Influence of Pt/Ru ratios on the oxidation mechanism of MCrAlYTa coatings modified with Pt Ru overlays

This study investigates the influence of varying Pt/Ru ratios on the oxidation mechanism of NiCoCrAlYTa coatings with electrodeposited, vacuum-annealed Pt-Ru overlays. Weight change measurements, scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used for high-temperature oxidation analyses, showing superior resistance with higher Pt contents. This was attributed to the creation of a denser, thinner, and more homogeneous layer of alumina (α-Al2O3) in the thermally-grown oxide (TGO) layer. On the contrary, an increase in Ru contents led to the development of other oxides and microcracks along with alumina in the TGO layer, undermining oxidation protection. The accommodation of Ti and Ta, in the minimally-deteriorative form of carbide, along with Y into the TGO layer with increasing Pt contents further enhanced oxidation resistance. In addition to the explored significant impact of the Pt/Ru ratio on oxide scale characteristics and oxidation resistance, the lower cost of Ru compared to Pt suggests the potential for designing cost-effective systems through optimized Pt/Ru ratios and microstructural engineering.