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The demand for separation and purification applications under harsh conditions has grown strongly in recent years. Silicon carbide (SiC) ceramic membranes have broad prospects in this aspect due to their unique characteristics, but its pore size control is a crucial problem. Therefore, it is of great significance to develop simple and feasible methods for precise control of the pore size of SiC membranes to improve membrane selectivity and expand their application range. This review describes the pore formation process in the preparation of SiC membranes, focusing on the selection of SiC particles, sintering temperature, sacrificial template, sintering aids, oxidation process and other factors affecting the pore size and analysis. Finally, the control of SiC membrane pore size is summarized and the outlook is proposed. [ABSTRACT FROM AUTHOR]

Abstract: Exploratory experiments of laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. The corresponding mechanisms were discussed in detail. Results showed that the laser-welded seam had non-equilibrium solidified microstructures consisting of FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and some fine and dispersed Ni3Al γ′ phase and Laves particles as well as little amount of MC short stick or particle-like carbides distributed in the interdendritic regions. The average microhardness of the welded seam was relatively uniform and lower than that of the base metal due to partial dissolution and suppression of the strengthening phase γ′ to some extent. About 88.5% tensile strength of the base metal was achieved in the welded joint because of a non-full penetration welding and the fracture mechanism was a mixture of ductility and brittleness. The existence of some Laves particles in the welded seam also facilitated the initiation and propagation of the microcracks and microvoids and hence, the detrimental effects of the tensile strength of the welded joint. The present results stimulate further investigation on this field. [Copyright &y& Elsevier]

High Nb containing TiAl alloys have prospect to be used for turbo wheel and exhaust valve for vehicle engine. Friction welding is a suitable process for fabricating these components. For investigating the weldability of these alloys, cylindrical samples of Ti–45Al-8.5Nb-0.2W-0.2B-0.02Y (in at%) alloy with a diameter of 10 mm were welded by continuous drive friction welding process, and the microstructures and the mechanical properties of the joints were analyzed in this paper. The results showed that the weldability of the present alloy was very good. At parameters of rotational speed of 2400 r/min, friction pressure of 320 MPa, burn-off distance of 3 mm and upset pressure of 360 MPa, completely metallurgical bonding interfaces were obtained. The joint had a severely plastic deformation zone (SPDZ) with a biconcave lens geometry. The thicknesses of the center and periphery of SPDZ were about 40 μm and 800 μm, respectively. There existed a transition zone (TZ) between parent metal (PM) and SPDZ. SPDZ exhibited the deformation flow lines and had a randomly-oriented recrystallized duplex (DP) microstructure with the average grain size of 2.5 μm, in contrast, PM presented a nearly lamellar (NL) microstructure with a colony size of 150 μm. TZ showed a mixture microstructure combining deformed lamellar colonies and partially recrystallized grains. At room temperature, 750 °C and 800 °C, welding joints had better tensile properties than PM. • As-cast Ti–45Al-8.5Nb-0. 2W-0. 2B-0. 02Y alloy has good friction weldability. • The joint had a severely plastic deformation zone with a biconcave lens geometry. • Fine-grained DP microstructure of welding joint showed random orientation. • Welding joint had better tensile properties than parent metal. [ABSTRACT FROM AUTHOR]

Abstract: With the development of superconducting technology, high magnetic fields (HMF) provide unique opportunity for materials and physics scientists to extend or exploit high performance of existing materials. In this paper, we report our findings of the improvement of compressive strength and ductility in a NiAl based eutectic alloy induced by high uniform magnetic field treatment. It shows that the compressive strength and ductility of NiAl–Cr(Mo)–(Ti,Hf) eutectic alloy were improved by 100 MPa and 12% respectively after 11T uniform magnetic field treatment. Microstructural characterization and fractography observation suggested that the modification of morphology and dispersed distribution of constituent phases through atomic diffusion induced by the HMF treatment could be responsible for the improvement of mechanical performance. [ABSTRACT FROM AUTHOR]

A three dimension thermodynamic model is used to investigate the steady wetting state of droplet on a single microstructure surface based on the lowest principle of droplet free energy. The cone, frustum (upright and inverted) and sphere in micro-scale are selected as studied structures. The results show that both the intrinsic contact angle and morphology parameters of microstructure surface affect the wetting depth and normalized Helmholtz free energy (NFE) of droplet. The wetting maps for minimum points of NFE of droplet on cone and frustum surfaces with respect to intrinsic contact angle and morphology parameters have been presented. These wetting maps provide a guidance for fabricating microstructures that is used to enhance droplet adhesion. The effect of three phase contact line tension on droplet NFE has been studied. Results indicate that the line tension slightly increases the droplet NFE and that causes the decrease of droplet wetting stability. The absolute differences between F τ * (NFE with line tension) and F * (NFE without line tension) are small both for 1 μL and 1 nL droplets. But the relative differences, (F τ *- F *)/ F *, of 1 nL droplet are significantly larger than that of 1 μL droplet. Therefore, for a droplet with small volume, the line tension effect on droplet free energy is relatively large and that results in the increase of instability of droplet wetting state. [ABSTRACT FROM AUTHOR]

Abstract: A process of laser cladding Ni–Cr–C–CaF2 mixed powders to form a multifunctional composite coating on γ-TiAl substrate was carried out. The microstructure of the coating was examined using XRD, SEM and EDS. The coating has a unique microstructure consisting of primary dendrite or short-stick TiC and block Al4C3 carbides reinforcement as well as fine isolated spherical CaF2 solid lubrication particles uniformly dispersed in the NiCrAlTi (γ) matrix. The average microhardness of the composite coatings is approximately HV 650 and it is 2-factor greater than that of the TiAl substrate. [Copyright &y& Elsevier]