Mechanical behavior of ytterbium disilicate EBCs investigated by nanoindentation and micro-impact measurements

Yb₂Si₂O₇ (YbDS) serves as a key environmental barrier coating (EBC) for SiC ceramic matrix composites in gas turbine systems. This study explores the static and dynamic mechanical properties of air plasma spray (APS) deposited YbDS coatings and bulk YbDS produced through field-assisted sintering (FAST). Using nanoindentation and micro-impact testing, the elastic modulus, hardness, and fracture toughness were evaluated. Scanning electron microscopy (SEM) analysis of the impact tests showed that the porosity in the APS samples may stop or deflect crack propagation, however the impact depth is deeper than that in the FAST samples. The FAST samples were more prone to chipping under the same impact conditions, though the FAST sample exhibits higher modulus and fracture toughness. Moreover, the fracture toughness and impact depth during single- and multiple-impact tests correlated with the hardness-to-modulus ratio (\:H/E). These results underscore the importance of optimizing the \:H/E ratio and controlling pore size and distribution to improve the performance and durability of YbDS for EBC applications.