Preparation and corrosion resistance of high-entropy disilicate (Y0.25Yb0.25Er0.25Sc0.25)2Si2O7 ceramics

With the increasing demand for high thrust-weight ratio aero-engines, the development of environmental barrier coatings (EBCs) for SiC-based ceramics is an enormous challenge, which requires both high temperature stability and resistance to molten calcium-magnesium-aluminosilicate (CMAS) corrosion. In this work, a novel high-entropy disilicate (Y0.25Yb0.25Er0.25Sc0.25)2Si2O7 ((4RE0.25)2Si2O7) EBC materials was prepared by a two-step process. The high-entropy disilicate powder was synthesized by sol-gel method, and then Y-Si-Al-O silicate glass was used as sintering aids to facilitate densification of the (4RE0.25)2Si2O7 ceramic by liquid sintering. The results of XRD, SEM and EDS showed that as-synthesized powders were pure high-entropy disilicate (4RE0.25)2Si2O7, and bulk (4RE0.25)2Si2O7 ceramic exhibited a dense structure, in which (4RE0.25)2Si2O7 grains were uniformly distributed into Y-Si-Al-O glass. Compared with single disilicate RE2Si2O7 (RE = Y and Er) ceramics, the high entropy (4RE0.25)2Si2O7 ceramic showed a good phase stability and almost no change in grain size during sintering at 1600 °C for in the holding time range of 5–15 h, suggesting a good high temperature stability. During molten CMAS corrosion, Ca2+ ions can diffuse into the Y-Si-Al-O glass phase wrapped on the surface of (4RE0.25)2Si2O7 grains, and then corrode (4RE0.25)2Si2O7 grains, thereby forming the corrosion zone consisting of reaction layer and diffusion layer. The Y-Si-Al-O glass can play a blocking layer role to suppress Ca2+ diffusion and mitigate molten CMAS corrosion, so that as-prepared (4RE0.25)2Si2O7 ceramic showed a relatively good ability for resisting molten CMAS corrosion. After molten CMAS corrosion at 1500 °C for 48 h, thickness of the reaction layer was only 73 µm. The results will be a solid foundation for the application of environmental barrier coating materials in long-period high temperature molten silicate environment.