Influence of Content of Al(2)O(3) on Structure and Properties of Nanocomposite Nb-B-Al-O films

Nb-B-Al-O nanocomposite films with different power of Al(2)O(3) were successfully deposited on the Si substrate via multi-target magnetron co-sputtering method. The influences of Al(2)O(3)’s content on structure and properties of obtained nanocomposite films through controlling Al(2)O(3)’s power were investigated. Increasing the power of Al(2)O(3) can influence the bombarding energy and cause the momentum transfer of NbB(2). This can lead to the decreasing content of Al(2)O(3). Furthermore, the whole films showed monocrystalline NbB(2)’s (100) phase, and Al(2)O(3) shaded from amorphous to weak cubic-crystalline when decreasing content of Al(2)O(3). This structure and content changes were proof by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). When NbB(2) grains were far from each other in lower power of Al(2)O(3), the whole films showed a typical nanocomposite microstructure with crystalline NbB(2) grains embedded in a matrix of an amorphous Al(2)O(3) phase. Continuing increasing the power of Al(2)O(3), the less content of Al(2)O(3) tended to cause crystalline of cubic-Al(2)O(3) between the close distances of different crystalline NbB(2) grains. The appearance of cubic-crystallization Al(2)O(3) can help to raise the nanocomposite films’ mechanical properties to some extent. The maximum hardness and elastic modulus were up to 21.60 and 332.78 GPa, which were higher than the NbB(2) and amorphous Al(2)O(3) monolithic films. Furthermore, this structure change made the chemistry bond of O atom change from the existence of O-Nb, O-B, and O-Al bonds to single O-Al bond and increased the specific value of Al and O. It also influenced the hardness in higher temperature, which made the hardness variation of different Al(2)O(3) content reduced. These results revealed that it can enhance the films’ oxidation resistance properties and keep the mechanical properties at high temperature. The study highlighted the importance of controlling the Al(2)O(3)’s content to prepare well-defined films with high mechanical properties and thermal stability.