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Abstract Tungsten alloys with high strength, high toughness and high-temperature stability are strongly desired in extreme conditions. The nanoengineering of potassium bubbles (5–50 nm) is a fascinating strategy to strengthen these properties. However, such nano potassium bubbles can only be acquired in tungsten wires through swaging and drawing process till now. Here, we report an intra- and inter-potassium nano-bubbles strengthened bulk tungsten fabricated via an industrially applicable process combining aluminum-potassium-silicon (AKS) doping and spark plasma sintering (SPS), which exhibits desirable strength and remarkable toughness, as well as high thermal-shock resistance. The AKS-doping incorporated the K-Al-Si-O particles inside the W grains and the rapid high-temperature sintering of SPS produced the nanometer K bubbles from the K-Al-Si-O particles and kept the K bubbles inside the W grains. Our K-bubble strengthened tungsten material displays high potential in high-temperature applications. This strategy is also potentially applicable to other refractory metals such as molybdenum. Highlights • Nanoscaled potassium-bubbles strengthened bulk tungsten alloy is prepared. • This alloy exhibits highly desirable mechanical and thermal properties. • Those properties further lead to a high thermal-shock resistance. • This nanostructuring strategy helps guide endeavors to design other metal system. [ABSTRACT FROM AUTHOR]

Abstract Tungsten-potassium-titanium (W-K-Ti) alloys were fabricated by spark-plasma-sintering (SPS) and traditional rotary swaging (RS) techniques. Doping conditions and sintering methods were compared on the relative density, microstructure, hardness, recrystallization temperature, and the thermal shock resistance properties. Transient heat loads under 0.37 GW m−2 were applied on the W-K-Ti samples at room temperature for different cycles and pulsed durations. It was found that moderate Ti-doping (0.05 and 0.075 wt%) in W-K alloys can enhance the thermal shock resistance. Low-cycle thermal fatigue test suggested better thermal shock resistance in SPS-sintered W-K-Ti alloy (SPS-W-K-Ti) using TiH 2 dopant. The main reason was that the decomposition of TiH 2 significantly reduced the oxygen content of the ingots, which improved the ductility and thermal shock resistance of tungsten alloys. Further fracture analyses indicated that Ti-doping through TiH 2 formed intra- and inter- Ti-rich voids in TiH 2 -doped W-K alloy, while only intergranular Ti particles were found lying along grain boundaries in the Ti-doped one. The formation mechanism of the Ti-rich voids was investigated in detail. This work provides a potential route for obtaining plasma facing materials with high thermal shock resistance. Highlights • Novel W-K-Ti alloys were fabricated by spark-plasma-sintering and rotary swaging. • Positive effect was found by proper Ti doping for enhancing thermal shock resistance. • Novel phenomenon of TiH 2 doping was observed, resulting in better heat resistance. • The different properties of W-K alloys are due to the respective forms of Ti dopant. • The formation mechanism of Ti aggregation is presented for the first time. [ABSTRACT FROM AUTHOR]

Abstract Elemental powder metallurgy is an effective way to improve the ductility and strength of nanostructured TiAl alloys. However, the high ductility of Al largely restricts the application of elemental powder metallurgy. Here we demonstrate a novel avenue in fabricating nanostructured Ti-45Al-8Nb alloys by cryomilling (CM) and Spark Plasma Sintering (SPS) from elemental powder metallurgy. Our work reveals that CM not only prevents the Ti/Al/Nb powder mixture from cold welding, but also makes the resultant powder homogeneous with an average particle size of 217 nm. The nano-powders were sintered by SPS at 900, 1000 and 1100 °C, forming ultrafine grained (UFG) equiaxed near-γ and lamellar structures. Particularly, as a result of grain refinement strengthening, the specimen sintered at 1000 °C shows excellent mechanical properties, with the compression yield strength, fracture strength and plastic strain as 1575 MPa, 2627 MPa and 23.5%, respectively at room temperature; and 955 MPa, 1041 MPa and 38.4%, respectively at 850 °C. This work demonstrates the superiority of the combined CM-SPS in fabricating nanostructured Ti-45Al-8Nb alloys with enhanced mechanical properties, which is considered as highly potential in exploring high-performance TiAl alloys. Highlights • Nanoscale Ti-45Al-8Nb alloy powder could be prepared by cryomilling. • Nanostructured Ti-45Al-8Nb alloys without segregations are fabricated by SPS. • The sintered alloys own the excellent compression properties. • Effect of microstructures on compression properties is elaborated. [ABSTRACT FROM AUTHOR]

Trace titanium and yttrium (~0.1 wt.%) were doped to the novel W-K-Mo-Ti-Y alloys to investigate their performance under simulated transient heat loads in fusion reactor. The micro-structure, Vickers micro-hardness, cracks formation and surface roughness after transient heat loads were analyzed through X-ray diffraction analysis (XRD), Vickers Micro-hardness device, scanning electron microscopy (SEM) and three dimensional (3D) industrial optical microscope, respectively. It indicated that the transient heat loads would lead to surface cracking and roughening on the loaded surface, as well as a decrease on micro-hardness. Further, trace titanium and yttrium doping in the samples could largely mitigate surface roughening after transient heat loads. Both titanium and yttrium have significant influence on the surface cracking threshold and plastic deformation, indicating the improvement of transient heat loads resistance in this novel alloy. [ABSTRACT FROM AUTHOR]

W-K-TiC alloys with different titanium carbide concentration (0.05, 0.1, 0.25, 1) wt.% were fabricated through spark plasma sintering (SPS) method. Single shot thermal shock tests with a length of 5 ms and 100 shots thermal shock tests with a length of 1 ms were carried out. The microstructure and Vickers micro-hardness of each sample were investigated. It is revealed that the surface of the samples began to recrystallize after thermal shock tests, and the samples with 5 ms for single shot had more serious recrystallization than the samples with 1 ms for 100 shots because of its higher surface temperature after thermal shock tests. The samples were annealed at 1400 °C, 1600 °C, 1800 °C, respectively. It is shown that the addition of TiC particles could slow down recrystallization of W-K-TiC alloy, and its recrystallization temperature can reach to between 1400 °C and 1600 °C. [ABSTRACT FROM AUTHOR]

Effects of helium plasma irradiation on spark plasma sintering (SPS) W-K, pure W and traditionally sintered commercial W-K have been studied, concerning the density, grain size and potassium content as the influence factors. Pinholes are formed under 120 eV He ions at 600 °C and 1 × 10 23 m −2 fluence on the surface of all samples. It is found that SPS-sintered W-K shows the best irradiation resistance among the present samples, and SPS-sintered pure W exhibits higher irradiation tolerance than commercial W-K. Different He-plasma tolerance was observed among the SPS-sintered W-K samples due to varied potassium content and grain size. In addition, the microstructure evolution under helium irradiation, the growth-migration of helium bubbles and their interactions of potassium bubbles have also been discussed. [ABSTRACT FROM AUTHOR]

Dense potassium-doped tungsten (W–K) ingots with homogeneously dispersed nanoscaled bubbles were fabricated by spark plasma sintering (SPS) using Al–K–Si (AKS) doped tungsten powder. Parameters such as sintering temperature, holding time and sintering pressure were considered to tune the grain size, density, microhardness, bubble formation and impurity contents. In addition, a two-step sintering scheme was designed to reduce Al/Si impurity contents and enhance the density. The sample prepared by the two-step sintering scheme displays both inter- and intra-granular nanocomposites, which is expected to have better creep resistance, high bending strength and fracture toughness. Potassium was detected inside the bubbles, determining the crucial role in the bubble formation process, and thus leading to compatible properties as plasma-facing material. [ABSTRACT FROM AUTHOR]