Aluminization of a Si-Y co-deposition coating to protect a Ti2AlNb based alloy from high temperature oxidation

Abstract Coatings were prepared by aluminization of a Si-Y co-deposition coating on a Ti2AlNb based alloy using halide activated pack cementation technique. The microstructure evolution and the high temperature oxidation behavior of the coatings were investigated. During the aluminization, the (Ti,Nb)5Si4 inner layer of the Si-Y co-deposition coating was consumed faster than the (Nb,Ti)Si2 outer layer. A (Ti,Nb)Al3 superficial layer and a (Nb,Ti)3Si5Al2 + (Ti,Nb)Al3 middle layer successively formed. Besides, (Nb,Ti)3Si5Al2 pieces appeared inside the outer layer when solid solution Al in (Nb,Ti)Si2 reached saturation. Both inward diffusion of active [Al] atoms and outward diffusion of Ti and Nb atoms controlled the coating growth. The outward diffusion of Ti and Nb atoms caused Al beneath the inner layer was enriched continuously. The Si-Y co-deposition + aluminization coating could provide better protection for the Ti2AlNb based alloy from oxidation at 1123 K than the Si-Y co-deposition coating, which was attributed to preferential formation of Al2O3 on the surface to prohibit formation of loose TiO2. After the oxidation for 100 h, a continuous, compact and adhesive oxide scale consisting of an Al2O3 main part and an Al2O3 + TiO2 + SiO2 lower part formed on the coating.