Hard protective coatings allow for increased lifetime of machining tools and more versatile applications. Although aluminium nitride based coatings have a rich history in material science with various improvements for their production, little is known about their non-reactive deposition using AlN compound targets. Aluminium nitride has the highest thermal conductivity among ceramic materials, a large electromechanical coupling factor as well as high temperature stability, and acoustic velocity. [1]

Reactive deposition of such AlN coatings is studied in-depth, showing that especially for sputtering the resulting microstructure and consequently properties (next to deposition rate) hugely depend on the N₂ partial pressure used. Alternatively, such nitrides can also be prepared non-reactively using nitride compound targets. Here, we use powder metallurgically prepared AlN compound targets to prepare coatings with pulsed DC magnetron sputtering as well as High-Power Impulse Magnetron Sputtering (HIPIMS).

The primary investigations focused on how mechanical properties such as hardness and indentation modulus depend on various deposition conditions, such as sputtering power density, pulse frequency, substrate temperature, substrate-to-target distance and magnetron condition. Additionally, several experiments were conducted by using differing concentrations of H₂ added to Argon gas to showcase the effect of a reducing agent during etching as well as depositing.

Detailed investigations by X-ray diffraction showed that preferential orientation of the coating could be guided with combinations of temperature and partial pressure. Moreover, the introduction of H₂ into the plasma increased stability at higher power densities, leading to increased deposition rate of up to 1μm/h. All coatings prepared were single-phase hexagonal close packed (hcp) wurtzite-type structured, showing various fractions of an amorphous phase present.

[1] V.S. Kudyakova., R.A. Shishkin, A.A. Elagin, M.V. Baranov, A.R. Beketov; Aluminium nitride cubic modifications synthesis methods and its features. Review, Journal of the European Ceramic Society, 37 (2017) 1143-1156. doi:10.1016/j.jeurceramsoc.2016.11.051