57 / 2021-06-30 09:04:14

Effect of additional Al doping on microstructure, mechanical and tribological properties of AlB2-type WB2 coatings by magnetron sputtering

reactive magnetron sputtering, nanocomposite, mechanical properties

Hard coatings have been widely used in many extreme working environments. In the past few decades, transition metal nitrides, such as TiAlN have already been used for many applications, such as metal cutting tools. Recently, attention has been captured by transition metal borides for their high hardness, good wear resistance and excellent chemical stability. Among all the borides, WB₂ has been becoming a competitive candidate as a protective coating, especially AlB₂-type WB₂. The nanocomposite-film approach can be used to further enhance the mechanical and tribological properties of the AlB₂-type WB₂ film. In this work, W-Al-B nanocomposite coatings with different Al content (0 to 44.04 at.%) were deposited by a dual-target direct-current magnetron sputtering system. The influence of Al content on the microstructure, mechanical and tribological properties of the nanocomposite coatings was evaluated in detail. The result shows that the W-Al-B coatings are polycrystalline structure consisting of nanocrystal WB₂ and amorphous Al₂O₃/Al. The hardness of the coatings increases initially and then decreases with the increasing of Al content. Coating with Al content of 2.22 at.% presents the maximum hardness of 34.42 GPa. Whereas the indentation toughness of the coatings deposited on (100) Si wafers deteriorates with the doping of Al element. Coating with Al content of 2.22 at.% also exhibits the best wear resistance with the wear rate of 2.20×10⁻⁷ mm³/Nm owing to its high hardness. The W-Al-B coatings perform better wear resistance than pure WB₂ due to the lubrication effect of the amorphous Al₂O₃ phase.