Abstract
Samples of a Ti-46Al-8Nb (at.%) alloy with Cr-0.5Si, Cr-5Si or Cr-66Si (CrSi2) coatings deposited by magnetron sputtering were oxidised in air under thermal cycling conditions at 700 °C and 800 °C for 80 h. Mass changes over time were measured periodically to evaluate reaction progress as well as susceptibility of the coating or scale to spallation. Vickers hardness, elastic modulus and adhesion of the coatings were determined before and after oxidation. Selected samples were oxidised for up to 1500–2000 h. The nature and extent of coating degradation in each case was evaluated through systematic analyses of surfaces and cross-sections using different techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). It has been found that coatings with the composition Cr-5Si (at.%) had the most promising combination of oxidation resistance and micromechanical properties.
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