Thin films of superhard nanocrystalline nc-W2N/amorphous a-Si3N4 composite have been prepared by plasma chemical vapor deposition at temperatures in the range, 500-550 degrees C. Maximum hardness of 5200 kg/mm(2) (about 51 GPa) and elastic modulus of greater than or equal to 500 GPa is reached at a silicon content of 7-8 at. %. During the indentation experiment the material shows a large elastic recovery of 80%, which compares favorably with those of hard a-C:H (hardness only about 2000 kg/mm(2)). The results are similar to those recently obtained with nc-TiN/a-Si3N4 and thus support our concept for the design of novel superhard composite materials with a variety of transition metal nitrides. The question of the upper limit of the strength of these materials is addressed and discussed.