High-Emissivity SiO2-SiC Hybrid Sol-gel Coatings over YSZ/NiCrAlY Layers for Ni-based Superalloy

To improve the emissivity, the hybrid sol-gel-based SiO2-SiC layer applied over YSZ layer and NiCrAlY bond layer for GH4099 superalloy was prepared. The NiCrAlY bond layer and YSZ layer was fabricated by plasma spraying. The high-emissivity SiO2-SiC hybrid sol-gel coatings were fabricated by dip-coating and sintering. The morphology of samples was characterized using a scanning electron microscopy and confocal laser scanning microscopy. Phases were identified by the X-ray diffraction analysis. The emissivity at 500 degrees C was measured. The results show that amorphous SiO2 appears for samples sintered at 700, 800 and 900 degrees C. A SiO2-SiC layer thickness of about 5 similar to 30 mu m is obtained with 10 consecutive dip-coatings without intermediate firings. There is no visible discontinuity at the interfaces between each of the 10 dip-coating layers. The penetrating cracks can be found, but no delamination of the coatings from the YSZ layer is evident, indicating acceptable coating adhesion with YSZ surface. The coatings exhibit high emissivity, with the mean value approaching 0.85 in the bands within 8 similar to 22 mu m.