Impact of working pressure on the crystallinity and mechanical properties of vanadium nitride coatings deposited in helium/nitrogen reactive plasma

In this study, vanadium nitride (VN) coatings were deposited via radio frequency magnetron sputtering in helium/nitrogen reactive plasma under varying working pressures (5–0.1 Pa). The coatings were systematically characterized for structure, morphology, elemental composition, and mechanical properties via x-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and nanoindentation. Results revealed that coatings deposited at 1 and 0.5 Pa exhibited a highly crystalline face-centered cubic structure with a dominant (200) orientation, attributed to helium-induced Penning ionization. This process enhanced nitrogen activation, promoting stoichiometric VN formation and preferential grain growth. Reducing the working pressure to 0.5 Pa resulted in denser, smoother surfaces and refined grain sizes, driven by increased adatom mobility and kinetic energy that facilitated atomic rearrangement and defect minimization. The study also highlights the critical role of working pressure in governing the microstructural evolution and mechanical performance of VN coatings. The optimized coating at 0.5 Pa achieved hardness of 36.68 GPa and Young’s modulus of 395.59 GPa, demonstrating the synergistic influence of plasma conditions, crystallinity, grain refinement, and microstructural densification. Such results indicate the benefit of controlling the working pressure to optimize the microstructure and mechanical properties of VN coatings.