The deposition of hard crystalline Al2O3 layers by means of bipolar pulsed magnetron sputtering

Crystalline Al2O3 layers with hardness values up to those of pure corundum (22 GPa) were produced by reactive pulsed magnetron sputtering of aluminum. Used for the purpose was a dual magnetron system with a bipolar pulsed square-wave power supply in the MF range. Via a variation of pulse parameters it was possible to exert an influence on the plasma density and therefore on the layer properties obtained. It is shown that the pulsed power supply substantially reduces the temperature needed for the deposition of crystalline alumina, i.e., especially of alpha-Al2O3. Irrespective of the chosen working point, the coating process can be performed in a stable long-term manner without the occurrence of hysteresis effects. Both plant and process are upscaled to the conditions of industrial application with respect to productivity and three-dimensional substrates. In addition, an adhesion-improving sublayer of another material can be applied; e.g., (Ti,Al)N, etc. Hence, facility is provided to coat not only hard metal components (e.g., cemented carbide inserts) with a hard layer of alumina but also temperature-sensitive materials such as tool steel.