Search

A novel method for preparing aluminum/aluminum nitride ceramics (Al/AlN) substrates is proposed in this paper. The method included two processes: (1) the surface of AlN was coated with a CuO thick film and sintered; (2) Al foil was put on the pretreated (in process 1) AlN surface and bonded to AlN through pre-heating at 400 °C and final heating at 660 °C in N 2 -H 2 reduction atmosphere. The experimental results obtained by optical and scanning electron microscope (SEM) observations as well as by X-ray diffraction analysis at the cross-sections of the joints and the fracture surfaces, suggest that the reaction mechanism starts with the reaction of CuO with AlN to form CuAlO 2 , when the AlN coated with CuO is heat-treated at high temperature. A Cu layer is produced by the reduction of CuO and Cu diffuses in the Al foil, forming strong Al/AlN joints. Elongated crystals of Al 2 Cu are developed in the reaction zone at the interface between Al and AlN. The results of mechanical tests showed that the peeling-off strength of the Al foil from the surface of the AlN substrate reached a value of 15.4 MPa for the Al/AlN couples produced after 30 min of heat treatment at 660 °C. [ABSTRACT FROM AUTHOR]

Perovskite ceramics with a formula of Ca 0.7 Ti 0.7 La 0.3 Al 0.3 O 3 (CTLA) were produced through a conventional solid-state reaction procedure following three different La 3+ -doping methods using powders of La 2 O 3 , or La 2 O 3 /Al 2 O 3 powder mixture, or LaAlO 3 . La 3+ doping favored grain growth and densification, affected the grain size distribution, and improved the dielectric properties of the produced sintered CTLA ceramics. The doping methods had a strong influence on these properties. More specifically, doping with La 2 O 3 and La 2 O 3 /Al 2 O 3 resulted in formation of solid solution, while a secondary phase formed in the CTLA ceramics doped with LaAlO 3 , which caused a coarsening of the microstructure and lowered the La 3+ doping effects on the dielectric properties. The experimental results suggest that La 3+ doping improves the dielectric properties of the sintered CTLA perovskite ceramics, which are further enhanced by doping with Al 3+ ions in small amounts. However, further increase of Al 3+ ions content jeopardizes them. [ABSTRACT FROM AUTHOR]

Abstract: Porous sialon ceramics have been cost-effectively prepared by pressureless sintering from a mixture of elongated SHS β-sialon powders with an α-sialon precursor composition composed of α-Si3N4, AlN, Y2O3 and Al2O3. The obtained porous sialon ceramics exhibited low shrinkage and homogeneous pore size distribution. The results of X-ray diffraction and scanning electron microscopy showed that a uniform microstructure with elongated and intermingled β-SiAlON grains, which were strongly connected by α-SiAlON phase, has been obtained. [Copyright &y& Elsevier]

• B-site precursor method can effectively inhibit the appearance of second phase. • B-site precursor method can obtain high reactivity Mg 4 Nb 2 O 9 powders. • B-site precursor method can promote integrality of the crystal structure. Mg 4 Nb 2 O 9 ceramics have been prepared by B-site precursor method in this work. Experimental results demonstrate that the uniform particles-size distribution of Mg 4 Nb 2 O 9 powders can be obtained, which exhibit high reactivity to promote the grain growth of Mg 4 Nb 2 O 9 ceramics. Moreover, the Mg 4 Nb 2 O 9 ceramics via B-site precursor method can be sintered at a wide range of sintering temperature from 1275 to 1375 °C with single phase Mg 4 Nb 2 O 9 composition and high crystallinity. Compared to the conventional solid-state method, the Mg 4 Nb 2 O 9 ceramics prepared by B-site precursor method exhibit excellent Q × f value by above 168,756 GHz. [ABSTRACT FROM AUTHOR]

BaO-Sm 2 O 3 –5TiO 2 (BST) added by Al 2 O 3 was prepared by solid-state reaction method. The main phase is Ba 3.99 Sm 9.34 Ti 18 O 54 of orthorhombic tungsten bronze structure, and the secondary phase is Ba 1.18 Al 1.90 Ti 6.09 O 16 of tetragonal structure, which has two types of grains: one is grey and cubic, and the other is white and quasi-rectangular. Microstructure was characterized by XRD, SEM, and Raman spectra. Micromechanical properties of different phases were assessed by nanoindentation and micro-scratch tests with Berkovich indenter. Volume fractions of different phases obtained by statistical analysis of grid indentation are in good agreement with those obtained by XRD analysis. Vickers hardness method is more appropriate for the determination of the fracture toughness of dielectric ceramics. BST ceramic without addition of Al 2 O 3 has better mechanical properties than BST-A with addition of Al 2 O 3 , indicating that addition of Al 2 O 3 impairs the micromechanical properties of dielectric ceramics. [ABSTRACT FROM AUTHOR]

We developed a newly-designed TiN/AgCuTi composite brazing alloy to significantly improve the bonding strength of AlN/Cu composite ceramics, which can endow high power electronic devices with superior compatibility with large current transport and high voltage resistance. Via the systematic microstructure investigation of the brazed joint by scanning electron microscopy and X-ray diffractometer, we found that added TiN particles could decrease the thickness of brittle reaction layer and promote the formation of fine TiCu particles in brazed joint, leading to dispersion strengthened and decreased CTE mismatch of the ceramic/metal composite. Importantly, the maximum bonding strength of 131 MPa was obtained for AlN and copper foil brazed joining via composite filler with TiN(4 wt.%)/AgCuTi, which is approximately 150 % higher than the case without TiN addition. [ABSTRACT FROM AUTHOR]

This work focused on the influence of hydrogen content on the microstructure and mechanical properties of ER5183 Al-Mg-Mn alloy wires for aluminum alloy welding. The hydrogen content of the ER5183 wires was measured, the macroscopic and microscopic morphologies of fractures were observed as well as the microstructure of the wires, and the tensile strength of the wires was also tested and investigated. The experimental results demonstrated three typical irregular macroscopic fractures of the wires appeared during the drawing process when the hydrogen content exceeded 0.23 μg/g. In the meantime, the aggregated pores were observed in the microstructure of the ϕ5.2 mm wire with the hydrogen content of 0.38 μg/g. Such defects may become the origin of cracks in subsequent processing and tensile tests. Moreover, higher hydrogen content in the ϕ5.2 mm welding wire will bring obvious changes in the fracture surface, which are internal cracks and micropores replacing the original uniform and compact dimples. With the higher hydrogen content, the tensile strength and plastic strain rate of ϕ1.2 mm wires would decrease. At the same time, unstable crack propagation would occur during the process of plastic deformation, leading to fracture. Considering the mechanical properties and microstructure, the hydrogen content of the ER5183 wires should be controlled below 0.23 μg/g. [ABSTRACT FROM AUTHOR]

Recently, there has been strong interest in inorganic solid-state electrolytes for all-solid-state batteries, among which the garnet electrolyte LLZO has attracted much attention due to its excellent properties, such as high ionic conductivity and broad electrochemical stability. The aim of our study was to improve the performance of Ta-doped LLZO (LLZTO) by co-doping Ga and Y at the Li and La sites using conventional solid-phase synthesis methods. We thoroughly investigated how Ga and Y affect the microstructure and electrochemical properties of LLZTO. The results show that the relative density of Ga- and Y-doped LLZTO increases significantly up to 94% under the same sintering conditions. This doping resulted in a significant increase in ionic conductivity from 2.0 × 10−4 S·cm−1 to 1.05 × 10−3 S·cm−1 and a decrease in electronic conductivity from 2.16 × 10−7 S·cm−1 to 9.18 × 10−8 S·cm−1. Subsequently, the symmetric cells were assembled and tested, and it was found that the interfaces of the doped solid-state electrolytes were much more stable and that the cycling time was longer. Thus, our study successfully coordinated the co-doping of Ga, Y, and Ta, providing valuable insights for the subsequent production of LLZO materials with higher densities and better performance. This study is a promising step toward the realization of safer all-solid-state batteries with higher energy densities. • Innovative further doping of two elements on top of LLZTO solid electrolyte, harmonizing the doping of three elements. • An order of magnitude increases in ionic conductivity of LLZTO solid state electrolytes after doping. • The doped LLZTO solid state electrolyte has better suitability with lithium metal anode. [ABSTRACT FROM AUTHOR]

Abstract: Ba2+-doped Sr2SiO4:Eu2+ phosphors were synthesized with the high-temperature solid-state reaction technique. The experimental results, summarized in the successful production of a single-phase powder with fine microstructure of spherical particles with smooth surface, suggest that Ba2+-doping favors the stabilization of α′-Sr2SiO4. Rietveld refinement of X-ray diffractograms suggests that Ba2+ and Eu2+ ions occupy the sites of Sr2+ in the lattice of α′-Sr2SiO4. The produced phosphors show two intense emission bands at green and yellow regions of spectrum, originated from Eu2+ ions accommodated at two different sites in the host crystal, whose peaks depend on the concentrations of Ba2+ and Eu2+. Intense and broad excitation spectra extend from ultraviolet to the blue region. [Copyright &y& Elsevier]

Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF2 and YF3 as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F2 and Ca12Al14O32F2. Liquid CaYAlO4 mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F2 at a relatively low temperature results in homogeneous YF3 distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity. [Copyright &y& Elsevier]

As a light-weighting structural material, aluminum alloy is being applied in the automobile and high-speed train, the property of which however is affected by the content of hydrogen, and much importance has been attached to the impact property of aluminum alloy. In this study, hydrogen was determined in ER5183 welding wire and afterwards the effect of hydrogen content on the impact property of Al–Mg MIG weld is investigated to clarify the mechanism of hydrogen action which provided a reasonable control range of hydrogen content in aluminum welding wire. The results show that the impact toughness of the weld is decreased with the increasing hydrogen content. In addition, the decohesion of impurities from the matrix and the formation of porosity are also observed in the weld. The morphology of impact fracture appears facet and porosity due to the "hydrogen-enhanced localized plasticity" effect on plasticity. Considering the good impact property as well as the fine microstructure of the weld, hydrogen content of the ER5183 welding wires should be controlled below 0.18 μg/g. • Introducing hydrogen by using ER5183 welding wires into Al–Mg weld. • Studying the effect of hydrogen embrittlement on impact properties of Al–Mg weld. • Investigating the influence of hydrogen on morphology of impact fracture of Al–Mg weld. • Describing the hydrogen-induced dislocation motion and multiplication phenomenon. • Giving a reasonable range of hydrogen content in ER5183 aluminum welding wire. [ABSTRACT FROM AUTHOR]