Using nanocrystalline particles of mullite and zirconia respectively with diameters in the range 20–30 nm prepared by a sol-gel route, aluminium metal-matrix composites have been synthesized. A hot pressing technique has been used with temperatures varying from 450–610°C. The vickers hardness values for the composites are found to be substantially higher than that of pure aluminium. An order of magnitude increase in hardness is achieved when Al₅Mo phase is grown in the composite.

Nanocrystalline cubic titanium silicon nitrides (TiSi$_x$N$_{(1−x)}$) with different Si concentrations have been synthesized at room temperature by mechanical alloying the stoichiometric compositions of ingredient powders in a nitrogenatmosphere. Structure and microstructure characterizations of unmilled and all ball-milled powders are carried out byanalysing respective X-ray diffraction patterns employing the Rietveld structure and microstructure refinement method.The presence of titanium, silicon and nitrogen in TiSi$_x$N$_{(1−x)}$ has been confirmed by energy-dispersive X-ray transmission electron microscopy analysis. Transmission electron microscopy image reveals that the average size of the spherical particles of 9-h-milled powder is $\sim$5 nm and size distribution is almost monodispersed, which corroborates well with the result of the Rietveld analysis. Bandgap energies of these solid solutions are determined by analysing respective UV–Vis absorption spectrum and it is found that the addition of silicon to insulating nanocrystalline TiN results in a reduction of bandgap energy and all solid solutions become wide-bandgap semiconductors with the addition of Si in different proportions.