Sputtering gas pressure and target power dependence on the microstructure and properties of DC-magnetron sputtered AlB2-type WB2 films

The study is mainly to optimize the process parameters (sputtering pressure and sputtering power) of the AlB2-type WB2 films deposited by DC magnetron sputtering by comparing their microstructure, elemental composition, and tribo-mechanical properties. As the argon pressure (PAr) increases (0.3-1.0 Pa), the particle density increases first and then decreases, with a corresponding decrease for particle energy. Under this condition, both the deposition rate and the B/W atomic ratio of the WB2 films increase first and then decrease under the competition effect between the sputtering and scattering process, the film orientation changes from (0 0 1) to (1 0 1), the microstructure changes from dense fine-fiber to porous column coupled with the stress evolution from compressive stress to increased tensile stress. Consequently, films deposited at PAr > 0.5 Pa have the poor hardness and wear-resistance. As the sputtering power increases (150-310 W), both the particle density and particle energy increase. Thus, the deposition rate increases greatly, the B/W atomic ratio declines slightly due to the resputtering process, the film structure becomes dense but rough by the particle bombardment causing the stress change from tensile stress to enhanced compressive stress, and the film orientation changes from the well-crystallized (0 0 1) to poor-crystallized (1 0 1). In conclusion, films with (0 0 1) orientation, high B/W atomic ratio, dense structure and proper compressive stress, which can be deposited at PAr = 0.5 Pa and sputtering current 0.5 A (corresponding to target power about 150 W), show the excellent tribo-mechanical properties with high hardness about 39.4 GPa and low wear rate of 2.2 × 10−7 mm3/mN.