The current standard application method for thermal barrier coatings (TBCs) on turbine blades for jet engines is electron-beam physical vapor deposition (EB-PVD) due to its high strain tolerance and low thermal conductivity. An emerging deposition method, plasma-spray physical vapor deposition (PS-PVD), presents an opportunity for a tailorable microstructure, and non-line-of-sight deposition that is faster and less expensive. To compare the lifetime behavior of both PS-PVD and EB-PVD coatings, samples subjected to 300 and 600 thermal cycles were measured during a 1 h thermal cycle to determine the strains, which were converted to stress, in the thermally grown oxide (TGO) layer of the TBCs using synchrotron X-ray diffraction (XRD). Room temperature XRD measurements indicated among samples that PS-PVD coatings experienced greater variation in in-plane room temperature strain in the TGO after cycling than the EB-PVD coatings. In-situ XRD measurements indicated similar high-temperature strain and no spallation after 600 thermal cycles for both coatings. Microscopy imaging after cycling showed greater rumpling in PS-PVD coatings that led to different failure modes between the two coatings' TGO layers. The tailorability of PS-PVD coatings allows for adjustments in the processing parameters to improve their overall performance after aging and bridge the differences between the two deposition methods.

This work presents a novel method of obtaining in situ strain measurements at high temperature by simultaneous digital image correlation (DIC), which provides the total strain on the specimen surface, and synchrotron x-ray diffraction (XRD), which provides lattice strains of crystalline materials. DIC at high temperature requires specialized techniques to overcome the effects of increased blackbody radiation that would otherwise overexpose the images. The technique presented herein is unique in that it can be used with a sample enclosed in an infrared heater, remotely and simultaneously with synchrotron XRD measurements. The heater included a window for camera access, and the light of the heater lamps is used as illumination. High-temperature paint is used to apply a random speckle pattern to the sample to allow the tracking of displacements and the calculation of the DIC strains. An inexpensive blue theatrical gel filter is used to block interfering visible and infrared light at high temperatures. This technique successfully produces properly exposed images at 870 °C and is expected to perform similarly at higher temperatures. The average strains measured by DIC were validated by an analytical calculation of the theoretical strain. Simultaneous DIC and XRD strain measurements of Inconel 718 (IN718) tensile test specimens were performed under thermal and mechanical loads and evaluated. This approach uses the fact that with DIC, the total strain is measured, including plastic strain, while with XRD, only elastic strain is captured. The observed differences were discussed with respect to the effective deformation mechanisms.

Electron-beam physical vapor deposition (EB-PVD) is widely used for the application of thermal barrier coatings (TBCs) to turbine blades in jet engines. An emerging method, plasma-spray physical vapor deposition (PS-PVD), is a hybrid technique whereby coatings can be applied via the liquid phase to form lamellar microstructures or via the vapor to form columnar microstructures similar to that of EB-PVD. In this study, PS-PVD and conventional EB-PVD coated samples of a columnar configuration were prepared and thermally cycled to 300 and 600 cycles. These samples were subsequently characterized in-situ, under thermal load using synchrotron x-rays. From the high-resolution x-ray diffraction (XRD) patterns, the residual and in-situ strain in the TGO layer was obtained during a thermal cycle. At high temperature, the TGO layer for both deposition methods displayed a constant near zero-strain for all samples as anticipated. In the samples with 300 thermal cycles, both deposition methods showed similar strain profiles in the TGO layer. For samples with 600 cycles, PS-PVD samples showed a more significant strain relief in the TGO at room temperature compared to similarly cycled EB-PVD samples. This could explain the coating lifetime performance between the two deposition methods. The findings support ongoing efforts to tune the manufacturing of PS-PVD coatings towards the goal of meeting or exceeding the performance of currently used coatings on jet engines. This will pave the way for more affordable high temperature coating alternatives that meet durability needs.

Gas turbine engines for aircraft propulsion require thermal barrier coatings (TBCs) to protect metallic components in the hot section from the extreme temperatures of operation, which may exceed 1200 ∘C. One standard method of coating deposition is electron-beam physical vapor deposition (EB-PVD), which produces a high quality and strain tolerant coating with a smooth surface, which does not impair aerodynamical flow. Plasma-spray physical vapor deposition (PS-PVD) is a promising technique that offers several advantages over EB-PVD, including lower cost, shorter coating time, customization of microstructure by varying processing parameters, and the possibility of non-line-of-sight coating. However, the properties and microstructure of PS-PVD coatings and their effect on performance are not fully understood. This work investigates the residual stress in the thermally grown oxide (TGO) layer of samples made by EB-PVD and PS-PVD, thermally cycled at multiple times (uncycled, 300 cycles, and 600 cycles), to evaluate the effects of these two deposition methods on coating lifetime. Area stress maps of the samples were made with photoluminescence piezospectroscopy (PLPS). The PS-PVD samples exhibited stress relaxation with cycling time, suggesting stress relief from damage, and the PS-PVD coatings exhibited greater stress relaxation between 300 and 600 cycles; however, no samples exhibited spallation. SEM imaging revealed different damage modes for the two coating types. These results reveal PS-PVD's potential as a candidate deposition method for coatings in aero-engine applications.