Corrosion resistance of multicomponent disilicate (Ho0.2Er0.2Tm0.2Yb0.2Lu0.2)2Si2O7 against CMAS and volcanic ash

Abstract

With the increasing operating temperature of gas turbine engines, calcium-magnesium-aluminosilicate (CMAS) poses a serious threat on environmental barrier coatings (EBCs) applied on hot-sections of aero-engines. Here, we have synthesized a novel multicomponent disilicate—(Ho_0.2Er_0.2Tm_0.2Yb_0.2Lu_0.2)₂Si₂O₇ (brief to (5RE_0.2)₂Si₂O₇), and comparatively studied its performance in the presence of synthesized CMAS and natural volcanic ash at 1400ºC. In comparison with Yb₂Si₂O₇, (5RE_0.2)₂Si₂O₇ has a shorter Si-O bond length and a larger RE-O bond length because of the larger average RE³⁺ radius. After CMAS corrosion, some apatite grains precipitate at the CMAS/(5RE_0.2)₂Si₂O₇ interface to develop a loose reaction layer, exhibiting a higher corrosion resistance than Yb₂Si₂O₇. Meanwhile, the consumption of CaO and release of SiO₂ during the chemical reaction process increase the viscosity of CMAS to some extent and thus weaken its infiltration propensity. For the volcanic ash case, it directly infiltrates into the interior of (5RE_0.2)₂Si₂O₇ along grain boundaries without any reaction due to the relatively low CaO content, exhibiting a more serious attacking behavior. In addition, (5RE_0.2)₂Si₂O₇ effectively increases the contact angle of molten volcanic ash due to its lower surface energy. These finds here provide a better understanding for the design and application of next-generation EBC material.