Diamond-Silicon carbide-coatings for cutting tools

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Thin diamond coatings on tungsten carbide tools (WC:Co) are particularly suitable for the machining of reinforced light metal, plastics and graphite due to its high hardness, wear resistance and low adhesion to non-ferrous materials. However, the cobalt binder of the tungsten carbides leads to negative effects on the coating adhesion. Therefore, the substrates are usually pre-treated by chemical etching procedures which remove the cobalt binder from the boundary zone of the tool substrate. This pretreatment may have a detrimental effect on the mechanical integrity of the tool and is highly time-consuming and costly. A promising method to gain a high coating adhesion and simultaneously reduce both the pre-treatment effort and the negative influence to the mechanical properties of the carbide tool is to apply a metal-carbide inter layer to the substrate. This interlayer acts as a diffusion barrier and thereby protects the diamond film against the cobalt binder phase. A high adhesion between interlayer and diamond is essential for the concept. Gradual diamond coatings for example could achieve this adhesion, which is investigated in this project. An interlayer system with high adhesion could possibly allow the carbide-tool-inserts to be coated with diamond without reduction of stability. The coating systems are qualified through residual stress measurements, model wear tests and cutting tests with the light metal AlSi17Cu4Mg.