Abstract
Nanostructure evolution and deformation of nanocrystallites in Ti–B x –N y thin films with different B contents were investigated using high-resolution transmission electron microscopy, X-ray diffraction and Monte Carlo simulations. The Ti–B x –N y films were deposited on unheated Si (1 0 0) substrates by reactive unbalanced direct current magnetron sputtering in an Ar–N 2 gas mixture. The results indicated that pure TiN films contained well-crystallized nanocrystallites, while incorporation of B into TiN led to the formation of nanocomposite thin films of nanocrystalline (nc) Ti(N,B) grains embedded in amorphous TiB 2–BN matrices. When the B content was relatively low (about 16 at.%), two differently sized nanocrystallites with average grain sizes of about 9 and 3 nm, respectively formed. Addition of more B (27 at.% or more) produced smaller and more uniform nanocrystallites, followed by a decrease in the distribution density of nanocrystallites in the amorphous matrix. With increasing B content, more [0 0 2]-oriented grains were formed, accompanied by a gradual decrease in grain size of the nanocrystallites. Twinning deformations were found to occur in nanocrystallites with incorporation of B, and were further activated with increasing B content, which was attributed to the decrease in grain size with B content and the formation of solid solution nc-Ti(N,B) via incorporation of B into the TiN lattice. Using Monte Carlo simulations, the effects of the mixed amorphous TiB 2–BN phase on microstructure evolution and grain growth in nc-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.
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