Degradation of Thermal Barrier Coatings by Fuel Impurities and CMAS: Thermochemical Interactions and Mitigation Approaches

Abstract

Degradation of free-standing yttria-stabilized zirconia (YSZ) and CoNiCrAlY coatings (300 lm) due to V 2 O 5 and a laboratory-synthesized CMAS was investigated at temperatures up to 1400°C. Reactions, phase transformations, and microstructural development in coatings were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The molten deposits destabilized the YSZ and reacted with the thermally grown oxide with various phase transformations and reaction product formation. A dense, continuous environmental barrier overlay, based on oxides, applied by electrophoretic deposition was effective in mitigating the molten deposit attack. Enriching CMAS composition with Al promoted the crystallization of anorthite platelets and MgAl 2 O 4 spinel, and mitigated CMAS ingression. EPD MgO overlay was also effective in protection against V 2 O 5 melt by formation of magnesium vanadates. EPD alumina overlay deposited on thermal barrier coatings with APS 8YSZ and bond-coated IN939 superalloy retained its adhesion and structural integrity after prolonged furnace thermal cycle test at 1100°C.

Review – Volcanic Ash and its Influence on Aircraft Engine Components

“…Although systematic investigations on the influence of volcanic ash on EB-PVD and APS TBCs are limited, it can be expected that the coatings will suffer severe degradation when exposed to molten VA [11][12][13][17][18][19][20][21][22]. Recent developments of new TBC systems lead to using rare-earth zirconates (REZ) as the ceramic insulation layer, primarily due to their lower thermal conductivity and higher resistance to sintering than state-of-the-art YSZ [23][24][25][26][27].…”

Adhesion of Volcanic Ash Particles under Controlled Conditions and Implications for Their Deposition in Gas Turbines

“…Adhesion of such particulate can lead (at relatively high levels) to disruption of gas flow through the engine, ranging from the blockage of cooling channels [9,10] to complete inhibition of air passage and combustion. At lower levels, short-or medium-term damage can be caused to protective ceramic coatings, with a particular danger of promoting spallation [11][12][13][14][15][16][17][18]. These effects are potentially of major concern, but they all depend on the likelihood of particle adhesion, with the sensitivity to this factor being much greater than that to the particulate burden of the ingested air.…”

Air-plasma-sprayed thermal barrier coatings that are resistant to high-temperature attack by glassy deposits

“…To that end, some approaches for mitigating CMAS attack on YSZ TBCs have been reported in the literature [18,[22][23][24]. Recently, a new approach for mitigating CMAS attack has been demonstrated by some of the present coauthors [14], where up to 20 mol.% Al 2 O 3 and 5 mol.% TiO 2 in the form of a solid solution have been incorporated into YSZ TBCs (referred to as YSZ+20Al+5Ti).…”