Effect of the addition of Si into Nb2O5 coatings on their structural, optical, and mechanical properties

There are many polymorphs of Nb2O5, each with interesting properties that have been explored for biomedical, photocatalytic, and optical applications. However, Nb2O5 is not generally used for mechanical applications owing to its low hardness (8 GPa). The objective of this work was to evaluate the effects resulting from the addition of silicon (Si) into the Nb2O5 structure, with the aim of increasing its hardness through the formation of a nanostructured composite coating. In this paper, the authors report the structure and mechanical properties of Nb2O5 as a function of the silicon content (0–5.5 at. %). The coatings were deposited on silicon and D2 steel substrates using a confocal-dual magnetron sputtering system using a mixture of argon and oxygen (80:20) with each magnetron (Nb and Si targets) independently driven. The coatings were annealed at 550 °C to obtain a crystalline structure. However, analysis of the optical properties indicated the persistence of a substoichiometric amorphous phase. Despite the contribution of the amorphous phase, the mechanical–tribological properties were slightly improved after Si incorporation. The hardness reached a maximum of 17.6 GPa for the samples deposited at 50 W in the Si target, coupled with a reduction in both the coefficients of friction and wear.