Search

In this paper, high quality Mo-(10–40) wt% Cu and W-(10–40) wt% Cu alloys were prepared by powder metallurgy using the ultrafine molybdenum and tungsten powders as raw materials. The molybdenum powder with the size of 100–200 nm and tungsten powder with the size of 50–100 nm were prepared by a two-step reduction-process composed of an insufficient carbothermal reduction reaction and the following deep reduction reaction by hydrogen. From the experimental results, it was concluded that at the sintering temperature of 1200 °C to 1300 °C, relative densities of the Mo-(10–40) wt% Cu and W-(10–40) wt% Cu sintered blocks can reach >98%, and at the same time, excellent physical and mechanical properties were achieved. Meanwhile, the larger the content of copper in the alloy, the lower the temperature required for densification. At 1300 °C, the relative density, microhardness and thermal conductivity of the Mo-10 wt% Cu and W-10 wt% Cu sintered blocks are 98.83% and 99.36%, 167 HV and 283 HV, 138.38 W·m−1·k−1 and 154.15 W·m−1·k−1, respectively. Whereas, at 1200 °C, the relative density, microhardness and thermal conductivity of the Mo-40 wt% Cu and W-40 wt% Cu sintered block are 99.68% and 98.87%, 150 HV and 207 HV, 138.38 W·m−1·k−1 and 154.15 W·m−1·k−1, respectively. The present method was much more convenient relative to the traditional infiltration method. • Mo Cu or W Cu alloys are one-step prepared by using ultrafine Mo or W powders. • The larger the copper content, the lower the temperature needed for densification. • The prepared alloys have fine grain size, high hardness and thermal conductivity. [ABSTRACT FROM AUTHOR]

Adiabatic foam has been successfully prepared through sintering sodium silicate which is modified by boric acid. The effect of the sintering temperature, boric acid content and modulus of sodium silicate on the thermal conductivity, density, compression strength and microstructure of the adiabatic foam was studied in detail. In the sintering process, B 3+ ion can take the place of the Si 4+ ion by incorporating into the Si–O–Si structure via Si–O–B bridges, increasing the chemical stability of the adiabatic foam. High temperature, low boric acid content and low modulus of sodium silicate can reduce the thermal conductivity, density and compression strength. In order to meet the application of exterior wall thermal insulation, 450–500 °C of the sintering temperature, 18–24 g boric acid per 600 g sodium silicate solution, and 2.5–2.8 modulus of sodium silicate are chosen. The samples with thermal conductivity less than 0.044 W/m·K, density less than 100 kg/m 3 and compression strength more than 0.7 MPa are obtained. [ABSTRACT FROM AUTHOR]

Abstract: An approach of selecting alloying elements to control the size of in situ formed reinforcement in metal melts is proposed. This approach is based on the effect of alloying addition on nucleation of reinforcement predicted by the extended Miedema model and Wilson equation and on growth of reinforcement predicted by diffusion coefficient model. Using this approach, the effect of alloying element addition on the size of in situ formed Mg2Si in (AlN+Mg2Si)/Mg composites is evaluated. The results show that the addition of Ti, V, Mo, Cr, Fe and Mn can delay the nucleation and promote the growth of Mg2Si, while the addition of Ge, Sn, Cu and Zn can promote the nucleation and hinder the growth of Mg2Si. The microstructure of (AlN+Mg2Si)/Mg with the addition of Ti has been investigated based on the theoretical prediction. [Copyright &y& Elsevier]

In order to relieve high residual stresses between ceramics and metals during brazing processes, an AgCuTi/graphene-reinforced Cu foam composite filler was developed and used to braze the ZrB 2 -SiC ceramic and Inconel 600 alloy. Microstructures and shear strengths of the joints were systematically studied. The joints are composed of TiFe 2 , TiCu, TiC, Cu(s, s), Ag(s, s), and Ti 5 Si 3 phases. It is found the addition of graphene on the Cu foam surface can effectively retard diffusions of metal atoms and avoid the collapse of the foam matrix. After being brazed at 900 °C, the joint can get a maximum shear strength of 157 MPa, much higher than those brazed without graphene addition. The high shear strength was investigated in detail and attributed to the integrity of the Cu foam, formation of the TiC and thickness of the reaction layer at the ceramic side. [ABSTRACT FROM AUTHOR]

Abstract In this paper, brazing behaviors between ZrB 2 SiC and Ti 6Al 4V by Cu foam interlayer were studied. The microstructure, formation mechanism, mechanical property and fracture surface of the joints were systematically studied. The results showed that the phases in the joints were α + β -Ti, TiCu, Ti 2 Cu, Cu(s, s), TiC, TiB 2 and Ti 3 SiC 2. An optimum shear strength reached up to 435 MPa at a brazing temperature of 910 °C and holding time of 20 min. Such a shear strength was 90 MPa higher than the one without the Cu foam. The obtained high shear strength of joint was discussed from microstructure and residual stress. With the increase of brazing time, Cu(s,s) gradually disappeared and the content of Ti 2 Cu intermetallic compound increased, which was harmful for the joint. Furthermore, the residual stress of joint with Cu foam was calculated to be 324 MPa, lower than the one without Cu foam interlayer. [ABSTRACT FROM AUTHOR]

To obtain ideal implant materials, we hot extruded Mg-2.0Zn-0.5Zr-3.0Gd solid-solution alloys, and studied extrusion temperature impacts on materials properties. Fine dynamic recrystallized (DRXed) grains (∼5 μm) and elongated coarse un-dynamic recrystallized (unDRXed) deformed grains turned out at the range of 470–490 °C, but changed to bigger ones (∼8 μm) and abnormal growth (30–40 μm) at 490–510 °C. Precipitated phases consist of rod-like (Mg, Zn) 3 Gd particles and newly precipitated Mg 2 Zn 11 rectangles. The alloy extruded at 490 °C meets all mechanical and anticorrosive requirements for biomaterials, thanks to evenly distributed second phases via the solid solution, and the grain refinements through the hot extrusion. [ABSTRACT FROM AUTHOR]

The BiOI/BiOCl composites with high photocatalyitic and adsorption ablities were prepared via a facile ionic liquid assisted ultrasonic method in several hours at room temperature. The BiOI/BiOCl composites with different contents of BiOI can be conveniently synthesized via changing the amount of 1-ethyl-3-methylimidazolium iodide precursor during the preparation process. Microstructures, morphologies, porosities and bandgaps of the as-prepared samples were determined through various experimental methods. A first-principles calculation was employed to explicate electronic structures of the complex. Photocatalytic results suggest that the obtained BiOI/BiOCl composite with 40% BiOI has the highest photoactivity for the degradation of rhodamine-B and quinoline blue under visible light irradiation. All the rhodamine-B and quinoline blue can be degraded in 25 min and 15 min, respectively. To observe the universality of the BiOI/BiOCl, the degradation results of colorless target pollutant (tetracycline) was also investigated. Based on experimental and computational results, origins of the photocatalytic abilities leading to the observed results were proposed. [ABSTRACT FROM AUTHOR]