Thermal Conductivity Analysis and Lifetime Testing of Suspension Plasma-Sprayed Thermal Barrier Coatings

Abstract

Suspension plasma spraying (SPS) has become an interesting method for the production of thermal barrier coatings for gas turbine components. The development of the SPS process has led to structures with segmented vertical cracks or column-like structures that can imitate strain-tolerant air plasma spraying (APS) or electron beam physical vapor deposition (EB-PVD) coatings. Additionally, SPS coatings can have lower thermal conductivity than EB-PVD coatings, while also being easier to produce. The combination of similar or improved properties with a potential for lower production costs makes SPS of great interest to the gas turbine industry. This study compares a number of SPS thermal barrier coatings (TBCs) with vertical cracks or column-like structures with the reference of segmented APS coatings. The primary focus has been on lifetime testing of these new coating systems. Samples were tested in thermo-cyclic fatigue at temperatures of 1100 °C for 1 h cycles. Additional testing was performed to assess thermal shock performance and erosion resistance. Thermal conductivity was also assessed for samples in their as-sprayed state, and the microstructures were investigated using SEM.

Thermal conductivity and thermal cyclic fatigue of multilayered Gd2Zr2O7/YSZ thermal barrier coatings processed by suspension plasma spray

“…Thermal conductivity of YSZ obtained in this work was similar to the trend reported by Pawlosky et al [42] & Curry et al [37,43] on suspension plasma sprayed YSZ coatings. In the case of standard APS sprayed YSZ, thermal conductivity decreases with increase in temperature up to 800ºC and then begins to increase due to sintering effects.…”

“…SEM micrograph of TCF failed single layer YSZ in Fig. 10(a) showed that spallation occurred at the bond coat and YSZ interface, which is the common mode of failure observed in suspension plasma sprayed coatings [37][38][39].…”

“…In particular, the recent developments of columnar-type coatings that mimic Electron BeamPhysical Vapor Deposition coatings have shown great promise as new TBC coatings [36][37][38][39].…”

Ceramic Top Coats of Plasma-Sprayed Thermal Barrier Coatings: Materials, Processes, and Properties

“…As a result of this microstructure, the thermal conductivity of SPS coatings is in a similar range with that of APS porous coatings and lower than the one of APS segmented coatings. The thermal shock resistance and thermal cyclic performance of the SPS coatings can be excellent (Ref 23,24). Recently, it also was discovered that the SPS process allows the formation of columnar structures.…”

Failure Analysis of Multilayered Suspension Plasma-Sprayed Thermal Barrier Coatings for Gas Turbine Applications

“…Columnar microstructures produced by suspension plasma spraying (SPS) are of significant commercial interest as SPS offers a cheaper alternative than the conventionally used electron-beam physical vapor deposition (EBPVD) process, whereas the coatings' thermal conductivity and lifetime are preserved or even improved (Ref [13][14][15][16]. Multilayered TBCs produced by SPS are of high relevance for the gas turbine industry as they can allow higher combustion temperatures and enhanced functional performances.…”