Recycling of a Healing Agent by a Water‐Vapor Treatment to Enhance the Self‐Repair Ability of Ytterbium Silicate‐Based Nanocomposite in Multiple Crack‐Healing Test

Yb₂Si₂O₇/Yb₂SiO₅ composites dispersed with silicon carbide (SiC) possess a self‐crack‐healing ability that makes them promising top‐coat materials for multilayered environmental barrier coatings (EBCs) of SiC/SiC gas turbine blades. Stress‐induced surface cracks can be fully healed at high temperatures by the volume expansion of SiO₂ glass and the newly formed Yb₂Si₂O₇ in the composite. The reaction between SiO₂ and Yb₂SiO₅ to form Yb₂Si₂O₇ is considered a critical step that determines the high healing efficiency of this composite, therefore, Yb₂SiO₅ is considered as the secondary healing agent apart from the primary one, SiC. However, once all the healing agents have reacted, the composite can no longer promote its crack‐healing ability. To retain this property, in this work, Yb₂SiO₅ is regenerated by a heat treatment in water‐vapor atmosphere at 1073 K. X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDS) analyses show that the healing agent can be partially recycled after the treatment. In addition, the composite treated in water vapor demonstrates a greater crack‐healing ability compared with the untreated composite. These results open a new path for the development of gas turbine blades and high‐temperature components possessing permanent crack‐healing ability.