查看更多>>摘要：? 2022 Elsevier B.V.In the present work, a series of new high-entropy rare-earth zirconates were prepared by a solid state reaction method. The crystal structure, microstructure and electrical properties of high-entropy rare-earth zirconates were characterized by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical impedance spectroscopy. All the high-entropy rare-earth zirconates have a single-phase pyrochlore structure with a relative density of more than 95.7%. The grain sizes of high-entropy rare-earth zirconates are 1.3–2.4 μm, which are finer than low-entropy rare-earth zirconates prepared by the same process. (Nd0.2Sm0.2Eu0.2Gd0.2Dy0.2)2Zr2O7 has the excellent electrical conductivity of 7.1 × 10–3 S·cm–1 at 1073 K.
查看更多>>摘要：? 2022 Elsevier B.V.The aim of this work is to study the kinetics of oxidation of new Fe-bearing titanium alloys produced by the innovative powder metallurgy route of induction sintering. The characterisation of the phases formed, surface topography, mass gain, microhardness and oxide layer thickness of the Fe-bearing titanium alloys oxidised at 700 °C in air reveals that a non-uniform oxidation layer composed of either TiO2 particles or vertically-grown TiO2 micro-pillars at short and long oxidation times, respectively, is formed. This results in a continuous increase of the total mass gain and microhardness with the oxidation time. It is found that the oxidation mechanism is controlled by the inwards diffusion of oxygen and the outwards diffusion of Ti and the presence of the alloying elements does not significantly affect the oxidation response. The study is complemented with the identification of a relationship useful to predict the degree of oxidation.
查看更多>>摘要：? 2022 Elsevier B.V.Ce2[Zr1?x(Mn1/3Sb2/3)x]3(MoO4)9 (x = 0.1–1.0) ceramics were prepared by a conventional solid-state method. (Mn1/3Sb2/3)4+ ions occupied the Zr-site, and Ce2[Zr1?x(Mn1/3Sb2/3)x]3(MoO4)9 solid solution was obtained. With x value increased, the εr decreased from 10.47 (x = 0.02) to 10.10 (x = 0.10), which was affected by bond ionicity of Zr/(Mn1/3Sb2/3)1–O4 bond. The Q·f value first increased and then decreased, which was controlled by varying packing fraction, relative density, and lattice energy (Ce–O bond). The thermal expansion coefficient and bond energy of Mo–O bond were associated with τf value. Besides, infrared reflection spectrum suggested that the properties were primarily derived from the absorption of phonon in the infrared range. Outstanding microwave dielectric properties of Ce2[Zr0.92(Mn1/3Sb2/3)0.08]3(MoO4)9 ceramics were obtained when sintered at 700 °C: εr = 10.29, Q·f = 91,981 GHz and τf = ?9.81 ppm/°C.
查看更多>>摘要：? 2022 Elsevier B.V.Excellent combination of mechanical properties of bulk metallic glasses (BMGs) are a class of relatively young and promising candidate materials for compliant mechanisms (CMs), which are usually associated with the nonlinear large-deflection deformation. In this study, an effective design strategy was proposed to enhance the flexibility of BMG cantilever beam quantitatively, which by means of increasing the ratio of loading distance to beam thickness. Moreover, the accuracy of modulus of elasticity in bending, Eb, which measured by cantilever bending test was affected seriously by the support compliance of the fixed end, and the accurate Eb value of BMG beam can be attained after eliminating this influencing factor. The critical boundary condition of cantilever beams within the scope of small-deflection deformation was identified, which situates at non-dimensional deflection parameter, δy/L, is 0.2. Correspondingly, the critical loading distance-to-thickness ratios, (L/t)c, of cantilever beams within small-deflection deformation were derived for BMGs and conventional crystalline metals, which provide a criterion to predict the potential to achieving large-deflection deformation. It is noticed that by plotting the flexural stress-δy/L relations for BMG and several conventional crystalline metals used in CMs, the unique advantages of BMG cantilever beam in the aspect of achieving large-deflection deformation and enduring higher flexural stress can be reflected more intuitively. These advantages of BMG cantilever beam are well suitable for CMs which designed to have a small footprint and requirement of large-deflection motions, such as in the fields of microelectromechanical systems (MEMS) and biomedicines.
查看更多>>摘要：? 2022 The Author(s)The novel all-d-metal Ni(Co)MnTi based magnetic Heusler alloys provide an adjustable giant magnetocaloric effect and good mechanical properties. We report that the second-order magnetic phase transition can be tailored in this all-d-metal NiCoMnTi based Heusler system by optimizing the Mn/Ti ratio, resulting in a reversible ferromagnetic-to-paramagnetic magnetic transition. A candidate material Ni33Co17Mn30Ti20 with a magnetic entropy change ?Sm of 2.3 Jkg?1K?1 for a magnetic field change of 0–5 T, has been identified. The TC and saturation magnetization MS can be controlled by adjusting the Ni/Co concentration and doping non-magnetic Cu atoms. The compositional maps of TC and MS have been established. Density functional theory (DFT) calculations reveal a direct correlation between the magnetic moments and the Co content. By combining XRD, SQUID, SEM and DFT calculations, the (micro)structural and magnetocaloric properties have been investigated systematically. This study provides a detailed insight in the magnetic phase transition for this all-d-metal Ni(Co)MnTi-based Heusler alloy system.
查看更多>>摘要：? 2022 Elsevier B.V.Pre-strain is often used as a powerful pre-treatment to tailor the microstructures and mechanical properties of traditional alloys. However, in high-entropy alloys (HEAs), the effect of pre-strain degree on the precipitates is still unclear. In this paper, we investigated the effects of pre-strain degree on the precipitation of Ni2CoCrFeTi0.18Al0.12 high-entropy alloys. The HEAs were cold-rolled with different thickness reduction of 30%, 50%, and 70% and annealed at 800 °C for 30 ~ 60 min, followed by high-resolution scanning electron microscope (SEM) analysis. Counter-intuitively, we discovered a non-monotonous effect of pre-strain on the precipitation behavior, that low pre-strain can accelerate the precipitation behavior while such accelerating effect is weakened under high pre-strain. This non-monotonous effect is attributed to the shortened defects existing time by recrystallization under high pre-strain. In addition, pre-strain can controllably tailor the precipitation strengthening, dislocation strengthening, and grain boundary strengthening of HEAs. These results not only uncover the mechanism of the non-monotonous pre-strain effect on the precipitates but also provides a pre-strain mediated scheme for tuning the precipitation-strengthened HEAs to targeted properties.
查看更多>>摘要：? 2022The effect of the cooling conditions after solidification of a hypoeutectic Al-7Si-0.4Mg alloy on the precipitation behavior during T5 heat treatment (artificial aging immediately after casting) was investigated. Al-7Si-0.4Mg alloys with two different cooling conditions, mold cooling and water quenching, were respectively fabricated by holding the sample in a permanent mold throughout solidification and by placing the sample in room temperature water just after solidification was completed. TEM analysis of the as-cast alloys confirmed that mold cooling after solidification led to the formation of a small amount of clusters, Si and B′ in the mold which may have pre-precipitated during cooling, increasing the hardness and strength of the as-cast alloy. However, the hardenability of the alloy with mold cooling during T5 heat treatment is less pronounced than the alloy with water quenching. This suggests that the pre-precipitation in the alloy with mold cooling suppresses the aging hardening response, reducing the overall strength of the alloy with T5 heat treatment compared to that of the alloy with no pre-precipitation. Analysis of precipitation kinetics and number densities of precipitates shows that the pre-precipitation can interfere with the precipitation of β", otherwise promoting the precipitation of coarse β', U2 and Si, which reduced overall T5 precipitation hardenability. Therefore, for the T5 heat treatment condition, we suggest that the cooling conditions after solidification are a key factor affecting the best performance of precipitation hardening.
查看更多>>摘要：? 2022 Elsevier B.V.Lanthanides doped vanadate luminescence materials have gained a lot of attention for their use in non-contact optical thermometry, because of the advantages of non-intrusive and real-time temperature detection. The approach of fluorescence intensity ratio (FIR) of two thermally coupled excited states is the most promising approach but their performance in a lower temperature range is limited due to thermal decoupling among the two emitting levels with a wide energy gap. Thus, in this work, the temperature sensing ability of ScVO4:2% Eu3+ phosphor synthesized successfully through a high-temperature solid-state reaction has been explored by employing the ground state thermal coupling approach. Various experimental and theoretical approaches were used to check the structure and compositional stability of the synthesized ScVO4:2%Eu3+ phosphors host lattice. The temperature-dependent emission intensity of 5D0→7F4 has been measured under 616.3 nm excitation corresponding to 5D0→7F2 absorption, which shows the remarkable increasing behavior with rising of temperature ranging from 113 K to 323 K. The highest value of the relative sensitivity reached 7.19% K?1 at 113 K which is higher than previously reported materials. The obtained results reveal that ScVO4:2% Eu3+ phosphor is a promising candidate for non-contact optical thermometry.
查看更多>>摘要：? 2022 Elsevier B.V.The high specific capacity of lithium-sulfur batteries makes them a potential next-generation energy storage device, but the shuttle effect and low electrical conductivity of sulfur hinder their development. In this paper, a one-step hydrothermal method was used to prepare cerium dioxide and metal organic framework composites to improve the electrochemical performance of lithium-sulfur batteries. Polar cerium dioxide has a strong affinity to polysulfides. Experiments further confirmed that CeO2 has a positive effect on the battery performance. UV-Vis tests were performed on the composites. After standing for 1 h, Zn@NPC-CeO2-2 showed the best adsorption of polysulfides. In addition, the specific discharge capacity of the battery was 569.3 mA h/g with 88% capacity retention after 200 cycles at 2 C. The results indicate that the addition of appropriate amounts of rare earth metal oxides can effectively improve the reaction kinetics of the battery and also provide a new idea for improving the performance of lithium-sulfur batteries.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, the crystal structure, magnetic phase transition and magnetocaloric properties of the ErCo2-xCux (x = 0.12, 0.24, 0.36 and 0.48) compounds have been investigated in detail. All of the compounds crystallize in the C15 cubic Laves structure (MgCu2-type) with the Fd-3 m space group. The substitution of Cu for Co is accompanied by an increase of the Curie temperature Tc from 31.5 K to 68 K for x varying from 0.12 to 0.48. The nature of the magnetic phase transition, determined by the results of the Arrott plots and Landau theory, changed from a first order to a second order in the ErCo2-xCux compounds with the Cu content increasing. The isothermal entropy change -?SM is calculated according to isothermal magnetization measurements using Maxwell's relation. For an applied magnetic field change of 0–5 T, the -?SM decreased from 30 J kg?1 K?1 for x = 0.12 to 10.9 J kg?1 K?1 for x = 0.48, whereas the working temperature range became wider due to that the magnetic transition type changed from a first order to a second order, which is a benefit for the application of the magnetic refrigeration. The corresponding refrigerant capacity RC values are 270.8 J kg?1, 194.1 J kg?1, 261.8 J kg?1 and 264.8 J kg?1, respectively.
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