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Diamond particles dispersed Zr-alloyed Cu matrix composites were produced by a gas pressure infiltration route. The thermal conductivity first increased and then decreased with ...increasing Zr content in the range of 0.0–1.0wt.%, yielding a maximum thermal conductivity of 930W/mK at 0.5wt.% Zr. The high thermal conductivity is attributed to the optimized thickness of interfacial ZrC layer formed between Cu and diamond. The interfacial layer thickness is crucial to the thermal conductivity enhancement in the Cu/diamond composites.
Abstract
A high-angle annular dark field scanning transmission electron microscopy study of the intermetallic compound Al
74
Cr
15
Fe
11
reveals a quasiperiodic structure significantly differing from ...the ones known so far. In contrast to the common quasi-unit-cells based on Gummelt decagons, the present structure is related to a covering formed by Lück decagons, which can also be described by a Hexagon-Bow-Tie tiling.
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•Highly oriented microtube arrays are prepared by a melt spinning method.•Microtubes are composed of high-entropy decagonal quasicrystal approximants.•Microtubes show a hardness of ...10.9 GPa and elastic modulus of 189.3 GPa.•Proposed the growth mechanisms of microtubes.
The unique structures of micro/nanotubular materials have received extensive attention, while the micro/nanotubular structures of quasicrystals or quasicrystal-related phases, especially oriented arrays, are rarely found. Here, oriented microtube arrays of high-entropy decagonal quasicrystal approximants are prepared in Al20Si20Mn20Fe20Ga20 alloy by simple melt spinning. Transmission electron microscopy revealed microtubes are mostly composed of alternating arrangements of (1/0, 2/1) quasicrystal approximant domains (lattice constants: a = 0.73 nm, b = 1.23 nm, and c = 2.24 nm) and defective (1/0, 2/1) domains. However, heat treatment leads to the change of the structure and morphology of microtubes. At 873 K, a primitive cubic phase existed, and at 973 K, microtube morphology disintegrated and the (1/0, 2/1)-related domain transformed into complex domains, showing instability. By nanoindentation testing, microtubes show the hardness of 10.9 GPa and the elastic modulus of 189.3 GPa. However, after heat treatment at 873 K, these values decreased to 5.3 GPa and 128.4 GPa, and to 3.2 GPa and 107.9 GPa at 973 K. We demonstrate that the formation of microtubes is mainly related to the temperature gradient, twinning growth of approximant domains, and also the insufficient supply of raw materials in the later stages of solidification.
Iron is a widely used catalyst for the growth of carbon nanotubes (CNTs) or carbon nanofibers (CNFs) by catalytic chemical vapor deposition. However, both Fe and Fe–C compounds (generally, Fe3C) have ...been found to catalyze the growth of CNTs/CNFs, and a comparison study of their respective catalytic activities is still missing. Furthermore, the control of the crystal structure of iron-based catalysts, that is α-Fe or Fe3C, is still a challenge, which not only obscures our understanding of the growth mechanisms of CNTs/CNFs, but also complicates subsequent procedures, such as the removal of catalysts for better industrial applications. Here, we show a partial control of the phase of iron catalysts (α-Fe or Fe3C), obtained by varying the growth temperatures during the synthesis of carbon-based nanofibers/nanotubes in a plasma-enhanced chemical vapor deposition reactor. We also show that the structure of CNFs originating from Fe3C is bamboo-type, while that of CNFs originating from Fe is not. Moreover, we directly compare the growth rates of carbon-based nanofibers/nanotubes during the same experiments and find that CNFs/CNTs grown by α-Fe nanoparticles are longer than CNFs grown from Fe3C nanoparticles. The influence of the type of catalyst on the growth of CNFs is analyzed and the corresponding possible growth mechanisms, based on the different phases of the catalysts, are discussed.
Seldom could metals and alloys maintain excellent properties in cryogenic condition, such as the ductility, owing to the restrained dislocation motion. However, a face-centered-cubic (FCC) CoCrFeNi ...high-entropy alloy (HEA) with great ductility is investigated under the cryogenic environment. The tensile strength of this alloy can reach a maximum at 1,251±10 MPa, and the strain to failure can stay at as large as 62% at the liquid helium temperature. We ascribe the high strength and ductility to the low stacking fault energy at extremely low temperatures, which facilitates the activation of deformation twinning. Moreover, the FCC→HCP (hexagonal close-packed) transition and serration lead to the sudden decline of ductility below 77 K. The dynamical modeling and analysis of serrations at 4.2 and 20 K verify the unstable state due to the FCC→HCP transition. The deformation twinning together with phase transformation at liquid helium temperature produces an adequate strain-hardening rate that sustains the stable plastic flow at high stresses, resulting in the serration feature.
A high-entropy dual-phase AlTiVCoNi alloy with a low density of ∼6.24 g cm
−3
is developed, and it consists of a hierarchical structure, including an ordered L2
1
phase, a disordered ...body-centered-cubic (BCC) solid-solution phase, and nano-sized L2
1
precipitates embedded in the BCC phase. It is found that this new alloy shows phase stability after the heat treatment at 1200°C for 24 h, and the compressive yield strength of this annealed alloy is approximately equal to that of the as-cast condition, ∼1.6 GPa. This alloy displays an exceptional compressive strength at room temperature and at 600°C, with the specific yield strengths of ∼261 and ∼210 MPa g
−1
cm
3
, respectively. The semi-coherent interface of the L2
1
and the BCC phases makes the alloy phase stable and regulates the work-hardening mechanism. Local dynamic-recrystallization behavior and grain evolution are observed in the as-prepared alloy during compression at 800 and 1000°C, which results in the high-temperature softening. This alloy with a muti-phase hierarchical structure would provide a new paradigm for the development of next-generation low-density, high-entropy structural materials for high-temperature applications.
Despite substantial advances in crystal structure determination methodology for polycrystalline materials, some problems have remained intractable. A case in point is the zeolite catalyst IM-5, whose ...structure has eluded determination for almost 10 years. Here we present a charge-flipping structure-solution algorithm, extended to facilitate the combined use of powder diffraction and electron microscopy data. With this algorithm, we have elucidated the complex structure of IM-5, with 24 topologically distinct silicon atoms and an unusual two-dimensional medium-pore channel system. This powerful approach to structure solution can be applied without modification to any type of polycrystalline material (e.g., catalysts, ceramics, pharmaceuticals, complex metal alloys) and is therefore pertinent to a diverse range of scientific disciplines.
Kinking of semiconductor nanowires grown by the vapour-solid-liquid (VSL) mechanism has long been observed and studied, particularly for Si. A large variety of turning angles for kinked Si nanowires ...(KSiNWs) has been reported in the literature, but most authors have studied the kinking mechanism rather than the structure and corresponding geometrical features of the kinks. Here, we have investigated the relationship between the turning angles and the structure (down to atomic level) of KSiNWs grown by VSL from indium nanoparticles. By using transmission electron microscopy, we have characterized the transition regions between different segments of KSiNWs of various crystallographic orientations. We have found that most turning angles can be viewed as rich combinations of different types of {111} coherent twins that coexist within the transition regions between different segments of KSiNWs.
The turning angles of kinked Si nanowires are governed by the different combinations of three types of {111} twins, where TBs are normal to (Twin I), inclined to (Twin II) or parallel to (Twin III) the axes of Si nanowires.
High-entropy alloys (HEAs) contain multiple principal alloying elements, but usually with simple crystal structures. Quasicrystals are structurally complex phases, but are generally dominated by only ...one element. However, nearequiatomic high-entropy quasicrystals have rarely been reported because they are difficult to prepare experimentally and predict theoretically. Therefore, the preparation and crystal structures of near-equiatomic high-entropy quasicrystals have drawn much interest. We report a quinary decagonal quasicrystal (DQC) with near-equiatomic alloying elements in Al
20
Si
20
Mn
20
Fe
20
Ga
20
melt-spun ribbons, which is the first to our knowledge. Meanwhile, the structural features of the DQC are characterized in detail. The configurational entropy of both the alloy and DQC satisfies the entropy-based criterion for HEAs, suggesting a high-entropy DQC. Our findings provide a new strategy to develop high-entropy quasicrystals.
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