Al-Si and Al-Si-Y coatings deposited by HS-PVD for the oxidation protection of γ-TiAl

In the present work, a total of five coating systems containing Al-Si and Al-Si-Y with different chemical compositions were deposited on γ-TiAl substrate by high speed physical vapor deposition (HS-PVD), which offers high deposition rates owing to hollow cathode discharge (HCD) and gas flow sputtering (GFS). The as-deposited coatings were characterized with regards to their coating thickness, morphology and phase composition. Subsequently, thermal cyclic oxidation tests were carried out at T = 950 °C in air. The results confirmed the high oxidation resistance of the Al-Si and Al-Si-Y coatings compared to the uncoated γ-TiAl substrates. Both Si and Y were found beneficial for the enhancement of oxidation resistance of the aluminide coatings by promoting the formation of α-Al2O3, YAlO3 and a continuous intermetallic scale of TiSi. Significantly suppressed inward oxidation and outward diffusion of Ti could be obtained by the sample coated with Al-Si-Y during cyclic oxidation test. The results of the conducted research reveal a high potential of the HS-PVD Al-Si-Y coating system for the oxidation protection of γ-TiAl at T > 850 °C in turbine applications.