In the emerging era of aircraft industry, silicon carbide (SiC) is regarded as an appropriate material for gas turbine engine blades. In order to protect this ceramic component against the oxidation and volatilization in hot steam environments, environmental barrier coating should be utilized. The composite of SiC/Yb 2 Si 2 O 7 Yb 2 SiO 5 with self-healing ability is a candidate for the top layer of this coating. In this study, the crack-healing behavior of SiC/Yb 2 Si 2 O 7 Yb 2 SiO 5 nanocomposites is investigated by pre-cracking followed by annealing in oxidizing environments. Comparing to previous studies, the healing time and healing temperature can be reduced to 15 min and 800°C by increasing the volume fraction of SiC to 20 %. In addition, nanocomposites with both selfhealing ability and superior strength were created in this research by combining two types of SiC filler (whiskers and nanoparticulates). The self-healing mechanism in these composites is the SiC oxidation and silicate transformation associated with their volume expansion, which is evidenced by X-ray diffraction and scanning electron microscope. According to the results, the best volume ratio between whisker and nanoparticulate is determined as 1/3.

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.

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The Nb2CTx prepared by hydrothermal-assisted in-situ HF generation etching was investigated in terms of its gas sensor performance. The Nb2CTx was obtained by mixing Nb2AlC with pure water, hydrochloric acid, and fluoride (LiF or NH4F) and then hydrothermally treated at 180 °C for 24 h. This in-situ HF generation etching by hydrothermal treatment was more efficient and safer in the synthesis of the Nb2CTx than the direct HF etching. The Nb2CTx etched with LiF had relatively wide interlayer spacing because the hydration radius of Li+ was larger than that of NH4+. The results also suggest that Nb2O5 is formed during the synthesis process. These results suggest that interlayer spacing, surface termination, and secondary phases formation can be controlled by the etchant, and that hydrothermal treatment extended the applicability of insoluble etchants. The Nb2CTx synthesized with LiF was evaluated as a gas sensor at room temperature in air in the presence of designated concentrations of 6 different gases, which exhibited good sensitivity and repeatability and fast recovery time, except for NH3. Hydrothermal-assisted etching contributed to providing sufficient interlayer spacing for the gas response without an exfoliation process.