Crystallization of amorphous AlN and superhardness effect in VC/AlN nanomultilayers

VC/AlN nanomultilayers with various AlN layer thicknesses have been prepared by multi-target magnetron sputtering. Microstructure evolution and mechanical properties of the multilayers have been investigated. Under the “template effect” of cubic VC, as-deposited amorphous AlN has been crystallized to cubic structure with AlN layer thickness < 1 nm, correspondingly the multilayers exhibit coherent growth and obtain significantly enhanced hardness with the maximum of 40.1 GPa. A further increase of AlN layer thickness causes the formation of amorphous AlN, which blocks the coherent growth of the multilayers, resulting in a rapid decline of hardness.