CONVENTIONAL AND NEW APPROACHES TOWARDS THE DESIGN OF NOVEL SUPERHARDMATERIALS

We present recent results on the preparation of stoichiometric C3N4 an d its hardness which is far below the theoretically expected value. A comparison with the turbostratic substoichiometric CN0.2-0.35 films pr epared by Sundgren et al. shows the dominant importance of the microst ructure. Based on some general rules a concept for the design of therm odynamically stable superhard nanocrystalline composite materials is p resented and verified experimentally on three systems: nc-TiN/a-Si3N4, nc-VN/a-Si3N4 and nc-W2N/a-Si3N4. Hardness of about 5000 kg mm(-2) (a bout 50 GPa) or more and a high elastic modulus of 550 GPa were found in all these systems. (C) 1997 Published by Elsevier Science S.A.