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Tungsten-reinforced Ti and Ti Á/6Al Á/4V composites were fabricated by powder metallurgical techniques from Ti, W and Al Á/V powders. The microstructure of the composites consists of partially dissolved tungsten particles within an a/b titanium matrix containing tungsten in solid-solution. Yield and ultimate tensile strengths increase linearly with tungsten content in the range 0 Á/15 wt.% W and decrease near-linearly with temperature in the range 25 Á/540 8C. Ductility follows the opposite trend and is within technologically acceptable values, except for Ti/15W at 315 and 425 8C and Ti/10W at 540 8C which fractured near the ultimate stress value. The Ti Á/6Al Á/4V/10W composite shows the best combination of high strength and ductility at all temperatures. At ambient temperatures, Ti/10W exhibits a stress Á/strain curve very similar to Ti Á/6Al Á/4V (with a slight decrease in stiffness), while eliminating aluminum and vanadium alloy elements. Further improvements in mechanical properties of these non-equilibrium composites are likely to be achieved through optimized heat-treatments, which affect the matrix microstructure and the degree of dissolution of tungsten and thus the relative importance of matrix solid-solution strengthening and composite strengthening. # 2002 Published by Elsevier Science B.V.

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Molecular dynamics investigation of plasticity in a model nanocrystalline silicon system demonstrates that inelastic deformation localizes in intergranular regions. The carriers of plasticity in these regions are atomic environments that can be described as high-density liquid-like amorphous silicon. During fully developed flow, plasticity is confined to system-spanning intergranular zones of easy flow. As an active flow zone rotates out of the plane of maximum resolved shear stress during deformation to large strain, new zones of easy flow are formed. Compatibility of the microstructure is accommodated by processes such as grain rotation and formation of new grains. Nano-scale voids or cracks may form if there emerge stress concentrations that cannot be relaxed by a mechanism that simultaneously preserves microstructural compatibility.