[en] Epitaxial Mo/NbN and W/NbN superlattices with modulation wavelengths Λ ranging from 1.3 to 120 nm were grown on MgO (001) substrates by dc reactive magnetron sputtering in Ar/N₂ mixtures. The superlattices were shown to be epitaxial with nearly planar layers using high- and low-angle x-ray diffraction and transmission electron microscopy. Computer simulation fits of the x-ray data indicated that interface widths were ≤0.3thinspnm. The epitaxial relationship between the layers was (001)_metal parallel(001)_NbN and [110]_metal parallel[100]_NbN. The nanoindenter microhardness values from W/NbN and Mo/NbN superlattices with 50 volthinsp% metal were nearly identical. The largest hardnesses were 30 GPa, observed at superlattice periods Λ=2 endash 3thinspnm, compared to rule-of-mixtures values of 10 GPa. The hardness decreased with increasing Λ above ∼3thinspnm, following the dependences H=10.3+26.70Λ^-0.38thinspGPa for Mo/NbN and H=12.88+22.1Λ^-0.3thinspGPa for W/NbN. Hardness versus metal volume fraction with Λ∼5thinspnm showed a flat-topped dependence. Brillouin scattering results for Mo/NbN superlattices showed a minor elastic anamoly at small Λ. The hardness results are compared with theories for strengthening of multilayers. copyright 1998 American Institute of Physics

[en] Nanocomposite coatings consisting of Ag and TiC_x (x < 1) crystallites in a matrix of amorphous SiC were deposited by high-rate magnetron sputtering from Ti-Si-C-Ag compound targets. Different target compositions were used to achieve coatings with a Si content of ∼13 at.%, while varying the C/Ti ratio and Ag content. Electron microscopy, helium ion microscopy, X-ray photoelectron spectroscopy and X-ray diffraction were employed to trace Ag segregation during deposition and possible decomposition of amorphous SiC. Eutectic interaction between Ag and Si is observed, and the Ag forms threading grains which coarsen with increased coating thickness. The coatings can be tailored for conductivity horizontally or vertically by controlling the shape and distribution of the Ag precipitates. Coatings were fabricated with hardness in the range 10-18 GPa and resistivity in the range 77-142 μΩ cm.

[en] Nanocomposite Ti-Si-C thin films were deposited by dc magnetron sputtering from a Ti₃SiC₂ target onto Si(1 0 0) and high-speed steel substrates at 300 deg. C. The as-deposited films consisted of nanocrystalline (nc-) TiC _x and amorphous (a-) SiC _x, as determined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Annealing in vacuum up to 1450 deg. C resulted in improved crystallinity and a decreased volume fraction of the amorphous phase. Additionally, differential scanning calorimetry (DSC) was used to monitor heat flows connected to the respective reactions in the material, where a broad exothermic peak attributed to grain growth of crystalline TiC _x appeared, while an exothermic reaction related to the formation of Ti₃SiC₂ was not detected. Tribological testing in a ball-on-disk setup was conducted at room temperature, 500 and 700 deg. C against an alumina counterpart. The room temperature measurement resulted in a coefficient of friction value of 0.8; at elevated temperatures the coefficient of friction decreased to 0.4