Strengthening mechanism of B_4C@APC/Al matrix composites reinforced with bimodal-sized particles prepared by hydrothermal carbonized deposition on chips

A B_(4)C@amorphous carbon(APC)/Al matrix composite was fabricated by using hydrothermal carbonized deposition on chips(HTCDC)process and solid-state synthesis process.The microstructure and mechanical properties of the B_(4)C@APC/Al matrix composite were investigated.After HTCDC process,nano-B_(4)C particles(50 nm)and micron-sized B_(4)C@APC core-shell spheres with a diameter of 2μm were found in the composites.The microhardness of the micron-sized B_(4)C@APC spheres is 1.66 GPa,which is greater than that of theα-Al matrix(1.06 GPa).Dislocation accumulation is observed around the micron-sized B_(4)C@APC spheres,indicating that the micron-sized B_(4)C@APC spheres have a strengthening effect on theα-Al matrix.Due to the formation of micron-sized B_(4)C@APC spheres,the reinforcement of nano-B_(4)C particles into the composites is transformed from single-sized particle enhancement to bimodal-sized particle enhancement.The strengthening mechanism for B_(4)C@APC/Al matrix composites with bimodalsized particles of nano-B_(4)C and micron-sized B_(4)C@APC spheres were analyzed,which includes thermal mismatch strengthening generated by the mismatch of coefficient of thermal expansion(CTE)between micron-sized B_(4)C@APC core-shell spheres andα-Al matrix,Orowan strengthening produced by nano-B_(4)C particles,Hall-Petch strengthening and load transfer strengthening produced by the bimodal-sized enhancement from nano and microspheres.A relationship model between the yield strength(YS)increment and the conversion rate(x)of micron-sized B_(4)C@APC core-shell spheres was estimated.

Functionalized TiO_2@ZrO_2@Y_2O_3:Eu^(3+) core-multishell microspheres and their photoluminescence properties

TiO2@ZrO2@Y2O3 ：Eu3＋ composite particles with a core-multishell structure were synthesized through the combination of a layer-by-layer （LBL） self-assembly method and a sol-gel process. The obtained sam- ples were characterized with scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS）, X-ray diffraction （XRD）, and fluorescence spectropho- tometry. The results showed that the composite particles had a core-multishell structure, spherical morphology, and a narrow size distribution. The presence of a ZrO2 layer on the TiO2 core can effec- tively prevent the reaction between the TiO2 core and a Y203 shell; the temperature for the reaction between the TiO2 core and the Y203 shell in the TiO2@ZrO2@Y2O3 ：Eu core-multishell phosphor can be elevated by 300 ℃ compared to that for TiO2@ZrO2：Eu. Upon excitation of the core-multishell particles in the ultraviolet （254 nm）, the Eu3＋ ion in the Y2O3 ：Eu3＋ shell shows its characteristic red emission （611 nm, 5D0→7F2）, and the photoluminescence （PL） intensity of the phosphor with the core-multishell structure was obviously greater than that of the core-shell TiO2@Y2O3 ：Eu phosphor.