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Tungsten and its alloys are widely recognized as key components in high-temperature environments. In this study, self-passivating W-Si-xY alloys with varying Y content were prepared using mechanical alloying (MA) and spark plasma sintering (SPS). The synergistic effects of Y content and milling time on the microstructures and oxidation resistance of the alloys were revealed. This study found that the oxidation resistance of the alloys increased as the Y content increased. However, the effect of milling time on oxidation resistance was complex. For W-Si-xY alloys with low Y content (0Y and 2Y), the oxidation resistance decreased with increasing milling time. In contrast, for W-Si-xY alloys with high Y content (4Y and 6Y), the oxidation resistance increased with increasing milling time. This enhanced oxidation resistance is due to the microstructural changes in the protective composite layer, including the size and distribution of W5Si3, Y2Si2O7 aggregates, and W-Y-O melt. The thickness of the oxide layer on the W-Si-6Y alloy after being oxidized at 1000 °C for 2 h was only 70.7 μm, demonstrating its superior oxidation resistance. [ABSTRACT FROM AUTHOR]

Self-passivating W alloys have excellent high temperature oxidation resistance and are expected to be used as a key component in high temperature environment. In this study, a series of W-Si-xY self-passivating alloys were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Effects of Y content on phase compositions, microstructures, and oxidation resistance at high temperatures were investigated systematically. The results show that the oxidation resistance of the alloys increases with the increase of Y content (0.0~5.0 wt.%), but the oxidation resistance of the alloys deteriorates when the Y content reaches 9.6 wt.%. The alloy with 3.8 wt.% Y shows the best oxidation resistance. The thickness of its oxide layer is ~249.1 μm when the oxidation time reaches 80 h, which is thinner than that of other alloys. Effects of Y content on the oxidation resistance are revealed. During the oxidation process, Y can react with other elements to form molten-like W-Y-O and Y2Si2O7 particles. It is found that these two phases play a key role in the oxidation resistance of the alloys. When the Y content is in the range of 0~5.0 wt.%, a W-Y-O covering layer gradually forms with the increase of Y content, which can prevent further oxidation of the alloy. In the meantime, small Y2Si2O7 particles were formed and the microcracks formed around these particles were isolated, which have little effect on the oxidation resistance of the alloys. However, when Y content reaches 9.6 wt.%, large Y2Si2O7 particles and extensive cracks around them are formed. These cracks are interconnected to form penetrating channels for O2 from the environment to the alloy interior, which deteriorates the oxidation resistance of the alloys. [ABSTRACT FROM AUTHOR]

Mechanical alloying (MA) is widely used to produce oxide‐dispersion‐strengthened (ODS) steels, which are potential candidate structural materials for the next‐generation fusion reactors. Here in this study, two kinds of ODS ferritic alloys, labeled A and B, are prepared through MA, followed by spark plasma sintering (SPS) and annealing. To prepare Alloy A, Fe powder, YH2 powder, and TiO2 powder are mixed for MA. To prepare Alloy B, a pre‐alloyed Fe–Cr–W–Y powder is first obtained by gas‐atomization, after which TiO2 powder is added for MA. Compared with the traditional MA method, where the highly stabilized Y2O3 powder is usually selected, the use of TiO2 powder successfully reduces the milling time since it should be more easily decomposed and dissolved into the ferrite matrix. Some TiO2–Y2TiO5 duplex oxide particles of about 50 nm are found to generate through diffusion‐induced in situ reactions in Alloy A. In Alloy B, in contrast, a high number density of well‐distributed Y2O3 particles of about 20 nm and ultrafine Y2Ti2O7 particles within 10 nm are observed. These nanoparticles maintain good coherent interfaces with the matrix, suggesting the precipitation mechanism. Herein, a new route for the efficient fabrication of ODS alloys is provided. [ABSTRACT FROM AUTHOR]

An oxide-dispersion-strengthened (ODS) 13Cr-1W steel has been fabricated through mechanical alloying (MA) and spark plasma sintering (SPS) using pre-alloyed Fe-Cr-W-Y powder and TiO 2 powder. Sufficient MA effects, indicated by homogeneous distribution of alloying elements and high level of lattice strain inside the powder, have been obtained within 20 h of high-energy ball-milling. Grain refinement of the bulk materials is successfully achieved by optimizing the sintering temperature and pressure during SPS. A fine-grained ODS steel with average grain size of 626.75 nm is prepared when sintered at 950 °C/80 MPa. Ultrafine oxide dispersoids, identified as Y 2 O 3 , Y 2 TiO 5 and Y 2 Ti 2 O 7 , are observed homogeneously distributed in the steel matrix after annealing. They have a number density of 4.5 × 1022 m−3 and an average size of 11.15 nm. Tensile tests from room temperature to 700 °C are conducted to this ODS steel. It exhibits an ultimate tensile strength and a yield strength of 1559.60 MPa and 1352.82 MPa at room temperature, respectively. Due to a good combination of dislocation strengthening, grain boundary strengthening and precipitation strengthening, this alloy wins superior tensile properties over most of the commercial ODS steels and those reported in some previous studies. • A nano-Y-Ti-O dispersion strengthened 13Cr-1W steel was prepared by MA and SPS. • MA process has been finished within 20 h using Y-containing pre-alloyed powder and TiO 2 powder. • Grain refinement was achieved by optimizing sintering temperature and pressure. • High number density of Y-Ti-O nanoparticles in-situ precipitated during annealing. • The steel possesses excellent tensile properties from room temperature to high temperature. [ABSTRACT FROM AUTHOR]

A Y–Ti–O oxide-dispersion-strengthened (ODS) Cu alloy has been successfully fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Excessive cold-welding during high energy ball-milling was effectively suppressed by mixing TiO 2 and pre-alloyed Cu(Y) powders as the raw powders. Microstructural evolutions during the MA and SPS processes and the subsequent annealing were investigated with a focus on the Y–Ti–O nano-oxides. The 12 h ball-milling failed to achieve super-saturations of Y, Ti, and O in Cu, which led to the in-situ formation of various types of oversized Y/Ti-rich oxides with very irregular morphologies during the SPS. With a prolonged ball-milling of 48 h, the subsequent SPS + annealing processes can promote a high density precipitation of ultra-fine Y–Ti–O nano-oxides. These nano-oxides were further identified as Y 2 Ti 2 O 7 mostly, with a high degree of coherency in Cu. Fabricating Y–Ti–O ODS-Cu alloys via MA was thus confirmed to be technically feasible, although the dispersion of nano-oxides desires further improvement. • A Y–Ti–O ODS-Cu alloy was fabricated via mechanical alloying. • Using pre-alloyed Cu(Y) powders reduced cold-welding risks during ball-milling. • A high number of Y–Ti–O nano-oxides (mostly Y 2 Ti 2 O 7) were produced in Cu matrix. [ABSTRACT FROM AUTHOR]

• ODS-Cu alloy containing a high number density (2.16×1024 m−3) of uniformly dispersed nanoscale Y 4 Al 2 O 9 particles (mean particle size: 4.8 nm) was fabricated. • Coherent interface between Y 4 Al 2 O 9 nanoparticles and Cu(Al) solid solution matrix was formed with an orientation relationship of (3 1 ¯ 2) Y 4 A l 2 O 9 ∥ (1 1 ¯ 1) Cu (Al) and a small lattice mismatch of 0.337%. • The microhardness of the ODS-Cu alloy was enhanced to 228.6 HV. A relatively high thermal conductivity of 269 W m−1 K−1 at 600 °C for the ODS-Cu alloy was maintained. The softening temperature of the ODS-Cu alloy was more than 1000 °C. Oxide dispersion-strengthened copper (ODS-Cu) alloys with yttrium oxide nanoparticles are promising heat sink materials in fusion reactor due to their high strength, thermal conductivity and thermodynamic stability. The particle size and number density of oxide nanoparticles can be improved via addition of microalloying element. In this study, the atomized Cu-Y alloy, Al and Cu 2 O were used as the Y source, the microalloying element and the oxidant material, respectively, to fabricate ODS-Cu alloy by mechanical alloying method. After spark plasma sintering and annealing, a ODS-Cu alloy with a microstructure containing Y 4 Al 2 O 9 nanoparticles homogeneously distributed in Cu(Al) solid solution matrix was successfully fabricated. It is found that a crystallographic orientation relationship of (3 1 ¯ 2) Y 4 A l 2 O 9 ∥ (1 1 ¯ 1) C u (A l) was formed between Y 4 Al 2 O 9 nanoparticles and Cu(Al) matrix and the lattice mismatch was 0.337%. The small lattice mismatch reduced the nucleation barrier for Y 4 Al 2 O 9 nanoparticles so a mean particle size of 4.8 nm and a number density of 2.16×1024 m−3 were obtained in the alloy. Consequently, the microhardness was enhanced via Hall-Petch strengthening, dislocation strengthening and dispersion strengthening. The softening temperature of ODS-Cu alloy was improved to higher than 1000 °C due to the thermodynamic stability and the pinning effect of Y 4 Al 2 O 9 nanoparticles. In addition, the thermal conductivity of Cu-1Y-9Al-0.3Cu 2 O alloy is close to other copper alloys as the volume fraction of Y 4 Al 2 O 9 nanoparticles is limited. Cu-1Y-9Al-0.3Cu 2 O alloy provides a good overall performance, which may be used as heat sink materials under severe conditions. [ABSTRACT FROM AUTHOR]

Abstract: Bulk dense composites of Al–Fe alloys containing 2.5–10at% Fe were fabricated by mechanical alloying (MA) and spark plasma sintering (SPS). Supersaturated Al(Fe) solid solutions were obtained by MA for 80h. The sintered samples are composed of nano and ultrafine needle-like Al13Fe4 phase and angular-shaped Al13Fe4 phase with a size range of 1–2μm uniformly distributed in the Al matrix. Needle-like Al13Fe4 phase originates from the precipitation of supersaturated Al(Fe) solid solutions, and angular-shaped Al13Fe4 phase originates from the reaction of undissolved Fe particles and the Al melt. The hardness of the alloys varied from 1.44 to 1.97GPa and Al–10%Fe exhibited highest specific yield strength of 391.1kNm/kg. The yield strength varied from 657 to 1130MPa, depending on the Fe content. Excellent plastic strain (>14.5%) were achieved in the alloys containing 2.5–5%Fe, but the Al–10%Fe exhibited elastic behavior only, failing without any macroscopic yielding or plastic strain. The lack of plastic performance of Al–10%Fe is attributed to large amount of undissolved Fe particles reacted with the Al melt to form angular-shaped Al13Fe4, leading to the absence of soft α-Al phase. [Copyright &y& Elsevier]