Coherent growth and superhardness effect in VC/Si3N4 nanomultilayers

A series of VC/Si3N4 nanomultilayers have been prepared by reactive magnetron sputtering in the mixture of Ar and C2H2. Microstructure evolution and mechanical properties of multilayers with various thicknesses of Si3N4 layer have been researched. The results show that the sputtered Si3N4 doesnʹt react with C2H2. In VC/Si3N4 multilayers, amorphous Si3N4 is crystallized at small layer thickness (≤ 0.71 nm) due to the template effect of VC. Correspondingly, multilayers exhibit coherent growth, and obtain significant hardness enhancement with maximum hardness of 45.9 GPa. Further increasing the thickness of Si3N4 layer (≥ 1.45 nm), Si3N4 transforms to be amorphous and blocks the coherent growth in multilayer, which leads to the gradual decrease of hardness.