PACVD-Beschichtung von Druckgußwerkzeugen unter ökonomischen und ökologischen Gesichtspunkten

摘要

Der heutige Stand der Technik im Aluminiumdruckguß erfordert den Einsatz von Formtrennmitteln. Zu deren Nebenwirkungen gehört aber eine Verschlechterung der Oberflächenqualität des Gußteils. Formtrennmittel beeinträchtigen die Arbeitsplatzqualität und sind unter ökologischen Gesichtspunkten als bedenklich zu betrachten. Um den Einsatz von Trennmitteln zu vermeiden und gleichzeitig die Standzeit der Druckgußwerkzeuge zu erhöhen, wurden nitridische, karbidische und boridische Schichten auf Titanbasis mittels DC-Puls-PACVD abgeschieden und im Hinblick auf ihren Einsatz im Aluminiumdruckguß optimiert. Durch die Be-schichtung konnte bei gleichzeitiger Steigerung der Qualität der abgegossenen Teile die notwendige Trennmittelmenge um 97 % reduziert werden. Die Standzeit der beschichteten Druckgußkerne im Vergleich zu unbeschichteten erhöhte sich durch die Beschich-tung um über das 300-fache.%Aluminium pressure diecasting is a frequently applied manufac-turing 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.