Superhard nanocomposite coatings are currently of great interest for wear protection of tools. Within this work, after some consideration of the design and failure of nanocomposites, results on nanocomposite Ti–B–N and Ti–B–C films are presented and discussed. Coatings with different compositions in the quasi-binary systems TiN–TiB2 and TiC–TiB2 were deposited onto austenitic stainless steel and molybdenum sheets by means of unbalanced d.c. magnetron co-sputtering using segmented TiN/TiB2 and TiC/TiB2 targets. Coating chemical, structural and mechanical properties were investigated using electron-probe microanalysis (EPMA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD), and depth-sensing nanoindentation. Coatings with elemental compositions of about 35–45 at.% Ti, 18–44 at.% B and 20–36 at.% N or 22–40 at.% C consist of a nanocrystalline arrangement of TiB2 and TiN or TiC, respectively, with crystallite sizes of 1–5 nm. Coating hardness varies between 50 and 70 GPa and elastic moduli are close to 500 GPa.

Ti–B–N films with a gradient in the chemical composition were deposited onto austenitic stainless steel sheets by means of unbalanced DC magnetron co-sputtering using a segmented TiN\Tib2 target. Film microstructure was characterized by means of electron-probe microanalysis (EPMA), transmission electron microscopy (TEM), electron energy-loss spectroscopy (EELS), and X-ray diffraction (XRD) as well as glancing angle X-ray diffraction (GAXRD). The mechanical properties of the coatings were measured using a depth-sensing nanoindenter. The composition of the films was found to lie close to the quasi-binary section TiN–TiB2 within the ternary system Ti–B–N. The grain size determined from TEM investigations range between 3 and 5 nm. Coatings consisted of a nanocrystalline fcc TiN phase (with boron atoms and oxygen impurities dissolved), and TiB2, TiB and B2O3. Microstructure as well as chemical composition of the films were not influenced significantly by the deposition parameters used in this investigation. Contrary, the mechanical properties were strongly influenced varying the ion bombardment. Hardness values exceeding 50 GPa and elastic moduli close to 500 GPa were obtained.

The aim of this work was to investigate the inter-relationships between the ion bombardment during film growth, the resulting chemical composition and microstructure and the optical properties of TiNx and ZrNx coatings. Samples were prepared by non-reactive d.c. unbalanced magnetron sputtering from TiN and ZrN targets. The energy and intensity of the argon ions impinging on the film surface was varied systematically using different bias voltages and different external magnetic fields applied via a Helmholtz coil system. Coatings were characterized using wave-length dispersive electron-probe microanalysis, X-ray diffraction, spectroscopic ellipsometry and CIE-L*a*b* colorimetry. For a brilliant appearance the formation of coatings with a well-defined crystal lattice and a chemical composition close to stoichiometry was found to be necessary. The metallic character of ZrNx coatings characterized by the plasma frequency seems to be more pronounced than for TiN-based films. Varying ion bombardment conditions resulted in TiNx coatings with different chemical compositions (x ranging from 0.85 to 1.02). Thus, also their optical properties were determined by their chemical composition. For ZrNx coatings, the lattice parameter was affected by the ion bombardment for given values for the ion intensity, giving rise to a close relationship to the coloration.

Coatings of the overall composition TiNx(MoSy)z have been produced by dc co-sputter deposition from a single unbalanced magnetron target composed of TiN and MoS2 halves. Compositional variation was obtained by placing stainless steel substrates at various positions with respect to the target. X-ray diffraction and photoelectron spectroscopy showed that the coatings were composed of distinct TiNx and MoSy phases in the form of a nanodispersive system. Pin-on-disk tribometry and nanoindentation demonstrated that coatings with a hardness exceeding 20 GPa and friction coefficients of about 0.1 could be produced by selecting suitable composition and deposition parameters. These coatings show potential for improved endurance with respect to current MoS2-based low-friction coatings and may be suitable for use in severe conditions, for example, as cutting tool coatings for dry machining.

Ti-B-N films with a gradient in the chemical composition were deposited onto austenitic stainless steel and molybdenum sheets by means of unbalanced dc magnetron co-sputtering using a separated TiN/TiB2 target. Different energetic contributions necessary for film growth were investigated adjusting suitable deposition parameters. Film microstructure was characterized by means of scanning (SEM) and transmission electron microscopy (TEM), X-ray diffraction (XRD), as well as glancing angle X-ray diffraction (GAXRD) and electron probe microanalysis (EPMA). Coating hardness was measured using a depth sensing nanoindenter. The microstructure of the films appears featureless using SEM fracture cross sections. The grain size determined from TEM investigations ranged between 3 and 5 nm. The composition of the films was found to lie on the quasi-binary section TiN-TiB2 within the ternary system Ti-B-N. Coatings consisted of nanocrystalline fcc and hcp Ti-B-N phases. Microstructure as well as chemical composition of the films do not seem to be influenced by varying the deposition parameters used in this investigation. Contrarily, the hardness was strongly influenced by varying the ion bombardment. Hardness values exceeding 50 GPa were obtained for Ti-B-N films.

An unbalanced d.c. magnetron sputtering unit was used to deposit titanium nitride and titanium boride films onto austenitic steel and molybdenum substrates using TiN and TiB2 targets. An external pair of Helmholtz coils was used to create an uniform axial magnetic field which allowed the ion/atom ratio incident at the growing film to be varied between 0.1 and 1.3. The characterization of the coatings was conducted by scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The aim of this work was to investigate the effects of different activation energies on the film growth and the microstructure of two different hard materials with comparable melting points. The microstructure of the coatings was mainly influenced by the ion bombardment of the substrate, i.e. ion energy and ion intensity. In the case of TiN, single-phase stoichiometric TiN coatings were obtained. The columnar, porous structure of the films occurring at low ion bombardment was changed to a dense structure as the ion energy and the intensity were increased. At the same time the (111) preferred orientation changed to a mixed orientation. The highest hardness values (∼3000HV0.01) were obtained at intensive ion bombardment. The TiB2 films exhibited a dense single-phase hexagonal TiB2 structure with (001) texture which altered to a mixed orientation as the energy of the incident ions was decreased. The Vickers microhardness of the coatings reached values ∼6300HV0.01.

The microstructure and microchemistry of polycrystalline Ti1-x-yAlxNbyN alloys and Ti1-xAlxN/Ti1-yNbyN multilayers grown on bcc ferritic stainless steel substrates at 450 degrees C by unbalanced-magnetron (UBM) sputter deposition and combined UBM/cathodic-arc (UBM/CA) deposition have been investigated using X-ray diffraction, scanning electron microscopy, Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy (XTEM), and scanning transmission electron microscopy with energy-dispersive X-ray microanalyses of XTEM samples. The growth experiments were conducted in a deposition system in which the substrates are continuously rotated past one Ti0.85Nb0.15 and three Ti0.50Al0.50 cathodes, each capable of being operated independently in either UBM or CA mode. CA ion-etching of the steel substrates prior to deposition produced a polycrystalline compositionally-graded altered layer with a depth of similar or equal to 20 nm when operating the are on the Ti0.50Al0.50 target and a much narrower, similar or equal to 6 nm, amorphous layer with the Ti0.85Nb0.15 target. Subsequent UBM or UBM/CA growth on substrates subjected to the former treatment resulted in local epitaxy with underlying grains for film thicknesses up to similar or equal to 200 nm before the growth front gradually broke down locally to initiate columnar deposition. Film growth on substrates CA ion-etched using the Ti0.85Nb0.15 target resulted in much smaller average column diameters with competitive grain growth. However, the fraction of the sample area covered by nodular defects arising from are-ejected droplets was reduced by a factor of similar or equal to 102. Thus the latter procedure was used for substrate preparation prior to multilayer growth. Ti1-xAlxN/Ti1-yNbyN multilayers with periods between 2.17 and 2.29 nm were grown by combined UBM/CA deposition. The multilayers exhibited flat, regular interfaces throughout film total thicknesses of up to 3 mu m. (C) 1997 Elsevier Science S.A.

Decorative coatings of lanthanum boride were deposited onto steel and molybdenum substrates employing d.c. magnetron sputter deposition using LaB6 targets. The characterization of the coatings was achieved by means of scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The results were discussed in connection with application-related properties, such as film hardness and colour determined by Vickers microhardness and CIE-L*a*b* colorimeter measurements. The aim of this work was the investigation of the interrelationships between the chemical composition, microstructure, hardness and colour of the coatings. Sputtering of LaB6 targets results in the formation of extremely fine columnar films with predominantly (100)oriented LaB6 crystals. With increasing process gas pressure, an increase in the (100) texture and a decrease in the lattice distortion were observed. Likewise, the boron-to-lanthanum atomic ratio decreased from 6.8 to 6.5. With increasing argon pressure, a distinct decrease in the brilliance value L* was observed, resulting in a shift in colour from dark violet to almost black. The maximum Vickers microhardness of the coatings was approximately 2900 HV0.01. The results of the investigations establish the correlations between the stoichiometry, microstructure, hardness and film coloration for decorative coatings based on LaB6.

Decorative hard coatings have to meet a variety of requirements such as attractive colour as well as high wear and corrosion resistance. After a review of PVD coatings used for decorative metal-finishing, an account is given of studies to extend the range of useful coating materials. Within the scope of the search for new colours several borides such as zirconium diboride ZrB2, lanthanum hexaboride LaB6 and zirconium dodecaboride ZrB12 were evaluated using magnetron sputtering. The nitrogen flow in a partially reactive process was used as an additional deposition parameter to influence film composition and properties. The interrelationships between structure, chemical composition and mechanical as well as optical properties were investigated. By means of non-reactive sputtering, crystalline films containing the ZrB2 or the LaB6 phase were formed. In the case of sputtering from the ZrB12, target, the ZrB2 phase was accompanied by a highly disordered boron or boron-rich phase. The incorporation of nitrogen leads to increasing lattice distortion and amorphous film growth at high concentrations. Among the coating types with interesting properties are nitrogen containing films sputtered reactively from ZrB2 target's that had an anthracite coloured surface and outstanding corrosion resistance. Violet coloured coatings deposited non-reactively from LaB6 targets are also potential candidates for decorative applications.

Decorative coatings of zirconium boride were deposited on steel and molybdenum substrates employing d.c. magnetron sputter deposition using ZrB12 targets and neon, argon and krypton as process gases. The characterization of the coatings occurred by means of scanning electron microscopy, electron probe microanalysis, X-ray diffraction, Vickers microhardness measurements and quantitative colour analysis. The effect of the ion bombardment caused by the applied bias voltage using various process gases on the film formation was investigated. Measurements of the deposition rates yielded the highest values for neon and argon. In the case of neon and krypton the stoichiometry of the extremely fine-grained films containing the ZrB2 and a distorted boron phase could be varied by using different bias voltages in a wide range, whereas the bombardment with argon ions seemed to have less effect on the stoichiometry. The maximum Vickers microhardness of the highly reflecting silver-grey films was found to be approximately 2200 HV 0.01.

Decorative coatings of zirconium boride and zirconium boron nitride were deposited onto steel and molybdenum substrates employing non-reactive and reactive d.c. magnetron sputter deposition using zirconium diboride (ZrB2) and zirconium dodecaboride(ZrB12) targets. The characterization of the coatings was by scanning electron microscopy and X-ray diffraction. The results are discussed in connection with measured mechanical and optical film properties such as microhardness and CIE-L*a*b* values. By means of non-reactive sputtering, fine-columned films with a predominantly (00l)-orientated ZrB2 phase were formed; in the case of sputtering from the ZrB12 target the ZrB2 phase was accompanied by the rhombohedric B phase. Reactive deposition at low nitrogen flow rates leads to the formation of a hexagonal Zr−B−N phase based on ZrB2 (using the ZrB2 target), accompanied by a highly distorted B phase (using the ZrBu target). The further incorporation of nitrogen leads to amorphous film growth. The maximum Vickers microhardness of the coatings was found to be approximately 2300 HV0.01. These coatings offer an excellent choice for decorative applications with colours from silver-grey to black combined with outstanding corrosion and abrasion resistance.