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Biomass-derived carbon has attracted extensive attention because of its unique form, wide range of sources and low cost. However, the construction of efficient biomass-based microwave absorbers with hierarchical structures and multicomponent magnetic/dielectric structures remains a great challenge. Therefore, CoNi-MOF was self-assembled in situ on the plant Juncus effusus by the microwave method, and CoNi/NC/C composites were prepared by in situ pyrolysis in a nitrogen atmosphere. The morphology, electromagnetic parameters, specific surface area and porous structure of the composites were adjusted by controlling the pyrolysis temperature. For a pyrolysis temperature of 600 ℃ and filling of 16 wt%, the composite was found to show an RL min value of − 64.3 dB at 12.88 GHz at a thickness of 2.5 mm, and the effective absorption bandwidth (EAB)reached 7.36 GHz. The excellent microwave absorption performance was attributed to conduction loss, dipole polarization, interface polarization, magnetic loss and balanced impedance matching. • Multimodal 3D structure CoNi / NC / C composites were synthesized by microwave and pyrolysis. • The RLmin of the sample was − 64.3 dB at 2.5 mm, with a broad effective bandwidth of 7.36 GHz. • Metal-O-C and Metal-N bonds were present in the composites. • The performance derives from multiple loss mechanism and tunable impedance match. [ABSTRACT FROM AUTHOR]

The composition complexity of Ti(C, N)-based cermets poses a great challenge to the controllability of their sintering process. The effects of both refractory TaC addition and original particle size of starting materials on densification behavior and microstructural evolution of Ti(C, N)-based cermets were investigated during liquid phase sintering. The particle rearrangement only plays a very limited role in promoting densification of Ti(C, N)-based cermets at the initial stage of liquid phase sintering, whereas the pore-filling in the presence of liquid phase becomes a dominant densification mechanism in the middle stage or even earlier. Enhanced densification of ultrafine Ti(C, N)-based cermets is realized by introducing refractory TaC additive based on the grain growth-induced liquid phase pore-filling mechanism, which is also verified by an extended study using other refractory carbide additives such as NbC, ZrC and HfC. This work provides a novel idea for the development of fully densified ultrafine Ti(C, N)-based cermets with outstanding mechanical properties, which are highlighted in machining applications of difficult-to-machine materials as well as other wear-resistant parts operating in high-temperature and high-stress environments. [Display omitted] • The effects of both TaC addition and the particle size of starting materials on the densification behavior of Ti(C, N)-based cermets are clarified. • Enhanced densification of ultrafine Ti(C, N)-based cermets is realized by introducing refractory TaC additive. • This work provides a novel idea for the development of fully densified ultrafine Ti(C, N)-based cermets. [ABSTRACT FROM AUTHOR]

Abstract: (Gd1−x Yb x )2Zr2O7 (0≤ x ≤1) solid solutions were prepared by pressureless-sintering process at 1973K to investigate the substitution effect of Yb for Gd on their electrical properties. Electrical conductivity of (Gd1−x Yb x )2Zr2O7 solid solutions were measured using complex impedance spectroscopy from 673 to 1173K over a frequency range of 2Hz to 2MHz in air. (Gd1−x Yb x )2Zr2O7 are oxide-ion conductor in the oxygen partial pressure range from 1.0×10−4 to 1.0atm at all test temperature levels. The measured values of grain conductivity obey the Arrhenius relation. The grain conductivity of (Gd1−x Yb x )2Zr2O7 increases with increasing temperature. However, the grain conductivity of (Gd1−x Yb x )2Zr2O7 gradually decreases with increasing ytterbium content at identical temperature levels. [Copyright &y& Elsevier]

Lanthanum-doped titanium-zirconium-molybdenum (La-TZM) alloys have good mechanical properties, including high strength and toughness due to complex secondary phases. Herein, the formation process of the secondary phases in the La-TZM alloy was revealed by thermodynamics calculations. The ΔG values of possible reactions during sintering were obtained. Results show that the formation process of the secondary phases was controlled by different reactions at different stages. At the first stage (0–500 °C), the main reactions are listed as follows: TiH 2 +O 2 (g)→TiO 2 +H 2 ↑(g), ZrH 2 +O 2 (g)→ZrO 2 +H 2 ↑(g), C 6 H 12 O 6 →[C]+ H 2 O↑, [C]+ O 2 (g)→CO 2 (g)↑, [C]+Mo→MoC, La(NO 3 ) 3 ·6H 2 O→ La 2 O 3 +NO 2 ↑+ NO↑+O 2 ↑+H 2 O; [C]+TiH 2 →TiC + H 2 (g)↑, [C]+ZrH 2 →ZrC + H 2 (g)↑. At the secondary stage (680–960 °C), the dominant reactions include: TiH 2 →Ti + H 2 (g)↑, ZrH 2 →Zr + H 2 (g)↑. At the last stage (≥1200 °C), the primary reaction is Ti + Zr+[O]→ZrTiO 4 . The secondary phases in the La-TZM alloy include TiO 2 , ZrO 2 , ZrC, TiC, MoC, ZrTiO 4, La 2 O 3 and the solid Ti and Zr phases. These results can guide the design of new ingredients for Mo alloys. [ABSTRACT FROM AUTHOR]

Pure h-BN ceramics were processed at different sintering temperatures and hold times using ball milled nanocrystalline or amorphous h-BN powders. Increases in sintering temperature induced greater grain growth but reduced relative densities and mechanical properties. Changes in sintering hold times caused further increases in grain sizes and relative density, but had little impact on mechanical properties. The grain sizes play an important aspect of strength in h-BN ceramics. The relationship of flexural strength and grain sizes in h-BN ceramics conforms to Hall-Petch behavior. When the grain size of h-BN ceramics increased from 0.3 μm to 8 μm, the flexural strength declined from 163 ± 6 to 84 ± 4 MPa. The mechanical properties of h-BN ceramics depend both on relative densities and grain sizes. [ABSTRACT FROM AUTHOR]

In order to improve the welding performance of WC–Co to steel, a multilayer functionally graded (WC–Co)–Ni composite (MFGWC) was successfully fabricated by sintering the multilayer green compact, and a Ni-rich layer was covered on the compact surface. The microstructure, composition and micro-hardness of the MFGWC were investigated in this paper, results showed that the MFGWC was composed of WC–Co substrate, multi-transitional layers and pure Ni layer. The key part, multi-transitional layers formed between Ni layer and WC–Co substrate, was obtained successfully. The micro-hardness of the composite gradually decreased from 1300 HV to 66 HV along the direction of WC–Co substrate to pure Ni layer, this was due to a decrease in the amount of WC particles and the corresponding increase of Ni phases. The multi-transitional layer played a role in reducing the residual stresses that were induced by the difference of thermal expansion between WC–Co substrate and steel. [ABSTRACT FROM AUTHOR]

The effects of a single additive (SnO 2 , Ta 2 O 5 , or WO 3 ) on the crystal structure, densification, and electrical conductivity of the GdSmZr 2 O 7 ceramic have been examined. The GdSmZr 2 O 7 ceramic with or without a single additive of 1 wt.% SnO 2 , Ta 2 O 5 , or WO 3 sintered at temperatures between 1773 and 1973 K exhibits a single cubic pyrochlore-type phase. The relative densities of different compositions increase with increasing sintering temperature. The total conductivity of different samples obeys the Arrhenius relation. The total conductivity of the GdSmZr 2 O 7 ceramic is not improved by the addition of 1 wt.% SnO 2 , Ta 2 O 5 , or WO 3 . A single additive, SnO 2 , Ta 2 O 5 , or WO 3 , is not an effective sintering aid for the GdSmZr 2 O 7 ceramic. [ABSTRACT FROM AUTHOR]

Abstract: High-energy ball milling and spark plasma sintering were adopted to prepare ZrC–SiC composite. Zirconium carbide, silicon, and graphite powders were used as raw materials. ZrC–30vol.%SiC was sintered to a relative density of >96.1% at 1800°C. The composite showed a fine microstructure. The fracture strength reached up to 523.4MPa, Vickers’ hardness 18.8GPa, fracture toughness 4.0MPam1/2, and elastic modulus 390.5GPa. [Copyright &y& Elsevier]

Abstract: Ceramic powders of Nd x Zr1−x O2−x/2 (x =0.1, 0.2, 0.3, 0.4, 0.5) were synthesized by chemical-coprecipitation followed by calcination method. The ceramic powders of Nd x Zr1−x O2−x/2 were pressureless-sintered at 1600°C for 15h in air to fabricate dense bulk ceramics. The relative density of sintered samples was measured by the Archimedes method. Structures of the synthesized powders and sintered ceramics were identified by X-ray diffractometer. The morphologies of ceramic powders were observed by transmission electron microscope. Various thermal analysis methods were used for thermal expansion coefficient, specific heat, thermal diffusion coefficient and DSC measurements in a temperature range of room temperature to 1400°C. The thermal conductivity was calculated from thermal diffusivity, density and specific heat. Nd0.1Zr0.9O1.95 ceramics consist of both monoclinic and tetragonal structures. However, Nd0.2Zr0.8O1.9 and Nd0.3Zr0.7O1.85 ceramics only exhibit a single fluorite structure. Nd0.4Zr0.6O1.8 and Nd0.5Zr0.5O1.75 ceramics have a pyrochlore-type lattice. With the increase of Nd2O3 concentration, the thermal expansion coefficients of Nd x Zr1−x O2−x/2 ceramics increase. The thermal conductivities of Nd x Zr1−x O2−x/2 ceramics were located in the range of 1.50–2.01Wm−1 K−1 from room temperature to 1400°C. [Copyright &y& Elsevier]

h-BN composite ceramics were prepared by hot-pressing using La 2 O 3 and Al 2 O 3 as additives to form liquid phases during sintering. The effect of the amorphization/nanocrystallization of raw h-BN powders by high-energy ball-milling on the microstructure evolution of h-BN composite ceramics was investigated. The amorphization/nanocrystallization of raw h-BN powders significantly promotes grain growth during liquid-phase sintering. The specimen prepared using ball-milled h-BN powders possesses a higher crystallization degree, larger grain size, higher texture degree and more significant anisotropic thermal conductivity than the specimen prepared using raw h-BN powders. Image 1 [ABSTRACT FROM AUTHOR]