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Despite their excellent tribological properties, the lifetime of stellites in some applications in metallurgical and mechanical engineering is not sufficient. This study describes the development of a duplex treatment for stellite 6B, which consists of either plasma nitriding (PN) or plasma nitrocarburizing (PNC), followed by the deposition of boron-containing hard coatings (TiBN or TiB2). The influence of the process parameters and the gas composition was investigated. Compositional and structural analysis was performed by: profilometry; XRD; SEM; WDS; and GDOS. Knoop hardness measurements, scratch tests, pin-on-disk tests and wear tests by ball cratering were determined in order to describe the mechanical properties. It is shown that plasma duplex treatment combines the advantages of both separate process steps. Case hardening during diffusion treatment offers a mechanical support to the coating, which exhibits a lower coefficient of friction than the diffusion-treated surface. The optimal combination consists of PNC, at high plasma energy, and a boron rich TiBN coating.

TiB 2 appears to be a promising material for the wear protection in various tribological systems, e.g. the diecasting of Al. This study focuses on the development of titanium boride coatings deposited by PACVD, a deposition method which is most suitable for the coating of substrates with complex shapes. All layers analysed are very smooth and exhibit a quasi-amorphous fracture surface. XRD and TEM analysis indicate a nanocrystalline structure with grain sizes in the order of 2 nm. The diffraction patterns can well be correlated to titanium diboride. WDS reveals an over stoichiometric B/Ti ratio. The layer hardness reaches the value of 33 GPa and the critical load in scratch tests rises to 35 N. Neither 100Cr6 nor Al as a counterpart in pin-on-disk tests leads to wear of the coating.

The deposition of TiCN and ZrCN layers on aluminium by radio frequency and pulsed-DC plasma assisted CVD technique using the metallo-organic compounds of the type tetrakis(diethyl)-amidometal (Me(N(C 2 H 5 ) 2 ) 4 ) was investigated. The deposition temperature was below 160°C. The chemical composition of the deposited layers depends on the plasma source and on the process parameters, e.g. plasma power. The growth rate is increased by using RF plasma compared to the pulsed-DC plasma. The TiCN layers deposited by pulsed-DC plasma have a hardness of up to 1800 HK0.005 and are harder than the layers produced by RF plasma. The ion bombardment during the layer growth seems decisive for the hardness increase observed.

The nitrides and borides of titanium are well known for their high hardness and excellent corrosion and wear resistance in many tribological systems. Titanium boronitrides are expected to combine the advantages of both binary layers and allow optimization for the demands of each specific application. This study focuses on the influence of the process gas composition as well as the plasma parameters on the properties of PACVD coatings within the system Ti–B–N. The stoichiometry can be controlled by the process-gas composition. The layer growth rate increases with increasing N 2 flow. For a fixed gas composition, it can be related to the supply of active layer-forming species. A high layer hardness is obtained at high ion energies and increases with decreasing N 2 flow. At a constant N 2 flow, layers with low boron contents reach a hardness of up to 4000 HK0.005, whereas Ti(B,N) with B concentrations above 20 at.% exhibits a lower hardness than that of TiN.

The deposition of wear-resistant coatings by means of plasma-assisted CVD (PACVD) provides a successful means of depositing homogeneous pinhole-free coatings on substrates with complex shapes. In applications such as chemical apparatus processing and the food industry, however, the mechanical loads occurring are superimposed by corrosive attack. In this study, layer types of the system Ti–C–N were deposited by means of pulsed d.c. PACVD using either a Cl-containing or an organometallic metal donor. The coatings were characterized by XRD, SEM, EDS, WDS, XPS and SAM. Further, hardness, adhesion and friction tests as well as cyclovoltammetric and impedance measurements in relevant media were carried out. The PACVD technique permits the deposition of dense and pinhole-free coatings with high hardness and an apparent corrosion resistance. Stoichiometric TiN is electrochemically stable in most electrolytes. If the formation of micropores is not suppressed by the optimal choice of deposition parameters, the low alloyed steel substrate corrodes, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A comparison of Ti(C,N) coatings deposited from Cl-containing and Cl-free precursors did not reveal any difference with regard to their corrosion behaviour. High Cl-containing TiC coatings still exhibit an excellent corrosion resistance.

One of the major manufacturing techniques for aluminium precision parts is the pressure diecasting process. However, nowadays the state of the art involves the application of large amounts of lubricants. Their side effects include a decrease in the surface quality of the cast as well as ecological risks. The deposition of wear-resistant coatings provides a means of minimising the use of lubricants while at the same time increasing the lifetime of the diecasting tools. In this study, nitrides, carbides and borides of titanium were synthesized with regard to their composition, structure, hardness, adhesion, wetting behaviour and corrosion resistance to aluminium melt. The coated cores were exposed to diecasting praxis tests under tightened-up conditions, reducing the amount of lubricants. The optimal PACVD coating led to an increase in lifetime by a factor of 300 compared to an uncoated tool. A reduction of 97% of the original amount of lubricants could be achieved.

Titanium nitride TiN, titanium boronitride Ti(B,N) and titanium carbonitride Ti(C,N) coatings were deposited by PA-CVD on tempering and stainless steel substrates. The deposition process can be supervised by OES. The coatings were characterized by XRD, SEM and WDS as well as hardness, adhesion and friction tests. Electrochemical impedance measurements and cyclic voltammetry in praxis relevant media were carried out. Mechanical and corrosion properties of the coatings can be controlled by the PA-CVD process parameters. The incorporation of chlorine in the coating can be varied by the process parameters with TiCl 4 or completely avoided using metallo-organic precursors. No influence of the chlorine content on the corrosion behavior was observed. Even coatings with extremely high chlorine content still exhibit an excellent corrosion resistance. Thus, the microstructure of the coating is the key to the corrosion properties of hard coatings on steel. A new micro electrochemical scanning droplet technique with a lateral resolution of 150 μm allows the investigation of TiN-coated substrates of complex geometry. The PA-CVD technique permits the deposition of dense and pinhole free coatings. On structures with simulated aspect ratios less than 3, a dense protective coating is proved. However, if the formation of micro pores is not suppressed by the optimal choice of deposition parameters, low-alloyed steel substrates corrode through pores, causing a detachment of the coating. On layers deposited on stainless steel, no sign of substrate corrosion could be detected. A model for the corrosion mechanism is given in Fig. 17.

Der heutige Stand der Technik in Aluminiumdruckgus erfordert den Einsatz von Formtrennmitteln. Zu deren Nebenwirkungen gehort aber eine Verschlechterung der Oberflachenqualitat des Gusteils. Formtrennmittel beeintrachtigen die Arbeitsplatzqualitat und sind unter okologischen Gesichtspunkten als bedenklich zu betrachten. Um den Einsatz von Trennmitteln zu vermeiden und gleichzeitig die Standzeit der Druckguswerkzeuge zu erhohen, wurden nitridische, karbidische und boridische Schichten auf Titanbasis mittels DC-Plus-PACVD abgeschieden und im Hinblick auf ihren Einsatz im Aluminiumdruckgus optimiert. Durch die Beschichtung konnte bei gleichzeitiger Steigerung der Qualitat der abgegossenen Teile die notwendige Trennmittelmenge um 97% reduziert werden. Die Standzeit der beschichteten Druckguskerne im Vergleich zu unbeschichteten erhohte sich durch die Beschichtung um uber das 300-fache. Application of Wear Resistant PACVD-Coatings in Aluminium Diecasting under Economical and Ecological Aspects Aluminium pressure diecasting is a frequently applied manufacturing process for the near netshape production of precision parts. State of the art production techniques still demand considerable amounts of die lubricants. But the side effects of these lubricants include a decrease in surface quality of the cast part as well as a prolongation of the casting cycle time. The job quality decreases and the waste and exhaust disposal during production and application of lubricants is ecologically risky. In this study different wear resistant coating systems have been developed in order to minimize the use of die lubricants in the casting process while at the same time increasing the service life of the diecasting tools. Nitrides, carbides and borides of titanium were synthesized by means of DC-pulse-PACVD. The influence of the process parameters gas composition, pressure, voltage and pulse/pulse repetition ratio was investigated. Compositional analysis was performed by analytical methods such as XRD, EDS, WDS and SIMS. Hardness, adhesion and friction behaviour of the layers were determined in order to describe their mechanical properties. The wetting angle was determined and the corrosion resistance was evaluated in dip tests in aluminium melt. A selection of the best coatings was then compared in diecasting praxis tests under tightened-up conditions reducing the amount of lubricants. TiN, Ti(B,N), TiC and multilayers of the system Ti-C-N were deposited exhibiting a wide range of stoichiometry. The coatings reached hardness values of up to 4400 HK0.005 and the friction coefficient μ was in the range of 0.3. In the diecasting praxis test the amount of die lubricant could be reduced by 97%. Under most severe conditions all layer types led to a minimum increase in the lifetime of the tool of factor 60 compared to an untreated dummy. A strong dependence on the layer type and on its stoichiometry could be observed. Ti(B,N) as the most successful coating in this study has not yet shown any sign of failure and already achieved an increase in lifetime of 300 times.

In this study Zr(B, C) and Zr(B, C, N) coatings were synthesized by means of DC-pulse-PACVD for applications in aluminium diecasting. In order to assess their ability to withstand the complex and severe loads arising from the diecasting process, the influence of the process parameters gas pressure, process gas composition and voltage on the layer properties was investigated. The layers were examined by light and scanning electron microscopy (SEM). Compositional analysis was performed by XRD, EDS, WDS and SIMS. The hardness and adhesion of the layers has been determined as well as the resistance to erosion and to alternating temperature loads. It is shown theat the composition of the coatings can be varied over a wide range via the process parameters. While the concentration of zirconium as well as of boron remains almost constant over a wide range of deposition parameters, carbon and nitrogen are found to substitute each other. Carbon-rich coatings exhibit hardness values of up to 2300 HK0.01, whereas nitrogen-rich coatings prove to be resistant to alternating temperature loading and to erosion in aluminium melt.

In dieser Arbeit werden zwei Verfahren zur Realisierung verschleis-und korrosionsbestandiger Oberflachensysteme beschrieben: Plasmadiffusionsbehandlung (PDT) und Plasmagestutztes CVD (PACVD). Neben den Plasmanitrierverfahren werden auch Plasmanitrocarburieren und Plasmanborieren von unterschiedlichen Substratwerkstoffen behandelt. Die Fortschirtte beim PACVD und die Entwicklung zu den Niedertemperaturbeschichtungsverfahren werden erlautert und Anwendungen dieser Techniken in der Industrie beispielhaft erwahnt. Develpoment of wear and corrosion resistant surface systems In this study two methods are described to realize wear and corrosion resistant surface systems: Plasma diffusion treatment (PDT) and Plasma assited CVD (PACVD). Plasma nitriding, Plasma nitrocarburizing and plasma boriding are used to treat different kinds of substrates. The advances of PACVD and the development of low temperature PACVD and industrial applications of these techniques are explained.