Fred Fietzke

Effect of the substrate temperature on the structure and properties of Al2O3 layers reactively deposited by pulsed magnetron sputtering

Alumina coatings were reactively deposited on steel substrates by pulsed magnetron sputtering at substrate temperatures (Ts) of 330–760 °C. Investigations into the structure and morphology of the layers were made via XRD and SEM techniques, respectively. As to the layer properties, the hardness was determined by nanoindentation, and the residual stresses were derived from the bending of the coated substrates. At substrate temperatures of less than 330 °C the Al2O3 layers are amorphous to X-rays, whereas γ-Al2O3 is detected at a substrate temperature Ts ≈ 480 °C. A further increase in substrate temperature to 560 °C results in the formation of a pronounced texture of γ-Al2O3. A phase mixture of textured γ- and α-Al2O3 is deposited at Ts ≈ 690 °C. At Ts ≈ 760 °C the layer consists completely of α-Al2O3 with crystallite sizes of about 1 μm. The occurrence of the crystalline γ phase at 480 °C is linked with a pronounced increase in hardness from 10 to 19 GPa. The layer hardness of pure α-Al2O3 amounts to 22 GPa and corresponds to the hardness of the bulk material.

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

Abstract Crystalline Al 2 O 3 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 α-Al 2 O 3 . 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.

Pulse Magnetron Sputtering with high power density – an attempt at a critical evaluation

In this paper specific advantages and disadvantages of different pulse magnetron sputtering processes (unipolar, bipolar and HIPIMS) as well as current and potential fields of application will be discussed. On the examples of ZrN, Ti and TiO2 the typical effects and their influence on film properties occurring during the transition from classical medium frequency pulse magnetron sputtering to high energy pulse sputtering will be described. The discharge current density was varied between 0.2 and 3.5 A/cm2. Aspects of energy feed-in and reactive process control in the transition mode will be considered. Furthermore the influence of rising ionisation on the occurrence of crystalline phases and on mechanical, optical and photocatalytic properties of the layers will be presented. The paper concludes with a placement of the processes related to other PVD-processes that is based on further own experimental results and evaluation of dependencies as well as considering published results of other groups regarding pulse magnetron sputter processes of high power density for the deposition of hard coatings and TCO.

Transparente und farbige Kratzschutzschichten

Mit hochproduktiven Vakuumbeschichtungsverfahren, wie dem Puls-Magnetron-Sputtern und der plasmaaktivierten Hochratebedampfung, lassen sich grosflachig transparente und/oder farbige Kratzschutzschichten mit verschiedenen Eigenschaften oder Eigenschaftskombinationen fur Anwendungen im Innen- und Ausenbereich realisieren.