Role of amorphous Si3N4 in the microhardness of Ti-Al-Si-N nanocomposite films

Abstract

Superhard quarternary Ti-Al-Si-N films were synthesized by using a hybrid coating technique involving arc-ion plating and sputtering methods. The relationship between microhardness and microstructural changes due to the percolation phenomenon of amorphous silicon-nitride in Ti-Al-Si-N films during the deposition process was investigated. The synthesized Ti-Al-Si-N films were revealed to be composites of (Ti, Al)N crystallites distributed in an amorphous Si3N4 matrix. Due to the percolation of amorphous silicon-nitride, the grain size of (Ti, Al)N crystallites was decreased with increasing Si content. When the Si content was about 9 at.%, the film: was characterized as a nanocomposite, nc-(Ti, Al)N/a-Si3N4, and showed a maximum hardness of about 55 GPa. This hardness value was significantly larger than that of a pure (Ti, Al)N film(similar to35 GPa). The increased hardness of the (Ti, Al)N film with Si addition was probably due to grain boundary hardening through both the Hall-Petch relation derived, from grain size refinement and the strong cohesive energy of interphase boundaries caused by the percolation of amorphous Si3N4 into the (Ti, Al)N film.