Modulation periodicity dependent structure, stress, and hardness in NbN/W2N nanostructured multilayer films

Abstract

NbN/W2N nano-multilayer films with a modulation periodicity, Λ, ranging from 5.1 to 157.4 nm have been deposited on a Si(100) substrate by reactive magnetron sputtering in Ar/N2 mixtures. The Λ dependent structural and mechanical properties for the resulting NbN/W2N multilayers have been evaluated by means of low-angle x-ray reflectivity, x-ray diffraction, high-resolution transmission electron microscope, and nanoindentation measurements. The finding is that for films with Λ ≤ 10.6 nm, fcc NbN layers are coherent with cubic W2N layers, resulting in NbN layers and W2N layers that are in the compressive and tensile states, respectively. In contrast, as Λ is larger than 10.6 nm, a phase transition from W2N to W occurs in the W2N layer, which is a result of the coherent interface strain relaxation. For this case, all layers are in the compressive state, and the coherent interface disappears. The intrinsic compressive stress evolution with Λ can be interpreted in terms of interface stress. The formation of coherent interface at small Λ (≤10.6 nm) is helpful for releasing point defects in layers, leading to a low compressive stress (≤1.1 GPa). The hardness for the obtained multilayer film increases with decreasing Λ, and approaches a maximum value of 43.7 GPa when Λ is 7.4 nm. The maximum strengthen at lower Λ is mainly attributed to coherent interface stresses and the modulus difference between the NbN and W2N layers. The increase in hardness with a decrease in Λ is interpreted by the Lehoczky model.

Composite Materials with Nanoscale Multilayer Architecture Based on Cathodic-Arc Evaporated WN/NbN Coatings

“…Many papers that studied different multilayer films have demonstrated that there is an optimal bilayer period that provides the best mechanical properties. For example, TiN/WN coatings showed maximized hardness at Λ = 8.1 nm, and an optimal bilayer period for NbN/WN multilayers was about 7.4 nm, while in both cases, increasing the Λ deteriorated their characteristics. Similar behavior of the WN-based multilayer system was observed in the present study.…”

“…Considering the characteristics of WN and NbN, multilayer coatings based on these nitrides should have excellent wear-resistant properties. The only paper on WN/NbN films deposited by magnetron sputtering was published by Wen et al 33 At a bilayer period of 7.4 nm, multilayers demonstrated a hardness greater than 40 GPa, but other properties were not reported. Therefore, we elected to conduct a more in-depth analysis of changes in the microstructure and tribological behavior of WN/NbN coatings upon variations in the deposition parameters.…”

Effect of bias voltage on the structural properties of WN/NbN nanolayer coatings deposited by cathodic-arc evaporation

“…Moreover, most published papers on multilayers with tungsten nitride used magnetron sputtering and ion-beam-assisted deposition [10][11][12]. Wen et al [13] studied WN/NbN nanostructured multilayer films with different modulation periods deposited by direct current magnetron sputtering. This system demonstrated superhardness of about 43.7 GPa.…”