Inherent brittleness, which easily leads to crack formation and propagation during use, is a serious problem for protective ceramic thin-film applications. Superlattice architectures, with alternating nm-thick layers of typically softer/stiffer materials, have been proven powerful method to improve the mechanical performance of, e.g., cubic transition metal nitride ceramics. Using high-throughput first-principles calculations, we propose that superlattice structures hold promise also for enhancing mechanical properties and fracture resistance of transition metal diborides with two competing hexagonal phases, $$\alpha$$α and $$\omega$$ω . We study 264 possible combinations of $$\alpha /\alpha$$α / α , $$\alpha /\omega$$α / ω or $$\omega /\omega$$ω / ω MB $$_2$$2 (where M $$=$$= Al or group 3–6 transition metal) diboride superlattices. Based on energetic stability considerations, together with restrictions for lattice and shear modulus mismatch ( $$\Delta a<4\%$$Δ a < 4 % , $$\Delta G>40$$Δ G > 40 GPa), we select 33 superlattice systems for further investigations. The identified systems are analysed in terms of mechanical stability and elastic constants, $$C_{ij}$$C ij , where the latter provide indication of in-plane vs. out-of-plane strength ( $$C_{11}$$C 11 , $$C_{33}$$C 33 ) and ductility ( $$C_{13}-C_{44}$$C 13 - C 44 , $$C_{12}-C_{66}$$C 12 - C 66 ). The superlattice ability to resist brittle cleavage along interfaces is estimated by Griffith’s formula for fracture toughness. The $$\alpha /\alpha$$α / α -type TiB $$_2$$2 /MB $$_2$$2 (M $$=$$= Mo, W), HfB $$_2$$2 /WB $$_2$$2 , VB $$_2$$2 /MB $$_2$$2 (M $$=$$= Cr, Mo), NbB $$_2$$2 /MB $$_2$$2 (M $$=$$= Mo, W), and $$\alpha /\omega$$α / ω -type AlB $$_2$$2 /MB $$_2$$2 (M $$=$$= Nb, Ta, Mo, W), are suggested as the most promising candidates providing atomic-scale basis for enhanced toughness and resistance to crack growth.

The use of silver-based antimicrobial materials has been growing recently. Considering the threat of developing silver-resistant bacteria, it is essential to address the endurance of such materials and the amount of silver released into the environment. Here we report on a durable, antibacterial Ag/TiB_x nanocomposite coating prepared by conventional magnetron sputtering. The coating consists of fine Ag clusters embedded in extremely hard, wear-resistant overstoichiometric TiB_x, which serves as a protective matrix. The highest E. coli growth inhibition of 97% is observed for the coating containing 24 at.% of Ag. A strong antibacterial effect is also maintained after 45 days of immersion in the Luria–Bertani + 5% HNO₃ solution. Despite a marked hardness decrease from 40 GPa for TiB_x to 6.4 GPa for Ag/TiB_x with 28 at.% of Ag, the coating maintains a good specific wear rate of 6 × 10⁻⁵ mm³/Nm. Moreover, the addition of Ag, which acts as a solid lubricant, decreases the coefficient of friction from 0.77 to 0.35, even at room temperature. Thanks to the combination of antibacterial properties and enhanced wear resistance, such material can find application as a protective coating for cutlery, door handles, water taps, and other daily-used objects in public areas.

Hexagonal ZrB₂ belongs to the group of ultra-high temperature ceramics representing an important class of materials with the potential to meet the high demands of today’s industry. However, this potential is limited by inherent brittleness and poor tribological properties. Here, the combination of density functional theory and experiment is used to investigate the effect of silver alloying on the mechanical and tribological properties of hexagonal ZrB₂ thin films. Calculations indicate strong insolubility of Ag atoms in the ZrB₂ metal sublattice and a significant effect on the mechanical properties, pointing out an improvement in ductility and tribological properties but at the cost of reduced hardness. The experiments confirmed the theoretical predictions of the strong insolubility of silver, where the magnetron-sputtered Zr_1−xAg_xB_2+Δ films form a segregated nanostructure consisting of separated hexagonal ZrB₂ and cubic Ag phases. With increased Ag content, values of Young’s modulus decrease from E^ZrB2.31 = 375 GPa to E^{Zr0.26Ag0.74B0.89} = 154 GPa, followed by a decrease in hardness from H^ZrB2.31 = 30 GPa to a value of H^{Zr0.26Ag0.74B0.89} = 4 GPa. The suppression of crack formation is also shown with the material flow around cube corner indents, indicating enhanced ductility. The improvement of tribological properties was also confirmed when the coefficient of friction (COF) was reduced from COF^ZrB2.31 ~0.9 to a value of COF^{Zr0.26Ag0.74B0.89} ~0.25 for all counterpart materials—steel (100Cr6), Si₃N_4, and WC/Co.

Doping of transition metal diborides (TMB₂) films with soft metals (Ag, Au, Pt) can extend their application potential to tribological and biomedical fields. Here, a combination of direct current unbalanced magnetron sputtering (DC-UBMS) with high-power pulsed magnetron sputtering (HiPIMS) was used to synthesize silver-doped CrB_2+x thin films on unheated substrates. All Ag–CrB_2+x thin films were over-stoichiometric with a B/Cr ratio ranging from 2.05 to 2.30 and silver content varying from 3 at.% to 29 at.%. X-ray diffraction demonstrates the amorphous character of the structure in the case of films with silver content ranging from 0 at.% to 8 at.%. A nanocrystalline structure containing a cubic Ag phase is formed in the films with higher silver content. The highest hardness of 26.6 GPa accompanied by the highest value of elastic modulus of 362 GPa was measured in undoped CrB_2.3 films. As the silver content in the Ag–CrB_2+x thin films increases, the hardness and elastic modulus values gradually decrease to 7.8 GPa and 187 GPa, respectively. The friction properties of CrB_2.3 films, expressed by the coefficient of friction against a steel ball of 0.72, are insufficient and limit their use in demanding industrial applications. However, silver doping significantly reduces the friction coefficient when the lowest value of 0.39 is measured in moderately hard Ag–CrB_2+x films with an Ag content of 17 at.%. The scratch test shows satisfactory adhesion of films to substrates even without additional heating during deposition.