Evaluation of hot corrosion behaviors of Al2O3-YSZ composite TBC on gradient MCrAlY coatings in the presence of Na2SO4-NaVO3 salt
Abstract
A Multilayer TBC system consisting of a gradient CoNiCrAlYSi bond-coat, and four layers with a different composition of Al2O3- YSZ was deposited on the IN738 super-alloy by using HVOF and APS techniques. Hot corrosion properties and microstructural changes of the gradient and conventional TBC systems were studied in the presence of Na2SO4-20 wt%NaVO3 molten salt at 880 °C for 220 cycles. Kinetics of hot corrosion was determined by measuring the weight changes of the specimens in each cycle. Characterization of the corroded samples was done by using X-ray diffraction, micro X-Ray diffraction, field emission scanning electron microscopy and electron probe micro-analysis techniques. The results showed that α-Al2O3 was the main protective oxide on aluminized CoNiCrAlYSi coatings. The presence of a high amount of Al2O3 in the first layer of the ceramic top-coat reduced the thermal mismatch of the TGO/top-coat and led to the good adhesion of TBC on the dense TGO. These resulted in decreasing thermal stresses and enhancing the cyclic hot corrosion resistance. Formation of the columnar YVO4 at the top-coat/bond-coat interface was also decreased, while hot corrosion resistance was promoted due to preventing the infiltration of oxygen and ionic components through Al2O3-YSZ layers.
- Publication:
-
Vacuum
- Pub Date:
- September 2019
- DOI:
- 10.1016/j.vacuum.2018.04.042
- Bibcode:
- 2019Vacuu.167..547M
- Keywords:
-
- Composite TBC;
- Hot corrosion;
- Gradient CoNiCrAlYSi;
- Thermal grown oxide;
- Thermal stress