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5191 |
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Development of bondcoat layer for high lifetime suspension plasma sprayed thermal barrier coatings |
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Mohit Gupta* / University West, Sweden Nicolaie Markocsan / University West, Sweden Xin-Hai Li/ Siemens Turbomachinery, Sweden Lars Östergren/ GKN Aerospace, Sweden Jan Wigren/ GKN Aerospace, Sweden |
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Development of Thermal Barrier Coatings (TBCs) manufactured by Suspension Plasma Spraying (SPS) is of high commercial interest as SPS has been shown capable to produce columnar microstructures similar to the conventionally used Electron Beam Physical Vapour Deposition (EB-PVD) process. Moreover, SPS is a significantly cheaper process than EB-PVD and can produce coatings with much higher deposition rates than EB-PVD. However, lifetime of SPS coatings needs to be improved further for them to be applicable in commercial applications. The bondcoat microstructure as well as topcoat-bondcoat interface topography affect the TBC lifetime significantly. The bondcoat layer in EB-PVD TBCs is typically deposited by Vacuum Plasma Spraying (VPS) in case of NiCoCrAlY bondcoats and Chemical Vapour Deposition (CVD) in case of PtAl bondcoats, while in case of Atmospheric Plasma Sprayed (APS) TBCs, the NiCoCrAlY bondcoats are typically deposited by High Velocity Oxy-Fuel (HVOF) spraying. It is not fully understood yet which bondcoat deposition process would be most suitable for SPS TBCs as the deposition process affects the bondcoat microstructure and interface topography, and thus TBC lifetime. The objective of this work was to investigate the feasibility of High Velocity Air Fuel (HVAF) spraying as bondcoat deposition process for SPS TBCs. In this work, NiCoCrAlY bondcoats were deposited by HVAF using different spray parameters and compared with commercial NiCoCrAlY VPS and PtAl CVD bondcoats. All bondcoat variations were prepared with and without grit blasting the bondcoat surface. Axial-SPS was then used to deposit the yttria stabilised zirconia topcoats on all samples using the same spray parameters. Lifetime of these samples was examined by thermal cyclic fatigue and thermal shock testing. The effect of bondcoat deposition process and interface topography on TGO growth and failure mechanisms in each case will be discussed. The results show that HVAF could be a suitable process for bondcoat deposition in SPS TBCs. |