Recent developments in hard materials

This paper reviews some new developments in hard materials during the last decade: new approaches to diamond synthesis including chemical vapor deposition and the laser QQC method, tetrahedral carbons, deposition of cubic boron nitride, ternary boron-carbon-nitrogen and boron-carbon-silicon phases. The issue of ultimate hardness of diamond reappeared again because of pseudopotential calculation of cohesive energy of a hypothetical beta-C3N4 structure. The stability of carbon nitride phases is analyzed in connection with the authors study of synthesis and structure of carbon nitride by nitrogen microwave plasma. Only soft graphitic CNx, x < 1 phase, stable up to 900 degrees C, survived criticism. (C) 1997 Elsevier Science Limited.