Microstructure and Mechanical Properties of TiN/Si_3N_4 Nanocomposite Films

A microstructure investigation of TiN/Si3N4 nanocomposite films with high hardness was performed by means of high-resolution transmission electron microscope, and a result far from the nc-TiN/a-Si3N4 model was presented. Instead of the isotropic one, TiN was pronounced nanocrystalline columnar grains with dimensions of 10nm in width and 100nm in length. Immiscible Si3N4 interfa-cial phases between TiN nanocolumns with a thickness of about 0.5-0.7nm existed in nanocrystalline structure and formed coherent interfaces with adjacent TiN nanocrystals. A succedent simulation employing two-dimensional TiN/Si3N4 nanomultilayers also implied that due to the template effect of crystalline TiN layers, sputter-deposited amorphous Si3N4 was forced to crystallize and grow epitaxially with TiN layers when its thickness was less than 0.7nm, accompanied by a significant enhancement in film's hardness. Due to the short-range nature of the template effect of TiN layers, the crystalline Si3N4 gradually transformed into amorphous when its thickness exceeded 1.0nm and the coherent interfaces were destroyed as a consequence, with a simultaneous film's hardness decline. By comparing the microstructure and corresponding hardness response of TiN/Si3N4 nanocomposite films with that of the nanomultilayered ones, a new explanation on hardening mechanism of TiN/Si3N4 nanocomposites was proposed.