Oxidation Behavior of γ-TiAl Alloy with NiCrAlY/Al Duplex Coating at 950 oC

Abstract:

A NiCrAlY/Al duplex coating was prepared by arc ion plating and magnetron sputtering. The effects of the duplex coating on oxidation at elevated temperature were investigated. After exposure in air at 950 oC for 100 h, the mass gain of the NiCrAlY/Al coated specimen is much smaller than that of the uncoated substrate, and no peeling is found in the NiCrAlY/Al coating. SEM, EDS and XRD have been used to study the microstructure, elements distribution vs. depth and phase formation of the two oxidized layers. Due to the loose structure, the scale on the bare substrate could not contribute a reliable protection against intrusive oxygen at high temperature. As an oxygen barrier, the NiCrAlY/Al coating is capable of forming a protective scale which is consisted of Cr2O3, α-Al2O3 and β-NiAl. The Al interlayer plays a role of aluminizing resource for the formation of protective Al2O3 layer. All the results indicate that the oxidation resistance of γ-TiAl alloy has been improved effectively by NiCrAlY/Al duplex coating.

Key words:γ-TiAl; NiCrAlY/Al duplex coating; oxidation resistance