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Ti-Si-N nanocomposite films were deposited by multitarget reactive magnetron sputtering. Energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy were employed to characterize their microstructure and a microhardness tester was used to measure their hardness. The influence of substrate temperature on these films was investigated, too. The results reveal that the films consist of TiN and Si 3 N 4 . Si 3 N 4 exists as amorphous, which strongly prevents the growth of TiN grains and causes TiN to form a nanocrystalline or amorphous phase. The hardness of films deposited at room temperature reaches the peak value of 36 GPa at a Si content of 4.14 at. %, and then decreases gradually with the increase of Si content. The enhancement of the substrate temperature weakens the restraint effect of amorphous Si 3 N 4 on the growth of TiN grains, which results in coarse TiN grains and subsequently leads to a lower peak value and a slower decrease of the hardness of the films.

A detailed TEM investigation on the microstructure of TiN/Si3N4 nanocomposite coatings, which is believed to be responsible for the coatings' remarkable mechanical properties, was carried out. Parallel simulation utilizing two-dimensional TiN/Si3N4 nanomultilayered coatings was further performed to study whether the variation of Si3N4 interlayer thickness has an influence on the coatings' microstructure and mechanical properties. The results revealed that, in nanocomposite coatings with high hardness, Si3N4 tissue has a thickness of about 0.5–0.7 nm and exists in the crystalline state. Low-energy coherent interfaces are formed between Si3N4 and neighbouring elongated TiN grains. For TiN/Si3N4 nanomultilayered coatings, Si3N4 modulation layers with thicknesses less than 0.7 nm were also found to crystallize and form coherent interfaces with the neighbouring TiN layers; at the same time, the hardness of the coatings is remarkably enhanced. When its thickness exceeds 1.0 nm, Si3N4 transformed its growth mode into amorphous and the coherent interfaces were damaged; as a consequence, hardness enhancements in the coatings vanished. The similarity of the microstructure and the mechanical properties response between nanocomposites and nanomultilayered coatings indicates that the crystallization of Si3N4 as well as the formation of coherent interfaces between TiN and Si3N4 is the main reason for the hardening of the nanocomposites.

Although superhardness effects have been extensively investigated for epitaxial ceramic nanomultilayer films with the same crystal structures in the last decade, those for multilayers with different crystal structures have been seldom studied. In this article, NbN/TaN nanomultilayers have been designed and deposited by reactive magnetron sputtering. The results showed that the crystal structures of NbN and TaN are face-centered cubic and hexagonal in superlattice films, respectively, and the lattice plane (111) of NbN is coherent with the (110) of TaN, i.e., {111}fcc-NbN∥{110}h-TaN. The results of microhardness measurement showed that the superhardness effects of NbN/TaN multilayers exist in a wide range of modulation period from 2.3 to 17.0 nm. This phenomenon is different from that of epitaxial ceramic multilayers where the maximum hardness usually takes place at a modulation period of 5.0–10.0 nm. It is proposed that the coherent stresses and the structural barriers (fcc/hexagonal) to dislocation motion between NbN and TaN layers are the main reasons for the high-hardness value in a wide range of modulation periods.

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