Arc evaporated W-alloyed Ti-Al-N coatings for improved thermal stability, mechanical, and tribological properties

Abstract

The protection of various tools and components through wear resistant coatings is imperative in highly efficient and precise industrial manufacturing processes. Especially, physical vapor deposited Ti1−xAlxN and Cr1−xAlxN coatings have been commonly used as hard protective coatings due to their outstanding thermal stability and mechanical strength. However, to increase the applicable working temperatures by simultaneously enhancing the wear performance (e.g., to allow for higher cutting speeds) further improvements are required.Therefore, we studied in detail the impact of tungsten (W)—in combination with the substrate bias potential (Ubias)—on the thermo-mechanical properties and wear performance of arc evaporated Ti1–x−yAlxWyN thin films. With increasing W content, the quality of our coatings significantly increases due to pronounced reduction of growth defects (quantity of macro particles). All coatings studied crystallize in a supersaturated, single-phased face-centered cubic Ti1−x−yAlxWyN structure and their hardness (H) increases whereas the indentation modulus (E) decreases with increasing W content. This results in increased H3/E2 values, with a maximum of 0.19GPa for Ti0.50Al0.41W0.09N prepared with Ubias=−120V (H≈35GPa, E≈483GPa). All W-alloyed coatings exhibit wear rates below 4∙10−5mm3/Nm during our dry sliding pin-on-disk tests against alumina balls at room temperature, with a tendency for reduced values if more droplets are present. The highest thermal stability, with respect to the decomposition of the supersaturated Ti1–x−yAlxWyN phase towards the stable constituents (at high temperature) TiN, AlN, and W, is obtained for Ti0.53Al0.42W0.05N prepared with Ubias=−80V. Here, the formation of the wurtzite-structured AlN can be delayed to 1000°C after 60min lasting isothermal annealings in vacuum.