Resistance of ytterbium silicate environmental barrier coatings against molten calcium-magnesium-aluminosilicate (CMAS): A comprehensive study

Abstract

Molten calcium‑magnesium-aluminosilicate (CMAS) poses a considerable threat to the environmental barrier coatings (EBCs) service life. Here, we have prepared ytterbium monosilicate (YbMS) and ytterbium disilicate (YbDS) coatings using air plasma spraying (APS), and comprehensively investigated their high-temperature response to two CMAS relevant to real sediments within gas turbine and Beijing sand-dust, which are defined as CaO-rich CMAS and CaO-lean CMAS respectively. In the CaO-rich CMAS case, either YbMS or YbDS coating exhibits a vigorous reaction and rapid precipitation of apatite phase, constructing a dense reaction layer and inhibiting the molten CMAS infiltration. Note that the YbMS coating always possesses a smaller infiltration depth than YbDS coating because of the synergistic effect of its higher reactivity and more stable crystal structure. In comparison, the molten CaO-lean CMAS infiltrates along the grain boundaries of both coatings without any barrier, only some re-precipitated YbDS grains exist at the CMAS/coating interface. This phenomenon is closely related to the relatively high Yb3+ solubility due to its lower CaO content relative to the CaO-rich CMAS. These finds in this work are expected to provide a better understanding for the design of next-generation EBCs material and proposal of effective methods to mitigate the molten CMAS attack.