Electron beam physical vapour deposition and mechanical properties of c-ZrO2-ZTA-coatings on alloy 617 substrates
Multilayered zirconia toughened alumina (ZTA) and c-zirconia coatings were prepared using electron beam physical vapour deposition (EBPVD). Characterizations of the morphology and chemical composition of the deposited coatings were performed using scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD). Scratch resistance, nano-indentation and bending strength were used for the evaluation of the mechanical properties. X-ray diffraction of the top ceramic TBC surface showed that it consists entirely of cubic ZrO2 phase. The energydispersive X-ray spectroscopy analysis (EDS) showed that a(Alpha)-Al2O3 is the only oxide phase present at the interface, while SEM indicated the presence of columnar c-ZrO2 as the only phase of the top coat. Delamination over a large region was observed in the case of double layer (ZTA) coating. In contrast, the multilayered (ZTA1 + ZTA2 + c-Z) coating showed neither delamination nor cracking. The hardness and scratch measurements showed that the top coat c-ZrO2 layer is harder than the ZTA layers. The thermal conductivity of the multilayer coatings was estimated using the theoretical density and thermal conductivity values of zirconia toughened alumina (ZTA) and cubic-zirconia (c-ZrO2) together with their experimentally measured data.