Introduction
Three collaborating groups, TCU, Unipress, and ELTE, work together on manufacturing and characterizing properties of diamond composites with silicon carbide bonding. Diamond phase usually accounts for 90% of the composite volume. These materials have many excellent physical properties, wear resistance similar to that of diamond and high hardness, and already found applications in practical devices. Their weakest point is relatively low fracture toughness, and unless this parameter is improved practical applications will be limited to those that exclude high impacts. It is generally accepted that hardness can be improved by reducing the size of crystals in SiC phase from micron to nanometer range. Our research program
A meaningful development of novel diamond nanocomposites of improved properties requires fundamental knowledge about nanosize crystals. The properties of nanoparticles are different than those of micron or millimeter size objects. The overall structure of an object is affected by its size if the size is comparable to the range of (short- and long-range) interactions between atoms. Thus, any dependence of a property on the particle size must be associated with a corresponding change of the specific atomic structure of the material. Our research interests are in determination of the structure of grains in powders, polycrystals, and composites with individual grain size in the range from several to 20 nm. The question that we face is how to detect and evaluate changes in the atomic structure of nanocrystals relative to larger size grains using diffraction experimental techniques.
Surface-related effects are due to a significant increase in the relative importance of surface and interface phenomena and show a complex origin. In diamond-SiC composites, the surface effects control interfaces between diamond and SiC and between SiC nanocrystallites and, thus, control the strength of bonding between these phases. Temperature, pressure, outgassing and/or controlled adsorption of foreign gases may modify surface properties of nanocrystals, and such surface engineering will be employed to prepare precursors for the manufacturing process.