NdYbZr2O7 thermal barrier coating resistant to degradation by volcanic ash and CMAS

Abstract

Environmental silicate debris such as sand, dust and volcanic ash is regarded as a major hazard for aviation safety. During the service process of gas turbines, these ingested silicate ashes can melt, impact and adhere to the thermal barrier coatings (TBCs) covered on the hot-section components, facilitating their structure and property instability. Here, we prepared a novel NdYbZr2O7 coating which is expected to mitigate this issue. We comparatively study the infiltration behavior of natural volcanic ash and synthetic CMAS within it at 1250 ºC and 1300 ºC. In the case of volcanic ash, the lower CaO content improves the Nd3+ and Yb3+ solubility, suggesting more NdYbZr2O7 coating has to be consumed to saturate the melt. The chemical reaction is delayed, and melt has more time to infiltrate. As a result, although volcanic ash has a relatively high viscosity, it exhibits a larger infiltration depth than CMAS. Apatite with a theoretical A4ⅠA6Ⅱ(SiO4)6X2 structure is the main corrosion product for either volcanic ash or CMAS. The calculated AⅠ:AⅡ ratios are 0.14 and 0.30 respectively, which indicates that precipitating per unit apatite needs to consume more NdYbZr2O7 coating. In comparison with traditional YSZ coating, NdYbZr2O7 coating exhibits a better anti-corrosion performance by rapidly precipitating crystalline grains (c-ZrO2 and apatite) and further building dense reaction layer.