Marián Haršáni

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.

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.

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.

The present work investigates the influence of isothermal annealing on the microstructure and oxidation behavior of nanocomposite coatings. AlTiSiN/TiSiN coatings with TiSiN adhesive layer were deposited onto a high-speed steel substrate via physical vapor deposition. The coatings were investigated in the as-deposited state as well as after annealing in air at 700, 800, 900 and 1000 °C, respectively. The microstructure and morphology of the coatings were observed using scanning electron microscopy and transmission electron microscopy. The chemical composition and presence of oxidation products were studied by energy-dispersive X-ray spectroscopy. The phase identification was performed by means of X-ray diffraction. In the microstructure of the as-deposited coating, the (Ti_1−xAl_x)N particles were embedded in an amorphous Si₃N₄ matrix. TiO₂ and SiO₂ were found at all annealing temperatures, and Al₂O₃ was additionally identified at 1000 °C. It was found that, with increasing annealing temperature, the thickness of the oxide layer increased, and its morphology and chemical composition changed. At 700 and 800 °C, a Ti-Si-rich surface oxide layer was formed. At 900 and 1000 °C, an oxidized part of the coating was observed in addition to the surface oxide layer. Compared to the as-deposited sample, the oxidized samples exhibited considerably worse mechanical properties.

Due to the increased demands for drilling and cutting tools working at extreme machining conditions, protective coatings are extensively utilized to prolong the tool life and eliminate the need for lubricants. The present work reports on the effect of a second MeN (Me = Zr, Cr, Mo, Nb) layer in WN-based nanocomposite multilayers on microstructure, phase composition, and mechanical and tribological properties. The WN/MoN multilayers have not been studied yet, and cathodic-arc physical vapor deposition (CA-PVD) has been used to fabricate studied coating systems for the first time. Moreover, first-principles calculations were performed to gain more insight into the properties of deposited multilayers. Two types of coating microstructure with different kinds of lattices were observed: (i) face-centered cubic (fcc) on fcc-W₂N (WN/CrN and WN/ZrN) and (ii) a combination of hexagonal and fcc on fcc-W₂N (WN/MoN and WN/NbN). Among the four studied systems, the WN/NbN had superior properties: the lowest specific wear rate (1.7 × 10⁻⁶ mm³/Nm) and high hardness (36 GPa) and plasticity index H/E (0.93). Low surface roughness, high elastic strain to failure, Nb₂O₅ and WO₃ tribofilms forming during sliding, ductile behavior of NbN, and nanocomposite structure contributed to high tribological performance. The results indicated the suitability of WN/NbN as a protective coating operating in challenging conditions.

This article is aimed to investigation of four different PVD coatings of STATON company in order to determine a wear behavior on twist drills when drilling C45 material. A pearlite-ferrite structure of C45 material is common material for automotive industry and highly abrasive to cutting tools. Our comparative study is focused on flank wear of the cutting wedge of observed drills deposited at STATON. The article shows differences in chemical composition and their effects on wear behavior at the corner of the drill and along the cutting edge. We also demonstrate that chemical composition has significant influence on the temperature of a build-up edge during cutting.