Microstructural modifications in powder-metallurgically produced Al0.675Cr0.275Fe0.05 targets during cathodic arc evaporation

Abstract

Recently, the authors showed that metallic droplets, originating from the Al0.675Cr0.275Fe0.05 cathode surface, play an essential role in the nucleation process of hexagonal crystallites in mixed cubic and hexagonal-structured cathodic arc-evaporated (Al0.70Cr0.25Fe0.05)2O3 films. Here, the authors investigated in detail the corresponding powder-metallurgically produced Al0.7Cr0.3 and Al0.675Cr0.275Fe0.05 targets (after the arc evaporation process) and the ejected macroparticles, which were intentionally separated and collected from the plasma stream. The 15–200 μm thick melting zone (under given process conditions not entirely covering the target surface) of both target materials predominately consists of intermetallic Al80Cr20, Al9Cr4 and dominating Al8Cr5 phases. The selective melting process, induced by the cathodic arc spot size and particle size distribution of the targets, led to the formation of Al-enriched areas. Oxide islands, which form on the target surfaces, especially contain Cr- and Fe-enriched particles. The latter are only present for Al0.675Cr0.275Fe0.05 targets, where the majority of Fe is basically dissolved in the intermetallic Al-Cr phases formed at the target surface due to the cathodic arc interaction. The chemical composition of the ejected macroparticles corresponds with these cathodic arc interaction zones. Based on here presented results, the authors can conclude that Fe-containing intermetallic phases, which are also present within the droplets, as well as Cr- and Fe-enriched particles, are the influential factors for the nucleation of hexagonal phases within arc-evaporated (Al,Cr,Fe)2O3 coatings.