Si-Al-Y Co-deposition Coatings Prepared on Ti-Al Alloy for Enhanced High Temperature Oxidation Resistance

Si-Al-Y co-deposition coatings were prepared on Ti-Al alloy by pack cementation processes at 1 050 °C for 4 h with different halide activators in the packs for enhancing the high temperature oxidation resistance of Ti-Al alloy. The structure, constituent phases, formation process and oxidation behavior of the coatings were investigated. The experimental results showed that the coatings prepared respectively with NaF and NH4Cl as activators were composed of a (Ti, X)5Si4, (Ti, X)5Si3(X represents Nb and Cr), and TiSi2 outer layer, a TiAl2 inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi2 in the outer layer and (Ti, X)5Si4 and (Ti, X)5Si3 phases were observed in the middle layer of the coating prepared with AlCl3•6H2O activator. Among the halide activators studied, the coating prepared with AlCl3•6H2O was thicker and denser, which is the only suitable activator for pack Si-Al-Y co-deposition coatings on a Ti-Al alloy. The oxidation results show that the coating can protect the Ti-Al alloy from oxidation at 1000 °C in air for at least 80h. The excellent oxidation resistance of the coating is attributed to the formation of a dense scale mainly consisted of TiO2, SiO2 and Al2O3.