Effects of nitrogen concentration on microstructures of WN_X films synthesized by cathodic arc method

Tungsten nitride films (WN_X) were deposited by the cathodic arc method in argon-nitrogen gas mixture changing nitrogen partial pressures. When the N₂/Ar+N₂ ratios were less than 0.1, the films showed α-W with hexagonal structures. On the other hand, the crystal structure changed to cubic W₂N with the ratios between 0.1 and 0.35. When the ratios exceeded 0.35, the films were hexagonal WN. The micro-hardness of α-W, cubic W₂N and hexagonal WN phase showed approximately 13, 24 and 28 GPa, respectively. The surface roughness of WN_X films were smooth with approximately 10 nm and, correspondingly, the grains are all small with 10-50 nm in size. In this paper, the changes in crystal structures of WN_X were investigated as a function of nitrogen flow and their mechanical properties were studied.