Yunshan Dong

Crystallization of Si3N4 layers and its influences on the microstructure and mechanical properties of ZrN∕Si3N4 nanomultilayers

ZrN∕Si3N4 nanomultilayers with different layer thicknesses of Si3N4 were synthesized to study the crystallization of Si3N4 and its effects on the microstructure and mechanical properties of multilayers. Results indicated that influenced by the template effects of crystalline ZrN layers, amorphous Si3N4 layers were crystallized into a rocksaltlike pseudocrystal structure when their thickness was less than 0.9nm. Then crystallized Si3N4 layers grew epitaxially with ZrN and formed strong columnar crystals, accompanied with a remarkable increase in hardness. When its thickness exceeds 1.1nm, the subsequently deposited Si3N4 grows as amorphous, blocking the epitaxial growth and leading to a quick decline of hardness.

Coherent epitaxial growth and superhardness effects of c‐TiN∕h‐TiB2 nanomultilayers

TiN∕TiB2 nanomultilayers with different TiB2 layer thicknesses were deposited by the multitarget magnetron sputtering method. Studies show that because of the template effects of the cubic TiN layer, the normally amorphous TiB2 layer crystallizes into a compact hexagonal structure when its thickness is less than 2.9 nm. As a result, the multilayers form a c‐TiN∕h‐TiB2 coherent epitaxial structure with the orientation relationship of {111}TiN∕∕{0001}TiB2,⟨110⟩TiN∕∕⟨112¯0⟩TiB2. Correspondingly, the multilayers show a significant hardness enhancement with a maximum hardness of 46.9 GPa. Further increase in TiB2 layer thickness leads to the formation of amorphous TiB2 that blocks the coherent growth of the films, and thus the hardness of the multilayers decreases gradually.

Crystallization of AlON layers and its effects on the microstructure and hardness of reactively synthesized ZrN/AlON nanomultilayers

By reactively sputtering Zr and Al2O3 targets in a gaseous mixture of Ar and N2, ZrN/AlON nanomultilayers were synthesized to study the crystallization conditions for AlON layers and how they influence the characteristics of multilayers. The composition analysis indicated that some of the oxygen atoms were replaced by nitrogen atoms in Al2O3, leading to the formation of aluminium oxynitride, AlON, during the procedure of the Al2O3 target being sputtered in the gaseous mixture. Further investigations showed that when their thickness was limited to less than 1 nm, amorphous AlON layers were crystallized under the template effects of crystalline ZrN layers, and then coherent interfaces formed as a result. Correspondingly, the multilayers were remarkably strengthened with hardness approaching a maximum of 33 GPa. After the layer thickness of AlON exceeded the critical value of 1 nm, the subsequently deposited AlON grew amorphously and blocked the epitaxial growth of multilayers, accompanied by the decline of hardness. Yet, on the other hand, the integrated hardness of multilayers was not sensitive to the thickness of the ZrN template layers and its value was maintained a bit higher than 30 GPa in a wide range of ZrN layer thickness variations.

Crystallization of Al2O3 and its effects on the mechanical properties in TiN∕Al2O3 nanomultilayers

TiN∕Al2O3 nanomultilayers with various Al2O3 layer thicknesses were prepared by multitarget magnetron sputtering method. The composition, growth structures, and mechanical properties of the nanomultilayers were studied by energy dispersive x-ray spectrometry, x-ray diffraction, high-resolution transmission electron microscopy, and nanoindentation. It reveals that when the thickness of Al2O3 layers is small (<∼1.5nm), the cubic TiN layers force Al2O3 to crystallize under the sputtering conditions where the formation of amorphous Al2O3 should be favored, and then the TiN and Al2O3 modulation layers grow coherently and epitaxially. Correspondingly, the hardness and elastic modulus of the multilayers increase abnormally and reach the maximum values of 37.9 and 402GPa, respectively. With the further increase in layer thickness, Al2O3 layers form an amorphous structure and block the coherent growth of the multilayers, and then the hardness and elastic modulus decrease gradually.