Duplex and functionally graded Al@NiCr/8YSZ thermal barrier coatings on aluminum substrates

Abstract

It is difficult to prepare non-ablative thermal barrier coatings (TBCs) on aluminum alloy owing to the sensitivity to oxygen and low melting temperature of the substrate and great difference of thermal expansion coefficient between the substrate and the coatings. In this work, the cladding-structured Al@NiCr was deposited as interlayer between the aluminum alloy substrate and the 8YSZ topcoat to enhance the bonding strength of TBCs. To avoid the oxidation of the bond coat and the substrate, different cooling systems were attempted. Al@NiCr/8YSZ functionally graded (FG) coatings were also designed and prepared on the aluminum alloy substrate. Microstructure, bonding strength and thermal cycling behavior were investigated and compared with the duplex TBCs. The results showed that selective oxidation of aluminum and chromium occurred for plasma-sprayed Al@NiCr interlayer, similar to traditional NiCrAlY bond coat. The aluminum oxides still wrap around NiCr splats in the coatings. With the application of dry-ice blasting, Al@NiCr interlayer presents more significant decrease in the porosity and the oxides than traditional NiCrAlY as well as more improvement in the bonding strength. Al@NiCr/8YSZ FG coatings have incremental density from ceramic to metal side and uniform layer density. The bonding strength of FG coatings was about twice as higher as that of the duplex ones. Al@NiCr/8YSZ TBCs on the aluminum alloy substrates exhibit an excellent thermal cycling lifetime.