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Keywords:

  • hardness;
  • magnetron sputtering;
  • metastable phases;
  • superhard coatings;
  • WB2

Abstract

WB2 nanocomposite coatings were synthesized by dc magnetron sputtering. The morphology, chemical composition, chemical bonding state, microstructure, hardness, and tribological properties were investigated. The columnar-structured coatings are dense and uniform. The as-deposited coatings were found to have a metastable AlB2-type structure as characterized by X-ray diffraction and further confirmed by high-resolution transmission electron microscopy. Coatings exhibit superhardness about 43.2 ± 5 GPa (taken from the plateau region) obtained by nanoindentation. In addition, the steady-state friction coefficient µ = 0.23 and wear rate K = 6.5 × 10−6 mm3 N−1 m−1 were obtained under dry sliding condition in ambient environments. These characteristics indicate AlB2-type WB2 coatings have high potential application as superhard and low wear coatings. Moreover, the AlB2-type WB2 can hardly be prepared using the conventional powder metallurgy technology without high pressure, and this study proposes a new practical approach to prepare it.