Suspension plasma sprayed ytterbium disilicate coatings: Phase stability and microstructural evolution in extreme environments

Suspension plasma spray (SPS) is a promising technique to deposit coatings with controlled microstructure. In this work, we explored this capability to produce ytterbium disilicate environmental barrier coatings with enhanced performance against steam and molten calcium-magnesium-aluminium-silicate (CMAS) corrosion. Steam exposure tests on the samples using steams with velocities of 1 m/s and 5 m/s at 1350 ᵒC for 96 h revealed that low-velocity steam caused silica volatilisation whereas the high-velocity steam caused both silica volatilisation and material erosion, yet no new cracks formed in the coating. CMAS degradation test for 5 and 240 mins at 1300 ᵒC on the coatings showed that the large aspect ratio of the splats facilitated reaction between CMAS and ytterbium monosilicate to form a dense layer that slowed further CMAS infiltration. These outcomes suggest that SPS has the proclivity to manufacture EBCs with improved resistance to steam and CMAS degradation.