HPPMS TiAlCrSiN - Influence of substrate bias and pulse frequency on cutting performance

Abstract

The machining of powder metallurgical high-speed steel leads to thermal and mechanical loads which cause damages such as abrasive and adhesive wear as well as oxidation of the tool. Due to the high hardness and thermal resistance of hard coatings, their application on cutting tools is the state of the art. In order to improve the tool lifetime and the performance of the cutting process and to fulfill the increasing requirements in machining, the complex coating TiAlCrSiN was developed. The embedding of the nanocrystalline grains in an amorphous Si3N4 matrix is expected to result in advantageous properties in comparison to the coating TiAlCrN. The thermal resistance and elastic-plastic properties, for example, are enhanced. The coating deposition was conducted in an industrial coating unit using a hybrid process consisting of direct current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering (dcMS/HPPMS). By using this hybrid process, the advantages of HPPMS, such as a dense morphology and high indentation hardness, are combined with the higher deposition rate of dcMS. In this work, the influence of the substrate bias and the pulse frequency of the HPPMS cathodes during the hybrid process are observed. The coating properties are only slightly affected by variations in the process parameters. Transmission electron microscopy investigations reveal the nanocrystalline microstructure of the coating. The compound properties between the different coatings and the indexable inserts made of tungsten carbide were improved by reducing the substrate bias. Furthermore, the coatings are tested by milling the powder metallurgically produced high-speed steel 1.3345. The milling tool coated with an increased frequency and a reduced substrate bias shows the highest tool lifetime during the cutting tests.