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Abstract: Amorphous carbon (a-C:H and a-C:H:Me) films respond very sensitively to local overloads. For example, during forming tool operation, hard abrasive particles and locally high stresses on the coating surface can cause crack initiation and early coating failure. Compared to the high hardness, wear resistance and excellent friction properties, in many cases, the adhesion of a-C:H films is relatively insufficient. Furthermore, the adhesion can be clearly influenced by the substrate geometry, e.g. at sharp edges or slim substrates. Adhesion and overload resistance of a-C:H and a-C:H:Me, prepared by reactive d.c. magnetron sputtering, can be influenced in a wide range by different interlayer systems. In this study, metallic interlayers were combined with metal nitride and metal carbide interlayers. Soft metallic interlayers can reduce internal stress, prevent local overload and they can also affect the growth of the following layers. Ductile metallic nitride interlayers, especially CrN, have a supporting function, they stop crack propagation and improve the adhesion of a-C:H coatings supplementary. Additional metal–carbon gradient layers act as a mediator between the different growth structures of the interlayer system and the a-C:H top layer. Especially the influence of chromium and tungsten containing layers on the adhesion of a-C:H top layers has been investigated. Additionally, the influence of the bias voltage on the coating properties will be discussed. Two well-adapted multi-coating systems, successfully tested for highly loaded tools and components, will be presented. [Copyright &y& Elsevier]

Abstract: The requirements for durable tool coatings continuously increase. In many cases, tool coatings combining different phases or several layers could provide an improvement in tool life. The broad range of mechanical properties of materials in the B–C–N and Ti–B–N ternary systems, from very soft to superhard, presents many possibilities to generate various combination coatings. Such coatings were prepared using reactive sputter techniques with different target materials. An outstanding example is a superhard 3 μm thick coating system with a 0.5 to 0.8 μm thick cBN top layer deposited on cutting inserts. Soft coatings like hexagonal boron nitride were found to be essential for machining operations under dry conditions. The coatings were characterized with respect to hardness, abrasive wear rate and friction coefficients. The correlation between properties and composition was revealed. Application test results of B–C–N and Ti–B–N coating systems on tools obtained under near production conditions will be reported. Specifically, turning tests performed with cemented carbide cutting inserts coated with a superhard coating system with a cBN top layer will be discussed. [Copyright &y& Elsevier]

Abstract: Hydrogenated amorphous carbon (a-C:H) films with silicon and oxygen additions, which exhibit mechanical, tribological and wetting properties adequate for protective coating performance, have been synthesized at room temperature in a small- (0.1m3) and a large-scale (1m3) coaters by low-pressure Plasma-Activated Chemical Vapour Deposition (PACVD). Hence, a-C:H:Si and a-C:H:Si:O coatings were produced in atmospheres of tetramethylsilane (TMS) and hexamethyldisiloxane (HMDSO), respectively, excited either by radiofrequency (RF – small scale) or by pulsed-DC power (large scale). Argon was employed as a carrier gas to stabilize the glow discharge. Several series of 2–5μm thick coatings have been prepared at different mass deposition rates, R m, by varying total gas flow, F, and input power, W. Arrhenius-type plots of R m/F vs. (W/F)−1 show linear behaviours for both plasma reactors, as expected for plasma polymerization processes at moderated energies. The calculation of apparent activation energy, E a, in each series permitted us to define the regimes of energy-deficient and monomer-deficient PACVD processes as a function of the key parameter W/F. Moreover, surface properties of the modified a-C:H coatings, such as contact angle, abrasive wear rate and hardness, appear also correlated to this parameter. This work shows an efficient methodology to scale up PACVD processes from small, lab-scale plasma machines to industrial plants by the unique evaluation of macroscopic parameters of deposition. [Copyright &y& Elsevier]

Abstract: This paper deals with the determination of Young''s modulus of thin films by indentation methods using cubic boron nitride (c-BN) as an example. This is a non-trivial task because the Young''s modulus of this material comes close to that of the diamond indenter. An analysis of results from literature revealed that Young''s moduli of c-BN thin films are generally distinctly smaller than bulk material values. We give reasons that this is at least to a large extent due to measuring problems, in particular the absence of a proper correction of substrate influence. In the experimental part we have used nanoindentation with spherical and three-sided pyramidal (Berkovich) indenters to obtain the data, and employed both standard (Oliver and Pharr) and own theoretical methods (Image Load Method, ILM) for data evaluation. Two groups of samples were investigated: i) a 1.8-μm thick polycrystalline c-BN film on silicon which was well-adherent thanks to a graded (B,C,N) interlayer, and ii) heteroepitaxial c-BN thin films on single-crystal diamond. The polycrystalline c-BN film had a Young''s modulus of 800±30 GPa as determined using the ILM. In contrast the standard method mentioned above delivered a depth-dependent modulus reaching 775 GPa for a indentation depth to film thickness ratio of 1.3%. For the 456 nm heteroepitaxial film on diamond a modulus of 900±100 GPa was measured which is very close to c-BN bulk material values. It was demonstrated that the ILM delivers trustworthy results without noticeable substrate influence also in the complicated cases of a superhard film on a much more compliant substrate (silicon) as well as on the even stiffer diamond substrate. Concluding the article we discuss limits of the method and possibilities to overcome them. [Copyright &y& Elsevier]

Abstract: High rate deposition processes for hydrogenated diamond-like carbon films (a-C:H) were developed using microwave plasma enhanced CVD (PECVD) techniques. Basic investigations were carried out in a laboratory scale deposition apparatus (0.04m3 chamber) and after that the processes were transferred to an industrial scale PECVD machine (1m³) and optimized therein. The application of an asymmetric bipolar pulsed mid-frequency substrate bias allowed controlling the ion fluxes to the growing films independently of the generation of film forming species (radicals and ions) by the microwave plasma source. After preliminary experiments using five different hydrocarbon precursors, more thorough investigations were done with the selected precursors acetylene (C2H2) and isobutene (C4H8; isobutylene, 2-Methyl-1-propene). The a-C:H films were characterised with respect to deposition rates, hardness, abrasive wear rates, internal stresses and topography. Wear resistant, atomically smooth a-C:H films with a hardness above 25GPa were deposited at a very high rate of 15μm/h. The combination of high rate and high hardness values should be promising for industrial applications, even for in-line technologies. For the both mentioned precursors C2H2 and C4H8 some differences in hardness–rate relations were observed. [Copyright &y& Elsevier]