An investigation on high entropy alloy for bond coat application in thermal barrier coating system.

Abstract The paper aims to investigate standalone FeCoCrNi 2 Al, FeCoCrNiAl 0.3 , FeCoNiAlTi 0.4 and NiCoCrAlSi high entropy alloys (HEA) as a possible bond coat material for thermal barrier coating (TBC) system. For this high entropy alloys prepared by mechanical activated synthesis (MAS) were densified by spark plasma sintering (SPS). MAS HEAs were investigated for phase formation, melting temperature and coefficient of thermal expansion by X-ray diffractometer (XRD), Differential scanning calorimetry (DSC) and Dilatometer respectively. Isothermal oxidation of sintered samples was carried out at 1050 °C for a period of 5, 25, 50, 100, 200 and 300 h in the air. The formation and growth of thermally grown oxides (TGO) were investigated by Raman spectroscopy, X-Ray Diffraction, and Scanning electron microscopy (SEM). The oxidation study shows that FeCoCrNi 2 Al and FeCoNiAlTi 0.4 HEA follow parabolic rate weight gain due to the formation of TGO enriched in Al 2 O 3. Discontinuous weight changes due to the formation of CoAl 2 O 4 , NiCrFeO 4, and Cr 2 O 3 phases were observed in FeCoCrNiAl 0.3 HEA. TGO enriched in Al 2 O 3 and NiAl 2 O 4 were observed in NiCoCrAlSi HEA, whereas FeCoNiAlTi 0.4 HEA shows the formation of TGO enriched in Al 2 O 3 , NiAl 2 O 4 , Ti 2 O 3, and Al 2 O 5 Ti. Increase in coefficient of thermal expansion (CTE) with increasing temperature is observed for FeCoCrNi 2 Al and FeCoNiAlTi 0.4 HEA. FeCoCrNi 2 Al HEA showing average CTE of 15.16 ± 0.25 × 10−6/K, good mechanical properties, and containing α-alumina TGO layer, makes it a potential candidate for a bond coat material. Highlights • Standalone high entropy alloys (HEAs) were explored for possible bond coat material. • Thermal expansion, mechanical properties and oxidation behavior were investigated. • The coefficient of thermal expansion for studied HEAs lies in 12.8–15.7 × 10−6/K. • FeCoCrNi 2 Al HEA consists of α-Al 2 O 3 oxide scale at 1050 °C upto 300 h. • Spinal oxides were observed in FeCoCrNiAl 0.3 , FeCoNiAlTi 0.4 , and NiCoCrAlSi HEAs. [ABSTRACT FROM AUTHOR]