Characterization of advanced thermal barrier coatings

The recent installation of Portech’s 3MB-PT-ID APS torch facilitated the successful production of thermal barrier coatings (TBCs) comprising NiCoCrAlY+HfSi bond coats (~175 microns thickness, ~12% porosity) and 8wt% YSZ top coats (~380 microns thickness, ~9% porosity). Developed under controlled conditions, these coatings achieved porosity and roughness levels suitable for industrial applications. Notably, the 3MB-PT-ID torch is designed for operation in confined geometries, with a total length of 7.0 cm and the ability to effectively spray coatings within a minimum inner diameter (ID) of 15 cm (6”), ensuring a 0.5 cm safety gap. For this study, coatings were produced in an outer diameter (OD) configuration at a spray distance of 7.5 cm, demonstrating the versatility of the torch. The bond coat roughness (Ra ~11 microns) meets the recommended values for enhancing adhesion and top coat performance, while the 9% porosity of the YSZ top coat is within the typical range observed for aero-engine TBCs. Bond strength, measured via ASTM C633, averaged 15.4 ± 0.7 MPa across five samples, positioning it at the upper end of values reported for TBCs with similar parameters. Failure analysis revealed cohesive failure within the YSZ top coat and adhesive failure at the YSZ/bond coat interface, with the bond coat consistently adhering to the substrate. These results confirm that the 3MB-PT-ID torch can produce TBCs with comparable microstructural integrity and mechanical properties to those created using conventional 3MB torches. Its capability to operate effectively in confined geometries without compromising coating performance positions it as a transformative solution for advanced thermal barrier coating applications.

Keywords: Thermal Barrier Coatings (TBCs), MCrAlY, Bond Coat, YSZ, Top Coat, APS, ID- torch.