Coherent epitaxial growth and superhardness effects of c-TiN/h-TiB2 nanomultilayers

TiN/TiB2 nanomultilayers with different TiB2 layer thicknesses were deposited by the multitarget magnetron sputtering method. Studies show that because of the template effects of the cubic TiN layer, the normally amorphous TiB2 layer crystallizes into a compact hexagonal structure when its thickness is less than 2.9 nm. As a result, the multilayers form a c-TiN/h-TiB2 coherent epitaxial structure with the orientation relationship of {111}TiN//{0001}TiB2, <110>TiN//<1120>TiB2. Correspondingly, the multilayers show a significant hardness enhancement with a maximum hardness of 46.9 GPa. Further increase in TiB2 layer thickness leads to the formation of amorphous TiB2 that blocks the coherent growth of the films, and thus the hardness of the multilayers decreases gradually