Phase composition and transformations in magnetron-sputtered (Al,V)2O3 coatings

TL;DR

This study investigates the phase composition, microstructure, and thermal stability of (Al,V)2O3 coatings deposited by pulsed DC reactive sputtering, revealing how V content influences crystal structure, hardness, and oxidation behavior.

Contribution

It provides a detailed analysis of phase transformations and microstructural evolution in (Al,V)2O3 coatings as a function of vanadium content and annealing conditions.

Findings

Different crystal structures depend on V content, including {eta}-V2O3, defect spinel, and gamma-alumina-like phases.

Pure {eta}-V2O3 exhibits the highest V2O5 formation upon annealing.

Highest hardness (~24 GPa) observed in Al-rich oxides, decreasing with V content.

Abstract

Coatings of (Al1-xVx)2O3, with x ranging from 0 to 1, were deposited by pulsed DC reactive sputter deposition on Si(100) at a temperature of 550 {\deg}C. XRD showed three different crystal structures depending on V-metal fraction in the coating: {\alpha}-V2O3 rhombohedral structure for 100 at.% V, a defect spinel structure for the intermediate region, 63 - 42 at.% V. At lower V-content, 18 and 7 at.%, a gamma-alumina-like solid solution was observed, shifted to larger d-spacing compared to pure {\gamma}-Al2O3. The microstructure changes from large columnar faceted grains for {\alpha}-V2O3 to smaller equiaxed grains when lowering the vanadium content toward pure {\gamma}-Al2O3. Annealing in air resulted in formation of V2O5 crystals on the surface of the coating after annealing to 500 {\deg}C for 42 at.% V and 700 {\deg}C for 18 at.% V metal fraction respectively. The highest thermal stability was shown for pure {\gamma}-Al2O3-coating, which transformed to {\alpha}-Al2O3 after annealing to 1100{\deg} C. Highest hardness was observed for the Al-rich oxides, ~24 GPa. The latter decreased with increasing V-content, larger than 7 at.% V metal fraction. The measured hardness after annealing in air decreased in conjunction with the onset of further oxidation of the coatings.