Microstructure evolution and grain growth of nanocomposite TiN–TiB2 films: experiment and simulation

Titanium–boron–nitride (TiN–TiB2) films deposited onto Si (100) at room temperature with different boron contents by reactive unbalanced magnetron sputtering have been analyzed by a combination of high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Microstructure studies revealed that at low boron incorporation (up to about 9 at.%), the film microstructure was basically TiN with a [111] preferred orientation. As the B content increased to about 19 at.%, a two-phase nanocomposite structure was formed, showing nanocrystalline (nc-) solid solution Ti(N,B) grains within amorphous (a-) TiB2 matrices. Simultaneously, their preferred orientations gradually transformed from [111] to a mixture of [111] and [200]. When the B content reached about 27 at.% or above, nc-Ti(N,B) grains, embedding into matrix consisting of a-TiB2 and a-BN, became smaller and separate. These grains existed in either round or elliptical shape. Using Monte Carlo simulations, the effects of the mixed amorphous TiB2-BN phase on the microstructure evolution and grain growth in nanocrystalline Ti(N,B) were also studied. The results indicated that the formation of such an amorphous phase at the grain boundary could hinder the growth of Ti(N,B) grains and the mean grain size showed an exponential decay with boron concentration, in good agreement with our experimental observations.