Highly durable thermal barrier coatings made by the solution precursor plasma spray process

Abstract

The solution precursor plasma spray (SPPS) process offers the prospect of depositing highly durable thermal barrier coatings (TBCs) of low thermal conductivity. In this study, a Taguchi design of experiments was employed to optimize the SPPS process. The spallation life of SPPS TBCs on a MCrAlY bond coated Ni-base superalloy substrate deposited under the optimized processing conditions was demonstrated to be more than 2.5 times of that of a conventional plasma sprayed TBC with the same substrate and bond coat. The superior durability of SPPS TBCs is associated with their novel microstructures, which include: (i) a ceramic matrix containing micrometer and nanometer porosity, (ii) the presence of very fine splats (0.5 to 5-μm diameters), (iii) through-thickness cracks, and (iv) improved ceramic to bond coat adhesion. The failure of SPPS TBCs occurs within the ceramic top coat, near the ceramic/bond coat interface. Buckling spallation is the failure mode observed for all tested samples. It was also demonstrated that the SPPS process is capable of depositing thick (>2 mm) and durable TBCs.