Showing papers by "Mingwei Chen published in 2005"

Microstructural Characterization of Commercial Hot‐Pressed Boron Carbide Ceramics

Abstract: Two commercial hot-pressed boron carbide ceramics were investigated by transmission electron microscopy. Atomic-scale observations suggest that the grain boundaries of the two materials are free of grain-boundary films. Two triple-junction phases were found and characterized to be rhombohedral Fe 2 B 1 0 3 and orthorhombic Ti 3 B 4 . In addition, intra-granular precipitates, AIN, Mo 2 (C, B) and graphite, were identified and found to have coherent relationships with the boron carbide matrix. Micron-scale inclusions were also observed and most of them were determined to be graphite. The formation mechanisms of the secondary phases and their possible influence on mechanical properties are also discussed.

Comment on "Grain Boundary-Mediated Plasticity in Nanocrystalline Nickel"

Abstract: N anograin rotation via grain boundary sliding has been predicted as an important deformation mode in nanocrystalline materials as grain sizes approach less than 10 nm ([ 1 ][1]-[ 3 ][2]). However, definite experimental evidence beyond molecular dynamics (MD) simulations has been long sought.

Effect of heavy boron doping on pressure-induced phase transitions in single-crystal silicon

Abstract: The influence of applied loads and loading/unloading rates on pressure-induced phase transitions in lightly and heavily boron-doped silicon was systematically investigated. The resultant phases were plotted into two-dimensional maps with applied loads and loading/unloading rates as the coordinate axes. The formation region of the amorphous phase in the heavily boron-doped silicon was found to be much larger than that in the lightly boron-doped one, suggesting that heavy boron doping promotes the amorphization in silicon.

Redistribution of alloying elements in quasicrystallized Zr 65 Al 7.5 Ni 10 Cu 7.5 Ag 10 bulk metallic glass

Abstract: We report experimental evidence on redistributions of alloying elements in a partially quasicrystallized ${\mathrm{Zr}}_{65}{\mathrm{Al}}_{7.5}{\mathrm{Ni}}_{10}{\mathrm{Cu}}_{7.5}{\mathrm{Ag}}_{10}$ bulk metallic glass. Energy-filtered elemental maps show that the partitioning of silver, zirconium, and aluminum occurs in the quasicrystallized glass. Silver is found to enrich into quasicrystals, but zirconium and aluminum are slightly depleted from the quasicrystals. These observations suggest that the amorphous-to-quasicrystal transformation in this alloy is not a simple polymorphous reaction and a long-range diffusion is involved in the devitrification, probably prior to the quasicrystallization.