Synthesis, characterization, and performance evaluation of a self-healing thermal barrier coating based on Ti5(Si1-X,AlX)3 particles against thermal cycling and hot corrosion

In this study, a self-healing thermal barrier coating (TBC) was developed utilizing Ti 5 (Si 1-x ,Al x ) 3 particles synthesized via self-propagating high-temperature synthesis (SHS). X-ray diffraction (XRD) analysis of the synthesized samples with x=0.2, 0.3, and 0.4 revealed that the sample with x=0.3 possessed the highest phase purity of Ti 5 Si 3 and the lowest amount of secondary phases (such as TiSi 2 and TiAl 3 ), and was therefore selected as the optimal composition. A continuous protective oxide layer (∼37 μm thick), composed of Al 2 O 3 and Al 2 SiO 5 , was formed on the optimized particles through selective oxidation at 1100 °C for 60 minutes under an argon atmosphere. Conventional yttria-stabilized zirconia (YSZ) and self-healing TBCs (containing 10 wt.% of the coated particles) were deposited on a NiCrAlY/Hastelloy-X substrate using air plasma spraying (APS). Isothermal oxidation tests were conducted at 1100 °C, and hot corrosion tests were performed at 900 °C in the presence of a molten salt mixture of Na 2 SO 4 +V 2 O 5 . The results of microstructural (SEM/EDS) and phase (XRD) analyses before and after testing demonstrated that the self-healing coating exhibited superior oxidation and hot corrosion resistance compared to the conventional coating. Specifically, it withstood 5 cycles of hot corrosion, whereas the conventional coating failed after 4 cycles. The self-healing mechanism was identified as the key factor in sealing cracks and improving coating performance. This mechanism involves the oxidation of Ti 5 Si 3 particles and the subsequent formation of ZrSiO 4 and ZrTiO 4 phases with positive volumetric expansion. This research demonstrates that surface engineering of particles through alloying and selective oxidation is an effective strategy for developing next-generation coatings with autonomous damage repair capabilities.