Thermal barrier coatings are used inside aeroplane engines to increase the operating temperature and thus the performance of the turbine due to a more efficient fuel combustion.[1] The good mechanical properties of zirconia that is stabilized with $\sim$7 wt.% $Y_2O_3$ (7YSZ) are the reasons why it is the state-of-the-art materials for such application. Furthermore, 7YSZ features good thermocyclic behaviour, low thermal conductivity, high thermal expansion coefficient and high strain tolerance.[1,2,3] A phase separation of the materials metastable phase limits the applicability to 1200 °C.[3,4,5] A candidate for the substitution of 7YSZ are high-entropy oxides (HEOs), that are defined as oxides with an equimolar amount of metal cations distributed on one sub lattice and a configurational entropy $\textit{S}_{config}$ larger than 1.5 $\textit{R}$.[6,7]

Next to the applications of HEOs as thermal barrier coating, they often also act as an environmental barrier coating (EBC) to protect engine parts from corrosives, such as molten silicate deposits. This debris mainly originates from volcanic ashes and mineral dust and its main components are calcia, magnesia, alumina and silica (short: CMAS). Depending on the composition of the CMAS, the melting point, viscosity and acidity is changing.[8] The interaction of the molten CMAS debris with the T/EBCs causes various damaging mechanism and irreparable TBC failure.

In this project high entropy zirconates with the general formula $A_2Zr_2O_7$, where the A-site is occupied by five trivalent rare earth cations, are investigated concerning their future application as T/EBCs in airplane turbines. For a deeper understanding of the C(M)AS interaction with the zirconates, not only the high entropy materials, but also the single rare earth zirconates are mixed with $C_{33}M_9A_{13}S_{45}$ (CMAS, ratio of the corresponding oxides in mol%) and $C_{24}A_{17}S_{59}$ (CAS, ratio in mol%). After various reaction times at 1300 °C, the reaction products and newly occurring phases are determined using powder X-ray diffraction and scanning electron microscopy.

References

[1] D.R. Clarke MRS Bull., 2012, 37, 891.

[2] M. Rudolphi J. Therm. Spray. Technol., 2021, 30, 694.

[3] K. Ren Scr. Mater., 2020, 178, 382.

[4] R.L. Jones J. Therm. Spray. Technol., 1997, 6, 77.

[5] J.A. Krogstadt J. Am. Ceram. Soc., 2011, 94, 4548.

[6] C.M. Rost Nat. Commun, 2015, 6, 8485.

[7] A. Sarkar Adv Mater, 2019, 31, 1806236.

[8] A.R. Ericks J. Am. Ceram. Soc., 2022, 105, 3665.