Origin of the hardness enhancement in superhard nc-TiN/a-Si3N4 and ultrahard nc-TiN/a-Si3N4/TiSi2 nanocomposites

The ideal shear strengths of a variety of TiN/SiNx/TiN interfaces have been calculated with the ab initio density functional theory. Using these data, the high hardness H >= 105 GPa, which has been reported for the quasi-ternary nc-TiN/a-Si3N4/TiSi2 nanocomposites, can be explained on the basis of the Sachs average of polycrystal plasticity of randomly oriented equiaxed grains and pressure-enhanced flow stress.