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

Abstract

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.

Improving self-healing ability and flexural strength of ytterbium silicate-based nanocomposites with silicon carbide nanoparticulates and whiskers

“…Recently, we found that in the SiC/Yb-silicate composites, the healing rate is also influenced by the existence of Yb 2 SiO 5 around the SiC particles, because the monosilicate readily react with the oxidation product of SiC (i.e SiO 2 glass) to form disilicate. This is the reason the apparent activation energy of the crack healing in our SiC nanoparticulate composite (313 kJ/mol) 32) is lower than those of mullite composite (413 kJ/mol) and Al 2 O 3 composite (334 kJ/mol), 33) though our composite were fabricated with smaller amount of SiC (10 vs. 15 vol %). On the other hand, Vu and Nanko, investigated yttrium silicate/SiC composites and found that the monosilicate/disilicate ratio (Y 2 SiO 5 /Y 2 Si 2 O 7 ) determines the level of the activation energy: the larger amount the monosilicate is in the composite, the lower the activation energy.…”

“…The lowest annealing temperature that can activate healing behavior in a SiC/Yb-silicate composite is 800°C, as confirmed in the previous study. 32) Therefore, in this research, the composites dispersed with 20 vol % SiC were annealed at 800°C, for 15 min.…”

Self-healing ability and full strength recovery at medium temperatures of low content titanium carbide/alumina composites

“…The oxidation of a healing agent, an essential step in the healing process, will not occur when temperature is lower than a particular point (e.g. 800 °C for SiC 9) ). Therefore, the quest for finding an alternative healing agent that can be oxidized actively in mid-range temperatures (400-800 °C) is in demand.…”