Jörg Patscheider

Structure-performance relations in nanocomposite coatings

Properties of hard nanocomposite coatings, especially hardness, can be explained by their nanostructure. Hardness maxima are found for different nanocrystalline/amorphous materials deposited by different techniques at typically 20% of the amorphous phase. A zone model is proposed which correlates the hardness to the relative phase content. The hardness of nanocomposite coatings peaks at the common minimum of the grain size of the crystalline phase and the grain separation. For an adequate description of the performance of a coating, the thermal stability, oxidation behavior and frictional behavior should be included in addition to hardness. In a friction situation involving at least two friction partners, the overall behavior of the system is determined by many-body interactions. While thermal stability and oxidation properties as inherent material properties can be directly linked to the nanostructure of the coating, the frictional behavior of a coating cannot be generalized independent of the friction conditions.

Improving the properties of titanium nitride by incorporation of silicon

Abstract Thin films of Ti–Si–N have been deposited by physical vapor deposition (PVD) with the intention to improve the wear resistance of TiN coatings. The coatings are prepared by reactive unbalanced magnetron sputtering using two separate Ti and Si targets and a rotating substrate holder. The silicon concentration in the deposited films varies between 0 and 15 at.%. SEM observations and X-ray diffraction analysis (XRD) show that the addition of Si to TiN coatings transforms the [111] oriented columnar structure into a dense finely grained structure. From TEM investigations and XRD analyses, the crystallite sizes of TiN are observed to be below 20 nm. XPS analysis shows the presence of silicon nitride, while electron and X-ray diffraction results do not suggest the presence of crystalline Si3N4. This result clearly indicates that these films have a composite structure consisting of TiN nanocrystallites embedded in amorphous silicon nitride. The hardness of the nc-TiN/a-SiNx coatings reaches 3500 HV0.1. The abrasion resistance measured by ball cratering can be enhanced by a factor of 6 in comparison with TiN deposited under the same conditions.

Nanocomposite TiC/a–C:H hard coatings deposited by reactive PVD

Abstract Thin films of titanium carbide and amorphous hydrogenated carbon at various compositions have been deposited by unbalanced reactive magnetron sputtering from a metallic titanium target in the presence of argon and acetylene. XRD probed the presence of nanocrystalline TiC and, at high titanium concentrations, of metallic titanium. The XPS examinations allowed one to determine the amount of TiC produced at any concentration of titanium. Raman spectroscopy proved the presence of a-C:H up to 38 at.% of titanium. The coatings have a pronounced hardness maximum of 35 GPa at a composition of approximately 80% TiC and 20% a-C:H. The hardness at 60% TiC and 40% a-C:H as well as that of 100% TiC does not exceed 18 GPa. The mean separation of the crystallites, whose diameter is approximately 4 nm, amounts to a few atomic distances. At the maximum hardness a coefficient of friction of 0.25–0.3 is obtained. The coatings thus provide, at the optimum composition, high hardness at low friction.

From alloying to nanocomposites: Improved performance of hard coatings

Nowadays a variety of different hard coatings are commercially available, the most widely used ones are TiN, TiC, TiCN, TiAlN, CrN, Al 2 O 3 , and combinations thereof, as well as some coatings with lubricating properties such as diamond-like carbon (DLC), WC/C or MoS 2 . To fulfil the industrial demands for improved coatings, a lower friction, a longer lifetime, a desired biological behavior or a better thermal stability in different environments, improved and application adapted coatings are developed. The different properties of a coating can be tuned to a desired value by alloying with suitable elements. Composite materials such as multilayer coatings and isotropic nanocomposite coatings, having structures in the nanometer range, can even show properties which can not be obtained by a single coating material alone. The authors review research and development work on the improvement of the overall coating performance, It mainly addresses alloying, the development of multilayer systems and the recently emerged field of nanocomposite coatings.

Decomposition pathways in age hardening of Ti-Al-N films

The ability to increase the thermal stability of protective coatings under work load gives rise to scientific and industrial interest in age hardening of complex nitride coating systems such as ceramic-like Ti1−xAlxN. However, the decomposition pathway of these systems from single-phase cubic to the thermodynamically stable binary nitrides (cubic TiN and wurtzite AlN), which are essential for age hardening, are not yet fully understood. In particular, the role of decomposition kinetics still requires more detailed investigation. In the present work, the combined effect of annealing time and temperature upon the nano-structural development of Ti0.46Al0.54N thin films is studied, with a thermal exposure of either 1 min or 120 min in 100 °C steps from 500 °C to 1400 °C. The impact of chemical changes at the atomic scale on the development of micro-strain and mechanical properties is studied by post-annealing investigations using X-ray diffraction, nanoindentation, 3D-atom probe tomography and high-resolution...

Nanostructural and mechanical properties of nanocomposite nc-TiC/a-C:H films deposited by reactive unbalanced magnetron sputtering

Thin films of nc-TiC/a-C:H nanocomposite have been deposited by reactive magnetron sputtering at substrate bias values of −240 and −91 V. The grain size and grain separation, which together define the nanostructure, are correlated to the amount of the amorphous phase. From the size of the TiC grains measured by x-ray diffraction and the amorphous hydrogenated carbon (a-C:H) phase content determined by x-ray photoelectron spectroscopy, the mean grain separation is estimated using a simple model for the nanostructure. Films deposited at −240 V show a hardness enhancement for a-C:H phase contents in the range 10% to 30% with TiC grain sizes around 5 nm. The mean grain separation for such films was estimated to be 0.3 nm. Films with higher a-C:H phase contents still have 5 nm small grains, but their mean grain separation is larger than 0.5 nm; their hardness is thus determined by the properties of the amorphous matrix. A less pronounced hardness enhancement is observed for films deposited at −91 V. They have ...

Wear protective coatings consisting of TiC–SiC–a-C:H deposited by magnetron sputtering

Hard coatings of the composition Ti Si C which consist of TiC, TiSi , a-SiC and a-C:H, have been deposited with the aim of xy z x depositing self-lubricating Ti SiC . The films were prepared by reactive unbalanced magnetron sputtering from elemental titanium 32 and silicon targets in the presence of argon and acetylene. The coatings are composed of nanocrystalline TiC and, depending on the composition, of titanium silicides, amorphous hydrogenated carbon and amorphous silicon carbide. Nanohardness values of up to 30 GPa could be obtained for coatings with friction values below 0.25 against steel in an unlubricated pin-on-disk setup. Low friction coefficients against steel were measured for higher concentrations of amorphous carbon at hardness values of approximately 15 GPa. In contrast to coatings composed of titanium, silicon and nitrogen, the hardness maximum is observed at TiC grains sizes of 25 nanometers. 2002 Elsevier Science B.V. All rights reserved.

XPS investigation of the a-C:H/Al interface

Abstract The original state of the interface between ultrahard amorphous hydrogenated carbon (a-C : H) and aluminum was analyzed by non-destructive in-situ direct ion beam deposition (CH 4 , −400 V) as well as angle resolved XPS (X-ray photoelectron spectroscopy) analysis through a thin a-C : H coating. Depending on the deposition conditions a 0.6 to 1.9 nm thick Al 4 C 3 interlayer, held responsible for the good adhesion between a-C : H and Al, could clearly be resolved. Furthermore, an interaction between a-C:H and Al 4 C 3 at the a-C : H/Al 4 C 3 interface was detected. The ability of C and Al to form a reactive Al 4 C 3 interface as well as an interaction of a-C : H with Al 4 C 3 has also been confirmed by XPS and AES sputter depth profile analysis.

Structure of sputtered nanocomposite CrCx∕a-C:H thin films

This work presents the structural evolution of nanocomposite CrCx∕a-C:H coatings prepared by unbalanced magnetron sputtering of a metallic Cr target in Ar+CH4 glow discharges using low negative dc bias voltages. Raman spectroscopy and x-ray photoelectron spectroscopy were used to characterize the phase composition and the chemical bonding in the films deposited at different experimental conditions. The results were correlated to the chemical composition obtained by elastic recoil detection analysis. The coating microstructure was investigated on selected samples by high-resolution transmission electron microscopy combined with electron energy-loss spectroscopy analysis. The nanocomposite coatings can be divided into hard CrCx dominated films, when prepared at low CH4 partial pressure to total pressure (pt) ratios (pCH4∕pt 0.4. The structure of the low-friction a-C:H dominated coatings consists of 2–10nm sized fcc CrC crystallites ...

Photochemical and electrocatalytic water oxidation activity of cobalt carbodiimide

Cobalt carbodiimide is introduced as a heterogeneous non-oxidic water oxidation catalyst prototype with dual photochemical and electrocatalytic activity in neutral and basic media. CoNCN exhibits higher initial turnover frequencies of (TOF/SBET: 2.1 × 10−1) for visible-light-driven oxygen evolution than cobalt oxide catalysts (TOF/SBET: 3.5 × 10−3) and a 18% higher oxygen yield (Ru-dye sensitized standard setup). Furthermore, CoNCN maintains stable current densities in electrolysis over 20 h, and structural tuning through cationic substitution revealed that mixed (Co, Ni)NCN catalysts with low Ni contents display higher current densities than pristine CoNCN. A wide range of bulk (XAFS/EXAFS, XRD, FTIR) and surface (XPS, EELS, HRTEM) analytical methods together with catalytic parameter variations and reference experiments were performed to confirm the stability of CoNCN under standard operational conditions. The carbodiimide matrix thus offers a straightforward structural alternative to oxide systems and a clear-cut starting point for optimization strategies and for mechanistic studies on the possible role of active carbon or nitrogen sites. This paves the way to metal carbodiimides as a novel catalyst design platform for heterogeneous energy conversion systems.