Triggering the Phase Evolution Within (Al,Cr)2O3-based Coatings by Alloying and Microstructural Concepts

Christian Martin Koller,Beno Widrig,Jürgen Ramm,Szilárd Kolozsvári,Jörg Paulitsch,Paul Heinz Mayrhofer,Rainer Hahn

doi:10.1007/s00501-016-0506-2

Christian Martin Koller, Beno Widrig + Show 5 more

Open Access

https://doi.org/10.1007/s00501-016-0506-2

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Abstract

The synthesis of (Al,Cr)2O3 coatings by PVD frequently results in metastable cubic structures next to the thermodynamically stable and mechanically favourable hexagonal corundum phase. By alloying small amounts of Fe to powder-metallurgically produced Al0.7Cr0.3 targets – used to synthesise (Al,Cr)2O3 films by cathodic arc evaporation – a considerable increase of the hexagonal phase fraction is observed. Detailed transmission electron microscopy studies show that the growth of hexagonal crystallites of a solid solution (Al,Cr,Fe)2O3 can be triggered by small Cr- and Fe-enriched spherical particles, so-called droplets. In contrast, larger spherical or flat-shaped Al-rich droplets induce re-nucleation of undesired cubic film growth. Extending these studies to additional (Al,Cr)2O3 coating systems revealed similar mechanisms, albeit by far less frequent than in the case of Fe-alloyed films. Modifications of the chemical composition of the target by small amounts of dopants may reduce droplet generation and contribute to controlled coating nucleation. Therefore, the cathode surface used is compared with particles, intentionally selected from the plasma stream.

Highlights

Al2O3 and Al-based oxide coatings are potential candidates whenever applications require chemical inertness and outstanding thermo-mechanical properties [1,2,3,4]
Originalarbeit the stable corundum structure, initiating the formation of crack networks and stresses, which can lead to failure of the coating
Experimental (Al,Cr)2O3 and (Al,Cr,Fe)2O3 coatings were synthesised in a batch type cathodic arc evaporation system Oerlikon Balzers Innova using powder-metallurgically produced 6-inch Al0.7Cr0.3 and Al0.675Cr0.275Fe0.05 targets (Plansee Composite Materials GmbH)

Summary

Introduction

Al2O3 and Al-based oxide coatings are potential candidates whenever applications require chemical inertness and outstanding thermo-mechanical properties [1,2,3,4]. The present study represents a summary of investigations focused on the effect of Fe as alloying element on the structural evolution in cathodic arc evaporated (Al,Cr)2O3 films and the role of small incorporated particles as potential nucleation sites for the desired hexagonal structure. 2. Experimental (Al,Cr)2O3 and (Al,Cr,Fe)2O3 coatings were synthesised in a batch type cathodic arc evaporation system Oerlikon Balzers Innova using powder-metallurgically produced 6-inch Al0.7Cr0.3 and Al0.675Cr0.275Fe0.05 targets (Plansee Composite Materials GmbH).

Results

Conclusion