Anisotropic super-hardness of hexagonal WB2±z thin films

Transition metal diboride-based thin films are promising candidates to replace state-of-the-art protective and functional coating materials due to their unique properties. Here, we focus on hexagonal WB2-z , showing that the AlB2 structure is stabilized by B vacancies exhibiting its energetic minima at sub-stoichiometric WB1.5. Nanoindentation reveals super-hardness of 0001 oriented alpha-WB2-z coatings, linearly decreasing by more than 15 GPa with predominant 10 (1) over bar1 orientation. This anisotropy is attributed to differences in the generalized stacking fault energy of basal and pyramidal slip systems, highlighting the feasibility of tuning mechanical properties by crystallographic orientation relations. [GRAPHICS] IMPACT STATEMENT First report of an anisotropic elastoplastic behaviour in super-hard PVD AlB2 structured WB2-z. Theoretical and experimental verification of thermodynamically most stable sub-stoichiometric alpha-WB2-z coatings by structural and mechanical analysis.

Automated summary

Transition metal diboride-based thin films, with unique properties, are potential alternatives to current protective and functional coatings. This study focuses on hexagonal WB2-z, where the AlB2 structure is stabilized by sub-stoichiometric WB1.5 due to B vacancies. Experimental results show that alpha-WB2-z coatings exhibit super-hardness with anisotropy, and the mechanical properties can be tuned by crystallographic orientation relations.