NOVEL THERMODYNAMICALLY STABLE AND OXIDATION-RESISTANT SUPERHARD COATING MATERIALS

A theoretical concept for the design of novel, nanocrystalline and the rmodynamically stable materials with hardness of greater than or equal to 50 GPa (about 5000 kg mm(-2)), elastic modulus of greater than or equal to 500 GPa and a high stability against oxidation in air up to 8 00 degrees C is described together with its experimental verification on several systems nc-Me(x)N/a-Si3N4 (Me = Ti, W, V). The concept is b ased on avoiding the formation and multiplication of dislocations in t he nanocrystalline phase, and blocking the crack propagation in a 0.3- 0.5 nm thin amorphous tissue. The theoretical principles of the design of such materials and the thermodynamic criteria for the segregation of the nc- and a-phases, which is necessary for the preparation of suc h materials, are discussed. Several micron thick films of such materia ls have been prepared by plasma CVD at a rate of 0.6-1 nm s(-1) from t he corresponding metal halides, hydrogen, nitrogen aad silane at depos ition temperatures of less than or equal to 550 degrees C. A low conte nt of chlorine of less than or equal to 0.3 at.% assures their stabili ty against corrosion in air. Upon microindentation up to a load of gre ater than or equal to 100 mN the films show a remarkably high elastic recovery or about 80%. Unlike diamond, c-BN, and C3N4 these materials are thermodynamically stable and relatively easy Lo prepare.