.
Revista:
MATERIALS
ISSN:
1996-1944
Año:
2023
Vol.:
16
N°:
10
Págs.:
3618
This study investigated the synthesis of Ag-SnO2-ZnO by powder metallurgy methods and their subsequent electrical contact behavior. The pieces of Lambda g-SnO2-ZnO were prepared by ball milling and hot pressing. The arc erosion behavior of the material was evaluated using homemade equipment. The microstructure and phase evolution of the materials were investigated through X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy. The results showed that, although the mass loss of the Ag-SnO2-ZnO composite (9.08 mg) during the electrical contact test was higher than that of the commercial Ag-CdO (1.42 mg), its electrical conductivity remained constant (26.9 +/- 1.5% IACS). This fact would be related to the reaction of Zn2SnO4's formation on the material's surface via electric arc. This reaction would play an important role in controlling the surface segregation and subsequent loss of electrical conductivity of this type of composite, thus enabling the development of a new electrical contact material to replace the non-environmentally friendly Ag-CdO composite.
Revista:
JOURNAL OF ALLOYS AND COMPOUNDS
ISSN:
0925-8388
Año:
2022
Vol.:
890
Págs.:
161631
Hot Isostatic Pressing (HIP) is a well-known technique that lately is gaining more interest because of its growing involvement in the Additive and Near-Net Shape manufacturing fields. When HIP is used for near net-shape manufacturing, the raw gas atomized powders assume the uttermost importance, and special attention should be given to their quality and characteristics. Based on this statement, the powder should be sieved directly after production to select only those that best suit the HIP process. Typically, a broad Particle Size Distribution is indicated for HIP purposes and looks economically advisable because it leads to a higher yield. Despite this, if the PSD is not strictly controlled, particles with high Oxygen content or chemical inhomogeneity could enter the production chain, leading to compacted components with insufficient mechanical properties. In this paper, Nickel-based superalloy Astroloy particles were assessed in depth both at their surface and in the core, dividing them into sub-batches via mechanical sieving. This procedure evidenced which contribution was brought to the final raw material by each sub-batch. Furthermore, physical properties such as flowability and tap density were studied as a function of the PSD. Next, a complete morphological assessment was conducted to understand the possible defects of each sub-batch better. Similarly, every particle group was chemically studied to determine the Oxygen, Carbon, Nitrogen, and Hydrogen content of each sub-batch. Micro and nano indentations combined with EBSD were used to understand how the particle size may affect the mechanical properties of the powders during the Hot Isostatic pressing. Furthermore, EDS and XRD analysis were used to thoroughly understand how Ti segregation starts forming and what effects are likely to develop. Based on these investigations, it was possible to rationally identify the upper and lower boundary for particle PSD without excessively limiting the overall process yield. (c) 2021 Elsevier B.V. All rights reserved.
Revista:
MATERIALS
ISSN:
1996-1944
Año:
2022
Vol.:
15
N°:
4
Págs.:
1434
Astroloy is a Ni-based superalloy with high-volume fraction of gamma ', which gives high temperature properties but reduces its forgeability. Therefore, powder metallurgy manufacturing processes such as Near Net Shape HIPping are the most suitable manufacturing technology for Astroloy. However, NNSHIP has its own drawbacks, such as the formation of prior particle boundaries (PPBs), which usually tend to decrease material mechanical properties. The detrimental effect of PPBs can be reduced by optimizing the entire HIP processing route. Conventional HIP cycles have very low cooling rates, especially in big components from industry, and thus a series of post-heat treatments must be applied in order to achieve desirable microstructures and improve the mechanical properties. Standard heat treatments for Astroloy are long and tedious with several steps of solutioning, stabilization and precipitation. In this work, two main studies have been performed. First, the effect of the cooling rate after the solutioning treatment, which is driven by the materials' thermal mass, on the Astroloy microstructure and mechanical properties was studied. Experimental analyses and simulation techniques have been used in the present work and it has been found that higher cooling rates after solutioning increase the density of tertiary gamma ' precipitates by 85%, and their size decreases by 22%, which leads to an increase in hardness from 356 to 372 HB30. This hardness difference tends to reduce after subsequent standard heat treatment (HT) that homogenizes the microstructure. The second study shows the effect of different heat treatments on the microstructure and hardness of samples with two different thermal masses (can and cube). More than double the density of gamma ' precipitates was found in small cubes in comparison with cans with a higher thermal mass. Therefore, the hardness in cubes is between 4 and 20 HB 30 higher than in large cans, depending on the applied HT.
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.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2021
Vol.:
64
N°:
4
Págs.:
331 - 340
Different approaches to take advantage of powder metallurgy in the manufacturing of diamond-impregnated components were studied. Three different powders were used as starting materials; two pre-alloyed powders, based on Fe-Cu and Fe-Cu-Sn systems, and one pre-mixed Fe-based powder. Different manufacturing routes as a strategy to obtain tailored mechanical properties were studied, with the influence of alloying elements such as graphite, iron phosphide and Mn-Ni-B master alloy to reinforce the iron-based powders. Both uncoated and coated commercial synthetic diamonds were introduced in the systems to analyse the surface reactions that depend on both metallic matrix and processing parameters. Hardness values from 88 to 105 HRB were obtained with a wide range of transverse rupture strength values from 1250 to 1640 MPa. An appropriate combination of metallic matrix, alloying elements and processing parameters makes the materials analysed here suitable powders for the manufacturing of diamond-impregnated tools.
Autores:
Martinez, C. (Autor de correspondencia); Briones, F.; Aguilar, C. ; et al.
Revista:
MATERIALS LETTERS
ISSN:
0167-577X
Nanocrystalline Ni (Ni-nc) obtained by mechanical milling may present improved mechanical properties paired with high abrasion resistance. Different sintering processes were used to consolidate Nanocrystaline Ni: hot pressed (HP) and hot-isostatic pressed (HIP). The microstructure, mechanical properties, and tribological were evaluated to compare the processes. X-ray diffraction patterns showed that HIP-consolidated specimens had larger crystallite sizes and 37% less microstrain when compared to the HP specimens. The nanohardness of the HIP specimens was also carried out and it was 50% lower than that of HP specimens, whereas its coefficient of friction found was 25% higher. These results show the advantages of the HP process over the HIP since the high pressure. The low sintering temperature of HP inhibited the grain growth, which leads excellent mechanical and tribological properties of Ni.
Revista:
FUSION ENGINEERING AND DESIGN
ISSN:
0920-3796
Año:
2019
Vol.:
146
N°:
Part.B
Págs.:
1596 - 1599
Compared to pure tungsten, self-passivating tungsten based alloys for the first wall armor of future fusion reactors shall provide a major safety advantage 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 preventing the formation of volatile and radioactive WO3. Recently developed W-Cr-Y alloys produced by mechanical alloying and hot isostatic pressing (HIP) exhibit a strong reduction of oxidation rate compared to pure W and high mechanical strength. A heat treatment after HIP at 1555°C results in a one-phase material with a high thermal shock resistance. Nevertheless, the microstructure is metastable and its thermal stability under operational conditions has to be assessed. In this work results of thermal stability tests on heat treated W-10Cr-0.5Y alloy subjected to temperatures of 650, 700, 800 and 1000°C for times ranging from 50 to 1000h are presented. After 1000h at 650°C and 100h at 700°C no visible change of the microstructure is detected. After 100h at 1000°C a complete decomposition takes place with the formation of a uniform, fine-scale mixture of W- and Cr-rich phases, typical for spinodal decomposition.
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.
Revista:
DIAMANTE. APPLICAZIONI & TECNOLOGIA
ISSN:
1824-5765
Año:
2018
Vol.:
95
Págs.:
22 - 30
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.
Autores:
Guzman, D. (Autor de correspondencia); Garcia, C.; Soliz, A. ; et al.
Revista:
METALS
ISSN:
2075-4701
Año:
2018
Vol.:
8
N°:
6
Págs.:
417
The aim of this work was to study the synthesis and electrochemical properties of Ti 2 wt %-Si alloys prepared by mechanical alloying (MA) and heat treatment. The MA process was performed under Ar atmosphere. The structural, morphological, and compositional evolutions during the milling and subsequent heat treatment were investigated by X-ray diffraction, energy-dispersive spectroscopy, and scanning electron microscopy. The electrochemical behavior was evaluated by open circuit potential and linear sweep voltammetry measurements. The results showed that the MA process promotes the formation of a supersaturated alpha-Ti-Si solid solution. During heat treatment, the Si remaining in the mechanically alloyed powders and the Si from the alpha-Ti-Si supersaturated solid solution reacted with Ti to form Ti-Si intermetallic compounds. These compounds have a fine and homogeneous distribution in the alpha-Ti matrix, which cannot be achieved by conventional casting methods. Additionally, the electrochemical evaluations revealed that the mechanically alloyed and heat-treated Ti 2 wt %-Si powders have better corrosion resistance in 1.63 M H2SO4 than the pure Ti and MA Ti-Si samples. This is likely due to the particular microstructure produced during the milling and subsequent heat treatment.
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.
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.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2016
Vol.:
59
N°:
2
Págs.:
128 - 141
Present empirical correlations to predict the median particle size of water atomised powders have a validity restricted to a particular atomiser and alloy family. This work proposes a mathematical function that takes into account the influence of the heat transfer coefficient and, therefore, of the solidification time on the median particle size. This equation is applied in combination with previously proposed empirical correlations to extend their validity to a broader range of alloys. Experiments were conducted with alloys of different melting point (Fe base, Cu base and Sn). Quantitative measurements of the median particle size, tap density and several shape factors, and qualitative observations of the particle shape confirmed the importance of the heat transfer rate. It is shown that the inclusion of the solidification time effect results in a better agreement between calculated and experimental data when both low and high melting temperature alloys are taken together.
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.
Autores:
Guzman, D.; Muñoz, P.; Aguilar, C.; et al.
Revista:
APPLIED PHYSICS A-MATERIALS SCIENCE AND PROCESSING
ISSN:
0947-8396
Año:
2014
Vol.:
117
N°:
2
Págs.:
871 - 875
Nowadays, Ag-CdO alloys are widely used in electrical contact applications, because of their good electrical and thermal conductivity is as well as high resistance to arc erosion and contact welding. Considering the restricted use of Cd due to its toxicity, it is necessary to find a material that can replace those alloys. The objective of this work was to study the possibility of obtaining an Ag-ZnO alloy from an Ag-Zn solid solution powders by means of a mechanochemical method. The mechanochemical process was carried out in a SPEX 8000D mill, under air and with ethanol as a reaction agent. Based on the results obtained, it can be concluded that an Ag-ZnO alloy with a fine and uniform ZnO distribution in the Ag matrix can be obtained by applying the mechanochemical process for 25 h.
Revista:
POWDER METALLURGY
ISSN:
0032-5899
Año:
2013
Vol.:
56
N°:
5
Págs.:
362 - 373
The sintering behaviour of prealloyed powder compacts has been studied as a function of the sintering atmosphere in free sintering experiments. Atmospheres with different hydrogen/nitrogen ratios and even vacuum have been used in the sintering cycles. Powder compacts with and without diamond additions have been sintered. Three different grades of diamond were used in the experiments, all of them synthetic manmade diamond. Two had different levels of metallic inclusions and one was coated with Ti. The interaction between bond/atmosphere/diamond has been characterised analysing the density, microstructure, bend strength and degradation of the diamonds after dissolving the matrix. Diamonds from atmospheres with low hydrogen content show evidence of strong degradation. Moreover, any diamond additions strongly decrease the strength of the bonds, acting as defects. The strength is also affected by the sintering atmosphere and sintering temperature but not significantly by the type of diamond.
Autores:
[Martinez, C.; Ordonez, S.; Guzman, D.; et al.
Revista:
JOURNAL OF ALLOYS AND COMPOUNDS
ISSN:
0925-8388
Año:
2013
Vol.:
581
Págs.:
241 - 245
Phase evolution during mechanical alloying (MA) of elemental Mg and Cu powders and their subsequent heat treatment is studied. Elemental Mg and Cu powders in a 2:1 atomic ratio were mechanically alloyed in a SPEX 8000D mill using a 10:1 ball-to-powder ratio. X-ray diffraction (XRD) shows that the formation of the intermetallic Mg2Cu takes place between 3 and 4 h of milling, although traces of elemental Cu are still present after 10 h of milling. The thermal behavior of different powder mixtures was evaluated by differential scanning calorimetry (DSC). The combination of DSC, heat treatment and XRD has shown a sequence of phase transformations that results in the intermetallic Mg2Cu from an amorphous precursor. This amorphous phase is converted into Mg2Cu by heating at low temperature (407 K). Short MA times and the formation of the amorphous precursor, together with its subsequent transformation into Mg2Cu at low temperatures; represent an advantageous alternative route for its preparation. (c) 2013 Elsevier B.V. All rights reserved.
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:
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:
REVISTA DE METALURGIA
ISSN:
0034-8570
Año:
2010
Vol.:
46
N°:
3
Págs.:
240 - 248
Se estudió la evolución microestructural de composites de SiC/aleaciones Cu-Si obtenidos a través del proceso de infiltración reactiva a 1400 °C. Se detectaron tres zonas en los composites obtenidos: zona de reacción, transición e infiltrada. En la zona de reacción y de transición, la microestructura resultante estuvo compuesta por una fase metálica, láminas de grafito y partículas de SiC. Se encontró que el SiC se descompone en estas zonas por efecto de la aleación Cu-Si, por lo que el silicio disponible forma una solución líquida que a temperatura ambiente estuvo formada por una solución sólida a y una fase Y (Cu5Si). El carbono resultante de la descomposición del SiC precipitó como láminas de grafito. Además, la descomposición del SiC fue disminuyendo a medida que la cantidad de silicio en la aleación inicial se incrementó.
Revista:
REVISTA DE METALURGIA
ISSN:
0034-8570
Año:
2010
Vol.:
46
N°:
3
Págs.:
240 - 248
The microstructural evolution of composites of SiC/Cu-Si alloys obtained through process of reactive infiltration to 1400 degrees C was studied. Three zones were detected in the obtained composites: the reaction zone, the transition zone and the infiltrated zone. In the reaction zone and transition zone the resulting microstructure was composed of a metallic phase, graphite laminae and SiC particles. It was found that SiC decomposes into these areas because of the alloy Cu-Si, so the available Si forms a liquid solution that a room temperature consisted of a a solid solution and a gamma phase (Cu(5)Si). The carbon resulting from the decomposition of SiC precipitated as graphite laminae. In addition, the SiC decomposition was decreasing as the initial amount of Si in the alloy increased.