Thermal insulation of CMAS (Calcium-Magnesium-Alumino-Silicates)- attacked plasma-sprayed thermal barrier coatings

Abstract

The impact of the penetration of small quantities of calcium-magnesium-aluminosilicates (CMAS) glassy melt in the porous plasma-sprayed (PS) thermal barrier coatings (TBCs) is often neglected even though it might play a non-negligible role on the sintering and hence on the thermal insulation potential of TBCs. In this study, the sintering potential of small CMAS deposits (from 0.25 to 3 mg.cm-2) on freestanding yttria-stabilized zirconia (YSZ) PS TBCs annealed at 1250°C for 1 h was investigated. The results showed a gradual in-depth sintering with increasing CMAS deposits. This sintering was concomitant with local transformations of the tetragonal YSZ and resulted in an increase in the thermal diffusivity of the coatings that reached a maximum of 110 % for the fully penetrated coating.

Design, Fabrication, and Characterization of New Materials Based on Zirconia Doped with Mixed Rare Earth Oxides: Review and First Experimental Results

“…Melting point, • C 2700 Evaporation rate µm/h × 10 −5 at 1650 • C 670 Density, g/cm 3 5.6 at 1927 However, at temperatures above 1200 • C in the long term, YSZ loses its phase stability but the main critical issue is calcium-magnesium-alumino-silicate (CMAS) attack that lowers the thermal insulating power [18,19]. Therefore, it is desired to develop new TBCs that can operate at a temperature above 1200 • C. An actual research topic is doping ZrO 2 ceramics with different rare earth oxides due to their high temperature transformation and the low thermal conductivity, which allow to increase the operating temperatures of turbines.…”

Thermal Insulation of YSZ and Erbia-Doped Yttria-Stabilised Zirconia EB-PVD Thermal Barrier Coating Systems after CMAS Attack

“…The sintering phenomenon, mostly due to CMAS infiltration in our case, is a well-known factor that reduces the thermal insulation of EB-PVD coatings [ 30 , 31 ] and can therefore explain the increase of the thermal diffusivity of the 8YSZ coatings exposed to CMAS. In a previous work, similar CMAS deposits (0.25 to 3 mg·cm −2 ) were used on freestanding plasma-sprayed YSZ coatings, and an increasing trend of the thermal diffusivity was observed with increasing CMAS deposits [ 22 ]. However, such a clear increasing tendency is not observed for the EB-PVD coatings in this work.…”

“…The melting operation was operated a second time to improve the glass homogeneity. Following the same technique described in previous studies [ 22 ], CMAS deposits of 0.25, 1, and 5 mg·cm −2 were applied on both types of coatings ( Table 1 ) and heated at 1250 °C for 1 h. Thereafter, the samples were slowly cooled down in the furnace until room temperature to avoid spallation.…”

“…For the corrosion tests, a CMAS mixture whose composition is representative of low melting deposits observed in CMAS-attacked aero-engines (36 CaO,6 MgO, 5 Al 2 O 3 , 52 SiO 2 , and 1 Fe 2 O 3 in mol.%) was obtained by melting a mixture of the different individual oxides at 1400 • C for 4 h in a Pt-10Rh crucible followed by crushing the resulting glass in a mortar after cooling [7,12,22]. The melting operation was operated a second time to improve the glass homogeneity.…”

Experimental and Simulation Analysis of the Evolution of Residual Stress Due to Expansion via CMAS Infiltration in Thermal Barrier Coatings

“…Thermochemical and mechanical properties of Eyjafjallajökull volcanic ash were studied by Webster et al [4]. The thermochemical and mechanical reaction of CMAS can dramatically promote the destabilization of YSZ [5]. Phase transformation would occur, and the content of the zirconium and yttrium elements decreases with the evaporation of ZrO 2 and Y 2 O 3 during the supersonic atmospheric plasma spraying process [6].…”