Corrosion behavior and mechanism of ytterbium monosilicate by molten calcium-magnesium-alumino-silicate melts at 1400 °C and 1500 °C

Abstract

Thermochemical interactions of Yb2SiO5 block, a potential environmental barrier coating (EBC) material and a synthetic CMAS with the composition of 33CaO–9MgO–13AlO1.5-45SiO2 at 1400 °C and 1500 °C have been investigated. Corrosion tests showed that CMAS dissolved Yb2SiO5 and caused precipitation of Ca2Yb8 (SiO4)6O2 crystalline phase. At 1400 °C, Ca2Yb8 (SiO4)6O2 tended to form a continuous reaction layer at the CMAS/Yb2SiO5 interface. This reaction layer became thicker and denser with increasing time, which effectively inhibited molten CMAS penetration into Yb2SiO5. However, at 1500 °C, a dense and continuous layer could hardly form. Due to the low viscosity of the CMAS, it quickly infiltrated Ca2Yb8 (SiO4)6O2 along grain boundaries, and Ca2Yb8 (SiO4)6O2 dissolved in molten CMAS followed by re-precipitation in the form of tiny Ca2Yb8 (SiO4)6O2 crystals during cooling. The results show that Yb2SiO5 has good CMAS corrosion resistance at 1400 °C, but its protective capabilities are limited at temperatures above this threshold.