*Article* **Crack-Resistance Behavior of an Encapsulated, Healing Agent Embedded Bu** ff**er Layer on Self-Healing Thermal Barrier Coatings**

**Dowon Song 1, Taeseup Song 1,\*, Ungyu Paik 1, Guanlin Lyu 2, Yeon-Gil Jung 2,\*, Baig-Gyu Choi 3, In-Soo Kim 3 and Jing Zhang 4**


Received: 3 May 2019; Accepted: 29 May 2019; Published: 31 May 2019

**Abstract:** In this work, a novel thermal barrier coating (TBC) system is proposed that embeds silicon particles in coating as a crack-healing agent. The healing agen<sup>t</sup> is encapsulated to avoid unintended reactions and premature oxidation. Thermal durability of the developed TBCs is evaluated through cyclic thermal fatigue and jet engine thermal shock tests. Moreover, artificial cracks are introduced into the bu ffer layer's cross section using a microhardness indentation method. Then, the indented TBC specimens are subject to heat treatment to investigate their crack-resisting behavior in detail. The TBC specimens with the embedded healing agents exhibit a relatively better thermal fatigue resistance than the conventional TBCs. The encapsulated healing agen<sup>t</sup> protects rapid large crack openings under thermal shock conditions. Di fferent crack-resisting behaviors and mechanisms are proposed depending on the embedding healing agents.

**Keywords:** crack healing; encapsulation; healing agent; thermal barrier coating; thermal durability
