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To investigate the growth and the thermoelectric properties of nitrogen-doped diamond, samples were grown by microwave plasma chemical vapor deposition with varying nitrogen flows as well as with a high nitrogen flow and varying methane flows. The samples were characterized according to their morphology, phase composition, electrical conductivity, and Seebeck coefficient. It was found that an increased nitrogen flow leads to a higher fraction of sp2-bond carbon. Furthermore, a structure consisting of graphene nanowalls which exhibits many cavities is created. For nitrogen flows above 70 sccm, the electrical conductivity increases abruptly and significantly from less than 0.3 s m to more than 4.3 s m . A lower methane flow inverts this development. It was not possible to find a clear dependency of the Seebeck coefficient on the nitrogen flow. Seebeck coefficients were measured between − 17 μ V K at 23 °C and − 34 μ V K at 110 °C.

Here we report a novel structuring technique for diamond coatings using a copper masking on a previously deposited diamond layer to epitaxially grow a subsequent diamond layer only at the exposed areas of the mask. An 8 μm thick copper mask is applied onto the substrate using physical vapor deposition and structured by standard photolithographic methods. Hot filament chemical vapor deposition is used to grow the 14 μm thick structured diamond layer on the diamond coated silicon wafer. Micro and nano crystallinity of the diamond layers are varied, as well as the doping with boron to verify the applicability of the new structuring method for different kinds of diamond qualities. It is shown that four-inch wafers can be fully structured with this high temperature masking technique and the resolution was mostly affected by the quality of the printed mask used for the photolithographic structuring of the copper mask. This diamond structuring method could pave the way for diamond being used in electronics or adding additional functionalities to diamond coated tools.

Nano- and micro-crystalline diamond foils with a thickness of at least 30 μm are manufactured by hot-filament chemical vapor deposition (HFCVD) in an industrial coating machine. Some of them are doped with trimethylborate. The diamond foils are exposed to air at 450 °C and 500 °C and oxidized for up to 738 h. At these temperatures all investigated diamond foils exhibit a substantial weight loss, which is measured with a high precision balance. Nanocrystalline diamond foils show a high weight loss rate compared to microcrystalline diamond foils. At 500 °C the weight loss rate is two to seven times higher than that at 450 °C. Grain boundaries and small diamond crystals are etched much faster than larger diamond crystal. The incorporation of boron does not significantly affect the oxidation of the diamond foils.

and fibre textured diamond films are grown on SSiC sliding rings by hot filament CVD and are tribologically tested in dry planar contact under ambient air. The wear of the self-mated textured diamond coating takes place initially at protruding grains of the as-deposited micro rough diamond surface. After 10 km of dry sliding against textured diamond the respective counterparts with and textures exhibit smoothly polished diamond faces without visible surface failures. After dry sliding against textured diamond as static counterpart {100} diamond faces of isolated grains show Hertzian cone cracks and propagation of cracks preferred along {111} easy cleavage planes whereas {111} diamond faces reveal no crack propagation in substrate direction. The results are visualised in a tribo map in which the linear wear of the dynamic diamond face is plotted against the mean coefficient of friction. The best tribological behaviour in terms of low friction and little diamond wear is achieved for sliding couples with fibre texture on the rotating sliding ring and fibre texture on the static ring as mating diamond faces.

Since diamond coating via hot filament chemical vapour deposition (HFCVD) processes is possible, the coating of steel substrates is in the focus of research programs. As the direct deposition onto steel is not possible yet, the role of interlayers is of extraordinary importance. In this work, we deposited diamond onto steel samples with chromium carbide interlayers at temperatures above 800 °C without film delamination after deposition. Further advantages of this process are an improved chemical activation of the surface at high temperatures, a higher growth rate and a higher quality (sp3-ratio) of the diamond film. The mismatch in thermal expansion of diamond, interlayer and steel leads to high residual compressive stresses in the diamond layer, but about 30% less than theoretically expected. We ascribe this stress reduction to the specific thermal expansion characteristics of a certain class of steels, which show a α-γ phase transformation during cooling down from 850 °C. This transformation from closer packed γ-phase (fcc-structure, austenite) to α-phase (bcc-structure, ferrite) comes along with a volume expansion of approx. 1% and enables the reduction of the high residual compressive stresses in the diamond film, analysed via Raman spectroscopy.

Diamond coated silicon carbide (SiC) bearings can be used in pumps to enable dry running or mixed lubrication conditions. Dependent to different test parameters the coefficient of friction and the wear behaviour shows big differences. In this work α-SiC bearings were coated in a hot filament chemical vapour deposition process (HF-CVD) with a diamond layer thickness of 4 μm. Diamond coated rings were tested in a tribometer under dry running conditions in a ring–ring geometry. During tribological tests under various atmospheres (oxygen, argon, nitrogen, ambient air) the coefficient of friction shows values in a range from 0.1 to 0.4. These values can be ascribed to different chemical and mechanical processes between the mating surfaces. Tribological tests of self mating diamond layers generate wear debris between the mating surfaces. This diamond wear debris can convert from sp 3 hybridized to sp 2 hybridized carbon. Against common expectations tribological tests at ambient air with high sliding velocities and normal loads did not show wear debris, despite of high wear rates. Under inert gas (argon or nitrogen) the sliding surface shows agglomerated areas with sp 2 hybridised carbon. The reason is the absence of oxygen, which is necessary for combustion of carbon species. The coefficient of friction remains nearly constant during the test in oxidizing atmosphere, but shows high fluctuations in inert gas atmospheres. The authors explain this tribological behaviour by a new combustion wear model for self mating diamond coated bearings.

We designed a new hot-filament plant which features some new operating states for chemical vapor infiltration (CVI) with diamond. Most characteristic for the new hot-filament plant is the possibility of a forced flow of the activated gas species through a porous substrate. Separate feeding of hydrogen, methane and oxygen above or underneath the substrate ensures the production of pertinent carbon growth species like CH3 directly at or in the substrate or rather in the pore. We infiltrated porous substrates by using several operating states and compared the results with standard processes. For these first experiments we have set the addition of oxygen aside, which was viable for the infiltration experiments described in Part I of the paper. In order to achieve good infiltration results it was necessary to use very low methane concentrations between 0.2% and 0.3%. We were able to infiltrate at high growth rates (> 0.5 μm/h) combined with a good diamond quality (> 90%). Moreover it was possible to alleviate the “bottleneck” effect which we described in Part I of the paper. Raman spectroscopy and SEM were used to characterize the deposited or rather infiltrated diamond.

Diamond/metal or diamond/ceramics penetration structures have a high potential as, e.g. heat sinks in the microelectronic industry and for tribological applications. To learn more about the basic principles in fabricating these new composites, we infiltrated porous structures of silicon carbide with diamond by chemical vapor infiltration (CVI). As a result we get a 3D penetration structures of diamond and substrate. This requires substrates with an open pored structure. An acceptable growth rate, a high amount of sp3-bondings in the coating and the complete infiltration of the substrate are important requirements on the CVI-process. These requirements should be fulfilled with an effective variation of the process parameters gas pressure, gas flow, gas composition of the feed gas and the substrate temperature. The diffusion rate of the important gas species for diamond growth (H, CH3) should be high compared to their durability. With a forced convection the transport rate of the gas species should be improved. For this, we designed a new hot filament apparatus for CVI, which allows some new operating states. Furthermore, we have investigated the fabrication of diamond penetration structures by CVI using a standard microwave plasma deposition reactor (ASTeX AX 6350) and a standard industrial hot filament apparatus (CC800D). Raman spectroscopy and SEM were used to characterize the diamond films.

Well adherent CVD-diamond coatings were deposited onto 41Cr4 steel substrates using chromium carbide diffusion interlayers. The influence of coating parameters on microstructure and composition of chromium carbide layer and substrate was investigated. In situ heat treatment allows for a variation of physical and mechanical properties of the substrate. We assume that the adhesion of CVD-diamond coatings depends inter alia on the carbon concentration on top of chromium carbide layer. This possible effect is discussed as well.

The pressure dependence of the growth rate, quality and morphology of CVD-diamond films in an industrial hot-filament plant (CC800D) were investigated by SEM and Raman. Additionally, the concentration of atomic hydrogen near the filament was determined via a calorimetric measurement method. At a substrate temperature of 850 °C the smallest growth rate (0.1 μm/h) and the best quality of diamond coatings were obtained at the pressure with the highest hydrogen concentration (20 mbar). The growth rate increases strongly with decreasing pressure and achieves the maximum value of 0.7 μm/h at 3 mbar. At the same time the diamond coating quality decreases.

CVD diamond coatings on Ti-6Al-4V substrates were found to be highly effective in reducing fretting fatigue which, for example, can occur in the root section of aerospace compressor blades. Optimization of a mechanical polishing process leads to significant improvements in the tribological properties of these diamond coatings. This is shown by extremely low wear rates and low coefficients of friction against bearing steel, alumina and diamond. The wear and friction behavior was investigated in a ball-on-disk tribometer and characterized by profilometry, scanning electron microscopy (SEM), atomic force microscopy (AFM) and micro-Raman spectroscopy.

CVD-diamond films were deposited ontothe titanium alloy Ti6Al-4V. Samples were investigated in a ground and ultrasonically pretreated stage and after different times of deposition. The coating time was varied between 1 and 210 min. SEM, XPS and Micro Raman spectroscopy were used to characterize different stages of deposition. A model describing the process of chemical vapor deposition of diamond onto Ti6Al-4V is developed.

In contrast to their excellent mechanical properties, titanium alloys possess poor wear characteristics. Diamond coatings appearto be a promising solution for the wear problem. Using standard deposition parameters for silicon (diamond scratched surface; microwave chemical vapour deposition, 500 W, 800 °C for 4 h, 50 mbar with an atmosphere of 1% CH 4 + 99%H 2 ) good coatings on pure titanium were obtained. The mechanical properties of the titanium are strongly influenced by the processing temperature and the gas atmosphere. As a result of the hydrogen adsorption, grain coarsening and formation of titanium hydride occur and subsequently the low cycle fatigue strength decreases by an order of magnitude. However, by annealing in vacuum (800°C for 2 h, furnace cooled) the hydrogen can be removed again and the initial mechanical properties can almost completely be restored. Based on scanning electron microscopy micrographs, Auger analysis, X-ray diffraction and microhardness measurements a basic understanding of the microstructural changes was developed. The surface structure may be visualized as consisting of five zones, created during the deposition process (diamond layer/nucleation zone/reaction layer/gradient layer/affected substrate).