The coherent growth and mechanical properties of non-isostructural TiN/TiB2 nanomultilayers

Abstract

TiN/TiB2 nanomutlialyers with different TiB2 layer thickne ss were prepared using multi-target magnetron sputtering method. The effects of TiB2 layer thickness on the growth structure and mechanical properti es of nanomultialyers were studied by X-ray diffraction, high-resolution transmi ssion electron microscopy and nanoindentation respectively. The results reveal t hat the normally amorphous TiB2 layers crystallize in close-packed he xagonal structure when its thickness is less than 2.9 nm due to the template eff ect of cubic TiN layers. Coherent growth is found between TiN and TiB2 layers with the orientation relationship of {111}TiN//{0001}Ti B2,〈110〉TiN//〈1120〉TiB2. Because of th e lattice misfit, an alternating tensile/compressive stress field develops in th e nanomultilayers, which leads to the anomalous enhancement of hardness and elas tic modulus. Maximum hardness and elastic modulus of 46.9 and 465GPa are obtaine d at TiB2 layer thickness of 0.6nm. With increasing TiB2 l ayer thickness, amorphous TiB2 forms and blocks the coherent growth of the multilayers. Consequently, the hardness and elastic modulus of the films decrease gradually.