TiAlSiN(Ag) coatings for high temperature applications: The influence of Ag alloying on the morphology, structure, thermal stability and oxidation resistance

Abstract

The influence of Ag content on the morphology, structure, hardness (H) and reduced Young's modulus (E), thermal stability, and oxidation resistance of TiAlSiN(Ag) coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing Ag contents from 0 up to 15.9 at.%. All coatings exhibit a fcc type structure. The coating with 1.5 at.% Ag content displays the highest H and E values as a result of the coating densification and the grain refinement caused by the co-deposition of immiscible phases. Further Ag concentration degrades the H and E values of the coatings due to the incorporation of a softer Ag phase in the structure. Annealing at 800 °C in protective atmosphere for 2 h enhances the coatings crystallinity, with small increments in the H and E values. The dynamic thermal gravimetric oxidation curves reveal that Ag additions do not affect the starting point of oxidation of the coatings (~990 °C). However, it enhances their oxidation resistance. The improved oxidation resistance of the coatings with Ag incorporation is caused by the diffusion of Ag through the oxide scale to the surface, which modifies the composition of the Ti-Al-O layer, producing a more protective Al rich layer.