Atmospheric plasma sprayed thermal barrier coatings with high segmentation crack densities: Spraying process, microstructure and thermal cycling behavior

Abstract

Thermal barrier coatings (TBCs) with high strain tolerance are favorable for application in hot gas sections of aircraft turbines. To improve the strain tolerance of atmospheric plasma sprayed (APS) TBCs, 400μm–500μm thick coatings with very high segmentation crack densities produced with fused and crushed yttria stabilized zirconia (YSZ) were developed. Using a Triplex II plasma gun and an optimized spraying process, coatings with segmentation crack densities up to 8.9cracksmm−1, and porosity values lower than 6% were obtained. The density of branching cracks was quite low which is inevitable for a good inter-lamellar bonding.Thermal cycling tests yielded promising strain tolerance behavior for the manufactured coatings. Samples with high segmentation crack densities revealed promising lifetime in burner rig tests at rather high surface (1350°C) and bondcoat temperatures (up to 1085°C), while coatings with lower crack densities had a reduced performance. Microstructural investigations on cross-sections and fracture surfaces showed that the segmentation crack network was stable during thermal shock testing for different crack densities. The main failure mechanism was delamination and horizontal cracking within the TBC near the thermal grown oxide layer (TGOs) and the TBC.