The protection effects of an environmental barrier coating (EBC) consisting of silicon bond coat and mixed ytterbium monosilicate and ytterbium disilicate composite topcoat are directly evaluated by measuring the strength retention rate of SiC f /SiC composites completely wrapped up by the previous EBCs after soaking in a mixed oxygen and water vapor environment at 1300 • C for up to 200 h. The results show that the mixed topcoat exhibits not only extremely excellent phase stability but also fantastic protection effects toward composites. After 200 h of corrosion, the fully protected composites are unveiled to present not only dramatically reduced weight gain ratios, less than .6%, compared to ∼10% for those unprotected ones, but also extremely higher strength retention rates, more than 90%, compared to only 10%-15% for those unprotected ones. Further, the fully protected composites show a quasi-ductile load versus displacement curve, suggesting the retention of the oxidation-prone pyrolytic carbon interphase of current composites.

Environmental barrier coatings (EBCs) are crucial to the reliability and durability of SiCf/SiC composite components seeking applications in hot sections of next‐generation advanced aero‐engines. The cracks initiated and developed in EBCs owing to various reasons during service greatly undermine their lifespans. To address this problem, in this work, silicon carbide (SiC) in the forms of particles and whiskers with various amounts have been introduced to ytterbium disilicate (Yb2Si2O7), the mainstream EBC topcoat materials, so as to gain some self‐healing potential. The results reveal that, the SiC inclusions in Yb2Si2O7 in the presence of ytterbium monosilicate (Yb2SiO5) can trigger the following reactions. Specifically, SiC self‐healing agents are oxidized to form viscous SiO2, which actively reacts with Yb2SiO5 upon encountering it, forming Yb2Si2O7. This has brought twofold beneficial effects including ① silicon supplementation of disilicate topcoat, whose silicon element tends to be “dragged out” by water vapor, leading to the deterioration of thermal mismatch; as well as ② crack self‐healing resulting from the volume expansion induced by the above reactions. Then the two aspects of self‐healing agents, namely the “promptness” and “sustainability”, have been discussed in detail. The former is unveiled to be more pertinent to the repairing of large cracks, whilst the latter is more relevant to the self‐healing of tiny cracks at initiation or early stage of propagation. The current work sheds some lights on the design and development of more durable and robust EBCs with self‐healing capability.This article is protected by copyright. All rights reserved