Microstructure and oxidation resistance of Si modified aluminide coating on TiAl based alloys

Two γ-TiAl based alloys of Ti–48Al–2Nb–2Cr (at-%) and Ti–45Al–2Nb–2Mn–1B (at-%) were used as substrate materials. The coatings’ deposition process was prepared using the slurry method. After the deposition of water based slurry containing Al and Si powders on the substrates, diffusion treatment has been carried out at 1000°C for 6 h in Ar atmosphere. The structure of the silicon modified aluminide coatings is as follows: (a) an outer layer consisting of a TiAl₃ matrix and Ti₇Al₅Si₁₂ grains dispersed within this matrix, (b) a middle layer composed of a TiAl₃ matrix and columnar grains of Ti₅Si₃ and (c) an inner layer as TiAl₂ phase. According to the energy dispersive spectroscopy analysis results, it can be concluded that Cr had a high tendency to move towards the Si enriched compounds. The results of isothermal oxidation test of 1000°C/200 h showed that the formation of Si modified aluminide coatings on γ-TiAl alloys by slurry method can greatly improve their high temperature oxidation resistance.