28-04-2014, 03:01 PM
characterization of thermal barrier coatings with a gradient in porosity,
ABSTRACT
A major problem in thermal barrier coatings (TBC) applied to gas turbine components is the spoliation of ceramic coating under thermal cycling processes. In order to prevent spoliation and improve the thermo-mechanical behavior of the TBC, graded ceramic coatings can be produced. For this purpose we are developing a new concept of Thermal Barrier Coating (TBC) that consist of a conventional NiCoCrAlY bond coat and an atmospheric plasma sprayed ZiO2-8 wt.%Y2O3 top coat graded in porosity on an Inconcl 738 LC substrates. The aim of this work it to produce coating with low thermal conductivity and better thermo-mechanical behaviour due to the gradient in porosity which reflects a gradient in the elastic properties. Absolute porosity was measured with a mercury porosimetry and by image analysis. The second technique was also used to estimate the porosity variation along the cross-section. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to observe the morphology and coating micro structure. The micro hardness was measured with a Vickers indenter and 0.981 N loads. The micro hardness has been evaluated for coatings in as-sprayed condition and after annealing at 1100 0 C during 100 h. The results shows a fast increase of the hardness alter annealing. After thermal sock heating at 1000 0 C, 1 h and quickly cooling in water no spoliation was observed for 100 cycles.